THE INF'I-LUENOE. 0E MMEocuMATE MN m; ”if ESTABLISHMENT AND EARLY suavaL ME PLANTED BED PINE PINUS HES____L___N0$A m 5N SOUTHWESTERN MICHIGAN THESIS FOR THE DEGREE 0F PH D MICHIGAN STATE UNWEHSITY HDBEBT KETTH HUDSOH T 9 5 T ~ g {FLA E (a R ‘1" 321:: 3 rate U 11 versicy \. THE INFLUENCE OF MICROCLIMATE ON THE ESTABLISHMENT AND EARLY SURVIVAL OF PLANTED RED PINE, ELUH§ RESINOSA Ait., IN SOUTHWESTERN MICHIGAN By ROBERT KEITH HUDSON AN ABSTRACT Submitted to the School for Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Forestry Year 1957 Approved /6 /€5/7{4( Robert Keith Hudson ABSTRACT A study was carried out in l95h and 1955 at the Kellogg Forest, in southwestern Michigan, to investigate the relationship between micro-climate and the establish- ment and early survival of planted red pine (Pinus resi- ggsg Ait.). One main study plot, consisting of two sec- tions and twenty-four treatment-plots,was established on each of two slopes with contrasting micro-climates. One slope faced northwest and the other one faced south. In- tensive investigation of the soils on both lepes indi- cated that the soils were ecologically similar, as was the low, sparse, old-pasture vegetation on the two slopes. Instrumentation to evaluate the direct and indi- rect expression of the micro-climates on the two slopes involved the use of air- and soil-thermometers, air- and SOil-thermographs, radio-atmometers, gypsum blocks and SOil-moisture meter, recording precipitation gauges, an- emometers, and chemical-absorption hygrometers. Treat- ments included furrowing and scalping, and the use of seedlings and transplants. A total of 1296 trees were planted in the spring of l95h. Daily and weekly observa- tions were carried on for seventeen months, with weekly checks on the survival of planted trees. Every effort Robert Keith Hudson was made to determine causes of any mortality that occurred, in order to segregate causal factors of the living environ- ment from those of the non-living environment. The summers of l95h and 1955 were among the hottest and driest in the record of climate for southwestern Michi- gan. Analysis of instrumental data indicated that the ef- fects of drought were intensified on the south-facing slope as compared with the northwest-facing SIOpe. About eighty percent of the mortality on either lepe occurred during the droughty summer of l95h. Total mortality was about twice as high on the south-facing lepe as on the northwest- facing one. Of a total of 648 trees planted on each slope, 629 survived the first two growing seasons on the northwest- facing lepe, and 607 survived on the south. Symptoms of all trees that died led to the conclusion that mortality was attributable to drought. Data on survival were ana- lyzed for statistical significance. Differences in survi- val between the two lepes were found to be significant, but no significance was found among treatments, among rep— lications, or for interaction. It was concluded that unfavorable micro-climates on Open sites in southwestern Nfichigan may result in signif- icantly higher mortality from drought, among planted red pines, than would result if sites with more favorable micro- climates were selected for planting. THE INFLUENCE OF MICROCLIMATE ON THE ESTABLISHMENT AND EARLY SURVIVAL OF PLANTED RED PINE, PINUS RESINOSA Ait., IN SOUTHWESTERN MICHIGAN By ROBERT KEITH HUDSON A THESIS Submitted to the School for Advanced Graduate Studies of Michigan State University of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Forestry 1957 ACKNOWLEDGEMENTS The writer is grateful to Dr. T. D. Stevens for his advice and constant guidance during the pursuit of the field study, and for his unfailing assistance in the preparation of the manuscript. The writer wishes fur- ther to express his appreciation for the indefatigable efforts of Dr. Eugene P. Whiteside in directing and as- sisting with the topographic and edaphic survey. Spec- ial gratitude is due also to Dr. William D. Baten, who assisted generously with the design and statistical an- alysis of the study. Special acknowledgement is due to Dr. William B. Drew, Dr. Leslie W. Gysel, Dr. Lee M. James, Profes- sor Forrest C. Strong, Professor J. O. Veatch, and Dr. Louis A. Wolfanger for much of their time cheerfully given in consultation about, and advice on, the details 0f the study. Lastly, the writer is indebted to his wife, Lois, who has shared generously in the organization of the data and in the preparation of the manuscript. Experience: Final Examination: Robert Keith Hudson candidate for the degree of Doctor of Philosophy Dissertation: The Influence of Microclimate on the Establishment and Early Survival of Planted Red Pine, Pinus Resinosa Ait., in Southwestern Michigan. Outline of Studies: Major Subject: Forestry Minor Subject: Soil Science Biographical Items: Born: August 15, l9lh. Wyanet, Illinois. Undergraduate Studies: University of Illinois, l939-l9hl. Michigan State University, 1941-19A3. Graduate Studies: Michigan State University, l9h3-19hh; 1948-1956. Scientific Assistant in Forestry, University of Illinois, 19h5. Fores- ter, Southwestern Forest and Range Experiment Station, U. S. Forest Ser— vice, l9h5-l9h7. Instructor, Fores- try, Michigan State University, l9h8- 1949. Assistant Professor, Forestry, Michigan State University, l9h9- 1957. Member: Phi Kappa Phi, Society of the Sigma Xi, Xi Sigma Pi, Society of American Foresters. LIST OF LIST OF CHAPTER I. II. III. IV. < OF CONTENTS ACKNOWLEDGEMENTS . . . . . . . . . . . TABLES o O o u t o o 0 o o o o FIGURES C O O I O O O O O O 0 INTRODUCTION . . . . . . . . . THE PROBLEM . . . . . . . . . . Statement of the Problem . Purpose of the Study. . . . Application of Results . I REVIEW OF THE LITERATURE . . . THE KELLOGG FOREST . . . . . . Location . . . . . . . . . Climate . . . . . . . . . . Topography . . . . . . . . History of Land Use . . . . Soils . . . . . . . . . . . DESCRIPTION OF THE AREAS STUDIED Location, Orientation, and Slope Soils I D O O O O O C 0 0 . Vegetation . . . . . . . . 0 PAGE 11 viii l3 17 21 33 33 33 35 35 37 38 38 39 A0 CHAPTER VI. STUDY PROCEDURE: METHOD OF INVESTIGATION. Basic Approach . . . . . . . . . Reasons for Location of Plots . . Reconnaissance . . . . . . . . . Preliminary Investigation of Soils, and Main-Plot Layout . . . . . Preliminary Instrumentation . . . Elimination of Shrubby Vegetation Layout of Treatment—Plots . . . . Furrowing and Scalping . . . . . Classes of Planting Stock Used . Grades of Planting Stock Used . . Planting Technique Used . . . . . Weather Before, During, and After Planting . . . . . . . . . . . Measurement of Precipitation . . Measurement of Air Temperatures . Measurement of Soil Temperatures Measurement of Soil Mbisture . . Measurement of Solar Radiation . Measurement of Wind Movement . . Measurement of Relative Humidity Measurement of Absolute Humidity H) Measurement 0 Evaporation and Transpiration . . . . . . . . . O O 0 PAGE 1+6 #6 1+8 52 53 61 61 62 62 65 66 68 72 71+ 75 77 81 85 88 9h 95 96 vi CHAPTER PAGE The Chemical-Absorption Hygrometer: Operational Details . . . . . . . . . 10h VII. SITE: FACTORS OF MORTALITY AND SURVIVAL . . 112 Drought . . . . . . . . . . . . . . . . 112 Exposure . . . . . . . . . . . . . . . 115 Vegetation . . . . . . . . . . . . . . 119 Soils . . . . . . . . . . . . . . . . . 120 Planting Technique . . . . . . . . . . 12h Genetic Variations . . . . . . . . . . 128 Insects . . . . . . . . . . . . . . . . 129 ‘ Rodents and Other Large Animals . . . . 130 w Parasitic Disease . . . . . . . . . . . 132 ‘ Non-Parasitic Disease . . . . . . . . . 136 Diagnosis: Symptoms of Drought Injury . 139 VIII. RESULTS OF THE STUDY . . . . . . . . . . . 1&2 j Precipitation . . . . . . . . . . . . . 1h2 Air Temperatures . . . . . . . . . . . 153 ‘ Soil Temperatures . . . . . . . . . . . 160 Soil Moisture . . . . . . . . . . . . . 17A 1 Solar Radiation . . . . . . . . . . . . 190 Evaporation and Transpiration . . . . . 195 Mortality and Survival . . . . . . . . 206 Statistical Analysis of Survival . . . 22h vii CHAPTER PAGE IX. SUMMARY AND CONCLUSIONS . . . . . . . . . . 228 ‘ Methods of the Study . . . . . . . . . 228 4 Findings of the Study . . . . . . . . . 230 % Practical Implications in Planting ‘ Practice . . . . . . . . . . . . . . 232 3% Suggestions for Further Research . . . 233 LITERATURE CITED . . . . . . . . . . . . . . . . . 236 ”T ‘3 g \L TABLE 1. viii LIST OF TABLES PAGE Species Composing the Vegetation on the Northwest-Facing Slope and on the South-Facing Slope . . . . . . . . . . . hh-h5 Soil Types Encountered at Different Sampling Points During Preliminary Investigation of Soils on Northwest-Facing Slope and South- Facing Slope . . . . . . . . . . . . . . 60 Precipitation Totals on Northwest-Facing Slope and on South-Facing SIOpe, 195h-l955, in Terms of Inches per Week . . . . . . . 1h7-lh9 Precipitation Totals on Northwest-Facing Slope and on South—Facing Slope, 1954-1955, in Terms of Inches per Month . . . . . . 152 AiJuTemperature-Sums for Northwest-Facing Slope and South-Facing Slope in Terms of Arbitrary Units and Percent, by Months . 157 AirhTemperature-Sums for Northwest-Facing Slope and South-Facing Slope in Terms of .Arbitrary Units and Percent, by Seasons 159 sOil-Temperature—Sums for Northwest-Facing 310pe and South-Facing Slope in Terms of Arbitrary Units and Percent, i-Inch Depth, by Months . . . . . . . . . . . . 168 8. 10. 11. 12. 13. 1h. Soil-Temperature-Sums for Northwest—Facing Slope and South-Facing Slope in Terms of Arbitrary Units and Percent, lfi-Inch Depth, by Months . . . . . . . . . . . . Number of Hours that Soil-Temperatures Above 1200 F. were Recorded on Northwest- Facing SIOpe and on South-Facing Slope . Number of Hours that Soil-Temperatures Below 320 F. were Recorded on Northwest— Facing SlOpe and South—Facing Slope . . . Differences in Soil-Moisture Averages Be- tween Northwest—Facing Slope and South— Facing Slope, by Mbnths . . . . . . . . . Differences in Soil-Moisture Averages Be- tween Northwest-Facing Slope and South- Facing Slope, by Quarters . . . . . . . . Solar Radiation Received at Northwest- Facing Slope and at South-Facing Slope, by Weeks . . . . . . . . . . . . . . . . Comparative Daytime Evaporation, Night- time Condensation, and Net Effective Evaporation for Northwest-Facing Slope and for South-Facing Slope, l95h . . . . ix PAGE 170 172 173 ISA-185 189 l92-19h 202-203 TABLE PAGE 15. Comparative Daytime Evaporation for Northwest-Facing Slope and for South- Facing Slope, 1955 . . . . . . . . . . . 20h-205 16. Mortality of Planted Trees on Northwest- Facing Slope and on South-Facing Slope, 195h—1955. . . . . . . . . . . . . 220-221 1?. Mortality on Northwest-Facing Slope and on South-Facing SIOpe in Terms of Num- ber of Trees Dead per Main Study Plot and per Sections of Main Study Plots . . 222 LIST OF FIGURES FIGURE la. 1b. 2a. 2b. Basic Layout and Dimensions of Main Study Plot on the Northwest-Facing Slepe . . . . . . . . . . . . . . . . . . Basic Layout and Dimensions of Main Study Plot on the South-Facing Slope . . Layout of Randomized Treatment-Plots in Upper and Lower Sections of the Main Study Plot on the Northwest-Facing Exposure . . . . . . . . . . . . . . . . Layout of Randomized Treatment—Plots in Upper and Lower Sections of the Main Study Plot on the South-Facing Exposure . Soil-Temperature Frame and Shelter for Air- Thermograph and Soil-Thermograph, South- Facing Exposure . . . . . . . . . . . . . Soil-Temperature Frame on South-Facing Exposure . . . . . . . . . . . . . . . . Livingston Radio—Atmometer Installation on South-Facing Exposure . . . . . . . . Anemometer Tower Near Center of Main Study Plot on South-Facing Exposure . . . . . . Detail of Anemometer Tower on South— FaCing Exposure . n . o o o a o 0 O O O 0 xi PAGE 57 58 63 6h 76 8O 87 90 92 xii FIGURE PAGE 8. Main Study Plot on South-Facing Exposure . 103 9. Main Study Plot on Northwest-Facing Exposure . . . . . . . . . . . . . . . . 107 10. Vegetation on Main Study Plot on Northwest- Facing Exposure . . . . . . . . . . . . . 121 ll. Vegetation on Main Study Plot on South- Facing Exposure . . . . . . . . . . . . . 122 12a-12b. Precipitation Totals on Northwest- Facing Slope and on South-Facing Slope, in Inches per Week . . . . . 150—151 13. Air-Temperature-Sums for Northwest-Facing Slope and for South-Facing Slope . . . . 158 14- Soil-Temperature-Sums for Northwest-Facing Slope and for South-Facing Slope, i-Inch Depth . . . . . . . . . . . . . . . . . . 169 15- Soil-Temperature-Sums for Northwest—Facing Slope and for South-Facing Slope, 1%- Inch Depth . . . . . . . . . . . . . . . 171 léa‘léb- Soil—Moisture Averages at lé-Inch Depth for Northwest-Facing Slope and for South-Facing Slope . . . . . 178-180 17a-l7c. Soil-Mbisture Averages at 6-Inch Depth for Northwest-Facing Slope and for South—Facing Slope . . . . . . . . . 181-183 xiii 18a. Soil-Moisture Averages at lé-Inch Depth for Northwest—Facing Slope and for South-Facing SIOpe, by Months . . . . . . 186 18b. Soil-Moisture Averages at 6-Inch Depth for Northwest-Facing Slope and for South-Facing Slope, by Months . . . . . . 187 18c. Soil-Moisture Averages at 2u-Inch Depth ‘for Northwest-Facing Slope and for South-Facing Slope, by Months . . . . . . 188 19. Dead Seedling in Scalp, South-Facing Exposure . . . . . . . . . . . . . . . . . 209 20. Dead Seedling in Furrow, Northwest— Facing Exposure . . . . . . . . . . . . . 212 21- Dead Seedling in Furrow, South-Facing Exposure . . . . . . . . . . . . . . . . . 215 22. Dead Seedling in Furrow, South-Facing Exposure . . . . . . . . . . . . . . . . . 218 23. Precipitation in Inches per Month, and Mortality in Number of Trees Dying per Month, on Northwest-Facing Slope and on South-Facing Slope, l95h-1955. . . . . 223 2h- Mortality of Planted Trees on Northwest- Facing Slope, l95h-l955 . . . . . . . . . 226 25- Mortality of Planted Trees on South- Facing Slope, 195h-1955 . . . . . . . . . 227 CHAPTER I INTRODUCTION Especially during the last three decades the study Of the local climates of forest regions, which meteorolo- gists formerly had almost completely neglected, has be— come a subject of intensified investigation. Foresters, along with other biological scientists, are exhibiting increasing interest in the influence of local climate on forest growth. This local climate, or so-called micro— climate, is undoubtedly an important one among all the faetors of site bearing upon problems of reproduction and early growth of forests, whether the trees reproduce nat- urally or are planted. Now, in many countries, consider- able research is being devoted to special studies of the relationship of micro-climate to the culture of forest trees. A new branch of climatology, forest micro-climatol- Ogy, has come into existence. Notable among the earlier investigators of the generalized aspects of forest micro-climatology were Wal- len, of Sweden, Geiger, of Germany, and Shreve, of the United EStates. These men carried out ingenious pioneer lnveStigations in the 1930's. Shreve (1931) effectively summarized the generalized significance of the apparent interrelationship between organisms and local climates with the statement: Students of the relation of environmental condi- tions to the distribution of organisms have long rec- ognized the fact that relatively great differences in conditions may occur within areas of very restricted size. Certain environmental conditions are more con- stant from spot to spot than are others. . . It follows that the customary manner of measuring climatic condi- tions, so well suited to the purely physical require— ments of meteorology, can give the student of environ— ment nothing more than a normal base from which to de- termine the departures in the various habitats of an area. Planting has become an established technique in forest reproduction in nearly every modern country. As the technique becomes more intensive, and as knowledge is accumulated, the conviction that greater attention to micro-climatological factors is necessary for successful Plantations gains strength. Experience shows that condi- tions are so varied from locality to locality, and that they are so adverse in many places for successful tree growth, that planting should not be attempted on the most unfaVOrable areas until research has fully established feasibilities in each locality. In any new region a com- plete cycle of seasons should be studied before any serious effort is made to establish a commercial planting. Total annual precipitation is often not so critical a determin- ant of Success as is its distribution. Macro—climatic fa°t°rs may be drastically modified by local physiographic factors (Clements 1905) . 3 As the need for reforestation becomes more press- ing in this country, and as costs increase, the chief con- sideration in selecting sites becomes an economic one. The question is what are the best sites and how can the young forests be established at the least cost per acre? In the Lake States Region of the United States the area which was once covered with forest and which is not suitable for agriculture or other intensive use at Present is very large. Much of this land, in terms of valuable species and types of forest, is reproducing poor- 1y or not at all. Estimates of the acreage which will re- Quire planting range upwards from about two million to two and one-half million acres, which is a planting job or great magnitude. Repeated fires in the not so remote Past have swept away nearly all good timber growth of de- sirable species on many acres of cut-over lands. In many instances little prospect for natural reproduction can be foreseen. In some places lumbering plus fire, or even lum- bering alone, have destroyed the effective nucleus of nat- ural reproduction. The only reasonable possibility of re- Storing such lands to productivity in terms of good forest grOWth in the next few decades seems to be an ambitious planting program with native conifers. Experience with the difficulties accompanying successful plantation estab- lishment :indicates that this work should be approached With SOUuui information and mature judgement. The renewed and intensified interest in forest planting engendered by the recently established Soil Bank Program of the Federal Government, and the many complex problems of selection of site for good prospects of success- ful regeneration, make increased knowledge of critical survival-factors even more important than before. It may be.anticipated that the area that could eventually be plant- ed under the program might be unprecedented in North Amer- ican forestry. Prospects that demands upon forest-tree nurseries for planting stock during the next decade will become very heavy are high. Stock for forest plantations iS now in short supply, and has been for many years. It is predictable that the shortage will become even more stringent in the near future. If the best use of a limited SuPplyof planting stock is to be made, only the most prom- ising sites should be selected for plantations, at least during the early years of the program. Inducements to es— tablish plantations are high. Not only may payments repre- Senting up to eighty percent of the cost of establishing a tree cover be obtained by farmers placing land under the Conservation Reserve of the Soil Bank Program, but more and more farmers are beginning to appreciate that on poorer croplands trees can bring greater returns than almost any other myver that could be established. Slowly but steadily the idea <3f farm forestry is beginning to take hold among the rural people of this country. — ,,,,,, So great is the planting job confronting us, and s o slowly is it being accomplished, that special efforts would seem to be justified in order to recognize those areas where reforestation is most urgently needed and where it will be the most effective. Probably the most outstand- ing problem in the Lake States Region is the planting of old logging areas, burn areas, and old fields. On recently cleared land the problem is probably of less urgency, al- though increasing in importance. It would seem that in the northern part of our country, and in Canada, planting should be done only where absolutely necessary and where prospects of success are apparently the best. Where seed trees presently exist in sufficient numbers to assure a good chance of at least ac- ceptable natural reproduction, natural processes should be depended on, at least for the present (Smith 1955). Repxroduction may not come in as rapidly as desired, nor be of ideal composition, but it will usually not be the prob- lem that it is on bare lands. Similarly, filling in the blalnks in existing forests which have been recently but imwltroperly cut is probably not the main problem, even where reptrroduction is returning very slowly. The acreage urgent- 1Y'szeeding planting immediately, and which has needed it [hr a long time, is too large to justify heavy expenditures IMer- e any reasonable probability of satisfactory natural rep:— Oduction still remains. Good planting is not an impossible task where knowledge of the main factors of site affecting mortal- ity and survival is adequate. Planting can be done suc- cessfully on most potential forest lands. Selection of proper sites, use of the proper techniques in planting, and other details of knowledge necessary for good results depend upon an adequate basis of research. A great deal 0f such research has already been carried on in North America, from about 1910 up to the present. Soil, com- peting vegetation, planting techniques, nursery practice, grades of stock to use, diseases, animal pests, climate, and other aspects of planting problems have been investi- gated. In relation to all the other factors of site, however, comparatively little has been done until recent- ly in studying the influence of micro-climate as a deter- minant of the suitability for planting of specific, local- ized sites. T—— CHAPTER II THE PROBLEM Statement of the Problem. One Of the most per- plexing problems which confront foresters in practice is that of determining, as well as possible, causes of heavy death losses in young reproduction which has been estab- lished either naturally or artificially. Often causes are fairly obvious, so that they may be ascribed either to mane reasonably definite single factor or to a recognizable complex of a single class of dominating factors such as prevailing climate. More frequently the main causes re— main obscure. Losses incurred in such instances are usu- ally attributed to that vague catch-all, "adverse site conditions." ‘ In artificial reproduction by planting, climatic conditions, especially those of the micro-climate, are probably of infinitely greater significance than in natural reDPOduction where the site offers partial protection and cover, In any event, no species should be selected for planting on any particular site until the intimacy of the Correlation of its requirements with at least the more ob- v5-0113 factors of the site is definitely settled by either dlreCt or indirect methods. IIIIIIII--—________ J-I-I-Il Forest plantation areas are usually rather large, and thus they are affected by the factors of extreme ex- posure. Climatic extremes are not only more common and more often sharply operative on plantation sites, but they are also more variable and more widely fluctuating. Air temperatures, for instance, oscillate between greater ex- tremes more frequently and more erratically in the open than they do under conditions of Optimum forest cover (Zon In general, summer temperatures are cooler under 1927) . cover, and winter temperatures are warmer, than they are in the open (Geiger 1950). The generally favorable ef- fect of forest cover on soil temperatures in both winter and summer is well known. However, details of these phe- nomena, like those of air temperatures, are insufficiently understood in relation to forest plantations (Pearson 1911+; Zon 1927; Baxter 1952). Similarly, favorable effects of forest cover on air humidity near the ground, on intercep- tion of desiccating winds at low levels, and on protection rom intense, drying, direct solar insolation are known to e lacking on exposed plantation sites. Detailed evalua- Ons are few. It has long been believed that if air tem- r'atures are known for the four hottest months of the a Close approximation of the chance for survival of [1" given species with known heat requirements can be ar- ed at . A recent attempt at calculating evapo—transpira- in has been described by Thornthwaite (1948). His meth- 9 (m:is an empirical one, using air temperature as the single Rtermfinant for approximating expected evapo-transpiration fi;any given locality, particularly in the South. The problem with which the study here prefaced is mainly concerned is that of the influence of one particu- lar class of site factors on survival and mortality in forest plantations. More specifically, the study deals with some effects of micro—climate on establishment and early survival in two small plantations of red pine (Pings resinosa Ait.) in southwestern Michigan. If an experimenter wishes to study weather conditions in tflie field to determine, if possible, some of the local factors that are favorable or unfavorable to coniferous plantuations, he must devote his attention primarily to the micro-—climate. The macro-climate is essentially uniform from sseason to season over any extensive area for any given Perioci of years. Of course fluctuations in the macro-climate arni usually do, occur in broad cycles of several to can, many years' duration. Yet whatever the characteristics of themaCPO-climate, be it uniform or variously changeable, Ithelwe is Ilittle or nothing that the practitioner can do at least in his considerations of the suitability about it 9 The general ap- fOI‘ plinrting of any given small locality. plicability of familiar species for reforestation inside tile :Limits of broad regions is already rather well known. 