STUDIES OF ENVIRONMENTAL FACTORS AFfECTING JACK PINE (PINUS BANKSIANA LAMB.) REGENERATION ~ Thesis for the Degree of PII. D. «MICHIGAN STATE UNIVERSITY ' ELWOOD L. MILLER 1970 xxx ""\‘-"-‘- «~33? «rm - ” VHF" , so . E , , In. L I B RA R Y ‘ Michigan State A, University «3- . .- r... \.. This is to certify that the thesis entitled Studies of Environmental Factors 1 Affecting Jack Pine (Pinus Banksiana Lamb) Regeneration presented by Elwood L. Miller has been accepted towards fulfillment of the requirements for Ph.D Forestry ' degree in Major professor Date July 31, 1970 0’169 BINDING av ’5 _ "ME & SUNS' WWIN'IQERUE- .l 1“ ABSTRACT STUDIES OF ENVIRONMENTAL FACTORS AFFECTING JACK PINE (PINUS BANKSIANA LAMB.) REGENERATION BY Elwood L. Miller The effects of several environmental factors on jack pine germination, survival, and growth were investi- gated under both laboratory and field conditions. Field comparisons were made between direct seeded and container- grown seedlings and between seedlings raised in two types of containers. Potted jack pine seedlings were raised in controlled environment chambers for ten weeks under six combinations of three temperatures and soil moisture treatments. Day and night temperatures were controlled at 32°C and 21°C, 24°C and 13°C, and 16°C and 5°C, respectively. Soil-water suction was either maintained below 0.1 atm or allowed to fluctuate between 0.0 and 15.0 atms. All other factors were held constant at levels which simulated natural conditions. Elwood L. Miller Temperature and soil moisture treatments had a pro- nounced affect on seedling height, stem diameter, and dry weight. The soil moisture X temperature interaction was highly significant for every growth parameter measured. With adequate soil water, seedlings at the high and moder- ate temperatures had approximately two times more dry mat- ter than those at the low temperature. By the tenth week, seedlings at the moderate temperature appeared to be larger and more vigorous than those at the high temperature. Trees under conditions of soil-water stress showed little response to temperature differences. The presence of ample soil water increased total dry weight by more than two times at the high and moderate temperature, but only about 30 percent at the low tempera- ture. Root mortality and a resultant decline in root dry weight seemed to be closely associated with fluctuations in soil-water suction. At the low temperature, terminal bud set appeared to be influenced by the amount of avail- able soil water. The first-year response of direct seeded and con- tainer-grown jack pine seedlings to site modifications in- fluencing wind, light, soil moisture, and competition was examined under field conditions in northern Lower Michigan. Seedlings were raised in either split-plastic tubes or Elwood L. Miller Jiffy-7 pellets for comparison with each other and with seedlings from direct seeding. Experimental plots were arranged in a split-plot design, and treatments included: (1) reduction of the prevailing wind an average of 45 per- cent on one-half of the plots; (2) reduction of the light intensity an average of 55 percent on one-half of the plots; (3) maintenance of soil water near field capacity on one-half of the plots and allowing it to fluctuate be- tween field capacity and wilting point on the remaining plots; (4) elimination of competition on one-half of the plots with direct seeded or plastic tube seedlings, and re-establishment of competition permitted on the remaining half. Growth and development prior to planting was gener- ally good in both types of containers; however, evaporative cooling in the Jiffy-7 pellets seemed to decrease the rate of germination. During the first growing season, the presence of partial shade increased germination 19 percent and increased survival 21, 25, and 8 percent for direct seeded, Jiffy-7, and plastic tube seedlings, respectively. Seedling growth was improved by partial shade, ample soil moisture, and the removal of competition. The presence of partial shade benefited terminal growth for all seedlings, while the Elwood L. Miller soil moisture treatment had its greatest affect on the growth of direct seeded and Jiffy-7 seedlings. The presence of competing vegetation reduced the total dry weight of direct seeded and plastic tube seedlings by an average of 20 and 35 percent, respectively. In general, there was no significant difference in growth parameters measured during the first growing season between trees growing with wind protection and those without. By the end of the first growing season, seedlings in Jiffy-7 pellets were almost twice as tall and had pro- duced 160 percent more total biomass than seedlings in split plastic tubes. Cool spring temperatures delayed germination in the field and gave container-grown seedlings a seven-week advantage over seedlings from direct seed. By the end of the growing season, this advanced start resulted in container-grown seedlings which averaged eight times more total biomass than trees from direct seeding. STUDIES OF ENVIRONMENTAL FACTORS AFFECTING JACK PINE (PINUS BANKSIANA LAMB.) REGENERATION By 1‘" k\. I" t Elwood LI Miller A THESIS Submitted to Michigan State University in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Forestry 1970 VITA Elwood L. Miller Candidate for the Degree of Doctor of PhilosoPhy Final Examination: July 31, 1970 Guidance Committee: Drs. G. Schneider (Chairman), D. P. White, J. W. Hanover, S. N. Stephenson, R. J. Kunze, V. J. Rudolph, and