10 From the standpoint of a broad, regional consider- afionthe practitioner can select for planting those species of'Mees of known adaptability to the prevailing climate. anis true whether the species are indigenous to the re- gim10r are known to be adaptable exotics. Similarly, Merenwrtality in plantations is apparently the result of anden, unpredictable, or otherwise drastic changes in Mm gamral weather pattern, there is practically no re- cmnse but to replant. Such occasional losses are usually widespread, readily apparent as to cause to the trained observer, and the conclusions arrived at from field obser- vations are usually corroborated in the records of standard climatological data. In terms of predictability, the micro-climate, dom- inated by determinants near the soil surface, is in a sense more reliable as an evaluable site factor than the macro- The determinants of the micro-climate are rela- climate. Although tively fixed in place and time~—on the ground. the nxichL-climate generally reflects in some degree the extrenmns and fluctuations of the macro—climate, the micro- climate is essentially more stable. The dominant influence of topography, exposure, vegetation, and other factors can exercise either an ameliorating or an intensifying effect lpon the over—all working of the macro-climate. This ef- 'ect is important to the life and health of forest plan- ations. 11 A In some respects, in reference to a particular, smau.locality, the interpretable effects of micro-climate ulterms of its expected influence on vegetative growth are Imus complex and more difficult to analyze in sufficient detail than to make a similar analysis of macro-climate. Many of the apparent effects of micro-climate seem to have an elusively subtle correlation, if any, with the survival or death of newly planted trees. Yet better knowledge of micro-climatological phenomena are desirable, since they are seldom expressed definitively in conventional climato— logical records. In many ways similar to those in which the effect of the macro-climate on vegetation is expressed, the ef- fect of micro-climate is also expressed. Micro-climate exerts its influence either directly through atmospheric factors or indirectly through changes brought about in lo- cal edaphic or biotic factors. Notable among the more im- portant indirect factors of physiography and exposure which alter the direct micro-climatic factors are those which in- fluence wind direction, wind velocity, air turbulence and mass interchange, and air humidity. Simultaneously influ- enced are such factors as rate of evapo-transpiration and rate of delivery of soil water to roots. Important biotic factors which work indirectly through the direct micro- climatic ones appear to be those concerned primarily with the reaction of plant covers back upon the site. %;____ 12 The reaction of plant covers upon the site, in terms of micro—climatological modification, is of little significance in the management of most plantations. They are usually situated on nearly bare areas. However, any irregularity of tepography or surface cover that does ex- ist may involve effective modifications of temperature and wind movement near the soil surface. It is here that the destiny of a young plantation may be early decided. In- volved also in any micro—climatological modifications are changes in the humidity of the air near the soil surface, Which may hinder or accelerate desiccation of struggling young plants. Any irregularity of surface soil or cover which accomplishes a reduction of evapo—transpiration, through shading effect or otherwise, may be variously ben- eficial. Anything with either a hindering or accelerating effeCt on surface wind-movement, diversion or concentra- tion of precipitation, interception of precipitation with a resultant reduction of mass impact effect of rain drops on the soil, or otherwise similar effects may have a sur- prising influence in determining survival. It has been Often stated that, once tree seedlings are past the suc- Culent Stage, no other factor is so intimately bound up with their health as water relations, both in the atmos— phere and in the soil. The general problem would seem to bee XPreSSible in terms of balance between water absorp- tion by roots, and evapo-transpiration. 13 Purpose of the Study. The main purpose of this study 'was an attempt to learn something about why planta- tions of a given species known to be generally adaptable to the: southwestern Michigan region might fail when loca- ted orl particular exposures with possibly unfavorable micro-climate. Under the average economic limitations of forest Plantuation conditions and practicable planting techniques in angr region, a survival of 100 percent can not ordinar- ily be: expected. Most planters are content, if not satis- fied, 'with an average survival from about 85 to 90 percent under~ prevailing practice. Mortality in such instances may reasult in some measure from the planting of a few weak trees, excessive Competition from ground vegetation around Particnalar trees, poor planting technique by unskilled or careleass labor, localized variations in soil characteris— tics, or‘other reasons. Too often, however, it has ap— peared ‘that two or more nearly identical plantations, ap- parentlbr different from one another mainly in the contrast- ing expcnsures upon which they are located, exhibit survi- val PFObeibilities that are widely variable. If soil char- aCteriStics on the various exposures are as identical as can be aScertained, if planting techniques and grade of stock Useuj are as uniform as possible, if weather condi- tions at 'time of planting and subsequently are apparently Identical, what causes differential mortality? 11+ It would seem likely that, if recognizable factors of s SLlirvival and mortality could be kept as similar as pos- tr §.. the difference between survival percentages on con- ae tbing exposures might be traceable to contrasting micro- Q11mates. If no drastically upsetting factor such as bio— logical disease or insect attack can be recognized on some exposures to the exclusion of others, and if the general weather on slopes near to each other is the same for all, then there would seem to be even more reason to suspect that differences in mortality might be of micro-climatological origin. It is such a possibility that this study has sought ‘ to determine, at least in one particular instance. Inso- far as micro-climate is a measurable factor, the purpose oi‘the study was to investigate whether this factor is sig- i Iiificant in this instance, after other recognized factors vvere kept as uniform as possible, in accounting for mortal- :it): differences. An attempt was made to select two slopes sixnilar in every respect other than micro-climate, and to ccxrrelate the early survival of a small plantation of red pixie on each site with the micro-climate on each site. Secondary to the investigation of micro-climatic :factxors, the purpose of this study was to investigate and 9V81l4late, if possible, certain interrelated physiographic and 6* daphic factors as they affect the initial establish- ment and early survival of the plantings. The study was designed to compare and evaluate the 15 p0Ssible differences in survival of two classes of red pine :::nting stock, seedlings and transplants, randomly dis— QQnt:ted by class and method of soil preparation on two Eisting sites. Two different methods of soil prepar- a't‘lohwere used, furrowing and scalping. It was hoped to complete a project that, within the limits of experimental practicability, might provide information of a nature suf- ficiently broad to make it applicable to problems of gen- eral forest planting and, by inference, to problems of nat- ural reproduction also. After cost, the most important initial measure of success in forest plantations is sur- ‘Vival. Any information that might help to provide a sound- eI'basis for the selection of suitable sites for planting oi‘any commercial species could be helpful. No unalterable conclusions as to which one factor, 01“ combination of factors, is most important as a deter- Inirnant of plantation survival can be drawn as a result of a.ssingle, localized experiment. It is well known that ccuistant variations in the influences affecting survival, exerted separately and in combination by the many factors ixrvolved, render the isolation and determination of the ixxflzlence of any one variable factor practically impossible. 11: sesaems entirely possible, however, to determine by field expez— iments the average influence on survival that can be EXDeC‘Z‘ ed from changes in location, technique, or procedure of pla, :Intings . 16 Despite the efforts in this study to isolate the fac t9}? of micro—climate from the general factor-complex, I I no a t ttZempt was, or is, made to argue the exclusive impor- élr, Q of micro-climate as a site factor. Micro-climate can be determining only insofar as other influences remain relatively equal and constant. This has been recently em- phasized by Hills (1952) in his expression of his holistic or so-called "total site" concept of site classification, by the statement, "No single feature or feature group can in itself adequately define site." Hills points out that micro-climate, as correlated with land form and local re— lief, is separable as an entity from regional climate, climatic soil types, forest or other vegetative cover, single soil characteristics, and other features only inso- .far as all these stated factors remain uniform. This con- cenat is merely a reiteration of the generalized holistic corLcept of site emphasized by other ecologists who warn against over-emphasis on any single factor, or limited com- biJlation of factors, as a criterion. Hills explains some of‘ the details of his concept with the statement: Site must be conceived as a complex system in which forests become established, grow, and disappear. It .is necessary to look upon site as the total environ— ment, including the forest. Site is the integrated C .omplex of all the features within a prescribed area. . 1-“t is possible to classify a whole by a few parts pro— V::iiding it is realized that the whole is something more tP——1an the sum of the parts. 1? ; Application of Results. As the population of . th 1 . . S (:ontinent increases, and as the pressure of demand on 0b e . at g‘t: land for wood products increases, the present rel- iv $3ly'slow rate of artificial regeneration will have to e drastically increased. Artificial regeneration is ex- pensive. Current inflationary developments in the major countries of the world, at a rate approaching one to two percent per year, indicate that future costs of planting are not likely to become lower. If future planting is to be accomplished in the Lake States with maximum efficiency, classification of land and prospective planting sites must be done in such a way that only the most promising sites are planted first. If the results of this study contribute in any annall measure to the recognition of more favorable planting :iites, the profession and practice of forestry will be ben- eIELted. The selection of proper planting sites is one of 'trua main ways in keeping costs of planting low. The main cxfiiterion of an artificial regeneration project is economy arni simplicity in establishment of a commercial crop suited tC) the site. Those factors which contribute to the success 01*.fefllure of any given plantation in terms of economy and 6836? of establishment vary with each locality. High costs be'I" '98eneration of forest trees on adverse sites are or- dinaxtzzély not justified, except in special instances. ;____— 18 It is hoped that the results of this study may be 0f a 80me assistance to forest administrators in Michigan rid ing the other Lake States in solving some of the multitud- problems of reforestation of open and non—restocking 1&“QS that lie ahead. Upwards of a million acres of land are estimated to be urgently in need of planting in Michi- gan alone, before forests will grow on it in the near fu- ture. These lands appear to be better suited now to the growing of forests than to any other purpose. Although if protected from fire for a long period they would prob- ably restock themselves, such natural restocking is usually so slow that it would be an economic detriment to society to allow them to remain unproductive for a long period. Ifurthermore, even if these lands were to restock naturally, tflie resultant composition would likely be undesirable in txerms of economic value. Much of the present unstocked 01“ poorly stocked land is close to existing markets and is Iieeeded for timber production now. Indications are that truis land can be returned to forest production within a reuasonably short time only by artificial reforestation of true most skillful type. The justification for artificial rekarestation, other than for purposes of soil stabiliza— tion in critical areas, is in the high economic or socio- logicf._al value of obtaining productive forests in the short- est. pCZ7:Ssib1e time on those sites best suited for them. 19 The expenses incurred in the replanting of fail areas where environmental conditions have been unfavorable for a high percentage of survival can best be avoided by not planting the most unfavorable areas at all. The abil- ity to recognize the potentialities of locally unfavorable sites, and thus to avoid the waste of time and the expense of attempting to establish plantings on them when the pros- pects of failure are high, is an important asset to the planter, to the administrator, and to the planting planner. No planting program need of necessity contemplate a one— hundred-percent coverage over a very large planting pros— pect. Exclusion of planting from at least the most un- favorable local sites is an economic and practical desir- ability. The magnitude of the total planting job that should be accomplished in the Lake States, balanced against the anticipated rate of accomplishment, by the most optim- istic estimates, would seem to make all efforts well spent to attain the objective as cheaply and as rapidly as pos- sible. Ability to recognize the most unfavorable exposures, and other sites where intensified local drought~ and heat- effects are likely to make plantings unsuccessful, may well be the mosH; valuable skill of the planting planner. Re- search th31;‘:an help to describe and define the indicative qualities of such sites should provide a useful tool. 20 Possibly the most significant application of hissnmdy is that it appears to point to the desirabil- f tycfi‘more research of a similar type but on a broader asis. Such research should probably make use of more [dcfifferent kinds of sites, different species of trees, minew and improved techniques as they are developed. Ither study of micro-climate and its associated factors, ich favor or militate against the successful pursuit forest planting programs, would seem to be highly de- 'able. CHAPTER III REVIEW OF THE LITERATURE Interest in forest planting has been increasingly ctive in EurOpe and in the United States for at least the ast seventy years. However, after searching the litera- Ire, the author of this study is convinced that little >nc1usive work has been done in investigating the influ- lce of micro-climate on the initial survival of planted ’ees on open sites in specific localities. This is not say that much investigation of many of the other vari- S aspects of the survival problem has not been done, ather'directly or indirectly. The literature of at ast the past half-century is replete with observations the generalized effect of the various site factors on Be growth. Most especially is there a great store of bzvnation on the influence of edaphic factors, both upon eS 111 plantations and upon those growing under natural ditixons. There is an equally great accumulation of data the adaptability'of various species to planting in dif- ant broad soil-regions, on the suitability of different :iess, seed, or planting stock of different racial and finial. origins, and on other factors having to do with Success of plantations within many large regions. 22 Memeregions exhibit the diverse influences of widely con- ;rmNdng general climatic types. However, problems of damflfication of local sites for prospects of good or ’mn'plantation survival on the basis of measurable micro- limatic differences seems mostly to have been neglected. In the last forty years, at least in North America, daphic factors have apparently been considered as one of he most useful criteria for calculation of the potential- ties of sites for successful reforestation. Other criter- a and combinations of criteria have also been studied, ither in relation to soil or separately. As would be ex— acted, there seems to be no feeling among the authors con- tlted that any single criterion, edaphic or otherwise, is reliable basis for classification of sites. Rather, a ear appreciation of the ecological law of compensating ctors is apparent in the frequent reiteration that site ality is determined by the combined effect of all oper- ive factors acting in unison, instead of by the intensi- Of One or'a few. Notable among the investigators who '9 recently studied either edaphic factors by themselves, in (xxnbination with other factors, in order to arrive a SYetem of classification of local sites in terms of SPects of plantation survival is Minckler (19hla, 1914b)- ckler‘éitudied the survival factors operative on planta- 11 sites in old fields in eastern Tennessee. He recog- ed the apparent, importance of micro-climatic factors — 23 at least to the extent of including in his classification an estimate of the influence of direction of slope, topo- graphic location, and density and composition of native vegetation. He included also characteristics of the grow- ing season, on a regional basis. Minckler amplified his initial observations, and summarized his conclusions, in Later publications (191.3, 1946). Still later, in collab- >ration with Chapman, he published a rather comprehensive :reatment reemphasizing his earlier principles and stress- ,ng also regional precipitation characteristics as a site- ,lassification criterion (191.8). Minckler was apparently ot concerned, however, with the direct measurement of icro—climatic factors on an intensive basis for local de- erminations of prospects of survival as related to site. As time passes, the tendency to look more closely [to aspects of micro-climatic control of survival and mor- lity in forest plantations has been evident among inves- gators in forestry. Emphasis, however, has been mainly mi cro-climatic phenomena in general rather than on their -ationship with plantations on local sites. Attempts at Lluation of gross climatic factors by the direct method instrumentation and observation received great impetus ing and since World War II. But a similar impetus to- 1 intensive investigation of micro-site factors seems Lave been missing, perhaps because of the economic lim- 21» itations on micro-site research. Detailed and intensive measurements and evaluations of micro-climatic site fac- tors can be very complicated, difficult, time-consuming, and expensive. In terms of any given site, the unit-area cost is usually very high. Even after the recognized fac- tors are measured, their isolation and interpretation in terms of their exclusive effect on vegetation is highly problematical. Intensive investigation of micro-climate >n local sites may seem to be fruitful only in the immed— ,ate locality of the investigation. However, if critical .icro-climatic characteristics could be predicted on rec- gnized exposure-types, for instance, as a result of inten- ive investigation of typical sites, much benefit might esult. Pertinent works in the field of general site class- ‘ication include those of Diebold (1935), stressing base ntent of soil, and soil drainage conditions. Earlier, yes and Wakeley (1929) investigated Spacing of planted ees and also the significance of soil-moisture relations. Ll-moisture relations and soil temperatures as plantation :e factors were investigated by McCulloch (1937) and Ru- f (1937, 1939). George (1939) and Schopmeyer (191.0) died soil-moisture relations and climate. Wilde (l9h6, 9) studied the more general recuirements of soils for :essful reforestation of cut-over lands in Wisconsin. 25 Heiberg (1933) studied the relationship of soil and climate to plantation survival in eastern New York. Pruitt (191.7) carried on a study similar to Heiberg's for southern pines, with special emphasis on the relationship of soils and climate to mortality caused by excessive soil moisture. The tendency to look upon soil characteristics as the dominant influence in plantation survival is re- peatedly apparent in North American forestry literature. The effects of drought, either local or general, Ln reducing available soil moisture below the limits of .he endurance of forest trees is emphasized in the liter- ture. Korstian and Coile (1938) consider the effects of rought similar to those of intense competition under ense canopies. They state: The intermittent and occasionally prolonged lack of available soil moisture is of great significance in accounting for the failure of tree reproduction . . Forest trees are distinctly and differentially limited in their capacity to survive a limited supply of soil moisture. Similar conclusions to those of Korstian and Coile re reached by Wood (1936, 1938) in the course of his in- stigations of natural and artificial reproduction of pine l oak in New Jersey. It has been observed that small, planted trees on y open sites suffer drought injury very commonly in the 3 States during the initial establishment period (Rudolf Gevorkiantz 1933; Rudolf 1937b) . The effects of drought 26 afun'winter planting of southern pines in the Southeast hawacaused many investigators to consider it the princi— phacause of plantation mortality in that very hot quarter oftme United States (Smith 1932; Schopmeyer 1939; Chapman 19M” Hursh 19h8). Similar convictions are expressed by Baun'(l9h9), who states that his investigations indicate int drought, combined with direct heat-injury, is a major unme of mortality in young coniferous plantations. Haig £,gl (l9u1) earlier came to similar conclusions concern- ng young western white pine reproduction. In reporting heir investigations of white pine reproduction in some of he drier, mountainous areas of the West, Haig and his as- aciates state: Hazardous conditions for the survival of young seedlings, particularly in dry seasons, are intensified during the summer by a high percentage of clear, sunny days with low humidities and high evaporation rates. . . Not only does clear weather aid in reducing soil mois- ture, but on exposed sites where moisture content of the topsoil is low it produces very high surface-soil temperatures, which severely injure or kill young plants by causing lesions at the ground line. ey add: Because of the high initial losses, knowledge of tflne conditions affecting seedling survival and meas- ures by which they can be modified is essential to ‘the sniccessful practice of silviculture. It is worthy of note here that investigators gen- lly consider drought as a special danger to all young es, knit that ordinarily they regard direct heat-injury Likely only when the trees are so small as to be still 27 in the partially succulent stage. Early in twentieth- century investigations into causes of mortality in natural and artificial tree reproduction, Hartley (1916) described some of the effects of drought and heat on young seedlings. Z'Ie noted that direct-heat injury was most important when seedlings were still succulent, insolation on exposed sites >eing often intense enough to kill stem cambium at the soil mrface. Larsen (1921.) held the same Opinion for young eproduction of western hemlock, western white pine, and 'estern red-cedar on eXposed, south-facing slopes. Wah— enberg (1925, 1930) reported that drought appeared to be he cause of the heaviest losses among western yellow pine eedlings on exposed slopes. He recorded soil-surface tem- aratures up to lhso F. in one instance. Lorenz (1939) >ncluded that the threshold of heat injury for young seed- .ngs when their cortical tissue is imperfectly hardened . a surface-soil temperature of about 1310 F. When stem ssue is essentially green, succulent, and the external yers are imperfectly hardened, other investigators have fined critical temperatures in ranges from 1170 F. to )0 F. , depending on the age and species of the seedling tker 1929;.Isaac 1938; Bates and Roeser 1921.). The lar- * and sturdier the seedling, accompanied by a correspon- gly greater degree of hardening of cortical tissue, the s likely is the danger of direct-heat injury, and, rel- vely, the more important becomes the danger of drought- 28 inmuy; Bramble (1952) summarizes his estimates of the rehndve importance of heat-injury and drought-injury in hisreport of the results of attempts at reforestation of smnl banks in Pennsylvania. Bramble states: Certain facts become of vital importance to suc- cess of plantings under extremes of local conditions. Prominent among these are the extreme surface temper- atures that occur on . . . southerly exposures and which are undoubtedly a critical factor on many spoil banks. Surface soil temperatures of 1300 F., which are not uncommon on spoil banks, are usually lethal to very young seedlings before their stems have formed corky bark. While such damage is not ordinarily shown by older seedlings from nurseries, a few cases of heat lesions have been observed on trees planted in grey shale. More important to planted stock, however, is a combination of the high surface heat with drought, causing an excessive loss of soil moisture in surface layers . . . during the first three years after planting. Wakeley (1935) is emphatic in his indictment of rought at the climatic factor he thinks is the one most > be dreaded in connection with reforestation, at least I the southern pine region. Wakeley states: Severe drought early in the growing season is to be dreaded most of all, because it catches the trees ‘before they have had time to establish their root sys- tems in the new environment, and they lose water by transpiration faster than the roots can supply it. Spring droughts result in high mortality. Conclusions similar to those of Wakeley were reached flitnr'by'Baldwin (1933) after his study of natural repro- :ticu1<3f spruce and fir in New Hampshire. Minckler (l9hla, .1b) found that establishment and survival of hardwood ntings on old—field sites was better on north-facing n.cn1 scnith-facing slopes in the Southeast. Isaac and 29 Meagher (1936), working with natural reproduction of Douglas- firin Oregon, also found that slope and exposure had a danded effect upon establishment and survival in the first tmayears after a fire. Later studies by Isaac (1937, 1938) xnroborated his first findings that first-year seedling psses often amount to as much as 66 to 90 percent of those intially established. Isaac found that, of the six main auses of mortality that he recognized, drought injury com- ined with direct-heat injury apparently ranked first. He ccounted for other mortality as resulting from rodents, rost, insects, and competition, all of these together anking second to drought and heat. Isaac studied various Limatic and micro-climatic factors of site, including air emperature, soil temperature, and comparative solar radi- Lion received at different locations. In Canada, Horton (1953), studying the causes of .riation in the initial restocking of burn areas by lodge- 1e pine, found that medium and steep south-facing and uthwestmfacing slopes were almost uniformly poorly stocked. ftnuui that east-facing and north-facing slopes were :h more fully stocked. Horton noted that the slopes st severely exposed to solar insolation had the poorest .roduction, and he ascribed mortality on the exposed .pes primarily to injury from heat and drought. There seems little doubt, at least from North Am- 3O enican experience, that, barring intervention of such factors as have already been mentioned as not being dir- ectly related to climate, drought is the most common cause of high initial mortality in pine plantations (Shir- ley-and.Meuli 1939; Daubenmire 1913; Fowells and Kirk l9h5). The effect of drought on the transpiration rate of trees has stimulated much recent research on the use of trans- piration-inhibiting coatings such as various organic oils, waxes, and resins (Marshall and Maki 19h6; Allen and Maki 1951;.Maguire 1952). These substances are applied to stem and foliage of planting stock just previous to planting, with the intended function of reducing the transpiration rate to levels which will permit survival during the in- itial establishment period, despite the desiccating ef- fect of sun and wind during spring and early summer. Not only does the coating substance appear to retard injury from excessive transpiration, but it also appears to in- hibit damage from winter sunscald (Miller g£>g1 1937). Such sunscald injury is usually more prevalent on south- ?acing and west-facing slopes during the first spring af- Ler fall.pflantings, although it may also occur in the same ocations with any thin-barked species like eastern white ine when it is very small, regardless of the season of lanting. (1f the climatological phenomena apparently exert- 31 ing considerable, if not dominant, control of survival in forest plantations, physiological drought seems to have received the most attention in recent years. The tendency among field investigators seems to be to assume that if no reasonable doubt exists that there are no ed- aphic causes of mortality in young plantations, if no ev- idence of insect infestation, biological disease, or heavy competition from adjacent vegetation is found, and if the quality of the planting stock and of the planting technique is uniformly high, drought injury is probably the main cause of the mortality that may occur. Wilde (191.6) states that climatic conditions should be investi- gated if no other primary adverse factor is revealed in field examinations. On south-facing and west-facing slopes, strong winds, great diurnal temperature extremes, and sum- Ier drought can be devastating to newly planted growth, .lmost regardless of the soil type upon which it is planted. nder such circumstances, planting in the bottoms of deep urrows often helps to reduce the desiccating action of in and wind (Wilde and Albert 191.2; Moulopoulos 191.7). 1 any planting technique, primary consideration must be .ven to precautions to reduce transpiration during the itical initial period when the roots of the newly anted trees are developing effective contact with the [1. 32 Where root systems of forest trees are well devel- oped, and the average size of the trees is from poles to standards, much experimental data is available to give re- searchers a good idea of the amount of soil water that is transpired and evaporated by a stand of healthy trees. In the South, Moyle and Zahner (195k) and Zahner (l95h) have found that coniferous stands apparently use from 0.2 to nearly 0.3 inch of soil water per day during periods of active transpiration. When available—water for evaporation and transpiration is deficient in the soil, the growth rate of forest trees, as indicated in dendrometer studies, falls off sharply (Byram 1950; Glock 1955; Kozlowski 1955). When- ever there is a water deficiency in the soil, insofar as the water requirements of growing trees is greater than the ability of the soil mass about their roots to supply it, a situation of drought exists in the physiological sense. If the deficiency is not great, it may have no perceptible effect upon survival in plantations, or upon growth oiTInature trees. Toward the end of long, rainless periods, however, the soil approaches the wilting point. This is EH1 especially dangerous situation during the first season's growth of plantations, where the problem is com— plicated by poor establishment of the young root systems. The soil is soon depleted of water, and what water remains is ever more tightly held (Rowe and Colman 1951; Lassen et a1 1952; Ashcroft and Taylor 1953). CHAPTER IV THE KELLOGG FOREST Location. The Kellogg Forest, an experimental and demonstrational area owned by Michigan State University, is located in Kalamazoo County in southwestern Michigan, about halfway between the cities of Kalamazoo and Battle Creek. ) Climate. The climate of the Kellogg Forest is in general typical of that of the Southern Great Lakes Region of North America. Extremes of temperature, somewhat more frequent in other parts of the region, are relatively un- common here. The climate is moderated by prevailing west- erly winds from the direction of Lake Michigan. It may be characterized in general as humid, microthermal, and with precipitation averaging adequate at all seasons (Thorn- thwaite 1931; Van Dersal 1938). Local climate varies with- in narrow limits throughout the southwestern area of Mich- igan, maily as a function of topography and relative prox- imity to the lake. Average annual precipitation in Kala— mazoo County varies between 32 and 36 inches. Of this to- tal, an average of 18 to 20 inches occurs during the warm season, from May through September (U. S. Dept. of Agri- culture 19h1). Cold-season snowfall averages about 30 to 31+ 50 inches. Although the humidity characteristics of the Kel- logg Forest area are generally those of a typical forest region, with precipitation averaging adequate at all sea- sons, warm—season droughts of sufficient length to inter- fere with the establishment of forest reproduction are a factor to be reckoned with. At such times, severe droughts of about ten to twenty days' duration, during which there may be little or no rain, may result in rather high death losses in plantations. Whether or not accompanied by drought, summer air-temperature maxima of 900 F. to 1000 F. are common nearly every summer. Maxima of 1050 F. to 1100 F. are occasional. Such high air temperatures, occur- ring on sunny days, are frequently accompanied by surface— soil temperatures on south-facing and west-facing slopes as high as 1200 F. to 11.00 F. The duration of such tem- peratures on any given day may range from about one-half to two and one—half hours. Extremely high air temperatures and soil temperatures were especially notable at the Kellogg Forest during the unusually hot summers of 195A and 1955, when the field work for this study was carried on there. The mean summer air temperature in Kalamazoo County averages about 670 F., calculated for the four hottest months from June through September. Mean air temperature in January, the coldest month of the year, averages about 2h° F. 35 Topography. The topography of the Kellogg Forest is predominantly broken, typical of the unstratified mor- ainic hill country of much of the originally forested area of southern Michigan. Hills vary from gently rolling to Slope inclinations are commonly above ten percent, Glacial de— steep. and occasionally as steep as fifty percent. posits are thick, with no bedrock exposed or near the sur- face. Modifications of the original topography by accel- erated erosion induced by improper land use, occurring mainly in the earlier part of the twentieth century, are marked in some instances. History of Land Use. Except for a few scattered remnants, approximating forty acres, of the original pre— dominantly hardwood forest types, all of the Kellogg Forest had been cleared and either farmed or pastured for many This history of land use is typical Most years prior to 1929. of that in the hillier regions of southern Michigan. of the original forest was removed at least by the decades late in the nineteenth century. Varying agricultural use prevailed thenceforth until the period of frequent land— abandonment in the middle 1930's. During the last half of the nineteenth century and up to about 1915 the land fur- nished a livelihood for several farm families at a standard of living apparently typical of Michigan farmers at that time. However, as time went on, yields and income from 36 agriculture progressively decreased. Very heavy depletion from soil erosion was characteristic on the tillable slopes during the pre-abandonment period, so that in many instan— ces the topsoil was stripped completely from the land. The untillable, steeper slopes were pastured, if used at all, so that erosion on these areas is usually not severe. It is on such an old—pasture area that the field plots for this study were located. The particular compartment where the study was carried out was acquired by purchase in the middle 19h0's. It has a histpry of continuous pasture use before purchase that extends backward indefinitely for many years. As the farms that were once located on what is now the Kellogg Forest declined in productivity, the farms were all eventually abandoned and the most productive, level fields were tilled by adjacent farmers. By the early 1930's even these fields had been abandoned. The decline in productivity of the original farms was primarily due to the sloping character of the land and to faulty agriculture. All the land except a few acres of bottom land along Augusta Creek has a relatively high erosion potentiality. Since 1932 the Kellogg Forest, a gift of Mr. W. K. has been under the administration of Michigan Kellogg, State University. It is now used for research and for dem- onstrations of the multiple uses of depleted land. 37 The soils of the Kellogg Forest, typical Soils. ofthose in southwestern Michigan, are predominantly of the zonal order. These zonal soils are pedalfers, or forest soils, having supported in times past various com— ponents of the Deciduous Forest Formation probably con- sisting primarily of elements of the Oak-Hickory Associa— tion (Braun 1950). They are typical of the light-colored, podzolized soils of the humid, cool-temperate to temper- ate forest regions of North America, being members of the Great Soil Group of Gray-Brown Podzolic soils. General- ly they exhibit grayish-brown to light yellowish-brown variably leached "A” horizons over stronger and darker 1 brown "B" horizons containing a considerable concentration Of alumino-silicate clays (U. 8. Dept. of Agriculture 1938, Veatch 1928, l9hl, 1953). Parent material of the soils on the areas studied is Predominantly glacial drift of the Wisconsin age, un- stratified morainic phase. Typical irregular morainic relief is the rule, composed of mostly sandy to gravelly, Somewhat calcareous materials. Subsequent to glaciation, much of the parent material may have been shifted by wa- ter and wind. CHAPTER V DESCRIPTION OF THE AREAS STUDIBD Location, Orientation, and Slope. The two ex- posures studied are located in Compartment 26 of the western portion of the Kellogg Forest. The northwest- facing exposure overlooks a broad valley and is oriented at an angle of about thirty degrees west of north. The south-facing exposure is oriented directly south. It overlooks a narrow, deep valley, with a steep, high slope Opposite it and facing it, about eighty yards distant. Variation in percentage of slope on each exposure is from about twenty-one percent to about twenty-six percent. Both exposures and the valleys fronting them are open to the sweep of prevailing westerly winds. No intervening high forest cover, which might hinder free wind—movement across the slopes, is within one hundred fifty yards of either exposure. Free air-drainage down and across the Slopes and down the valleys is not impeded. No shading effeCt from adjacent topographical features occurs in the fourteen hours about midday in the summer, nor in the eight hours about midday in the winter. 39 Soils. The soils on the two particular expos- ures studied may be considered essentially similar ecolog- ically, if not identical. This appraisal is substantiated by the opinion of a well-known soil scientist and pedo- logic ecologist of the Department of Soil Science of Mich- igan State University who very kindly assisted the author in the preliminary reconnaissance and in the intensive investigation and mapping of soil types requisite to the selection of the two exposures as experimental areas.1 The soils are pedalfers, representative of the gray-brown podzolic soil group developed under the influ- ence of an original, predominantly hardwood forest cover. Textural range of the surface soil is from a sandy loam through loamy sand to occasional sand. Soil fabric was found to be non—stratified at all investigated points. Series range is from Boyer to Bellefontaine. Extreme range of pH of surface soil at all investigated points was found to be from 5.5 to 7.0. Extreme range of pH of the "C" horizon at all investigated points was found to be from 6.1 to 8.0. Soils vary from medium well- drained to well-drained, with a low content of clay and with ar1 inherently high infiltration and percolation rate. No indications of former plowing are in evidence. 1Dr. Eugene P. Whiteside. 40 is fire is no known history of agricultural cropping or Other intensive agricultural practice on the exposures studied, after the original forest was cleared. The best evidence available indicates no fire history and no history of use more intensive than for natural hay pro- duction and for occasional pasturage. Evidences of ac- celerated erosion are negligible. Vegetation. In the preliminary reconnaissance for the purpose of locating suitable sites for the study, an effort was made to find two contrasting exposures on which, nevertheless, the basic vegetative types would be as similar as possible. The reason for this effort was that it was thought that if the types on the two exposures were radically different, and if these two types were 'well developed as a result of long-time establishment and.little disturbance, their effect on initial estab- Jgishment and early survival of the planted trees might prx>ve to be considerably different on the two sites. If ccuitrasting vegetative types accompanied by a high degree (If occupation of the soil mass by roots of established vegetation were to be present, it was thought that the conunarable results of the study might be adversely af- fected. This fear was held despite the furrowing and scalp» ing that was done, which was designed to minimize comps tition to the planted trees from adjacent vegeta- tion during the first two growing seasons. Where the pri- 41 "a b purpose of the study was an attempt to test the di- eCt and indirect effects of contrasting micro-climates on early survival, the presence of contrasting, well- developed and active vegetation types might prove to be a confounding factor, regardless of the methods of soil preparation employed in an attempt to minimize this fac- tor. Actually an effort to locate contrasting sites xNhere vegetative types are closely similar puts an in- ‘Jestigator in a rather paradoxical position. General ecological theory and principle would point out that if sites were really very contrasting, if vegetation had been allowed to grow and develop on them for some indef- inite but considerable period of years, and if this per- iod were long enough to permit of some appreciable matur- ity and stabilization of the vegetative community, one could not expect to find ecologically similar, if not equivalent, types on them at all. However, the period of total abandonment of the experimental sites for ag- ricultural use of any kind, even though any such use seems to have been no more than sporadic pasturage, is no nusre than about two decades. It would seem that this woul<><><><><><>< >< >4 NNN ><><>< South >4>< MNKMNN MM CHAPTER VI 'UDY PROCEDURE: METHOD OF INVESTIGATION gsic Approach. In order to study the influence :limate on the establishment and early survival 1gs of red pine, an attempt was made to select as similar as possible in every respect other >-climate. It was prOposed to establish, under 1 conditions, a plantation of red pine on each 3 sites, install instruments to measure the mate and other factors on each site, and to use collected in an attempt to correlate the early on each site with the individual micro-climate ite. no exposures on similar slopes with micro-climates to be as different from each other as could be the Kellogg Forest were selected. It was hoped ntrast approximating optimum local growing condi— the one slope, and representing very extreme con- f‘summer heat and drought on the other, were se- In the summer of 1953, preliminary, partial ob- s of soil temperatures were made, in order to 'substantiate the initial estimations of the in- r. 1+7 The literature consulted preliminary to the study d a seemingly prevalent opinion among past workers ation problems that, insofar as micro-climatic >ns affect survival, those associated with the first season after planting may be of predominant impor- ompared to conditions in any subsequent seasons. , after the study had been carried out for the in- ;ummer season of 1951+, and into the fall of that Lt was decided to re-institute the study in order Lect further data to support the conclusions. Con- tly, Operations were resumed in the late fall of Lnd continued through the second growing season; .3, through the summer of 1955. Had weather conditions approached what might have considered optimum for growth and survival during all st of the period in which the study was carried out, .e basis for comparison or contrast between the two sures might have existed. However it was fortunate, east for the purposes of the investigation, that the em of 1951+ and 1955 were two of the hottest and driest record in southern Michigan, and most unfavorable for ng plantations. The winter of 1951;-1955, while more rly normal, was characterized by considerable extremes warmth and cold, heavy snow cover and no snow cover, lalternate freezing and thawing of the surface soil. —. 48 Reasons for Location of Plots. The two slopes :1 -for comparison in this survival study were loca- the Kellogg Forest for a number of reasons. Fore- s the reason that, not only is the Kellogg Forest but it is owned and controlled by Michigan State sity. Consequently the continuity of the investiga- rlroughout any anticipated period of months or years 511 it might be wished to be pursued was assured. .ea that a replication of the entire study in place 1 time may be desirable at some tine in the future L11 held by the investigator-and his advisors. It is ole that the need for corroborative evidence may ar- or that additional data obtainable by the employment wer techniques or improved instrumentation might be ‘able and practicably acquired in the near future. lCh a situation arose, without the university having ment control of the original sites, a replication or nsion of the investigation might prove impossible. Disappointing experiences of many workers in the .have shown that, where long—time, relatively costly aarch is contemplated, indisputable control of the ex- imental site, as well as free access to it, is impera— e. All too many field experiments have been brought to Iremature end where misunderstanding of the requirements {objectives of the experiments, on the part of a pri- te landowner, has led to their abortive termination. 1+9 <3vnaezy after an initial exhibition of interest or ;husiasm for an experiment, develops an attitude of DI‘ gxwawing impatience toward it. This sometimes 3 kneedless or even deliberate interference with the , arni actual damage by such agencies as uncontrolled ick. ‘If 533 the future the desirability of replicating nestigation here reported becomes clear, and provid- at funds and personnel are available at that time to tiate it, the reserved sites will be at the experi- 's' diSposal. Meanwhile, during the seventeen months she first eXperiment was carried on, freedom from rbance or interference was assured. The second reason for locating the survival study e Kellogg Forest was that a suitable tOpography, where exposures of sufficient size and contrasting micro- 1tesosure could be efficiently accomplished. The ex- selected are within one-quarter mile of each other. Another reason for the location of the study was was thought the exposures should be on areas that >ported forest growth previously. This requirement >arently satisfied. Another requirement, based upon sional judgement and experience, was that the soils be light and well-drained, not excessively disturbed dad, and of a generalized nature reasonably to be ex- L to be suited to the growth of such Species as those a northern Eiggg group, or of Quercus or Eggyg. It it that this requirement was also satisfied. Some nce of this. is to be found in the good growth of older, ed pines in the immediate vicinity of the experimen- sites. Further assurance was obtained from publica- 5 in which the probable nature of the original forest r is reconstructed, based on correlation with modern maps (Veatch 1928, 191.1, 1953; Whiteside 33 §_1_ 1956). study areas were located within the larger, general Hickory Association region. The local type on the War soils appears to have been dominated by oak and Rory, especially on the better drained parts, with sec- .ary components of beech, sugar maple, basswood, ash, lcherry. Frequent admixtures of eastern white pine 51 e also predicated. Not the least of the reasons for selecting the logg Forest as the location for the experiment was .t on.a.certain portion of the property the morainic to- ;raphy is characterized by having soils of gratifying Iilarity in different places. On the basis of the best ailable professional judgement these soils appear essen- ally alike in terms of origin, develOpment, predictable owth-affecting characteristics. The theoretical, but actically unrealizable, ideal would be to have two ex- sures of abolutely identical description except for cro-climate, if such a situation were recognizable. cro-climate should be sharply contrasting. Soils on e two exposures should be as similar as possible, in ear to minimize, if not entirely obviate, the possible >nfounding effect of differences in soil influences on .uyival. ,According to the best judgement of Dr. Eugene . Whiteside, who directed and otherwise assisted with hegneliminary investigation of the soils on the exposures elecmxh these soils are indeed essentially or sufficiently rimilar in their ecological relationships for the purposes >f the experiment. Thus it is hoped that a primary objec- tive of obtaining practical soil identity as between the two exposures was satisfied. 