Mr. J. H. Cooley. Dissertation: Studies of environmental factors affecting jack pine (Pinus banksiana Lamb.) regeneration Biographical Items: Born August 10, 1941, Rochester, Minnesota Married, one child Education: Northern Arizona University, B.S.F., 1963 Oregon State University, M.F., 1965 Michigan State University, Ph.D., 1970 Experience: January, 1965 to September, 1967 Assistant District Ranger, Lincoln National Forest, U.S. Forest Service Summers, 1964 and 1963 Forester, Coconino National Forest and Santa Fe National Forest, U.S. Forest Service Summer, 1962 Research Aid, Intermountain Forest and Range Experiment Station, U.S. Forest Service Summers, 1961 and 1960 Fire Control Aid, Coconino National Forest, U.S. Forest Service Organizations: Phi Kappa Phi Sigma Xi Xi Sigma Pi Society of American Foresters ii ACKNOWLEDGEMENTS The author is indebted to the members of the Guidance Committee--Drs. G. Schneider (Chairman), D. P. White, J. W. Hanover, S. N. Stephenson, R. J. Kunze, V. J. Rudolph, and Mr. J. H. Cooley--for their guidance and assistance throughout the course of this study. The assistance and cooperation of the U.S. Forest Service is also acknowledged. The author is especially grateful to Ken Adams, District Ranger, Mio Ranger District, for his cooperation and encouragement during the course of the field study. Appreciation is also extended to Dr. C. E. Cress for the individual assistance given concerning all statis- tical aspects of this study. The author extends his gratitude to Michigan State University and the Department of Forestry for financial support in the form of an N.D.E.A. Fellowship. Most of all the author is forever indebted to his wife, Barb. The successful conclusion of this study would not have been possible without her constant encouragement, careful and constructive criticism, and willingness to endure financial and physical hardship. iii VITA O O O O O O O 0 ACKNOWLEDGMENTS. . . LIST OF TABLES . . . LIST OF FIGURES. . . Chapter I. INTRODUCTION. TABLE OF CONTENTS II. REVIEW OF LITERATURE. . . . . . Regeneration Characteristics. Seed production . . . . . . Germination . . Seedling establishment and early development . Growth. . Regeneration methods. . . . III. STUDIES UNDER CONTROLLED ENVIRONMENT. Methods . . Results . . Discussion. iv iii vi ix 10 14 14 22 33 Chapter IV. V. LITERATURE CITED APPENDIX Methods Results Discussion. SUMMARY AND CONCLUSIONS STUDIES UNDER FIELD CONDITIONS. 85 91 Table 1. 10. LIST OF TABLES Temperature and soil moisture effect on total height (cm) of 10-week—old jack pine O O O O I O O O O O O O O O O O O O 0 Temperature and soil moisture effect on stem diameter (mm) of lO-week—old jack pine O O O O O O O O O O I O O O O O O O 0 Temperature and soil moisture effect on total dry weight (mg) of lO-week-old jaCk pine O O O O O O I O O O O O O O O O 0 Temperature and soil moisture effect on shoot dry weight (mg) of 10-week-old jaCR pine O O O O O O O O O O O O O O O O 0 Temperature and soil moisture effect on root dry weight (mg) of 10-week-old jaCk pine O I O O O O O O O O O O O O O O 0 Average shoot/root ratio over a ten-week period as influenced by temperature and soil moisture. . . . . . . . . . . . . . . Average percent of total dry weight in needles, stems, and roots over a ten-week period as influenced by soil moisture. . . Average percent of total biomass in needles, stems, and roots over a ten-week period as influenced by temperature at low levels of soil water . . . . . . . . . . . . . . . . A representative profile and soil properties of Grayling sand on the study area . . . . Classification of percent ground cover on a representative jack pine site in northern Lower Michigan . . . . . . . . . . . . . . vi 22 24 25 27 28 31 31 32 42 43 Table 11. Comparison of climatic observations during the 1969 growing season with 15- and 30-year averages I O O O I I O O O O O I O O O O I O 12. Percent germination as influenced by partial shade and wind protection. . . . . . . . . . 13. Growth of jack pine seedlings grown from broadcast seed, by sampling period for all treatments 0 O O O I O O O O O I O O O O I O 14. First year response of direct seeded jack pine by treatments. . . . . . . . . . . . . . . . 15. Rooting depth (cm) of fourteen-week-old jack pine seedlings as influenced by partial shade and competition. . . . . . . . . . . . . . . 16. Stem diameter (mm) of fourteen-week-old jack pine seedlings as influenced by wind protec- tion and competition . . . . . . . . . . . . 17. Growth of jack pine seedlings raised in two types of containers by sampling period for all treatments . . . . . . . . . . . . . . . 18. First year response of container-grown jack pine by treatment. . . . . . . . . . . . . . 19. Influence of soil moisture and type of container on terminal growth (cm) of twenty-week-old jack pine seedlings averaged over all shade and wind treatments. . . . . . . . . . . . . 20. Influence of shade and soil moisture on shoot/ root ratio (length) and terminal growth (cm) of all container-raised jack pine seedlings twenty-weeks old . . . . . . . . . . . . . . 21. Significance of main effects and interactions on the growth of ten-week—old jack pine seed- lings in controlled environment chambers . . 22. Total height (cm) of jack pine seedlings as in- fluenced by soil moisture and temperature over a ten-week period in controlled environ- ment chambers. . . . . . . . . . . . . . . . vii Table 23. 24. 25. 26. 27. 