52 Reconnaissance. The search for two suitable ex- osures upon which to carry out the field phases of this tudy involved an examination of topographic and edaphic eatures over nearly a square mile of territory. Perhaps he attempt made to find two different exposures between hich the greatest micro-climatic contrasts would be ex- ibited, but which would be closely similar in every other espect, could be subject to some criticism. Some inveS- igators might feel that the results would be applicable 0 only a small portion of the forest area of any given egion. However, time and funds available were insuffic- ent to permit any considerable portion of the whole south- estern Michigan region to be sampled. There was also he consideration of exclusive control, previously men— ioned. Furthermore it was thought that extreme contrasts dght provide more definite results in a limited study. The extreme effects upon survival of an abnormally wt and dry summer during the first growing season have een noted by many investigators in forest-tree nurseries Lnd plantations, especially on unfavorable sites. It is bought that on very hot exposures, before roots of plant- :d trees are completely established, imbalance between :oil-moisture requirements and accelerated transpiration exerts a pronounced effect upon early survival and growth vf young trees. 53 Preliminary;Investigation of Soils, and Main-Plot gyggt. The opinion has very often been expressed in he literature that investigation of soil characteristics, 3 a factor of site, should provide the forester with the cans to adequately predict survival of planted trees. any authorities disagree, however, stating their opinions hat soil characteristics alone are not a reliable criter- on of site quality. This investigator shares the latter elief. Site appears to be a complex interrelationship. vnterrelated factors are well known to be both compensa- .ing and conflicting. Even though it may not be neces- tary to recognize and describe all of the component fac- ;ors of a site, in order to arrive at a workable classif- .cation for any given purpose, it seems that too little .nvestigation into the positive correlation between plan- ;ation survival and soil characteristics recognizable in :he field has been reported. Consequently this investiga- ;or thought it necessary to obtain the Opinion of a rec- >gnized pedologic ecologist in order to establish, as con- fidently as possible, the ecological equivalence of the Soils on the two exposures used for the study. Considerable research is reported on the relation between site-index of mature trees and the characteristics cu‘the soils upon which they grow, but relatively little appears to have been done on the subject of site and plan- tatunlsurvival. It has been reported that the texture 5h ofthe "A" horizon of forested soil is a useful criterion ofsite quality in immature red pine plantations in Con- nmmicut (Haig 1929). Similar conclusions have been re- pmted by Coile (1935, 1948), as a result of his investi- gafipns into the relation of site-index for shortleaf ohm with physical properties of the soil. Coile's cal- however. are presented in the form of rather mflations. complicated formulae applicable primarily to well estab- lished, relatively mature, natural coniferous growth. These calculations appear not to be directly applicable to the special situation of young, recently planted trees. Methods somewhat similar to those of Coile were developed by Hicock gt Q1 (1931). Their work in Connecticut was with red pine, but again their emphasis was upon the growth of well-established, older trees. Westveld (1936) stated rather simply his estimation of the relationship of the growth rate of white spruce to differences in soil drain- age. 11ers again the trees that Westveld worked with were larger“ than pole size, deeply rooted in the better drained soils cxf the locality, and growing on the highly podzol- ized.:soiLLs of the Upper Peninsula of Michigan. Other in- vestigators of soil correlations with coniferous growth jjlclinie 1&1141, Arnst, and Bond (l9h9) working together with Douglas—fir in the Northwest. However their conclusions are generalized and again apply primarily to older trees. 55 Rudolf (1950) appears to have done more work of a nature more nearly applicable to the problems of this study than anyone else, but his most notable publication is again broadly generalized and refers mainly to site-index and growth of mature trees and types. It does not describe specific, easily recognizable criteria that can be used with complete confidence in evaluating, soil-site in terms of predictable first- and second-season survival prospects in young coniferous plantations. In the preliminary investigation to establish the comparable characteristics of the soils on the two expo- sures selected, the first step was to locate the upper and lower sections of the main study plot on each expo- sure by means of standard plane-table mapping technique. A main control-stake was established at the corner of each main study plot. All locational details on each plot were then mapped in reference to these stakes. The upper and lower sections of the main plot on each eXposure were separated from each other by distances sufficient to provide area for installation of instruments and instrument shelters in a central location. The dis— tance between the upper and lower sections on the northwest- facing exposure was twenty-six feet. On the south-facing eXposure the distance was twenty-one feet. The instru- m o ents on each exposure, being placed near the center of 56 the main study plots, were thus at a practically minimum distance from the farthest corner of each plot. A separ- ation of at least twenty feet between the two sections of each plot was considered desirable in order to protect any part of each main study plot from shading effect by the instrument shelters. Each of the two sections of each main study plot was 108 feet long and 27 feet wide. The sections were disposed horizontally, or across the face of each expos- ure. A slight offset of 13 feet was made in the lower section of the northwest-facing main plot, in order to insure greater uniformity of soil and slope characteris- tics as compared to those of the upper section. Each section of each main study plot was divided into 12 rectangular treatment-plots 27 feet long and 9 feet wide, disposed horizontally across the face of the slope. Later, treatments were randomized for each sec- tion, by treatment-plots. Maps of each main study plot, showing orientation and location of sections and treatment- PlOtS, and control points, may be found in Figures la and lb; on pages 57 and 58. Detailed field examination of soil-profile char- aCteristics was accomplished by multiple soil-borings, 25 in number. Location of each boring at each sampling pOint was determined by mechanical spacing over the main ”Loam afioouuam a a mason H-~ mason a-~ Iowans o-~ mason cow saunas munwaamcmue vacuhwowueohna "Hum mmeaaeomm eao-pao~-oza "cum “names; I o-~ 38m HA raga o-~ 38m o-~ 38E; o-~ saunas H-~ mason o-~ rogues cuw canon eofipoom a noun: 65 oped to minimize surface run-off and erosion that might lossibly occur in the event of precipitous storms. The ridth of each furrow, including the adjacent slice, was :wo feet. Furrowing was kept intentionally shallow, to . depth of three inches. This was considered deep enough 0 kill all competing herbaCeous vegetation in the furrow ottoms and under the adjacent slices, yet shallow enough 0 effect a minimum of disturbance to the upper soil sur- ace. Scalping was accomplished by hand stripping of he tOpsoil and herbaceous cover, with grub hoes. Stripped aterial was deposited carefully on the downhill side of ach scalp. Each scalp was two feet square and three nches deep. The furrowing and scalping was completed about our weeks previous to the planting on the two exposures. his was done in order to allow the furrows and scalps o accumulate moisture from the spring rains, and thus, t was hoped, to contribute toward Optimum conditions at he time of actual planting. Classes of Planting Stock Used. Two classes of ed pine planting stock were used in each section of each ain study plot. These were: (1) 2-0 seedlings. (2) -1 transplants. The use of each class of stock on each ain study plot constituted a sub-treatment in itself, as 66 urrowing and scalping. Half of all the furrowed -plots were planted with 2-0 seedlings, and the f of the furrowed plots were planted with 2-1 ts. Similarly, half of the scalped treatment- 3 planted with seedlings and half with trans- All planting stock was obtained from the Bogue E Michigan State University. :ades of Planting Stock Used. Grading of the stock used in this study was carried out accord- 2 criteria developed by Pomeroy gt a; (1949) and .er and Limstrom (1950). The studies of these >ors indicate a definite advantage in survival as after planting, as a result of selection of )lanting stock according to their grading cri- 1 all operations they advise discarding the poorest trees in the usual run of red pine ,ined from forest nurseries. Like Pomeroy and ates, Stoeckler and Limstrom found that much vival resulted from planting only medium and es of stock, as compared to results when small— 1 was also used. They report that this phenom- specially noticeable after planted trees had severe heat and drought during the first grow- after planting. 67 Thepflanting stock used in this study was graded of<flose ocular examination of each individual ‘any doubt existed that any tree was of superior .was discarded. In every instance a tree of age-color, small size, excessive slenderness, g signs of poor growth in the previous season n out. If it exhibited inferior fibrous-root nt or showed any recognizable sign of wound, heat lesion, or biological disease it was like— cted. Trees were also graded for uniformity in am root collar to tip. Furthermore, crown de- and thickness, and root development, were con- vithin the limits of the so-called "medium" and ‘ades as mentioned above. In no instance was antly weak, stunted, sick, or otherwise sub- ,ree planted, insofar as the quality of the d be ascertained by the methods described. is recognized that no method of grading is ance for error. No attempt is made to deny ree planted might have had some unrecognizable incipient disease that might tend to confound 11 results. All that can be said is that no spared to obtain as high a degree of uniform- :stock planted as appeared possible by practical asently recognized. 68 Planting Technique Used. In planting the trees d in this study, exaggerated efforts were made to re- s the possibility that either poor stock or poor plant- technique might confound the later mortality results. The planting stock was carefully lifted and packed he nursery on the afternoon of Tuesday, April 27, 1951+. as taken to the planting sites at the- Kellogg Forest 1e morning of the next day. The weather during the ng operation at the nursery was cool and cloudy. All stock was planted during a single day follow- ie lifting, on April 28. Grading was done on the immediately before planting. The soil was moist ,furrows and scalps, following a two-week period quent, light spring rainfall and cool weather. The 2g weather on the day of planting was considered y the investigator and the other forester in charge planting. Upon receipt at the planting sites, the stock led by a crew of especially trained forestry stu- Lder the supervision of the investigator and an- ofessional forester. [mmediately after grading, the stock was careful- :d in dug holes, in the middle of the furrows and epared prior to the actual planting. The five students comprising the planting crew had been 69 riously trained in the Special method of planting that used. The object of employing such a large planting was to accomplish all Of the planting on both expo- ; in a single, ideal planting day. This precaution lesigned to avoid the possible confounding effect On val of having the trees planted on different days. tions on one day might not be so very favorable for .nitial establishment as on another. Each planting hole was dug with a shovel, either middle of a scalp or at the bottom of a furrow. Le for each tree was dug immediately before the tree Lnted. Every effort was made to keep organic mater- Other extraneous debris from falling into, or being i to, the holes during planting. To this end the ed soil was piled only on bare, mineral soil before turned to the holes. Each hole dug was a foot or diameter and approximately one and one-half feet : no time was dry soil allowed to come into contact roots of the trees. The trees were taken out Of king of moist Sphagnum moss only for a short time 1g and re-packing in the planting pans. ;e special method Of hole-planting used, although xpensive, laborious, and time-consuming one, is commonly recommended as the very best for insur- urvival. It allows ideal placement of roots in nsions, with Optimum radial distribution, and so 70 :most of the roots extend downward into the soil at an 'oximate forty~five-degree angle. This method simulates root disposition resulting from natural geotropic re- se of young trees growing under natural conditions, rhen undisturbed (Bates and Pierce 1913; Rudolf 1950) . method, called ”cone planting," is a variation of the iar center-hole method. In cone planting a relatively large planting hole ’ in cleared soil with a spade or a shovel. The ex- d soil is carefully piled on a cleared spot at the 7 the hole. Using the best topsoil from the mater- avated, a small, cone—shaped mound is then formed e hands, at the bottom of the hole. The cone must enough to permit all of the roots of the tree to ad out and distributed around the surface of the his is to prevent crowding of the roots, or jamming 1g back of the root tips. After the cone is formed, is then carefully placed upright on the top of or cone, the roots are gently separated with the s, and they are then spread radially and downward :one surface. This method is adapted to plants ding root systems, or to those that have been :1, rather than to plants having well develOped After the roots are arranged over the surface s of soil, more of the best topsoil is added ands . The soil is gently sifted between the ’71 pread-out roots and packed with the bare hands so that he roots are neither forced into a vertical nor a hori- >ntal plane. As the soil is sifted into the hole, and fore it is packed, the plant is raised slightly so that e root collar will be even with the surface of the sur- mding soil. When the tree will stand by itself, the t of the excavated soil at the side of the hole is ad- to fill up the hole, packed firmly with the bare hands, further firmed by being pressed down with the feet. It is thought that the method of cone-planting in loles is the highest practicable refinement developed r to assure the planting of young trees with a min- of disturbance, damage, or so-called "planting shock." ethod assures that adequate space is available for ing the roots, so that the tips will not be bent Jon themselves, as often happens in ordinary plant- .hods. Distribution of the roots in three dimen- n the soil mass is better assured than in any other >f planting, since each root is practically placed .ally. The sifting of the soil prevents desicca- the roots from the leaving of air pockets in the from inadvertent inclusion of masses of raw or- .erial . Mechanical damage to roots from compres- »act, or skinning is reduced to a minimum. 72 Weafimm'Before, During, and After Planting. It finned imperative for the success of the investi- twt the weather and soil-moisture conditions be ‘Uuatime of planting. Warm, dry, sunny weather ve made it difficult to keep the roots of the [at as they were being planted. A drought either aly preceding or following the planting might tried the soil that all or most of the little ;ht have succumbed at once on either or both of .ures, thus confounding the results. Such a mass 'under similar conditions sometimes nearly des— est plantations, no matter how vigorous the es, how carefully they are planted, or how well might be suited to them under normal circumstances. ccurrence when the trees for this investigation ted would have probably delayed the beginning of for at least a full year. 3 stated in the section on planting technique, yr for about two or three weeks immediately pre- 2 planting, and on the day of planting, was cool The planting day itself was cool, partly uactically without wind, and with an intermit- nuaters were inserted parallel to the soil sur- tc> be at a uniform depth at all points. Uni- pliacement in depth was checked by inserting 79 fine steel wire into the soil and down to the thermo- ter bulbs and thermograph elements, and measuring. The ems of the thermometers projected out from the frames 7ficiently far into a small recess in the surrounding .l to permit readings of all temperatures within the ges encountered. The recesses were covered with small, ulated wooden plates, to protect the thermometers from lanical damage and extraneous heat effects. The soil-temperature frames were placed with their r edges at an inclination of 23% percent, parallel the average slope on each exposure. Thus the frame 1e south-facing slope was inclined at an angle of 23% ant toward the south, while the frame on the northwest- g slope was inclined from the horizontal at a 23%- nt angle in a direction 30 degrees west of nerth. . V—shaped wooden diversion barriers were placed im- .ely uphill from each soil-temperature frame in or- protect it from possible accumulations of surface- water which it was feared might wash the soil out frames if intensive storms should occur. This lpset the continuity and accuracy of the data ob- with the frames. See Figure 3, page 76, and Figure 80, for illustrations of the method of placement soil — temperature frames . 80 Figure A. ilu-Tknnperature Frame on South-Facing Exposure. hezuncuneters Uncovered to Show Method of Placement. August, 195A. 81 Mamurement of Soil Moisture. In an attempt to motswmeof the relationships between available soil- .smne mm.direction of eXposure, six soil-moisture gflingsmations were located on each of the two main dyfflmms. These stations were spaced at mechanical nwals,three on the upper section of each main plot tfluee on the lower section. At each soil-moisture sampling station, moisture rminations were made at three different depths: (l) aches. (2) 6 inches. (3) 24 inches. At each depth 1youcos plaster-of-Paris resistance-block was embed— ,n a horizontal position. All resistance-blocks were and were soaked in distilled water for 2h hours be- being put into the ground. Thirty—six blocks were altogether. Holes for emplacing the blocks were bored with a runi soil auger, in order to disturb the surrounding s inttle as possible. In order to obtain good con- etween the blocks and the soil, fine, sifted soil :urwned to the holes and firmed around each block. .1. e}u:avated from the holes was segregated by depth, 11ru1eCi to the holes in reverse order from that in t was taken out. This procedure was followed in mat: Ialocks at different depths should be surrounded ‘ned soil as similar as possible to the natural the different depths . 82 he resistance-blocks were installed in early 954, in order to give them time to come into com- ilibrium with the surrounding soil. elative available-moisture conditions of the expressed by the electrical resistance of the .ocks, were determined by the use of a modified Le bridge. Specifically, a Model 351 Bouyoucos Meter was used, giving readings directly in ap- : percentages of available moisture in the soil :3 1950; Bouyoucos and Mick lQhO). This instru- s~the old-type, tinned-electrode moisture blocks. >nly relative differences in trends of available sture between the two exposures, and among the Lons on either exposure, were considered necessary, -moisture meter was not calibrated separately for ; on each exposure (Limstrom 1952). It was con- ;hat such calibration would have been necessary 'ery exact measures of available water were re- :ouyoucos and Mick 19AO). The investigator sub- :d this Opinion by personal consultation with the of the moisture meter.1 He advised that in his under the circumstances prevailing on the two ,, calibration was not necessary. He further ad- Dr. G. J. Bouyoucos. 83 sed that, with the soil types involved, and in View of afact that only comparative soil-moisture trends ap- red necessary, adjustment Of meter readings to compen- e for differences in soil temperature were not neces- 7. He stated that in his Opinion errors Of determin- m within a range of no more than plus or minus two ent of available moisture were likely under the most eme conditions that might be expected to be encoun- 1 on the two exposures. The range of sensitivity of the soil-moisture me- ncludes all of that available soil moisture between ilting point and field capacity. Moisture values >tained by merely noting the resistance readings on ter, after suitable adjustment. The meter dial is ted directly in percentage of moisture availability. Readings on the moisture meter of 60,000 ohms or corresponding to a percentage Of about 6 to 10 of le moisture at normal temperature ranges, were re- as approaching the critical point of permanent wil- ~ most plants. All moisture-meter readings were fore 8:00 a.m., when soil temperatures on the two 8 were most nearly comparable. With such precau- was considered that relative soil-moisture trends IO slopes were closely indicated. Thus the neces- -eading and recording separate soil-temperature 8h .lues at each of the 36 block locations each time the ter readings were taken was thought to be obviated. During the first few weeks of the investigation, {later during periods Of frequent rainfall accompanied variable soil-moisture values occurring within short iods of time, meter readings were made daily. Later, ar the essential pattern of the soil-moisture trends he two exposures was learned by experience, readings made only every other day or, occasionally, at longer ovals. It was learned that during periods Of drought, luring the winter when the soil was frozen or snow- ed, soil-moisture values would essentially stabilize pnsiderable periods. During drought periods the zppeared to dry out to certain points at all three , after which it seemed to become no drier. It is ‘3 that this condition may represent the critical .on in which possibilities of imbalance between re- ntake of moisture by roots, and accelerated trans- ‘1 by the crowns of the planted trees, may account for the mortality that occurred on both exposures. soil is frozen in the winter, the moisture meter practically inoperative, in the sense that solidly >il yields almost uniform readings of 10 percent 85 Measurement of Solar Radiation. Comparative so- .ar radiation received at the two exposures was measured 1y Livingston radio-atmometers (Fuller 191h; Weaver l9lt; ivingston 1915, 1935; Burns 1923; Thornthwaite 1940; errell 1953). A double comparison was made of evapora- ion differentials from a set of black and white Living- ton atmometers placed near the center Of each main study lot. This method provides for low-cost measurements of elative solar radiation between different locations. are it not for the prohibitive cost Of installation, nrheliometers would probably have been preferable. One black and one white atmometer was installed enach.study plot, with the atmometer bulbs about two et;:from each other and two feet above the soil surface. e tilack bulbs absorb more radiant energy than the white es. Therefore at any point the black bulbs will evap- ate rmare distilled water than the white ones. Evapora- 3r} fdxom each bulb is standardized by application of a Ltable conversion factor, varying for each bulb. A Tferwnnce in solar radiation falling on the south-facing >pe as compared to that on the northwest-facing slope expressed in terms of a percentage. The slope on which , largest amount Of radiation is indicated is taken as p percent, although, for comparative purposes only, the pe receiving the smaller amount of radiation might 86 s waU.be used. The formula by which the compara- nomum of solar radiation received at each slope ilculated is given below: Percentage of ra- diation received .wixOt level or the sixteen-foot level above the ground are desired for any given period of measurement, they >uld be calculated in terms of averages. The chemical- »sorption hygrometer permits determinations of mean val- :s of absolute humidity at any location by the most di- rct method. This is the method of abstracting all of Le water vapor from a measured volume of air, for any .ven period Of time, and then weighing the water. A itailed discussion of the nature and operation of the .emical-absorption hygrometers follows in the sections ,titled, "Measurement of Evaporation and Transpiration," .d, "The Chemical-Absorption Hygrometer," pages 96 to '2, and 10h to 111. 96 Measurement of Evaporation and Transpiration. The term "evaporation," in biological nomencla- lure, commonly means water loss to the atmosphere other when that lost by transpiration from plants (Geiger 1950). imilarly, "transpiration" refers to the escape of water rom leaves through stomata (Seifriz 1938). The combined nd practically inseparable total of evaporation plus ranspiration is designated as "evapo-transpiration." t is defined as, "The combined loss of water (through vaporation and transpiration) from the soil and vegetal over on an area of land surface." (Society of American oresters 1950). The primary purpose of the chemical- bsorption hygrometers used in this study was to give an stimate of comparative, if not absolute, evapo-transpir— tion from the two exposures studied. Recent studies in aerodynamics have supplied in- >rmation about atmospheric turbulence and the mechanism ? turbulent air-interchange which has made possible the avelopment of a method for determining comparative evapo- ~anspiration from land surfaces (Thornthwaite 1940, 1941; lornthwaite and Holzman 1939, 1940, 1942). This method lploys a closely calibrated chemical-absorption hygrom- Aar which draws measured volumes of air from two levels mi records simultaneously the total wind movement at Le same levels. 97 Water vapor is furnished to the atmosphere only rom the evaporating and transpiring surfaces of the land nd water (Geiger 1950). Transfer of water molecules way from a natural surface by turbulent mixing of flowing ir strata near the ground is many thousand times as ef- ective as molecular diffusion. It is almost entirely ue to this process that moisture is lost from evaporat- ng surfaces freely eXposed to the air (Thornthwaite and olzman 1942). Turbulence arises largely from the fric- ional resistance between the ground surface and a moving ir mass. This turbulence has been shown to be active or a number of hundreds of feet above the ground. Suc- essively higher strata of air move more rapidly in a orizontal direction than those which are lower. A shear ffect is thus set up, causing upward and downward dis- lacement of small masses of air which retain a large omponent of the horizontal movement they possessed be- are displacement. The vertical limits of detectable urbulence induced by frictional influences at the ground irface are called the "turbulent layer" in the atmos- mere. The mechanical mixing of the air which occurs in ie turbulent layer tends to establish an adiabatic dis- ribution of properties in the air. Changes in tempera- ire, and consequently in moisture concentration, which 98 :cur during the lifting or sinking of air masses, and liCh are due to processes occurring within the masses 1d not to addition or subtraction of heat from outside )urces, are designated as "adiabatic" changes (Trewartha 9h3). If mechanical mixing of air tends to establish 1 adiabatic distribution of properties, it tends also > eliminate differences in moisture concentration in 1e air. Thus if any given air mass were static horizon- 1lly, and if no moisture were added to or withdrawn from 1e bottom layer of the mass, the moisture content of the 138 would become uniform throughout. If a ground surface is warmer than the air layer .rectly above it, water vapor will be emitted from it > the air layer. Turbulence arising from air movement .11 cause this vapor to be transported upward and to be :attered throughout the turbulent layer. Thus, as long : water vapor is flowing upward into the turbulent layer, Le moisture concentration will be highest near the ground (d will diminish upward. Under such conditions a "posi- 've" moisture gradient is said to exist. Water vapor arly always goes upward except under special conditions dew formation confined generally to short night-hours leiger 1950). When dew is formed a so-called "negative" "inverted" moisture gradient is said to exist. A pos- ive gradient owes its existence to continuous additions 99 f moisture from below. If evaporation were to cease, ater vapor would soon be distributed uniformly by dif- ision through the turbulent layer. NO moisture gradient Duld then exist. Condensation of atmospheric moisture to form dew, process sometimes designated as "devaporation," can con- Lnue only so long as removal of moisture from the air :ratum contiguous to the ground surface continues. With given intensity of mixing in the turbulent layer to >me indefinite distance from the ground, the greater the zte of either evaporation or devaporation the greater .11 be the moisture gradient, positive or inverted, [ere evaporation is occurring, which is the usual situ- ;ion, moist air from near the ground is lifted upward (d is continuously replaced by drier air from above. Lis occurs at a rate proportional to the intensity of Lrbulent interchange. For a given moisture gradient to rrsist, the greater the turbulence the greater will be .e required rate of evaporation. The intensity of tur- .lence is prOportional to the difference between the te of horizontal movement of air near the surface and .e rate of horizontal movement of strata above. The ’eater the difference the greater the shear tendency. .us it is possible to determine the value for evapora- On from, or condensation to, a natural ground surface. 100 'his is done by observing the direction of the moisture ‘radient, or the difference in specific humidity, between wo selected levels in the turbulent layer, combined with measure of the turbulent mixing along this gradient Thornthwaite and HOlzman 1939). This technique involves he use of the chemical-absorption hygrometer. It pro- ides a method by which the actual evaporation from dif- erent areas can be directly compared, although not ac— ually measured in totality. The formula for calculation f evaporation or devaporation uses an arbitrary meteor— logical coefficient for turbulent mixing, and a value or the rate of change of moisture concentration or spe- ific humidity, with respect to height above the evapora- ing surface. Both of these values are determined from oservations of wind movement and specific humidity at NO levels in the turbulent layer for any given period 1ch as one hour or twelve hours. Density of the air is >nsidered uniform over the short distance between the vo levels where the wind movement and the moisture con- antration are measured. The formula for calculating a alue for comparative evaporation or condensation at any Lven location at the surface of the ground is given on 1e following page. This calculation does not involve 1y kind of correlation between observed evaporation from ins of various sizes, shapes, and exposure, and the ev- >o-transpiration losses from natural surfaces. Neither 101 s it correlated with the various macro-meteorological lements. (M1 ' Me)(W1 ' W8) _ Comparative evaporation or #752 V ‘- devaporation Where: M1 is A large moisture-concentration value from one of the levels measured, in grams. M is A small moisture-concentration value from the other level measured, in grams. W1 is A large wind-movement value from one of the levels measured, in miles. W is A small wind—movement value from one Of the levels measured, in miles. V is Volume of air measured, in cubic centi- meters. The chemical-absorption hygrometer was originally asigned to measure the actual emission of water vapor com a natural evaporating surface. Some years of exper- nentation with it convinced its originators that some rror in the evaporation equation, as it was derived, revents it from yielding a fully satisfactory value for :tual or absolute evapO-transpiration. However the same cperimentation established the utility of the instrument >r close determinations of comparative evapo-tranSpiration ilues among different sites, with multiple installations.l 1Personal communication, C. Warren Thornthwaite. 102 Within the limits of a small residual error, the :hemical-absorption hygrometer measures emission of water ‘apor from an evaporating surface in a manner analagous .o the measurement of water loss by surface outflow from reservoir. Here a weir or flume might be used. Dis- harge through a weir is the product of cross-sectional rea and current velocity. Similarly, water-vapor dis- harge into the atmosphere from an evaporating surface is he product of cross-sectional area, which is taken as nity, and the velocity of transport upward. This veloc- ty is expressed in terms of the intensity of turbulent ixing combined with the gradient of specific humidity. One of the main advantages of the technique is hat it permits approximations of the flow of moisture n either the upward or downward direction, so that either vaporation or devaporation values may be obtained. It s hOped that the absorption-hygrometer data accumulated 1 this study provides for a reliable estimate of the Dmparative tranSpirational effects as they are exhibited 1 the two exposures where the study plots were located. A general, panoramic view of the main study plot 1 the south-facing exposure is shown in Figure 8, on age 103, as an example of the location of the various istruments on either exposure. In the figure the instru- ant shelter for the air- and soil-thermographs is at the ar left. The anemometer tower, radio-atmometers, and 103 Figure 8. Main Study Plot on South-Facing Exposure. Five-Year-Old Plantation of Red Pine Surrounding Plot on North, East, and South Sides. August, l95h. 104 ain gauge are distributed about the center of the plot. he air-intake tower for the hygrometer, and the walk-in helter protecting the instrument, are on the right. The Chemical-Absorption Hygrometer: Operational etails. Other methods than that employing the chemical- bsorption hygrometer may be used for approximating rel- tive evapO-transpiration from natural surfaces, but they re ordinarily too expensive, too labor-demanding, or naccurate. Humidity may be measured also by any of three ompletely independent techniques. One of these involves he use of wet-and-dry-bulb psychrometers, which fail to ive a cumulative record of the humidity. They must be sad at frequent intervals, requiring the constant atten- ion of at least one Observer. Recording psychrometers re available, but their accuracy appears not to be de- endable, and they fail completely at temperatures below me freezing point. Hair hygrographs give a continuous, but inaccur- :e, record of the relative humidity. To obtain records 3 two heights some arrangement must be made for lowering 1e upper instrument for servicing. Hair hygrographs ive been used with some apparent success in many experi- ents, but they tend to drift out of calibration and thus ‘e notably unreliable. The labor involved in their fre- tent recalibration prohibits their general adoption 105 where accurate humidity measurements are required. The dew-point recorder is the most accurate in- strument for measuring humidity of the air, but it is a very expensive device not generally available for most meteorological investigations. This instrument records the temperature of a metal mirror which is maintained at the dew point . The chemical-absorption hygrometer draws air from the same two levels at which the anemometers are placed, permitting measurements of absolute humidity means for given periods, if desired. Essentially the hygrometer consists of a very closely fitted, electrically driven glass reciprocating pump which draws equal samples of air alternately from the two levels. The pump is driven by a special, six-volt, constant-speed, battery-Operated The battery is an ordinary, easily procurable, Storage batteries motor. so-called "hot shot" dry-cell type. may also be used. One dry-cell battery is ordinarily suf- ficient for a run of about 30 days, when Operated twelve hours per day, or half as long at 24 hours per day. The glass pump of the hygrometer is calibrated to draw approximately five cubic centimeters of air from me of the two levels at each stroke of the pump. The .i:~:is (irayni alternately from each level through two tandard desiccating U-tubes, one tube for each level of 106 Le atmosphere sampled. Each U-tube is filled with al- lina (aluminum oxide, A1203) and fitted with valve stop- :rs. Each tube contains enough oven-dried alumina for >out a 24-hour run, unless the relative humidity ap- ~oaches 100 percent all or most of the time. The alum- 1a is dried in an electric oven at a temperature of 50° C. for twelve hours. Tubes are then weighed on a {boratory balance, to an accuracy of plus or minus one en-thousandth of a gram. Installed in the hygrometer, 1e tubes will pick up all but about one-tenth of one arcent of the air drawn through them. By weighing the -tubes before and after a run, the weight of the water >stracted from the air at each level can be obtained. 1e volume of the air from which the water has been taken 5 it passes through either one of the tubes is deter- Lned by multiplying one-half Of the number of pump arokes recorded over the period of sampling, by the cal- >ration of the pump. Thus the weight of water abstrac- ad per unit volume of air gives the mean absolute humid- ;y for the period of sampling. Calculations with the Lfferences in the mean absolute humidity at the two lev- Ls from which air samples are taken will derive the mean >isture gradient for the period of sampling. See Figure 9, page 107, for a general view of 1e northwest-facing exposure, showing location of shel- 3rs and various installations. Figure 9. Main Study Plot on Northwest-Facing Exposure. Shelter and Air-Intake Tower for Absorption-Hygrometer :Left. Anemometer Tower at Right Center. Shelter for Air Thermograph and Soil Thermograph at Right. August, 1954. 108 A close approximation of the comparative evapo- ation on a given site is Obtained by combining wind- ovement data with moisture-gradient data, for any given sriod of about an hour or longer. This is accomplished v the use of an empirical formula (Thornthwaite and Holz- an 1942) utilizing as variables the moisture gradient ad the intensity of turbulent mixing. The latter vari- ble is derived from the wind gradient, which is usually asitive. Under unusual circumstances, such as when sur- ace-air drainage down a slope is rapid, an inverted ind gradient may be recorded for a time. This is when is horizontal movement of wind is greater near the soil urface than higher above it. However, the intensity of urbulent mixing is considered to be a direct function f the wind gradient, whether the gradient is positive r inverted. Thus only the moisture gradient and its irection is necessary to estimate the amount of evapora- lon or condensation. The wind gradient is simply the difference between me total miles of wind recorded at the two levels for me time interval to which the moisture measurements ap- Ly. The mean moisture gradient used in approximating vapO-transpiration on any given site, or, most practic- Lly, in measuring and comparing relative evaporation on ifferent sites where hygrometers are used, does not have 109 o be determined in terms of absolute humidity for each evel in the atmosphere. In the evaporation equation in ts simplified, practical form, the mean moisture gradi- nt is expressed simply in terms of the difference in rams of moisture abstracted at the two different levels or the period of sampling. For example, if in any given period of Operation f the hygrometer, The tube for the lower level abstracts 2.0000 grams The tube for the higher level abstacts 1.0000 gram The difference, 1.0000 gram, ndicates that net evaporation has occurred for the per- od of operation, with a positive moisture gradient of ne gram. If, however, the tube for the lower level hould pick up less than the tube for the higher level, negative or inverted net moisture gradient has prevailed. ondensation or devaporation has occurred for at least art of the time during the sampling period, or in any vent total condensation has been greater than total evap- ration. An inverted moisture gradient exists when con- ensation of water vapor out of the lower level of the tmosphere is more rapid than the water vapor can be re- laced by moister air drawn down from upper levels by he mechanism of turbulent air-mass interchange. 110 Knowledge of the mere existence of evaporation mnsation on a given site is not sufficient, how- 0 derive a comparative value for these phenomena. sture gradient must be multiplied by the wind t existing between the four-foot level and the -foot level in the atmosphere from which the mois- mples were taken. The product is multiplied by itrary constant #752. The new product is divided volume of air that passed through either of the tubes during the period of sampling. The quotient ject to an as yet undetermined but apparently asidual error, the amount of evapo-transpiration ansation that occurred during the period of the g, in inches. few further notes on the details of the Operation :hemical-absorption hygrometer may be helpful in .g the technique involved in its use. Various gents were tested by the originators of the ins- ‘before alumina was selected as the most nearly terial. Such an agent should remove all, or ll, the water vapor from the air sampled. It ave a very large water-holding capacity per unit a. It should be capable of complete reactivation axnethods, so that it may be used and re-used in- .yu It should be safe and convenient to handle 111 :the field as well as in the laboratory. Alumina ap- rently meets all these requirements more nearly than her available substances. Alumina will absorb (and sorb) nearly twenty percent of its weight in water. n air is passed through it, all but about 0.005 milli- ms Of residual water vapor per liter of air is taken of the air. When the chemical-absorption hygrometer is em- ed at evapo-transpiration-measuring installations, isions must be made for differences in absolute humid- at different seasons. The absolute humidity in sum- is usually much greater than it is in the winter. ’der that the desiccating tubes may not have their ities exhausted during periods of summer Operation, vgrometer pump is designed so that its rate of air 2- can be changed from about 9.0 liters per hour in nter to about 1+.5 liters per hour in the summer, ing upon the calibration of the pump. This is ac- shed by changing from a large winter motor-gear ialler gear for summer. The copper air-intake tubes leading from the air- tower to the hygrometer must be protected from ex- ; moisture or obstruction. Consequently the up- ; of the intake tubes are covered by a cylindri- to protect them from rain. The bottoms Of the screened against the entrance of insects. W CHAPTER VII SITE: FACTORS 0F MORTALITY AND SURVIVAL Drought. If drought injury during the first wing season after planting is indeed a main cause of 7y mortality in coniferous plantations planted in the .ng, it is thought that excessive transpiration, rath- han direct heat injury during hot, sunny days, is the ary factor. Evidence indicates that with newly ted trees the transpiration rate can soon become too I for the yet too poorly established root systems to ,ce the water that is lost from the crowns. It seems y that, no matter how carefully little trees are ed, so-called "planting shock" upsets their normal >logical functions for a period of days or even Possibly, in planting, unavoidable damage to the te primary absorbing structures of the fibrous root , such as root hairs or mycorrhizae, may be the ex- ;on for the phenomenon called planting shock. Com- verience certainly tends to indicate that some such nship could exist. Usually, the heaviest mortality at plantations after spring planting on Open sites -n the first growing season. 113 Early drought injury and planting shock would ap- ar to be inseparably related to the death of young aes unless some recognizable disease infection, insect Testation, or other catastrOphic early injury should ount for it. However, in order to avoid mortality ar- ng from anything but the most rigorous drought condi— as, every effort was made in this study to plant the 1g trees in such a manner and at such a time as to re- : shock to them to the smallest practicable minimum. only was extraordinary care taken to avoid mechanical ge, crowding, unnatural disposition Of roots, and r unfavorable occurrences in planting, but all of the ; of each Of the two classes planted were most care- ' selected for apparent sturdiness and vigor. It be conceded, then, that if definite drought condi- existed after the trees for this study were planted, isurements of the micro-climate on one exposure in- d that the general drought conditions were consid- intensified on that SIOpe in comparison to the and if no other recognizable causes appeared to 3 for any differential mortality, drought would be Lse most suspect. Drought, as an expression of both macro-climatic ro-climatic influences, is emphasized as a prime E‘ plantation mortality by Kittredge (1929). He 11h tates: Critical weather conditions such as prolonged periods Of drought and extreme temperatures are so important in certain years that they may be responsi- ble for the difference between success and failure in a plantation. . . A drought period Of more than ten days at the time of planting or during the first season following will usually cause heavy losses am- ong the planted trees. The sooner the drought peri- od follows planting, especially in the spring, the more severe is the loss. As a conclusion from later work, Haig 32 El (l9hl) xpress essentially the same Opinion as Kittredge about he effect of drought on newly planted trees. They say: Mature trees are frequently independent of grow- ing season precipitation. Young seedlings, however, particularly during the critical two to three years immediately following germination, are largely depen— dent upon current rainfall. Unless favorable mois- ture conditions prevail during the early portion Of the growing season, seedlings frequently fail to root deeply enough to Obtain sufficient moisture later in the season for survival. When this study was planned it was thought that, espite the possible confounding effect of compensation mong the various interrelated factors Of any site, the eneralized effect Of one class of factors, micro-climate, n the sites studied might be recognized and demonstrated, f such an effect exists. If organic factors such as par- sites could be confidently eliminated from consideration, 5 well as minor differences in recognizable soil charac- eristics, the determining nature of micro-climate might hen be anticipated. In the presence of extreme micro- limatic conditions on any site, where it is apparent hat no other serious disturbances are Operative, micro- 115 be rnight reasonably be suspected as the prime cause y kneavy mortality. Baxter (1952) states that, "High trainire and water deficiency are responsible, in gen- kar more early losses in plantations than are fungi .nsects." Earlier, Show (1930) emphasized the pre- mnrt influence Of general and local climatic condi- slas determinants Of survival and mortality of plant- (Jf western white pine in California. Show states: Of all the factors which influence what can and can not be done in reforestation, certainly none is more dominant than climate, particularly moisture. . The most conspicuous failures have been due either to failure to gauge correctly the difficulties to be overcome or to a false idea of the ease of planting based on success in one or two favorable seasons. Show was Of the Opinion that soil-site factors a a compensating effect in relation to drought resist- 2, in that the better the soil on which plantations started the less the need for shade. Show was also. the Opinion that stock quality is one Of the prime fac- svin survival, and that the better the planting stock better the survival, other factors being equal. He lulthat poor planting methods had much to do also with "unity, depending on the general quality of the plant- ; site. Exposure. The effects of direction of exposure slopes on heat values related to droughtiness are com- rfly mumgnized, at least in their general implications. 