28. 29. 30. Stem diameter (mm) of jack pine seedlings as influenced by soil moisture and temperature over a ten-week period in controlled environ- ment chambers. . . . . . . . . . . . . . . . 93 Dry weight (mg) of jack pine seedlings as in- fluenced by soil moisture and temperature over a ten-week period in controlled environe ment chambers. . . . . . . . . . . . . . . . 94 Shoot/root ratio of jack pine seedlings as in- fluenced by soil moisture and temperature over a ten-week period in controlled environment chambers . . . . . . . . . . . . . . . . . . 96 Significance of main effects and interactions on the growth of container-grown jack pine seed- lings, twenty-weeks old. . . . . . . . . . . 97 Average response of twenty-week-old jack pine seedlings raised in Jiffy-7 pellets, by treat- ment combination . . . . . . . . . . . . . . 98 Average response of twenty-week-old jack pine seedlings grown in split plastic tubes, by treatment combination. . . . . . . . . . . . 99 Significance of main effects and interactions on the growth of direct-seeded jack pine seedlings, fourteen-weeks old. . . . . . . . 100 Average response of direct-seeded jack pine seedlings fourteen-weeks old, by treatment combination. . . . . . . . . . . . . . . . . 101 viii LIST OF F IGURES Figure Page 1. Soil moisture characteristic curve for composite samples of the A and B horizons, Grayling sand SOil. O O O O O I O O O O O O O O O O O O O O 18 2. Replenishment of soil moisture with a hypodermic syringe to insure uniform moisture distribution 20 3. Temperature and soil moisture effect on total dry weight of jack pine seedlings over a 10- week periOd O O O O O O O I O O O O O O O I O 26 4. Relationship of root dry weight to soil moisture depletion cycles over ten weeks at temperatures of (A) 32°C day-21°C night, (B) 24°C day-13°C night, and (C) 16°C day-5°C night . . . . . . 29 5. Ten-week-old jack pine seedlings grown under day/night temperatures of (from top to bottom) 24/13°C, 32/21°C, 16/5°C, and soil-water suc- tions of (A) 0.0 to 0.1 atm, and (B) 0.0 to 15.0 atms . . . . . . . . . . . . . . . . . . 34 6. General view of study area near Mio, Michigan . 40 7. One complete replication of the design used to determine treatment effects of partial shade, wind, and soil moisture on jack pine regenera- tion. . . . . . . . . . . . . . . . . . . . . 46 8. Modifications of study area by the construction of (A) wind, (B) shade, and (C) soil moisture control structures. . . . . . . . . . . . . . 47 9. The planting of four-week-old container-grown seedlings in (A) split plastic tubes and (B) Jiffy-7 pellets . . . . . . . . . . . . . . . 55 ix Figure 10. Main effect of shade on first year germination and survival . . . . . . . . . . . . . . . . 11. Response of fourteen-week-old, direct-seeded jack pine seedlings to shade, soil moisture, and competition when protected from prevailing Winds O O O O I O I O O O O O O O O O O I O O O 12. First year survival of container-grown jack pine seedlings, in the field, as influenced by (A) shade, and (B) type of container . . . . . 13. Response of twenty-week-old jack pine seedlings, raised in Jiffy-7 pellets, to shade and soil moisture treatments when protected from pre- vailing winds. . . . . . . . . . . . . . . . . 14. Response of twenty-week-old jack pine seedlings, raised in split plastic tubes, to shade, soil moisture, and competition when protected from the prevailing winds . . . . . . . . . . . . . 60 63 66 67 CHAPTER I INTRODUCTION Prior to 1910, jack pine (Pinus banksiana)1 was largely considered a "weed tree" and was commercially utilized to only a limited extent (Pinchot, 1909). How- ever, between 1910 and 1945, jack pine gained in economic importance. The often pure and even-age stands, rapid early development, and long useable fiber make this species easy to harvest and highly desirable for use as pulpwood (Beaufait, 1960). Today there are almost 900,000 acres of jack pine in the state of Michigan, with over 50 percent of the total acreage located in the northern half of the Lower Peninsula (Chase gt 31, 1970). Use of this species for pulpwood has grown from 300,000 cords in 1937 to over 720,000 cords in 1966. Approximately one-fifth of the total pulpwood volume cut in the Lake States during 1966 was produced by the northern one-half of Michigan's Lower Peninsula (Blyth, 1967). The economic importance of this species is further 1Common and scientific names of all species are according to Gray's Manual of Botany, 8th Ed. (Fernald, 1950). 1963 pp. emphasized by the fact that it often grows and produces useable wood fiber on otherwise unproductive sites. Because of the importance of this species to Michi- gan's forest economy, forest managers are interested in the requirements necessary to obtain successful regenera- tion. The serotinous cone, which releases the seed only under the influence of high temperature, coupled with the necessity for exposure of mineral soil have generally resulted in unsatisfactory attempts to regenerate this species naturally. The planting of nursery-grown stock has been used extensively. However, the high cost of this technique has stimulated interest in finding alternative methods for regenerating this species. Direct seeding and the planting of container-grown seedlings are two such alternatives. To a large extent, these methods overcome the disadvantages of using nursery- grown seedlings and still retain the potential of produc- ing well stocked stands. A major problem associated with these methods is the exposure of the germinating seed or young seedling to unfavorable climatic conditions when they are in their most vulnerable state. Few studies have attempted to evaluate key environmental factor interactions that may influence jack pine establishment. The objectives of this study were: 1. To establish a long term field study investi- gating the response of both direct seeded and container-grown seedlings to modifications in wind, light, soil moisture, and competition. To examine the response of jack pine seedlings to controlled levels of soil moisture and tem- perature under laboratory conditions. CHAPTER II REVIEW OF LITERATURE Jack pine is the smallest and shortest-lived of the pines native to the Lake States (Eyre and Lebarron, 1944). Its range extends from northern New England and the Lake States, across Canada to the foothills of the Rocky Moun- tains (Fowells, 1965). Within Michigan, the botanical range extends down the east side of Lake Michigan and ter- minates at the southern tip of the lake. Commercial pro- duction of the species, however, is confined primarily to the upper one-half of the Lower Peninsula and most of the Upper Peninsula. Seven counties in the northeast corner of Michigan's Lower Peninsula have in excess of 100,000 cords per county of commercial jack pine (Rudolph and Schoenike, 1963). Jack pine is one of the most widely distributed pines in North America and, therefore, exists under a wide variation in habitat conditions. In general, the areas are characterized by warm-to-cool summers, cold winters and low-to-moderate rainfall. Daily mean temperatures in the middle of the growing season range from 55°F to 72°F, with annual precipitation averaging between 15 to 35 inches. Drought periods of up to thirty days in duration are common during the growing season from Michigan west to the Rocky Mountains (Cayford gt El! 1967; Fowells, 1965). In Michigan, jack pine grows most commonly on level to gently rolling sand plains, usually of a glacial outwash or lacustrine origin. Maximum development is reached on well drained loamy sands (Cayford gt 31, 1967; Fowells, 1965). The principle edaphic requirements are good drain- age and aeration coupled with a pH of 4.5 to 6.5. Throughout its range, jack pine grows in extensive pure even-age stands. In the Lake States it is frequently found in association with red pine (Pinus resinosa), east- 'ern white pine (Pinus strobus), quaking aspen (Populus tremuloides), paper birch (Betula papyrifera), red oak (Quercus rubra), Northern pin oak (Quercus ellipsoidalis), and black spruce (Picea mariana) (Fowells, 1965). Regeneration Characteristics Seed Production Jack pine is a prolific seed producer, with good seed crops produced in three to four year cycles (Fowells, 1965). The viability of seed stored in the serotinous cones remains virtually unchanged for the first five years after maturity (Eyre and LeBarron, 1944). The amount of seed stored in the cones can be considerable, with amounts varying from 1.7 to 13 pounds per acre (Roe, 1963b; Eyre, 1938). The serotinous cones which occur over most of the species range, are held closed by a bonding material that breaks at temperatures of from 116° to 122°F (Cayford gt a1, 1967). Along the southern edge of its range, a variety of jack pine produces nonserotinous cones which open promptly upon maturity (Fowells, 1965). Jack pine has one of the smallest seeds of all North American pines, averaging ap- proximately 131,000 seeds per pound (U.S.F.S., 1948). Germination Perhaps the most important requirements for satis- factory germination of jack pine seed is a suitable seed- bed. Exposed mineral soil has repeatedly favored germina- tion over all other types of seedbeds tested (LeBarron, 1944; Cayford, 1958, 1959, 1963; Beaufait, 1959; Eyre, 1938). Eyre and LeBarron (1944) reported almost three times more germination on bare mineral soil as compared to undisturbed duff. They summarized the beneficial effects of mineral soil as: (1) its lower wilting coefficient; and (2) the closer contact permitted between small soil particles and the seed. Germination may be inhibited by soluble materials leached from the litter and foliage of associated ground cover plants. Water extracts from the foliage of Prunus pumila, Gaultheria procumbens, and Solidago juncea have been shown to consistently reduce germination of jack pine seed (Brown, 1967). Germination of jack pine seed is subject to light control; however, once the moisture content of the seed reaches 10 to 20 percent, only a brief exposure to light is required for the seeds to germinate (Ackerman and Farrar, 1965). Environmental conditions which favor germination include: fine-textured seedbed, ample soil moisture, the presence of partial shade, and placement of the seed be- neath the soil surface (Fraser and Farrar, l953)- Beaufait, (1959) found that germination almost doubled when partial shade was provided, while LeBarron (1944) concluded that shade was only beneficial in dry years. Fraser (1959) found that germination was significantly decreased when the seedbed was exposed to more than four hours of direct sunlight. Jack pine seeds will germinate rapidly whenever a lO-day mean maximum air temperature reaches 65°F (Eyre and LeBarron, 1944). Even though germination has been shown to occur in every month from May to September, seedling estab- lishment is enhanced if germation occurs from April to June (Eyre and