116 'erson (1937), who spent much time and effort in the in- estigation of the factors Of mortality and survival in edwood plantations in California, became convinced that he correlation between drought damage and the direction f exposure Of plantations in mountainous areas was clear. erson states: It has been found in practically all planting studies that there is a definite relationship be- tween survival and exposure, particularly for northerly and southerly exposures. This is to be expected because two of the factors that affect planted stock most directly, moisture and temper- ature, usually vary with exposure. Where moisture deficiency, either owing to lack of soil moisture or excessive evaporation, and high temperatures are limiting factors, it is natural that norther- ly exposures would be more favorable for newly planted stock than southerly exposures. Person worked in conjunction with a number Of Cal- fornia timber companies to determine the effect Of dif- erent planting techniques, as well as the location of lantations, on survival. He concluded: Although there is a wide variation in survival among the plantings made by the different companies because of differences in planting conditions and methods, it is evident that the north and east expo- sures show a generally higher survival than the south or west. . . The differences in favor of north expo- sures as compared to south are definite both for the individual companies and for the averages of all the companies. Various phases of the relationship between direc- ion of exposure and other characteristics of the topog- aphy of a locality, accompanied by variations in the 117 micro-climate, have been studied by a number Of investi- gators since at least the beginning of the present cen- ;ury. Among the most notable of the early workers in :he field Of micro-climate and its effects upon plant .ife was the ecologist Cowles (1901), who emphasized the- lpparently dominant control by tOpography Of variations .n the micro-climate of a general region. He noted that :he control by tOpography is reflected in influences on evaporation rate, atmospheric humidity, wind movement, lir temperatures, soil temperatures, and the amount of solar radiation received from place to place. Fuller (1912) noted that relatively small differ- ences in local topographical features, particularly in ;he direction Of exposure, seemed to be the cause of dras- ;ic differences in rates of evaporation. Alter (1912), Loting that the solar radiation that a lepe receives is vncreased as its inclination increases toward the south, stimated that a slope inclined only five degrees from he horizontal is evidently as warm as the horizontal quivalent would be if it were moved southward for a dis- ance of three hundred miles. Shreve (1915) noted that outh-facing and west-facing exposures were decidedly armer and drier than north-facing and east-facing ones. e commented later (Shreve l92h) on the great differences bservable in soil temperatures on south-facing situations 118 mpared to those on north-facing ones. Pearson (1920) .ater Bates (1923) made numerous Observations on the :ts of topography on local climate, working through- the same general region of the Southwest as had Shreve. noted that the effect of direction Of exposure on survival of different species Of young forest trees nded on whether summer moisture or winter temperature 'OI‘S were the most critical. They found that on the : droughty soils, summer moisture deficiencies on :h-facing exposures could be sharply limiting. Wind effects on southerly exposures which face vailing winds appear tO intensify the inherent drought- ss Of the sites. In northern latitudes the warmer ex- ures generally are characterized by lower relative hu- ities than the cooler ones, since wind appears to re- :e the humidity of. the surface air by displacing moist r and mixing it with drier air. Gail (1921) found that a relative humidity on warm, windy, southwest-facing apes in Idaho averaged over twenty percent lower than at on cool, calm, northeast-facing slopes that were eltered from the prevailing winds. These winds are latively dry in that section Of the Northwest. It is [ought that the effect of drying winds in keeping rela- .ve humidities low on droughty lepes is most signifi- amtly manifested in an increased transpiration rate Mitchell 1936). _ 119 insistently higher evaporation rates on south-facing Opes than on north-facing ones in Indiana were report- by Potzger (1939). Vegetation. Because of the apparent general lilarity Of the vegetation types on the two exposures died, it is not thought that any differences that ex- ed had any appreciable effect upon the comparative rival and mortality results. When the two exposures a selected as sites for the study, the herbaceous veg- ion on them was noted to be closely similar in compo- On, density, and height. Furthermore, the thin com- nt Of woody vegetation that constituted the principal arence on the northwest-facing exposure from the con- »ns on the south-facing one was eliminated by spray- nd cutting in 1953. A silvicidal foliage-spray con- ng of an 0.5 percent solution of 2,L+-D was applied a smaller woody vegetation. The larger vegetation Lt Off flush with the ground surface, and the silvi- solution was applied to the out surfaces. Only a regeneration of low 3.112113 brush had appeared as 5 August, 1955. The bared soil in the scalps and in the furrow , as well as in the slices adjacent to the furrows, d free of any woody regeneration for the seventeen in which the study was carried on. Similarly, 120 ary little grass invasion occurred, mostly along the tside edges of the slices. A very thin growth Of low rbs appeared to be establishing itself at various spots the bare soil by August, 1955. Figures 10 and 11, .ustrating the condition Of the vegetation on the two osures at the termination of the field study in Sep- ber, 1955, may be found on pages 121 and 122. _S_oi_l_§_. Since every effort was made to select exposures for the study which would have soils as lar to each other ecologically as would be recogniz- , it is hoped that no Obscure edaphic differences could tend to confound the comparative survival re- ; existed. The best professional advice and assist- was secured for the soil investigation. No later nce has been recognized that would appear to indi- the existence of confounding soil differences. It is Of course proposed that the temporary and - marked soil differences in terms of contrasts in Oisture availability between the two slopes that ad during the droughty periods of the summers Of 1d 1955 are not ecologically insignificant. How- Le assumption may be made that such differences droughts are expressions Of the contrasting micro- 5. Therefore it is felt that such soil-moisture aces might better be considered as indirect fac- 121 Figure 10. ' Vegetation on Main Study Plot on Northwest-Facing Exposure. September, 1955. 122 . l ohms-Id. .ng,-“.1. J. -, . H. q,- a 'I Figure 11. Vegetation on Main Study Plot on South-Facing Exposure. September, 1955. 123 rs of the two micro-climates rather than as differences 1erent in the soils themselves. Although the study involved a consideration of ‘.l-moisture availability at different depthsin the 1, no attempt was made to prove any theory that soil- sture deficiency was the sole cause of the mortality ng the planted pines. In fact, no attempt was made prove theories of any kind, but rather all efforts a bent toward isolating a single complex of factors, ro-climate, from the possible dominance Of other fac- : singly or in combination. It was thought that if a ’erence in mortality between the two exposures great gh to be statistically significant might occur, it t be possible also to detect a significant correla- between this mortality difference and any measurable arence in micro-climate between the exposures. It ’ully realized that the possibility of isolation Of ingle factor, or single complex of factors, for sep- identification and evaluation in terms of differ- ]. mortality might be challenged by some persons. :udy was embarked on with a full realization that an Ligation of individual factors does not always, or t ever, solve vegetation problems. Vegetation is 11y conceded to be the result of many compensating Pallel factors working in concert. 12b From this and other studies it is apparent that >il moisture, in response to changes in micro-climate, rcreases very rapidly in exposed soils with the long riods of warm, sunny weather that are common in the te spring and through the midsummer period in many aces. Such a decrease would seem to be a very import— ; factor contributing to heavy mortality on exposed es. Planting Technique. Although it was intended in 3 study to employ the very best planting technique ;ible, which would nevertheless be only a refinement he customary techniques used in commercial forest ting, it is not unthinkable that some undetected dif- aces in the handling Of individual trees might have :ome confounding effect on the results Of the study. er, in an attempt to minimize, within practicable s, mortality which might be directly attributable stakes in planting technique, every effort was made anting the two slopes to maintain Optimum conditions. event it would seem that, if mistakes were made, Duld as likely have been made at random with one 3 with any other, and would as likely have occurred 'uently on one exposure as on the other. Conse- it is assumed that no cumulative effect Of possible zal instances of poor planting would have occurred 1" exposure. 125 It was not considered that planting technique is necessarily the sole, or even the predominant, deter- minant Of survival or mortality in forest plantations. It is realized, however, that both research and common experience indicate that very poor planting methods can Often result in unsatisfactory survival. The most comprehensive statement of the apparent mistake of over-emphasis on planting techniques as a cause of plantation mortality is probably by Wakeley (1951) in his treatise on the planting Of southern pines. Wakeley states: Incorrect planting is not the only, and may not be the most frequent, cause of poor initial survival. Assuming arbitrarily that all failures are the plant- er's fault Often results in costly annual losses which could easily be prevented by correcting some error in planting policy or nursery practice. . . Ex- aggerated notions Of the effects of planting tech- nique on initial survival have sometimes led to over- refinements of the planting process, including those Of tool design and manipulation. Even though poor planting technique may not be the commonest cause Of poor initial survival, good judge- ment dictates that reasonable efforts should be made to reduce planting errors to a minimum where other causes of mortality are to be investigated. The desirability Of good Planting practice is well summarized by Toumey and KorStian (l9h2), who state: j. Planting is always accompanied by more or less Injury to plants. Even under the most favorable con- gitions and with the exercise of the utmost care, ere ls always some arrest of growth. In planting: 126 growth should be interrupted to the least possible degree consistent with economy. This is necessary in order that trees may become established quickly. NO concessions of technique were made to economy in the planting for this study. Poor planting is in it- self poor workmanship. In many Michigan plantations in recent years, most Of the young trees that died during droughts have exhibited root developments inferior to those Of the trees that survived. Poor planting was sus- pected to be the most likely cause Of much of the poor root development (Rudolf 1937a). This indication alone was enough to impel the investigator to bend every effort toward Obtaining the best planting job possible for this study. The pre-planting technique of shallow furrowing and scalping was adopted although Minckler and Chapman (1948) recommend somewhat deeper Operations. They advo- cate also furrowing and scalping to at least a total 'width Of eight to ten inches for planting in heavy sod, dense broomsedge, and dense, rank weeds in the Central States Region. Shallow furrowing, if it is deep enough to kill and prevent the early regrowth Of competing her- baceous vegetation, has the advantage of giving the young trees more weathered soil with a higher nitrogen content to grow in. Furthermore the sod on either Of the exposures was not heavy, nor did either of the sites support a 127 growth Of dense, rank weeds. The bared soil in the fur- rows and scalps, being two feet wide, exceeded consider- ably the minimum recommendations Of Minckler and Chapman. It is hoped that an additional measure Of con- trol beneficial to the purposes of the research was achieved by completing all of the planting on the two ex- posures in a single, ideal planting day. The desirability of such a procedure in investigations of plantation prob- lems is emphasized by Wakeley and Chapman (1937). They state: Except in a test Of season-Of-planting, or Of weather-at—time-Of-planting, all blocks should be planted on one day. If they are not, some Of the stock will be subjected tO one set of weather con- ditions (risk of drying out, etc.) and some to an- other. In fact, a week of bad weather intervening between two planting days may seriously derange the experiment. Even though the most refined of planting tech- niQUGs can not but be accompanied by at least some plant- ing shock, the greatest danger in spring planting, namely the risk of the young root systems becoming too dry dur— ing lifting, planting, or during the first few weeks af- ter planting, would seem to have been minimized in the initial phase of this study. The careful lifting of the StOCK, the quick transfer Of the stock to the planting sites, the planting during the most favorable season and on a damp, cloudy day, and the unusual care taken in dig- ging the holes and emplacing the roots would seem to 128 have assured the least disturbance to the vitality Of the trees as is possible to Obtain in normal practice. Genetic Variations. It is impossible to evalu— ate with any confidence the problematical effect Of dif- ferences in genetic qualities or origin that may have ex- isted in the individual trees planted for this study. As is yet common in North American nursery experience, the nursery from which the trees were Obtained is ordin- arily unable to secure the large amounts Of certified seed of known origin that would be desirable for its extensive requirements. All that could be done to min- imize the problem of possible genetic differences existing among the little trees used in this study was tO be as~ sured that the stock Of each class was grown from seed Of a common lot, collected in one climatic region, and obtained all in one year. Comparatively little appears to be known of the significance Of genetic characteristics in relation to the response of planted trees to micro-climatic and other site factors. This investigator could discover little OI‘IMTUhing on the subject in the literature. Baxter (1952) in his comprehensive treammau;cd‘the broad sub- ject cfl?.forest pathology in general, does make one nota- ble comment. He states: Genetic resistance to drought is difficult to separate from environmental factors, and much re- 129 search must be done before it is possible to distin— guish clearly the effect of site on trees during dry years. Insects. None of the trees planted for this study showed any recognizable evidence Of insect infest- ation or damage, either when they were living or after they had died. All of the trees, either when they were living or after their death was conclusive, were examined closely for any indications Of attack from such common insects as European pine shoot moth, sawflies, aphids, and scale. None of these could be found on any Of the trees at any time, although an infestation of both shoot moth and sawfly on a few Older, planted red pines on other areas which were near to the planting on the north- west—facing exposure occurred early in the growing sea- son of 1955. This infestation was controlled very quick— ly by a pre— and post-emergence spraying with DDT, and by clipping and burning. When the soil mass dug up with each dead tree Was soaked Off, dried, sifted, and Otherwise examined, no grubs, root weevils, or other harmful soil insects could be found in any instance. An especially alert vig- ilance was maintained for any sign of root-destroying or- ganisms, since if trees had been found to be affected by these agencies there might have occurred a complete confounding Of the other results of the investigation. 130 It is the Opinion of the investigator that the possibil- ity that mortality on either exposure might have been caused, or contributed to, by insect attack can be com- pletely rejected. Rodents and Other Large Animals. Except in one unusual instance, no evidence of possible rodent damage to any of the small, planted trees was observable at any time during the course Of the field investigation. NO girdling of stems was Observed at all, either on those trees which survived or on those which died. Both mice and rabbits were occasionally Observed on or in the vic- inity of the plots, but these animals were apparently not a factor in the survival or mortality Of the trees. In one baffling instance, one apparently healthy tree on the south-facing slope was found to be cut Off cleanly near the soil surface with a smooth, diagonal cut, as with a sharp knife. NO trace Of the severed tOp could be found. The tree had been examined three days previous- ly, and had shown no trace of disturbance of any kind. It is to be speculated whether the top was cut off by a rabbit or other sharp-toothed rodent, and removed, or whether vandalism may have been the cause Of the damage. In any event the death Of this tree was not considered to be related to the Objectives of the investigation. It is thought to be an isolated, extraordinary instance, 131 and no consideration was given to it in the analysis Of the data. In addition to the single tree destroyed by un- known causes on the south-facing exposure, one tree on the northwest-facing one was also destroyed. This tree was found to be broken Off at a height of about one inch above the soil surface, and to have been crushed violent- ly into the ground. When examined three days previously the same tree had appeared to be perfectly healthy, with no trace Of damage or other disturbance visible. Perhaps again, vandalism, the carelessness Of a hiker, or tramp- ling by deer may account for the death of this second tree. Deer are not common on the Kellogg Forest, but are seen occasionally. In times of wet weather, deer tracks were Observed from time tO time on both exposures, but infrequently. NO evidence of any browsing by deer on the little pines was ever Observed. Since the death Of the second tree was apparently an extraordinary event, from causes unrelated to the factors in general under Observation in the study, no consideration was given to it in the analysis of results. There are no livestock on the Kellogg Forest, and visitors only rarely enter the compartment where the in- vestigation was carried on. Consequently it is consid- ered that no appreciable trampling effect or other dis- 132 turbance Of the soil from the activities Of large animals or unauthorized persons ever occurred on the study plots. Parasitic Disease. According to Boyce (l9h8) "disease" in plants may be defined as, "an interrelated group Of abnormal physiological processes resulting in variations from the normal structure, from the normal function, or both." This study deals primarily with the possibility that differences in survival that may occur on two particular sites with contrasting micro-climates may be traceable to the non-living environment, after organic factors have been eliminated from consideration so far as is practicable. The study is not primarily concerned with those diseases caused by the parasitism Of animals, fungi, or other pathogenic organisms unless such diseases, if recognizable, would have acted to con- found the results. Unfortunately, diagnosis of the cause or causes Of disease Of any kind in young pines, by means of di- rect examination of the individual plants themselves, can be a very uncertain proposition. Rudolf (1950) de— scribes this situation very succinctly, as a conclusion from his own plantation investigations. He states: Although some agents of mortality leave such un- mistakable imprints that it is very easy to deter- mine what they were, the great majority Of them do not. Another difficulty in diagnosis is that mortality often is induced by several factors act- ing in conjuction. Often the separate roles Of each factor cannot be determined. 133 The direct cause Of most infectious diseases Of trees and other plants is commonly recognized as micro- SCOpic fungi. These diseases are usually considered dis- tinct from non-infectious or non-parasitic diseases caused by the non—living factors Of site. Generally they are arbitrarily differentiated from injury or damage caused by macro-organisms such as insects or rodents. Many infectious and non-infectious diseases have common, if not always identical, symptoms. Isolation of the single or principal causative factor is practically impossible. Sometimes heat-injury or drought-injury in very young trees in nursery beds or in forest plantations may so weaken some Of the trees that they become highly sus- ceptible to attack by various micro-organisms which even- tually may kill them (Boyce l9h8; Baxter 1952). In such instances the affected trees usually die rather slowly, and their death may not be discovered until the end Of a long growing season or at the beginning of the next. What, then, is the primary cause of death, and what the secondary? If the tree dies very slowly, some sort of infectious disease is usually suSpected as a primary cause, but the full truth Of the situation usually re- mains problematical. Although infectious or micro-parasitical diseases may be transmitted by direct contact between a diseased 13h individual and a healthy one by such vectors as animals, water, and wind, and despite the fact that they are in- sidious and Often deadly, they are apparently not the main cause of mortality in most coniferous plantations in the Lake States Region (Rudolf 1950). Rudolf lists what he considers the common causes, in descending order Of importance, as follows: (1) Climatic conditions. (2) Competition. (3) Poor stock and careless planting. (A) Fire. (5) Animals, including insects. (6) Diseases, in the sense Of infectious or biological diseases. Other authorities also, writing Of conifers in general, and particularly of pines in any temperate-zone locality, place climatic influences at the head of the list Of causes of mortality (Smith 1932; Shirley and Meuli 1939; Schopmeyer l9h0; Daubenmire l9h3; Chapman l9hh; Hursh l9h8; Kozlowski and Scholtes l9t8). Perhaps the principal reason why parasitic dis- eases are apparently not nearly so important in the life and survival of young trees is the very fact that the trees are young. 01d trees, like Old animals, have gone through periods Of youth, maturity, and senility. During the aging puecess, intensive competition accompanying CrOWn- and root-closure, wounds from wind breakage and other mechanical damage, and the mere fact of the exis- tence Of Opportunity of long duration for disease to at- 135 tack, probably contribute to the high incidence of in- fectious disease in old trees. After consultation with a well-known forest path- ologist,l and following his advice, the investigator made no attempt to apply intensive histological diagnostic pro- cedures to individual trees after they were Obviously dead, in an attempt to determine the possible existence Of causative micro-organisms which might have caused death. 1 that it is impracticable The investigator was advised to carry out procedures designed to determine the nature of possible infectious diseases from the small volume Of dead tissue obtainable from little trees. He was further advised that if no apparent cause of mortality from infec- tious disease, insects above or below ground, or competi- tion from adjacent vegetation could be recognized from close ocular examination of the tOps, the roots, and the soil surrounding the roots, drought could be confidently assumed to be the primary cause of the death of trees. This Opinion is corroborated by Rudolf (1937a) who states that where no heat damage from direct insolation is evi- dent, and where the cause of death is apparently physio- 10gica1, trees may be assumed to have been killed by drought. In this study, diagnosis of apparent cause of __.. lProfessor Forrest C. Strong. L_ 136 death was based on the methods and criteria of Davis gt :11 (191.2). Non-Parasitic Disease. Non-parasitic diseases or injuries have been called the single most prevalent cause of poor initial survival in plantations Of conif- ers in North America. 0f the non-parasitic diseases, those caused by macro-climatic and micro-climatic condi- tions are usually given first rank, with drought being emphasized as the most important component of unfavorable climate (Kittredge 1929; Rudolf 1950; Wakeley 1951). Non-parasitic diseases or injuries are mainly re- sults Of the physical environment, with important excep- tions. Even those caused by competing vegetation or ani- mals may be indirectly related to the physical environ- ment. Non-parasitic diseases are usually Sporadic or localized within general areas. They are usually rather quickly lethal in their action. Often they are manifest- ed, in instances Of direct macro-climatic or micro-climatic injury, in terms of hours or days rather than in terms Of weeks or months. Generally speaking, moisture and tem— perature are probably the most important of the climatic factors, although these are inextricably connected with other peculiarities of the micro-site, mainly those Of physiographic and edaphic character. Physiographic fac- tors include elevation, exposure, degree Of lepe, and characteristics of surface drainage. 137 Macro-climatic conditions can change drastically and suddenly, and the factors Of micro-climate often have either an intensifying or an ameliorating effect. Sudden and extreme changes in macro-climatic conditions can, and Often do, kill young trees in plantations indi- vidually and wholesale, Often very rapidly (Boyce l9t8). Very unfavorable weather, especially drought, has long been thought to be the most common cause of non-infectious diseases (Hubert 1930, 1932). Rapid and extreme fluctu— ations in the available moisture Of the surface soil are held by some authorities to be primarily responsible for drought injury. Wind and insolation, especially on south- facing exposures, resulting in over-rapid transpiration rates, are commonly recognized causes Of drought injury often resulting in death. Physiological drought in young trees is tied up with all the physical factors Of site peculiarly Opera- tive in relation to the early struggle for establishment and growth. If availability Of soil water is high, trees may endure intense, prolonged meteorological drought. In terms of inherent droughtiness, lighter soils are gen- erally better for plantation sites than heavier soils, although internal drainage and the depth of the water table from the surface are undoubtedly important modify- ing factors. 138 Physiological drought as an induced factor of competition is thought to have been a negligible factor of mortality in this study. In no instance Of the death of individual trees was it considered that competition from adjacent vegetation was sufficient to be significant. Never was regrowth Of low vegetation on scalps or furrows heavy. When dead trees were dug up for examination, live roots Of possibly competing woody species could not be detected in the soil mass at a distance Of one and one- half feet or closer to the stems Of any of the trees. The elimination of woody growth on the northwest-facing slope in 1953 seems to have been completely effective. Re-establishment of low herbaceous vegetation on the bared soil on either exposure was very light, even by 1955. In no instance were trees, either dead or liv- ing, overtopped by adjacent vegetation, nor did there seem to be any appreciable shading effect on either ex- posure from vegetation adjacent to the bared areas. Kit- tredge (1929), reporting on the mortality percentages ob- served in young forest plantations in the northern Lake States, states that the percentage of trees dying in plan- tations supporting different densities Of sod, fern, blue- berry, filbert, or wild raspberry was not significantly different. Although the low vegetation on the two expo- sures was not identical, differences were considered too small to be of ecological significance. 