LeBarron, 1944; Rudolph, 1958; Cayford, 1961). Jack pine seed can be stored under dry conditions at 32° to 41°F for five years with no apparent decline in vigor (U.S.F.S., 1948). Cayford and Waldron (1966) did detect a decline in normal germination after seed treated. with Arasan-75, Endrin-75W, and aluminum flakes had been in storage for one year. Seedling Establishment and Early Development Survival Survival and establishment of jack pine seedlings is also enhanced by good soil conditions. In the Lake States, the chances of a seedling surviving the first two years is 9 to 12 times greater on exposed mineral soil than on undisturbed duff (Fowells, 1965; LeBarron, 1944). In Canada, first-year survival of jack pine seedlings av- erages two to four times higher on mineral soil seedbeds than on unprepared sites (Cayford, 1961; Cayford gt 31, 1967). High temperatures and drought are important factors causing seedling mortality (Beaufait, 1959; U.S.F.S., 1937; Cayford, 1963; Stoeckeler and Limstrom, 1950). The presence of partial shade may or may not improve survival, depending on the shade density and interactions between soil moisture and competition (Beaufait, 1959; LeBarron, 1944; Fowells, 1965; Cayford 23 El! 1967). Survival and establishment is greatly improved where the permanent water table is within three to six feet of the soil surface (Stoekeler and Limstrom, 1942). A labora- tory study determined that an optimum depth to water for one-year-old seedlings growing in sand is approximately 30 inches (Mueller-Dombois, 1964). The detrimental effect of competition on seedling survival is well documented (Rudolph, 1958; Shirley, 1945; Cayford, 1961; Jameson, 1961). Dense grass has resulted in a reduction in stand stocking levels of more than two- thirds (Cayford, 1959). Exposure to wind has also been found to contribute to seedling mortality. Jameson (1961) reported that pro- tection against wind and sun assisted the establishment of reproduction. In Newfoundland, Lewis (1954) cites exposure to wind as the most frequent cause of plantation failure. While wind appears to be an important factor in the estab- 1ishment of regeneration, little work has been done to investigate the response of jack pine to wind protection. Growth Growth of jack pine seedlings also varies with type of seedbed. Seedlings on exposed mineral soil tend to grow more rapidly than those on undisturbed sites (Jameson, 1961). However, seedlings grown on soil from just the B horizon were only two-thirds as large in terms of total dry weight as those grown on a normal profile (Beaufait, 1959)., Maximum seedling growth occurs on sites with ade- quate soil moisture and an absence of competing vegetation. Cayford (1963) reported that the total height of dominant 10 five—yearéold seedlings averaged 3.8 feet on moist sites and only 1.5 feet on dry sites. In another study, the total height of jack pine seedlings was reduced by 60 per- cent in the presence of grass competition (Sims and Mueller- Dombois, 1968). A direct relationship exists between growth and exposure to sunlight. After two growing seasons, seedlings with 0 hours of daily exposure to direct sunlight averaged two inches in height, while those with twelve hours daily exposure averaged eleven inches (Fraser, 1959). Shirley (1945) found that optimum height growth was reached at 43 percent of full sunlight over a four-year period. Logan (1966) found very similar results for the first four years, after which seedlings in direct sunlight surpassed those under partial shade. LeBarron (1944) found that one-year- old seedlings grown on a clearcut area were about 40 per- cent taller than those under a partial cut. Regeneration Methods Site Preparation The foremost prerequisite for the successful estab- lishment of jack pine regeneration is the presence of ex- posed mineral soil. Measures to prepare the site must be taken prior to the initiation of any attempt at regenera- tion. This is often accomplished by mechanical scarifica- tion or prescribed burning. Mechanical scarification has 11 consistently improved stocking, while the results of pre— scribed burning have been very unpredictable and failures not uncommon (Scott, 1966; Eyre, 1938; Benzie, 1968; Jarvis, 1966; Cooley, 1970; Chrosciewicz, 1959). Natural Regeneration In general, attempts to regenerate jack pine by clearcutting, seed tree cutting, or clearcutting in strips without further treatment have failed (Cayford et a1, 1967). Shelterwood cutting has been tried with some success in Southern Michigan, but is limited to those sites where the open-coned variety of jack pine is prevalent (Caveney and Rudolph, 1970). The scattering of cone-bearing slash on prepared sites has often been prescribed as a satisfactory method of regeneration (Eyre and LeBarron, 1944; Eyre, 1938; Cay- ford, 1958, 1966). The use of this method, however, re- quires intensive administrative supervision. In addition, the cones normally open and release the seed during the hottest portion of the growing season, jeopardizing suc- cessful germination and survival (Beaufait, 1959; Eyre, 1938; Eyre and LeBarron, 1944). Artificial Regeneration Planting of nursery stock is the most predominant method of artificially regenerating jack pine. Although jack pine plantations are generally successful, the high 12 cost of this method limits its use to the most productive sites. Early reports dealing with the prospects of direct seeding jack pine presented a rather pessimistic view (Eyre and LeBarron, 1944; Stoeckeler and Limstrom, 1950). The economic advantage of this method, however, has con- tinued to stimulate interest in its potential usefulness. Roe (1963a) has concluded that much of the pessimism re- garding the successful direct seeding of jack pine is un- warranted. Eighty percent of all successful direct seed- ing trials in the Lake States used jack pine seed. Almost 70 percent of the area seeded in Southwestern Manitoba had at least 500 stems per acre (Cayford, 1959). Day (1964) found an average of 1400 seedlings per acre three years after broadcast seeding over disced soil. As a compromise between the planting of nursery stock and direct seeding, the use of balled, potted or containerized seedlings is receiving widespread attention. The modern concept envisions the use of a plantable con— tainer rather than one which must be discarded prior to planting (Schneider, White and Heiligmann, 1970). Con- iferous seedlings have been successfully raised in several kinds of containers, including paper tubes, split-plastic tubes, wood fiber blocks, peat pots, peat pellets, and polyurethane "buns" (McLean, 1958; Carman, 1967; Huuri, 1966; Laitinen, 1965; Schneider gt a1, 1970; Walters, 1969). 13 The use of containerized seedlings offers several advantages, including: extension of the planting season, adaptability to mechanization, flexibility in meeting changing operational needs, efficient use of seed, minimum root disturbance when outplanted, and more efficient use of time and labor (Carman, 1967; Alm and Shantz-Hansen, 1970). In the United States and Canada, emphasis over the last decade has been directed toward the production of con- ifers in small, split-plastic tubes. First-year survival in these containers has been high (Carman, 1967; McLean, 1958; Alm and Shantz-Hansen, 1970). The split-plastic tube is convenient to handle, easy to plant, and more easily adapted to mechanization. This container does have several disadvantages, however, which detract from its initial appeal. The principle drawbacks are: (l) the impermeable plastic wall inhibits lateral extension of the roots into the surrounding soil; (2) the confined roots have only a small soil interface into which they can extend vertically; (3) the combination of the above makes the seed- lings susceptible to frost heaving; and (4) the container is non-bio-degradable (Schneider gt gt, 1970). CHAPTER III STUDIES IN CONTROLLED ENVIRONMENT CHAMBERS The literature abounds with statements describing the detrimental effects of high temperature and drought on successful jack pine regeneration. However, there is a lack of definitive studies which investigate the response of jack pine seedlings to carefully controlled levels of temperature and soil moisture. Before specific management prescriptions can be made with predictable results, there must be a basic understanding of what changes in seedling growth result from alterations in these environmental factors. The specific objectives of this portion of the study were: (1) to investigate the first year growth and survival of jack pine seedlings under conditions of con- trolled temperature and soil moisture; and (2) to examine the interactions of temperature and soil moisture on jack pine growth and survival. Methods Jack pine seedlings were raised in soil-filled plastic pots for approximately four weeks under uniform l4 15 conditions. Observations indicate that terminal growth is completed and winter buds are set within six to ten weeks after growth initiation (Kaufman, 1945). Thus, the dura- tion of this study was limited to ten weeks. Once estab- lished, seedlings were grown under six different tempera- ture and soil moisture treatment combinations. The tapered plastic pots in which the trees were grown measured approximately 14.5 cm in height, with a top and bottom diameter of 11.0 cm and 8 cm, respectively. Holes were drilled in the bottom of each container to per- mit adequate drainage. Each container was filled with 1050 g of soil on an oven-dry basis. The soil used was collected at the site of the field study described in Chapter IV. This soil, a Grayling sand, is typical of those soils supporting jack pine stands throughout Michi- gan. Samples were collected in the field by carefully removing layers approximately 2.5 cm in thickness to a depth of 10 cm. The top layer consisted entirely of the A1 horizon, while the remaining samples were taken from the B1 horizon. Each layer was kept separate from the others. The soil was passed through a 3 mm sieve to re- move litter and coarse debris and then air dried. The soil profile was then reconstructed in each pot by care- fully maintaining the sampling sequence and depth for each layer. 16 The seed used was collected in 1963 from several mature jack pine trees near the field study site on the Mio Ranger District, Huron-Manistee National Forest. For this study, germination tests conducted after cold soaking the seed for two days at 5°C indicated a 74 percent germina- tion capacity. Ten jack pine seeds were uniformly sown in each pot after the soil had been saturated by sub- irrigation. Following sowing, all containers were placed in a controlled environment chamber set at 30°C day temp- erature and 20°C night temperature, 60 to 100 percent relative humidity and a 14-hour photoperiod. Under the above conditions, germination was com- pleted within twelve days, after which both day and night temperatures were lowered to 24°C and 13°C, respectively. The seedlings were held under these conditions for about twenty-five days following germination. By this time, the seed coat had fallen from most of the cotyledons and the epycotyl was beginning to develop. Soil moisture was maintained near field capacity by surface watering through- out this period. Treatments Following the initial establishment period, the trees were thinned so that five uniform seedlings remained in each container. The containers were then randomly assigned to one of six combinations of temperature and soil moisture level. 