139 Diagnosis: Symptoms Of Drought Injury. The baf- fling problem Of diagnosis of non—parasitic diseases in general is emphasized by Rudolf (1950). He states: Physiological causes Of loss are particularly hard to diagnose. Trees killed by drought, heat, freezing, excess transpiration, and such causes us- ually do not differ sufficiently in appearance to distinguish which factor brought about death. Con- sequently it is necessary to know what has happened in the locality and then to make logical deductions in order to classify the cause of loss. Symptoms of drought injury may, and usually do, appear very suddenly and develop rapidly, or they may be somewhat prolonged through the early part Of the growing season (Boyce l9h8; Baxter 1952). The usual rapidity of the development Of symptoms Of drought injury is a matter of rather common agreement, however. The most character- istic symptom is yellowing and drooping Of the oldest needles, followed by a progressive change in color through successive shades of brown to an eventual copper-red col- or. Trees usually die rapidly from the tOp downward, and from the outside inward. Buds usually fail to Open, or if they do, initial elongation is abruptly terminated. The finer fibrous roots die at about the same time as the foliage, and disintegrate rapidly. The larger roots die and dry up soon afterwards, in contrast to symptoms at- tributable to direct-heat injury (Rudolf 1950). In small stock with stems less than 0.25 inch in diameter, stem shrinkage is common, with shriveling Of the bark but 1&0 without the whitish lesions usually characteristic Of di- rect-heat damage where the thin bark comes into contact with the hot surface-soil. Davis g3 g1 (19A2) state that diagnosis of summer drought injury is usually very dif- ficult and Often impossible if early-season freezing has caused so-called winter-killing, itself a form of drought injury. Direct-heat injury Often accompanies drought in- jury as an inseparable complication, however, especially in very young plants which have not sufficiently hardened , nor developed a bark that is thick enough to protect the stem at or near the soil level. Trees previously weak- ened by heat injury, as when still in the nursery, are thought to be rendered more susceptible to summer drought. Davis 22 El (1942) describe heat injury in some detail. They state: If examined within a day or two after occurrence, heat injury can be distinguished, at least in its best-known form, by the fact that the lesions are.at, or more Often just above, the soil level. They are usually very light in color, and their boundaries are sharply defined. . . Where heat is responsible for any considerable amount of killing, lesions that tend to be one-sided will be found mainly on the south and west sides Of stems, or on the upper sides of stems that are leaning over, and in (locations) that are especially eXposed, as on south lepes. These investigators note that heat damage appears to occur relatively rarely on Older stock with woody stems and comparatively thick bark. They add that killing in lhl such cases is usually limited to the south or southwest side of the stem, and that recovery from the effects Of such one-sided lesions is freouent. Occasionally, com-. plete heat-girdling may occur, resulting in death from starvation Of roots. In such instances, trees develop swollen growths above the girdling heat-lesions. However they die slowly and may remain alive for a year subse- quent to the injury. Kittredge (1929) does not agree that injury from drought and from direct heat are readily separable. He states: The periods Of extremely high temperature which occur almost every year also cause heavy losses, al- though the effect of the heating is difficult to dis- tinguish from that of drought, since the two condi- tions usually occur together. . . Temperatures above 1200 F. have been shown to be fatal to the life ac- tivities Of protOplasm, and it is only the protection by the bark of the trees that prevents complete loss under these conditions. Nevertheless Davis 33 gl (l9t2) are in general agreement with Boyce, Baxter, Rudolf, and others when they describe the ordinarily recognizable symptoms of drought injury where direct-heat injury is apparently not involved. They state: This . . . results in chlorosis and stunting, and in extreme cases in death. . . In some cases the Old- er needles have been killed and in others the young shoots. In trees entirely killed by drought, the roots apparently die as soon as the tOps. I‘» CHAPTER VIII RESULTS OF THE STUDY Precipitation. Measured precipitation for the summer period Of 195A, from June 28 through September 19, amounted to 7.39 inches on the northwest-facing exposure and 7.16 inches on the south-facing one, with a slight advantage of 0.23 inches for the cooler face. Two severe summer droughts occurred, accompanied by abnormally high sustained temperatures, considerable wind, and almost uniformly clear, sunny days. The soils on both of the two exposures entered the first drought with high soil- moisture contents, owing to the frequent and adequate precipitation of spring and early summer. . Precipitation for the 9 days from June 28, when the precipitation measurements were begun, to July 7, when the first drought began, was in excess Of 2.20 inches on each exposure. The last heavy rain, Of approximately 0.50 inch, fell on July 7. For 21 days thereafter the only rain that occurred was a light sprinkle Of 0.10 inch on July 11. The drought was partially broken by a fall of 0.15 inch on July 29, and of 0.12 inch two days later. Not until August 2 did a fairly heavy rain of 0.30 inch occur, to afford some relief from the drought. Thus, in 1h3 this critical period only 0.37 inch of rain fell for a full 25 days during the hottest part of the summer, be- fore the drought was broken. Semi-drought conditions, accompanied by frequent high temperatures, continued for 11 more days from August 2 until August 1h, when a soak- ing rain of 0.65 inch fell on the northwest-facing expo- sure, along with 0.57 inch on the south. One rain Of 0.20 inch occurred on August 10, along with three other ineffective sprinkles totaling only 0.33 inch, during the semi-drought period. For the 9 hot days intervening between August It and August 2h, 195A, 7 were without rain. About 0.37 inch Of water was supplied by two rains on the 17th and the 18th. 0n the 2hth a very heavy rain Of 1.50 inches on the northwest-facing exposure and 1.33 inches on the south occurred. This rain lasted for 3 hours and 10 min- utes. Infiltration on both exposures was rapid, with no observable surface run-off. A total of 0.35 inch came in the next two days. From August 26 to September 17, another severe drought occurred. Only two light rains fell in the 21 days of this second drought, one Of 0.08 inch on Septem- ber 2 and the other of 0.05 inch on the lhth. The drought was broken on the 17th and 18th of September by two storms which deposited a total of about 0.87 inch. 1AA For the fall period of l95h, from September 19 to December 22, a total of 11.90 inches of precipitation was measured on the northwest-facing exposure as compared to 12.03 on the south. The first snow occurred on Octo- ber 30. Nearly all precipitation between that date and the end of the fall season was in the form Of snow. Ex- cept for one unseasonably hot, rainless period of 7 days between September 21 and 29, and another warm, ll-day period between October 17 and 29 when only 0.15 inch of rain fell, precipitation was both adequate in amount and frequent in occurrence during the fall. Very heavy rains, of nearly 2 inches each, appeared on October A and 10, but the intensity of neither of these storms was high enough to exceed the infiltration rates on the two slopes for more than a few minutes at a time. Surface run-Off from neither of the slopes was observable. For the winter period Of December 22, 195A to March 22, 1955, the northwest-facing exposure received h.25 inches of precipitation and the south received h.07 inches, mostly in the form of snow. Snow covered the ground for most of the winter except for a two-week peri- od from February 19 to March 5, 1955, when thawing was frequent and over an inch of precipitation in the form of a warm rain occurred. The last light snow was re- corded on March 26. 1h5 During the spring of 1955, from March 22 to June i 22, the northwest-facing exposure received 7.17 inches ) of precipitation and the south received 7.72 inches. To- tal precipitation was well distributed, with only one es- pecially rainy period from June h to June 11. In this time 3.40 inches Of rain was measured on the northwest- facing slope and 3.60 inches on the south, a cumulative total resulting from three separate storms. One Of these storms exceeded 1.65 inches in an 18-hour period. Sur- face run—Off was not observable. The summer of 1955 was very similar to that of 195A, being abnormally hot, sunny, and droughty. Total precipitation recorded from June 22 to September 19 on the northwest—facing exposure was 7.90 inches. The pre- cipitation on the south—facing exposure for the same per- iod was 8.6L inches, a surprising gain Of 0.7A inch for the south. It is a matter of curiosity as to why the re- lationship between the two exposures was reversed in 1955 from what it was in 195A, in the amount Of rainfall re- ceived. Had vecto-pluviometers been available for in- ) stallation along with the reconnaissance gauges, some in- ‘ teresting data on the relationship between precipitation and prevailing winds on the two slopes might have been collected. Rain occurred every week between June 22 and 1&6 August 6, 1955, varying from about 0.10 inch to 1.00 inch per week, except for the week of July A to July 11. In this week 2.51 inches fell on the northwest-facing slope and 2.67 inches on the south, in two storms on two suc- cessive days. A very hot, windy period of severe drought com- menced on August 7 and lasted for four weeks. In the first two weeks of the drought, only about 0.17 inch of rain fell in two storms a week apart. The next two weeks were rainless. This drought was a week longer than either of the two droughts in the summer Of l95h. Temperatures were comparable. Collection of rainfall data was sus- pended after September 19. Drought conditions were undoubtedly more rigorous in 195h than in 1955, despite the longer duration of the drought in the second year. In l95h the first drought began a month earlier than the one in 1955, and undoubt- edly was a main factor in the high mortality which oc- curred among the planted trees. The second 195A drought, although it occurred late in the growing season, appar- ently was the cause of considerable mortality also. A summary of precipitation totals, by weeks, for 1954-1955 may be found in Table 3, on pages 147 to 1L9, inclusive, and in Figures 12a and 12b, on pages 150 and 151. Precipitation by months is shown in Table A, page TABLE 3. l“7 PRECIPITATION TOTALS 0N NORTHWEST-FACING SLOPE AND ON SOUTH-FACING SLOPE, l95h-1955. IN TERMS OF INCHES PER WEEK Inches Precipitation Week Remarks ‘ N.W. ‘ South 1951+ _.--- I - N 1-..: VLF-"MW“ -- ”W“ M 6—28 to 7-5 1.15 1.23 7—5 to 7-12 Last heavy rain on 7th 7 NW: 0.50 s: 0.45 1‘15 1'10 7-12 to 7-19 0.00 0.00 7-19 to 7-26 0.00 E 0.00 7-26 to 8-3 Drought broken on 7-29 ' 3 A NW: 0.15 S: 0.15 ) 0'57 Q 0‘57 8-3 to 8-9 i 0.44 . 0.43 ; 8-9 to 8-16 _ l 0.85 g 0.77 ; 8-16 to 8-23 NO rain, 8-19 to 8-2h O.h0 i 0.35 E 8-23 to 8-30 a Heavy rain on 2Ath: 3 A NW: 1.50 S: 1.33 1'85 ' 1'68' A 8-30 to 9-6 g 0.08 g 0.08 9-6 to 9-13 E “g 0.00 i 0.00 9-13 to 9-19 1 Drought, 8-26 to 9-17 1 0.90 § 0.95 9-19 to 9-26 g §; 0.50 ; 0.60 9-26 to 10-3 § A 1.44 1 1.48 n 10-3 to 10-9 1 Heavy rain on nth: y E NW: 1.80 s: 1.90 § 2°79 ; 2°90 10-9 to 10-15 A Heavy rain on 10th: 1: ; 3 NW: 1.95 s: 1.90 53 2°79 : 2°77 10-15 to 10-22 g A 0.57 5 0.62 . 10-22 to 10.30 fDrought, 10-18 to 10-29§ 0.48 g 0.48 3 10-30 to 11-6 )First snow, 10-30: 3.00? 0.53 l 0.41 f 11-6 to 11-13 5 i 0.00 g 0.00 ‘ i 8 4L TABLE 3. (Continued) lh8 PRECIPITATION TOTALS 0N NORTHWEST-FACING SLOPE AND ON SOUTH-FACING SLOPE, 195h-1955. IN TERMS OF INCHES PER WEEK .111_._-1. - Inches 1. Precipitation Week Remarks “wNIW.m?'SOuthH ‘"I954'“ -_-.._ -_ m__1 11-13 to 11-20 Snow 0.88 0.91 11-20 to 11-27 Snow 0.71 , 0.66 11-27 to 12-4 Snow 0.65 g 0.71 12-4 to 12-11 Snow 0.27 : 0.25 12-11 to 12-18 Snow 0.29 i 0.24 12-18 to 12-25 0.00 g 0.00 12-25 to 1-1 Snow 1.27 E 1.34 '__'_"I955 7'"” '_"‘”" *”"" g 1—1 to 1-8 . Snow 3 1.03 l 1.07 1 1-8 to 1-15 2 u 0.00 E 0.00 g 1-22 ! Snow g 0.10 . 0.10 1-29 } l 0.00 F 0.00 2-5 Snow. Depth: 3.00" g 0.18 z 0.20 2-12 Snow 2 0.15 g 0.35 2-19 Snow 0.h0 , 0.05 2-26 All rain, no snow. 0.h6 f 0.h0 3-5 All rain, no snow. 0.78 f 0.75 3—12 Snow 0.08 I 0.10 3-19 Snow 0.32 ; 0.30 3-26 Snow 0.75 ’ 0.75 h-2 All rain, no snow. 0.13 i 0.3h f 4-9 . 0.00 5 0.00 5 4-16 Rain 0.5L ; 0.5h ; 4-23 Rain 0.57 0.60 ' 4-30 Rain 1.25 1.28 J lh9 TABLE 3. (Continued) PRECIPITATION TOTALS ON NORTHWEST-FACING SLOPE AND ON SOUTH-FACING SLOPE, 195h-1955. IN TERMS OF INCHES PER WEEK Inches Precipitation Week Remarks fijfi: South , 1955 4-30 to 5-7 0.00 0.00 5-7 to 5-1h 0.35 0.35 5-1h to 5-21 0.00 0.00 5-21 to 5-28 0.75 0.8h '5-28 to 6-h 0.18 0.17 6-4 to 6-11 3.h0 3.60 6-11 to 6-18 0.00 . 0.00 6-18 to 6-27 0.11 j 0.13 6-27 to 7-4 0.77 ; 0.88 7-h to 7-11 2.51 2.67 7-11 to 7-18 0.69 0.67 7-18 to 7-25 0.09 0.12 7-25 to 8-1 0.79 0.95 8-1 to 8-8 0.99 1.03 8-8 to 8-15 Drought 0.08 0.12 8-15 to 8-22 Drought 0.06 0.08 8-22 to 8-29 Drought 0.00 0.00 8-29 to 9-5 Drought 1.52 1.6h 9-5 to 9-12 0.29 0.35 9—12 to 9-19 0.00 0.00 - **-_ .— -_ .mmmauémma .mmoqm 02Hooz o On .02” .0”; opoo mm ma 0 u. a a T.- II H vm. Q B 3 II N M. u . ‘U m I u s m 1 4 m 13H. 05:. n ma saqouI - uorueqtdroaxd mam; mam 9555.. me mzmmh. zH .mmoa .MEOAm 02Ho02 poo new wa< Haw - q q q q q . q q q q q q q . 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G a d 3 u. . 00a .23 mo «amass: fiéogu a: 33 B 53333:. «.ng .3 9.38. 2H .mmoa.4moa .ueoqw cause» -398 com a: 36.5 afiezdmaafimoa mom Emma 83-: .2 mange gamma-7&8 .63 .6: 3.34 :93: Pangaea gag. hon-Soon R ON on on ON OH ON ON OH R ON OH On ON OH H AN n J. L4 N o «P u 1" u w v u w b. . A: O llll "magma—um we w I "Mflfiowhl; m 3 V A a T: I a a. T? I T. . m . a . . . T. . a? , r u 0 u. G I I \ Lu 8 o“ Il‘\ a... u. n v 8 ..00H 6:5 18 88”"sz maéommfi 82 295 S .BHdmadga Sesame go mama. 2H .mmoa .aeoam ozHoaa umaDOm mom :5 mmogm quo a "wcaowmusz . / .. ON m . . x, Q n , ..0m w. by . I. - TL 1 x .. 3 w. . ’ U 1 a . I. . .. . .. Om .m. , .. . .. . , . ~ ' I; . u a, 4 8 TL . \> u ’ \\/ 7w; a a I ‘ \\ a .- o \ I 1'05 w L a \ II u. \ 7\ III a \\ A. on .m. U. 1' cm A. SH .823 .8 £913.52 maéommfi 32 225 E .EHdfldai BEBE .8 same 2H 4m? .mmogm was: -528 mom as $8.6 62349381152 mom Emma 53.6 2 mmoém: EBmHoz-dom .mS .on 9098962 59300 honaouaom pm=w5< .33. On ow oa 0m ow 0H 0m om 0H 0m ow OH on om OH H :3 IIIIII "mcflommunpSom m. 1 | umcflommapmoznpuoz :ON a m. UV :8 m .1. , m. .1 x :3 m . a TL . ._ u. H _ .v Om rA fillL _. . _ _ 9 _ I u 0 U. G 3 d 1. U: .03 .mfia no marinas: m<§omfimH 92¢ nude Hm .EHHHaHH<>< Bzmommm mo mime. 2H labom mom a: macaw 03041“ .RSARH .988 623: $3358: mom Emma 5:76 .2 magenta 35939-net. 3.23 none: beacon humane» . hon-Boon om ow 0H 0m ow OH mm 0 0H On 8 On On ON OH . p - I: I- n n - I III I "manomMum I "9509.732 n I u I I I 1 u u d .9: H o :3” a. u :8 m n4 V :8 A w w. :3 m. I u :3 A . .8 9 m. .2. m m .om .m. U. .8 8H .mba mo 8.33.sz ESOBEH 92¢ mh< Hzmummm ho mime. 2H .mmmH .wmoqm OZHOfim oEbom mom Qz< mmoqm OzHO< 559m”?! HHom .05” .93 38533 $59: hHE. 05;. he: Om ON OH Om ON OH on ON OH Om ON OH Om ON OH H _ . . . _ . 1 _ . . . . _ 1 o .. OH lllll "mGHommEosom d 8 I "mcHommupmozsphoz .. ON w m n4 u w. I a The I T. n4 A Widen Horn-9 18h TABLE 11. DIFFERENCES IN SOIL-MOISTURE AVERAGES BETWEEN NORTHWEST- FACING SLOPE AND SOUTH-FACING SLOPE, 1956-1955. IN TERMS OF PERCENT AVAILABILITY, BY MONTHS Fm“ _——-. - m-_._- —- _.—-—-_———_ _. _———-___ -—————— Northwe8;:Facipg South-Facifiép anth De th Hi h Low Hi h Low 1%. Secéion Section Plot Secgion Section Plot ; July, 16 77 73 75 59 62 61 . i l 6 8h 82 83 7h 79 76 l = 95“ 26 85 83 86 8o 83 81 i .@ -111_7_ __.. » mw__n,n 11.1.“. _ 1__1-61__ 1__ 1% 75 73 7h 63 63 63 , Aug. 6 g 79 73 76 62 66 66 . . _J 26 . 86 77 g 81 I 72 73 72 5 : _-.- _ .1 . . --4 . - .- 6---. _- __-___ _-_ _ -_._ e 18 7o ' 66 i 67 - 57 58 58 . ' Sept. 6 g 77 71 ! 7h 65 69 67 : 26 ; 79 L 76 . 76 68 81 76 __..__ -——-——-W _-.- - -- - _.-. - - - _- .- ..____.. L. ..... a 15 i 81 i 78 80 78 8o 79 ' Oct. 6 i 81 | 79 8o 78 78 78 l 26 ! 81 1 77 79 77 78 78 f 13 I 68 ' 65 67 65 65 65 JNov. 6 i 67 68 67 65 67 66 1 26 j 68 68 68 , 65 , 68 67 ..___ _----—- r— - - - T ----- - —+ - - - Y.” .- . I _ ————— .—-—— _———— 18 ‘ 66 63 63 :. 63 g 65 T 66 Dec 6 i 61+ 616 l 616 ' 63 § 63 63 i E 1 26 66 66 66 I 62 i 63 63 : kW 8 z; 3: 32? 32 32 32 : i 1955 26 6o 60 6o 59 i 60 60 g 5"” ”712 “13’ ” 1'3” " “i3"'?"”§6m"” 36 36 .‘ Feb ,1 6 1o 11 11 - 36 36 35 g ; _§ 26. 56 56 56 g 59 57 58 i ”I' 13 66 62 63 i 39 61 6o 3 Mar. 6 39 38 39 39 39 39 i 2h» 65 65 65 67 66 66 . - - . -- __-_-_. -111_HH-L , -11111-u______ _ i DIFFERENCES IN SOIL-MOISTURE AVERAGES BETWEEN NORTHWEST- TABLE 11. (Continued) FACING SLOPE AND SOUTH-FACING SLOPE, 1955. IN TERMS OF PERCENT AVAILABILITY, BY MONTHS ._.__._. .__ 185 ..—_..._. _.-_ -_-_ __N6¥£66686-888168'm' SonfiE-Facing M th 5'81 h ”' Low ’"”’ Hi h Low on Sec?ion_Sec§ion_fE°t Secgion Section Pl°t Apr., 81 77 79 79 78 79 1955 ! 83 81 82 82 82 82 g 80 78 79 80 79___._Z? E 77 73 Z 75 69 76 71 May a 79 77 5 78 71 8o 75 g 83 76 9 8o 73 81 77 __._ _. I . . -_ _- . -._._ _.___-+ -__.-.-__. ‘ 72 72 72 65 69 I 67 June ' 8O 86 83 76 8h 80 86 88 87 82 86 86 , 82 79 . 8o 73 77 75 July 3 84 1 85 85 80 85 83 A 90 r 86 g 87 . 87 89 87 . _ _ ..1_ _. .- --. I .. 1 -._...__ .. __.-_ 1-. - ._--.- .. .r. _._...._.__+| 4 67 62 66 61 38 39 Aug. 5 62 57 6o 55 58 . 56 7 26 86 75 L 81 81 76 I 78 _._ _. -: 1 _ 6__1__,6111- 1-1___11 . _-._ , 1113__1______1 : 7o 66 67 66 6o 63 Sept°! 76 69 3 71 . 69 65 67 1-3 i 82 76 g 79 g 79 76 77 3 6h 61 62 g 59 6o 60 Grandq 67 65 66 ' 63 66 66 \ Ave°$ 77 73 75 73 76 73 fi ___111_ .___.1_1 .m29202 Hm .HBHqu< Bzmommm mo mzmme 2H .mmma-¢mafl .mmoqm czHo< mmpamnguqum .unom.ms< hHsu mesa has .ha< .um: .pmm .amw .ooO .>oz .poO .unmm.w:< hst - q 1 1 < I q < ‘ . q .1... mnHowmunpdom mcHommuumwznppoz .mmH .uHm o 1. 0H d a J : ON a u n4 -. R w P. T: : 06 m to nu .. 0m hm . : 00 T. at . 2 m1 3 "u. I. ow m d m l' 8 .. 8H .mmazo: um .wquHm< azmommm mo mamas zH .mmoa-8mmH .mmogm ozHo< mmDBmHoz-gHom .an .on .uamm.ms< 5H2. 65:. mm: .631 .umz .pmm .826 .03 .>oz .900 53.992 .33. p n . p . - 1 d d 1 1 1 1 1 1 d 1 IT 1 l 0 III I I "mcHommunpzom l uwfiommnpmmzfiuoz O O" KQIIIQEIIEAV QUSOJGd Om : O [\ undau anal-9 OOH TABLE 12. 189 DIFFERENCES IN SOIL-MOISTURE AVERAGES BETWEEN NORTHWEST- FACING SLOPE AND SOUTH-FACING SLOPE, l95h-l955. IN TERMS OF PERCENT AVAILABILITY, BY QUARTERS . _._-___..______I.. . South—Facing I I I Northwest-Facing I 'Quar-I Depth High “mungN “I_ High Low ! ter :- In Section SectionIIP10 0t Section Section P1°t I II L — — _____, ‘-II:':‘:;:.-. ._.- -- -————~ -I July 5 18 76 70 I 72 :5 6o 61 61 I to I 6 8o 5 75 I 78 g. 67 71 69 ; Oct. 26 83 I 78 i 80 :7 73 79 76 5 Oct. I 18 71 I 69 . 7o ;: 69 7o 69 . to I 6 f 71 I 70 f 70 I; 69 69 69 I 489?.J1.3# I 71 I 70 ? 7o ;5 68 7o 69 5 Jan. - 1% I 31 3 30 I 30 I‘ 36 37 I 37 I to - 6 g 29 I 28 i 29 . 36 37 I 36 Apr. , 26 , 60 ; 60 60 I 62 - 61 I 61 " "? I I ; ' f " 'I‘"““'““j “‘” Apr. ' 18 I 77 ; 76 3 75 I 71 76 , 72 to 6 ; 81 ' 81 I 81 I 76 82 ; 79 July ' 26 ' 83 81 I 82 I 78 82 8o -_. --- - . . I III _ _ . . --__---16.____. July I 18 66 62 I 66 I 60 58 59 to f 6 73 70 I 72 ‘ 68 69 69 Oct. 1 26 , 86 I 78 I 82 82 79 81 4—-._.."._'_::__--..--_ _-.__ I“-.-_6_;__'..-_I-__- _.._ '-'“.- -::IL..- __-_IqI__ -- _- _._ 18 66 61 I 62 I 59 6o 60 'G d I ; ran 6 67 65 I 66 I 63 66 66 - ' A I . f I ve I 26 77 , 73 I 75 I 73 76 73 ; L .8- _ . - .. I . __ II. __ -- _-J______---_1 190 Solar Radiation. An estimate of the comparative amounts of solar radiation received at the two exposures in any given week during the warmer part of the year was provided by Livingston radio-atmometer installations. Ex- pressions in terms of arbitrary evaporation-units, indi- cating differences in solar radiation between the expo- sures, were reduced to percentages for convenience. For the total, five-season period from June 29, 1956 to July 28, 1955, during those times in which the radio-atmometers could be operated without freezing, the average estimated solar radiation received at the north- west-facing slope was 97.1 percent of that at the south- facing slope. Taking the figures for the south-facing lepe as 100.0 percent, the northwest-facing slope re- ceived 98.6 percent during the summer period of June 29 to September 19, 1956, the first growing season. During the period from September 19 to October 16, after which the radio-atmometers were removed to protect them from freezing, the estimate for the northwest-facing exposure was 98.6 percent. The radio-atmometers were re-installed on May 7, 1955. For the spring period of that year, until June 23, the estimate for solar radiation received at the north- west-facing exposure was 95.2 percent of that received at the south. From June 23 until July 28, 1955, when mea- surements of comparative solar radiation were terminated, 191 the figure was 96.1 percent. See Table 13, pages 192-196. From the estimates obtained, and if the measure- ments were within acceptable limits of accuracy, it would appear that the amount of solar radiation received at the northwest-facing exposure was consistently from about two to five percent less than that at the south-facing expo- sure. However, if the instruments functioned properly, if any inherent inaccuracies in either were not cumula- tive, and if the evaporating elements of each installa— tion were exposed to the sunlight at identical times, it might seem that indications of solar radiation at each lepe would be identical. This would seem to be eSpeci- ally true during the high-sun period of the warmer part of the year. In the winter on the northwest-facing slope with an average inclination of 238 percent, occasional undetected shading of the radio-atmometer elements might have been suspected from irregularities in the slope sur- face. However, since the instruments were used only in months of comparatively high sun, shading does not seem likely. Barring inaccuracies of instruments, or consistent, undetected error in taking data, it is to be speculated that re-radiation from the comparatively hot soil on the south-facing exposure may have increased the readings at that location. It would seem that long-wave re-radiation from the south would be greater than from the northwest. [I'll Ill-I'llllll': % u 6.86 6 6.66 m mam-6 1. 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Although in most re- generation surveys it is customary to consider that a five-year-old seedling has become indisputably established (Crossley 1955), a somewhat different criterion of estab- lishment was adOpted for this study. A primary reason for this was that it was impracticable to carry on the study for a period of more than two years, at least in the initial phase. A second reason is that long-time ex- perience and research in forestry has demonstrated that the most critical period for trees in plantations, where competing low vegetation has been removed for a consider- able distance around each tree, is apparently the first season after planting. The more conservative, five-year criterion of establishment is adopted mainly by workers on problems of natural regeneration, where young trees are usually affected rather drastically by root competi- tion from older, larger trees that may make up a rather heavy overstory. Support for the decision to adopt a one-year, or possibly two-year, criterion for establishment, in this study, is offered by Wakeley and Chapman (1955) in their report on recent plantation studies. They state: Initial survival may be defined as that shown by the planted stock after the occurrence of the mortal- ity more or less directly brought about by the whole process of planting, including the environment cho- sen for the planted trees. It is usually best mea— sured at the end of the first growing season, but in special cases supplementary measurements may be de- 207 sirable about the first week in June of the first growing season and at the end of the second or third growing seasons. A study of initial survival should not include effect of epidemics, insect infestations, or droughts after the planted trees are well estab- lished, and of course never includes later losses ar- ising from competition.as the crowns close. The fact that soil heaving in the first winter season after planting often appears to account for much of the initial mortality of planted trees makes apparent the desirability of carrying the study into the second summer. It is well known that soil heaving may be common in old fields where the water table is close to the sur- face (Spaeth and Diebold 1938), on heavy soils where the clay-and-silt content is thirty percent or higher (Le Bar- ron §£.