17 Three growth chambers (Sherer-Gillett model Cel-25) were utilized to create day and night temperature conditions of 32°C and 21°C, 24°C and 13°C, and 16°C and 5°C, respec- tively. These temperatures were controlled to within : 1°C and shall be referred to as the high, moderate, and low temperature treatment in the remaining discussion. Examina- tion of climatic data taken at the site of the field study indicated that these temperature conditions were well within the range normally encountered during the growing season. Within each growth chamber, the containers were randomly assigned to two soil moisture treatments. The soil moisture in one-half of the containers was allowed to fluctuate between 20 percent and 10 percent moisture con- tent, while in the remaining containers it fluctuated between 20 percent and 3.5 percent. All moisture contents are reported on a weight basis. When the soil in all con- tainers was saturated and then allowed to drain for 48 hours, the moisture content averaged 32 percent, as com- pared to an estimated field capacity of 10 percent. The upper control limit of 20 percent moisture content was chosen as a reasonable compromise to avoid possible aera- tion problems occurring at 32 percent, and to help insure an even moisture distribution which might have been a prob- lem at 10 percent moisture content. The soil-water suction under the high moisture regime never exceeded 0.1 atmos- pheres while that at the low moisture regime never exceeded 14.0.1 3... N s O H O o O 0‘ O u o O 0 Soil Moisture Content (0 by weight) fi c 2.0 18 b 12‘? g . o g3 _ {:10 o-u _ a; ‘ d 1 _ g: ' H 0 v1 ' 8 o 6-———+———+———+——4—-—4 — 0.1 0.5 0. Soil-Water Suction (atms) l 1 1 1 1 l 1 I 1 I 1 l 1 1 I l 0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0 Soil-Water Suction (atms) Figure 1. Soil moisture characteristic curve for composite samples of the A and B horizons, Grayling sand soil. 19 15 atmospheres (Figure 1). To insure that the soil mois- ture was evenly distributed upon re-watering, the necessary amount of water was injected into the soil at many depths and locations with a hypodermic syringe (Figure 2). Con- trol of soil moisture levels was obtained by comparing to- tal current pot weight with the weight at the desired soil moisture level. Pots were regularly weighed every three days, and as often as twice per day as the lower soil mois- ture limit was approached. Following growth initiation, corrections were made in total container weight to compen- sate for the wet weight of the seedlings. Throughout the ten-week period, the photoperiod was maintained at 14 hours of light and 10 hours of dark- ness. A light intensity of 2600 footcandles, at foliage level, was maintained by using ten sylvania cool white flourescent bulbs and eight 25-watt incandescent bulbs. The relative humidity was maintained between 45 and 55 percent during the light hours, and between 60 and 70 percent during the dark hours for all treatments. To avoid nutrient deficiencies, a complete nutrient solu- tion1 was applied periodically to the pots. The concen- trations and rates of application were varied so each pot received the same amount of nutrients. 1RX-30, manufactured by Garden Research Labora- tories, Ltd., Toronto, Ontario, Canada. 20 Figure 2. Replenishment of soil moisture with a hypodermic syringe to insure uniform moisture distribution. 21 Sampling Procedure and Statistical Design Twenty containers were randomly assigned to each combination of temperature and soil moisture treatment. At seven-day intervals, two containers were randomly selec- ted from each treatment combination. The tops of the seed- lings were separated from the roots at the root collar, and the needles were removed from the stem. Measurements were taken on total length of stem, stem diameter, and needle green weight. The soil was then carefully removed from the roots and the root, needle, and stem tissue was dried to a constant weight at 65°C. Factors of time and soil moisture level were repli- cated twice in this study, but the temperature treatment was unreplicated. Therefore, in the analysis of variance, the interaction of temperature and time was used as an estimate of the error mean square to test the main effect of temperature. As this interaction may be an underesti- mate of the true error, no probability statements have been reported on differences shown to be significant by this test. Standard analysis of variance procedures were used to test for significances of soil moisture level and time. 22 Results Effect gt Treatment g3 Total Height and Stem Diameter Total Height The maintenance of readily available soil water significantly increased total height by 14 percent and 21 percent at the high and moderate temperatures, res- pectively (Table 1). However, when soil water was limit- ing, temperature had no apparent effect on the total height of the seedlings. There was