§l 1938), where the soil is nearly bare of vegeta- tion or has only a scanty cover (Deters 1939), or where an unfavorable combination of these factors exists (Stoeck- ler and Limstrom 19h2). Soil heaving not only may often take a heavy toll during the first winter after planting, but it sometimes is operative as an appreciable factor in plantation mortality on the worst sites in the second win- ter, and occasionally even in the third. In instances where soil heaving is Operative, roots may be broken, the root collar may be lifted above the surface of the ground, or the trees may literally be pushed entirely out of the ground (Haasis 1923). ' Despite the open sites on which the plantations for this investigation were located, and the sparse veg- 208 etative cover on both exposures, in no instance where mor- tality occurred on either slope was there the slightest perceptible evidence that soil heaving, or so-called "frost heaving," was in any way responsible. In fact, during and following the winter of l95h-1955, little ev- idence of soil heaving could be seen anywhere on either exposure. It was thought that the soil was too light, and internal drainage was too good, to allow much chance for soil heaving to occur. Total mortality among the combined total of 1296 little trees planted on the two exposures, for the whole period of nearly 17 months from April 28, l95h to Septem- ber 20, 1955, was 62. Of this number, one tree on each exposure was destroyed by some unknown, violent means, apparently cutting and crushing. Consequently, since the deaths of these two trees obviously were not the result of the action of the normal, non-living factors of site, they were not considered in the calculations of the re- sults. The 60 trees that died from apparently normal causes constituted a combined mortality for both slopes of only b.63 percent. A survival-rate of 95.37 Percent at the end of two growing seasons, in ordinary forest planting practice, is not usually considered poor. How- every, the trees for this study were graded and planted with extraordinary care, they enjoyed almost ideal weather ‘ Figure 19. Dead Seedling in Scalp, South—Facing Exposure. ~ Note Sparseness of Adjacent Vegetation. JUlY 19, 1951+. / 210 conditions during and for nearly two months after planting, and no evidence was found that those that died suffered dam- age from other than apparent climatic and micro-climatic causes occurring mainly in the first summer. It is not surprising that the survival total was so high. Under normal but less favorable planting conditions the survi- val total would probably have been not nearly so gratify- ing. During the seventeen-month period after planting, the mortality rate on the northwest-facing exposure was only 2.93 percent. During the same time on the south it was 6.33 percent. This is a rate nearly 2% times as high as that on the northwest, and would appear significant. Only one tree died before July 7, l95h, when the first severe drought began. This was a 2-0 seedling in a furrow in the lower section of the south-facing main study plot, where soil-moisture availability averaged a little higher than that in the upper section. No confi- dent explanation can be offered for this seeming paradox. Rainfall and soil moisture would appear to have been ade- quate up to the time of this first tree's death. The tree had been examined a week previously and had appeared in satisfactory health. However, it rapidly became chlorot- ic, turned brown, and died. Its death can not be associ- ated with the first severe drought. 211 Severe drought conditions prevailed from July 7 to July 29, 195A. From July 11 to 18, surface-soil tempera- tures at the one-fourth inch depth on the south-facing lepe reached maxima of 1220 to 1280 F. every day. From July 19 to 25, maxima of from 1280 to 1300 F. were the usual occurrence about mid-day, and from July 26 to 28 the highest surface-soil temperatures of the summer of 195h were recorded. Air temperatures were also high. Temperature-sums for July were higher than those calcul- ated for any other month in the summer. Soil-moisture averages at the lé-inch and 6-inch depths reached their peak on July 7, above which they did not rise again in 195A. Soil-moisture averages at the shallower depths fell rapidly on the south-facing expo- sure after July 7. They continued to fall almost precip- itously until July 29, after which they rose again about as rapidly. The same general trend in soil-moisture val- ues was noted on the northwest-facing slope, except that values at the lé-inch depth on the cooler northwest 510pe never fell below 39 percent. They never fell below a figure of 62 percent availability at the 6-inch level. On the south, the minima were 23 percent and 36 percent, respectively, for the lé-inch and 6-inch depths. During the drought beginning on July 7, differ- ences in evapo-transpiration on the two slopes, as indi- Figure 20. Dead Seedling in Furrow, Northwest-Facing Exposure. Note Sparseness of Vegetation in Bottom of Furrow. July 26, l95h. 213 dicated by the chemical-absorption hygrometers, were al- most consistently in favor of the northwest-facing slope. Here the amount of evapo-transpiration ranged from about 0.01 to 0.14 approximate inches per day. The highest evapo-transpiration rates indicated on either slope oc- curred, as a general rule, during periods of hot weather when the intervals between rains were short. As soon as a long period of drought set in, evapo-transpiration rates fell rapidly to a rather low level. Nevertheless, differences between the slopes remained high. facing slope during the first week in July varied from 0.10 to 0.99 approximate inches per day, and on the north- indicated approximate inches per day on the south, and from 0.01 to 0.05 to 0.88 inches. From July 7 to 29, 195A, evapo—transpiration varied from 0.02 to O.hO 0.26 on the northwest. But the rate might be from 0.01 to 0.1A approximate inches more rapid each day on the south than on the northwest, even during a drought when the soil water was not being replenished, as was indicated ratios of For instance, indicated evapo-transpiration on the south- west from \ l l in this instance. The south-facing slope appeared to the first but, even were less continued lose over 33 percent more water than the northwest during week in July, when soil-water was plentiful, though total quantities lost from either slope when water was scarce, the south-facing slope to lose at a rate from 18.8 to 31.3 percent .—_-..._-.l 214 more than the northwest. In any event, the higher soil temperatures, low— er soil-moisture availability, and disadvantage in rate of evapo-tranSpiration on the south-facing lepe, accom- panying the first severe drought of l95h, were followed by an immediate and rapid gain in mortality as compared to the rather low mortality on the northwest. On July 12 the first tree to be found dead after the drought began was found on the south-facing exposure. The first one on the northwest was found a week later. By July 26, five apparently drought-killed trees were found on the south lepe, compared to three on the north- west. By the end of the semi-drought period, from July 29 through August 1h, the ratio was 17 trees dead on the south to 10 on the northwest. By the end of the second drought period, August 26 to September 17, the south led with 30 trees dead to the northwest's lh—-a ratio of more than two to one. This is not counting the first tree to die, on the south, before the first drought began. In all, 33 of the total of #1 trees that died on the south-facing slope did so in the first summer, when the soil was often very dry and surface-soil temperatures often exceeded 1200 F., even in September. This was 80.5 percent of the grand total on the south. No trees were found dead after September 19 on the northwest-facing ex- posure. Conditions during the second drought in l95h were Figure 21. Dead Seedling in Furrow, South-Facing Exposure. Note Sparseness of Vegetation in Bottom of Furrow. August 9, l95h. 216 essentially the same as in the first. There was only ab- out two weeks of respite for the trees between the two droughts. After the end of the summer of l95h, no trees were found dead on either slope until December 11, and from that date until spring, 1955, only six trees died on the south-facing lepe and four on the northwest. None of the dead trees were covered with snow when found, nor were they bent over as red pines often are when they have been covered with a thick blanket of snow for a con- ‘ siderable part of a winter. All trees that died turned brown and expired in a space of about two to three weeks for each tree. They appeared to be winter-killed. Once the snow was gone, it could be ascertained that not one of the trees on either exposure that had been covered with snow most of the time died while they were covered. Mbst of these little trees were pressed down nearly pros- trate against the slopes, but they did not seem to be in- jured in any way from being covered with snow for long periods. One tree died on the south-facing slope during the spring of 1955, of unknown causes. None died on the northwest, that spring. One tree died on each of the ex- posures during the summer of 1955, again of unknown causes. However their symptoms appeared to be identical to those 217 of the trees that died in the previous summer. Total mortality among all the trees planted on both slopes combined was 4.63 percent, with 60 trees dead. Mortality among all the transplants was 22, or 3.40 per- cent. Thirty-eight seedlings died, for a mortality of 5.86 percent. Transplant-mortality on the northwest was 5, or 1.54 percent, while for seedlings it was 14, or 4.32 percent. Seventeen of the transplants on the south died, or 5.25 percent, while seedling mortality was 24, or 7.41 percent. 0n the upper section of the northwest- facing slope, 2 transplants died, or 1.23 percent of a total of 162. Seedling mortality was 6, or 3.70 percent. On the lower section, 3 transplants died, or 1.85 percent, and seedling mortality was 8, or 4.94 percent. On the upper section of the south, 10 transplants died, or 6.17 percent. Thirteen seedlings died, or 8.02 percent. Average transplant mortality for slopes combined was only 57.89 percent of seedling mortality. Transplant survival was higher than that of seedlings on both slopes and on both sections of each slope. Total mortality of plants in furrows was 33, or 5.09 percent, while for scalps it was 27, or 4.17 percent. Mortality in furrows on the northwest was 12, or 3.71 per— cent. In scalps it was 7, or 2.16 percent. On the south slope, mortality in furrows was 21, or 6.48 percent. In scalps it was 20, or 6.17 percent. a f r ,r. .' Figure 22. Dead Seedling in Furrow, South-Facing Exposure. Note Sparseness of Vegetation in Bottom of Furrow. September 19, 1954. H u I. \ q. —____‘._—.-—u..—.-_-— ! I! 219 On the upper section of the northwest-facing slope, 5 trees died in furrows, or 3.09 percent. Mortality in scalps was 3, or 1.85 percent. On the lower section, 7 trees died in furrows, or 4.32 percent. Mortality in scalps was 4, or 2.47 percent. On the upper section of the south, 12 trees died in furrows, or 7.41 percent. IMOrtality in scalps was 11, or 6.79 percent. Average mortality of all trees in scalps was 81.82 percent of mortality in furrows. Survival in scalps was better than in furrows on both slopes, on both sections of the northwest, and on the upper section of the south. Survival was the same in scalps and furrows on the lower section of the south-facing exposure. In general, survival of transplants was higher than that of seedlings. There would seem to be a slight indication that use of transplants rather than seedlings is a more important assurance of high survival than is the use of scalps rather than furrows. However, statistical significance in these relationships could not be shown. Summaries of mortality on both slopes for 1954 and 1955 may be found in Table 16, on pages 220-221, and in Table 17, on page 222. Figure 23, on page 223, illus- trates the coincidence between precipitation in inches per month and the number of trees dying per month on each slope during 1954 and 1955. _ ._- Li..- '! l I w H “’7’ I kw gawk-P . \}O\ 02 900 new 92 H3. III... _ _ _ _ _ l. _ _ _ _ _ I , 0 AL q N - mm .- m in a? 88 an . 2 an E .mcwommsnpsom %. .1. ma 0. L - umcwommupmozfippoz O l '— 2 tn saqouI - uorqeqtdIOGJd 224 Statistical Analysis of Survival. During the summer period of 1954, total survival on the northwest- facing exposure was 97.84 percent. During the same per- iod, total survival on the south was only 94.91 percent. Total survival on the northwest for the five seasons of operation was 97.07 percent, and for the south 93.67 per- cent. The ratio between survival percentages on the two exposures was practically the same for all the five sea- sons of operation as it was for the first summer season alone. In each instance, mortality on the south-facing exposure was over twice as high as on the northwest. The first statistical calculations were performed to determine if the mean of the total survival-percent on the northwest-facing exposure for the 1954-1955 period was significantly different from the mean of the total survival-percent on the south for the same period. Total survival-percent for each exposure was calculated from the individual survival-percents of all the treatment- plots on each exposure. The difference between the means of the two total survival-percents was submitted to Fish- er's "t" test. It was found that survival on the north- west was significantly greater than survival on the.south. The probability that the two exposure-samples could have been taken at random from the same population was thus shown to be very small, or less than 0.01. 225 An analysis of variance was carried out for the northwest-facing exposure, after the first comparison of the two exposures was made and tested, involving separate analyses of variance for the upper and lower sections of the main study plot on the northwest location. No signif- icance was found among means of replications, or treatment- plots. No significance was found between the mean of the ‘upper section and that of the lower section of the main :study plot on the northwest-facing exposure. No signif- i.cance was found among the means of the four treatments investigated. No significance was found for interaction. An analysis of variance for the main study plot on.the south-facing exposure was carried out in the same inay as for the northwest-facing exposure. As in the case <3f the northwest, no significance was found among means (Jf replications, or treatment-plots, on the south-facing exxposure. Similarly, no significance was found between tflne mean of the upper section and that of the lower sec- 1:ion.of the main study plot on the south. Again, no sig- Irificance was found among the means of the four treat- nmnnts investigated. And lastly, no significance was found for interaction. See Figures 24 and 25, on pages 226 and 227, for diagrams showing the locations of all the trees that died on b0 th exposures, classified according to the periods in whijich the different trees died. .mmaaudmoa .mmonm caudmuamgmoz :0 mg Gage ho :Hdamg 3N .lo manna-suns "vohoupnoa "mmmH .ON .paom . H .ms< epHHeppgz “mmoH .m HHtQH - 4mmH .HH .oma euHHautoz "smmH .ou .aaom . m sHae spHHapugz IIEEI «moanmozH .mmmHIJmoa .mmoqm 02Ho3NNN IO QNMOZH CHAPTER IX SUMMARY AND CONCLUSIONS \- .Methods of the Study. After extensive prelimin- ry reconnaissance of topography, micro-climate, vegeta- ion, and soils in 1953, aul experimental study was set a in the spring of 1954 at the Kellogg Forest, in south- estern Michigan. The purpose was to investigate the re- ationship between micro-climate and the establishment nd early survival of planted red pine (Pinus resinosa it.). Two exposures with contrasting micro-climates, ut otherwise as similar as could be found, were selected or the main study plots. Close investigation of the oils on both plots established to the satisfaction of he investigator that the soils were ecologically similar. he average slope for both exposures was about 235 percent. ne exposure faced approximately 30 degrees west of north. he other exposure faced directly south. Instrumentation designed to determine, if possible, he direct and indirect expression of the contrasting icro-climates on the two exposures was carried on from une 28, 1954 until September 19, 1955. Using the most igorously careful planting techniques, 648 little 229 ed pine trees were planted on each exposure on April 28, 954 in the middle of an approximately eight-week period f ideal planting weather. Weekly counts of mortality n each exposure were made throughout the nearly seventeen onths from the time the trees were planted until the in- estigation was terminated. Two methods-of soil preparation were used on each xposure, as well as two classes of planting stock, con- tituting together four treatments. These were: A. Scalps with 2-0 seedlings. B. Scalps with 2-1 transplants. C. Furrows with 2-0 seedlings. D. Furrows with 2-1 transplants. wo sections, containing twelve treatment-plots each, con- tituted the main study plot on each exposure. Each treat- ent was replicated three times within each section. Lo- ation of treatments on treatment-plots in each section f each main study plot was randomized. Instrumentation on each main study plot involved he collection of data at twice-daily, daily, and weekly ntervals. Data were collected on precipitation, air emperatures, and soil temperatures by means of continu- usly-recording instruments. Soil-moisture blocks were sed for the determination of moisture availability at hree depths on both exposures. An indication of compar- tive solar radiation received on the two exposures was 230 »rovided by Livingston radio-atmometers. An estimation >f comparative evapo-transpiration and condensation on ;he two exposures was obtained by the use of chemical- Lbsorption hygrometers. All dead trees were closely examined for symptoms if injury from large animals, insects, parasitic diseases, :nd non-parasitic diseases. Data on survival and mortal- .ty of the planted trees were analyzed for statistical .ignificance. Findings of the Study. The spring and the first .wo weeks of the summer of 1954 were apparently ideal for ,he initial establishment and subsequent survival of the vlanted trees. Mbst of the summer of 1954 was featured y weather that was among the hottest and driest on rec- rd for southwestern Michigan. The fall of 1954, winter f 1954-1955, and spring of 1955 were essentially normal. he summer of 1955 was again one of the hottest and driest ecorded for the region. Instrumental indications pointed to considerable ontrasts in the micro-climates of the two exposures dur- ng the period of the study, especially during the two ummer seasons. At other seasons the contrasts were nearly 5 marked, although apparently not reflected in terms of onspicuous physiological effect on the planted trees. bout eighty percent of the trees that died on either ex- 231 ’sure did so beginning with the first drought of the sum- :r of 1954 and ending with the beginning of the fall. No re mortality occurred on either exposure until the last 0 weeks of fall. From that time until the end of the first ro weeks of the summer of 1955, about nineteen percent of .e total mortality that resulted on either exposure occur- d. One tree died on each exposure near the middle of the t, dry summer of 1955. Total mortality for any given per- d was about twice as high on the south-facing slope as on we northwest-facing one. Of a total of 648 trees planted . each slope at the beginning of the experiment, 629, or .1 percent, survived two growing seasons on the northwest- .cing slope, and 607, or 93.7 percent, survived on the south. Symptoms of all the trees that died on either of e exposures in any season led to the conclusion that mor- lity could be attributed to drought or its cold-season unterpart, winter-killing. No evidence was found of para- tic disease, insect attack, or injury from large animals either the below-ground or above—ground parts of the trees at died. One tree was destroyed on each exposure by un- OWn, violent means, possibly vandalism. These trees were t included in the calculations designed to analyze the gnificance of the comparative survival on the two expo- res, Since their deaths were considered to be extraor- narv, irrelevant occurrences. Statistical analyses of the survival on the two ex— 232 posures indicated that there was a significant difference in the survival on the two exposures during the summer of 1954, as well as for the whole period of the five sea- sons during which the experiment was carried out. Stat- .stical analyses of survival on individual exposures in- icated no significance between the two sections on ei- her exposure. Similarly, no significant differences are found among the four treatments used, among the rep- .cations, or for interaction. Practical Implications in Planting Practice. It concluded that appreciable contrasts in the micro— imates of different planting sites in southwestern Mich- an can, and may often, result in significant difference the percentage of survival to be expected in forest 9 plantings in that area. This appears to be true at st where the plantings contemplated are to be made on 2 sites or exposures where the confounding effect of cent or overtopping vegetation is minimized. No con- ions, other than by inference, may be drawn as to the 1138 that might be anticipated from underplantings or plantings on comparatively open sites where intensive preparation or other measures to minimize the effects mpeting adjacent vegetation have not been taken. It may be speculated that, if intensive planting [Hes are contemplated for comparatively large areas 233 of potential forest land in southern Michigan, economic Drudence would suggest that proposed planting sites in >pen or exposed areas should be examined rather closely vith the view of avoiding those areas where unfavorable licro-climates may preclude good survival. It may be :onsidered more economical, especially in relation to the ,arge planting program that appears to be needed in this tate, to confine plantings to those areas that appear 0 offer the best chances for good survival. Suggestions for Further Research. It is sugges- ed that, if opportunities and availability of suitable ersonnel and sufficient funds permit, this study be re- nstituted or replicated at some time in the near future. aw refinements of, or additions to, methods and means of istrumentation might be developed in the next few years tat cxnild enhance the significance of this and future ;udies. Possible and practicable improvements on the sign and method of operation of the chemical-absorption ’grometers were suggested to the investigator as a re- JJS<1f his work with the instruments during the course ‘tfiua study. It is speculated that the hygrometers ght.;x155ibly be replaced or supplemented by dew-point corders in future studies. Furthermore it is thought , at recording vecto-pluviometers might be a desirable Drovement over conventional recording precipitation 234 5. It may be suggested further that conventional an evaporimeters might be used to supplement the from the chemical-absorption hygrometers. These . be used, not to provide data supporting the evapo- spiration data obtained from the hygrometers, but to it the collection of simultaneous data on contrasts esults, as a study in itself. It is suggested that mum-and-minimum thermometers might be well justified In additional check on the accuracy of the air thermo- phs, and indirectly on the accuracy of the soil ther- raphs also. Furthermore, thermocouples might be used determine temperatures at the actual surface of the .1, rather than at one-fourth inch below it. It seems at recording wind-direction indicators might yield val- ale supplemental data. New and improved instruments for the frequent, if t continuous, determination of soil-moisture availabil- ;y are reported to be in the process of development, and Lll undoubtedly become available in the near future. It 3 possible that such instruments would provide more usa- le data than present equipment. It seems likely to this investigator that any fu- .ure studies might well be preceded by a longer and more :horough period and method of vegetation eoualization, to further minimize the possibility that undetected effects 235 in adjacent vegetation might confound the results. Pos- plyaatwo-year period of combined cultivation and treat- ,tcufthe planting sites with both silvicides and herb- desnfight effectively eliminate all or most of the al- cbrestablished, natural vegetation on the areas. Wheth- other sites of lesser percentages of slepe might have as found, or whether terracing of the present slopes it be preferable, in order to minimize potential ero- 1, remains to be investigated. 236 LITERATURE CITED 1. D4., and T. E. Maki. 1951. "Foliage Treatments .109 Early Mortality of Longleaf Pine Planted on arse Sites." Journal 92 Forestry 49:115. J. C. 1912. "CrOp Safety on Mountain Slopes." 3. D. A. 1912 Yearbook. United States Department AgricuIture. 309-318. t, G., and S. A. 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