no apparent differ- ence in total height between seedlings growing under the high and moderate temperature treatments at either soil moisture level. Table 1. Temperature and soil moisture effect on total height (cm) of 10-week old jack pine. Soil-Water Day/Night Temperature (°C) Suction 32/21 24/13 16/5 0 to 0.1 atm 2.85a 2.90a 2.45b b o to 15.0 atms 2.50b 2.40 2.40b aValues with the same letter in the superscript are not significantly different. During the eighth week, terminal bud formation occurred on five seedlings subjected to low temperatures and soil—water stress. Bud set took place as soil moisture approached the wilting point. Buds resumed growth shortly 23 after the pots were watered. Bud set again occurred during the tenth week, as soil water again approached the lower limit. Stem Diameter Stem diameter responded in a similar manner to tempearature when soil water was readily available (Table 2). Both the high and moderate temperature treatments increased stem diameter by 22 percent over the low temper- ature but were not apparently different from each other. However, when soil water was limiting, stem diameter was apparently different for every level of temperature. Seedlings grown at high temperatures had an average stem diameter of 11 percent larger than those at low temper- atures. The average stem diameter of seedlings at the moderate temperature was 5 percent larger than that at the low temperature. Stem diameter was significantly increased by the presence of readily available water at every temperature. An increase in stem diameter of 28 percent was found at the moderate temperature, while ample moisture at the high and low temperatures caused increases of 21 and 5 percent respectively. For both total height and stem diameter, the temperature x soil moisture interaction was highly significant. 24 Table 2. Temperature and soil moisture effect on stem diameter (mm) of lO-week old jack pine. Soil-Water Day/Night Temperature (°C) Suction 32/21 24/13 16/5 0 to 0.1 atm 0.86a 0.86a 0.67b o to 15.0 atms 0.71C 0.67d 0.64e aValues with the same letter in the superscript are not significantly different. Effect gt Treatment g3 Dry Weight There was an apparent increase in total dry weight as the temperature was increased from the low level to the moderate and high levels (Table 3). When soil water was readily available, seedlings growing under moderate temp- eratures produced 143 percent more dry matter and those at high temperatures 114 percent more dry matter than seed- lings at the low temperature. There was no apparent dif- ference in dry weights at high and moderate temperatures. The presence of readily available soil moisture significantly increased total dry matter production irres- pective of temperature level. At the moderate temperature level, maintenance of the soil moisture level above 10 per- cent increased dry matter by 142 percent, as compared to 98 and 31 percent increases at high and low temperatures, respectively (Table 3). 25 Table 3. Temperature and soil moisture effect on total dry weight (mg) of lO—week old jack pine. Soil-Water Day/Night Temperature (°C) Suction 32/21 24/13 16/5 a a b 0 to 0.1 atm 79 90 37 o to 15.0 atms 40b 38b 28c aValues with the same letter in the superscript are not significantly different. Differences in total dry matter production between temperatures and soil moisture treatments became evident very early in the ten week period (Figure 3). Differences between temperature levels were observed by the end of the third week, while soil moisture level began to have a sig- nificant influence by the end of the fourth week. Restric- tion in dry matter production with increasing soil-water suction was noted. Shoot and Root Dry Weights The individual responses of the shoot and root dry weights to the treatments paralleled that of total dry weight. When soil water was not limiting, shoot dry weight increased 145 percent and 113 percent, respectively, when moderate and high temperatures were compared to the low temperature (Table 4). The average increase declined to about 30 percent with increasing soil-water suction. The presence of ample soil moisture caused significant increases Total Dry weight (mg) 300 250 200 150 100 50 100 50 26 Soil-Water Suction--0.0 to 0.1 atm Day/Night Temperature (°C) A - 16/5 3 - 32/21 C - 24/13 B O n __ n - B .. + + A L. *- .. g. g. i + * 1 1 1 1 1 1 1 1 1 1 11 L F 1 1 1 1 1 1 1 1 1 1 1# 0 1 2 3 4 5 6 7 8 9 10 Week Figure 3. Temperature and soil moisture effect on total weight of jack pine seedlings over a 10vweek pgiiod 27 in shoot dry weight of 114 and 157 percent at the high and moderate temperature levels, respectively. At the low tem- perature, this increase declined to 30 percent. Table 4. Temperature and soil moisture effect on shoot dry weight (mg) of 10-week-old jack pine. Soil Moisture Day/Night Temperature (°C) Regime 32/21 24/13 16/5 0 to 0.1 atm. 47a 54a 22b 0 to 15.0 atms. 22b 21b 17c aValues with the same letter in the superscript are not significantly different. When soil moisture was not limiting, seedlings grown under high and moderate temperatures had increases in root dry weight of 107 and 133 percent, respectively, over that of seedlings grown at the low temperature (Table 5). When soil moisture was limiting, the increase declined to approximately 50 percent. There was no apparent differ- ence between the results at the high and moderate tempera- ture levels at either level of soil moisture. The presence of ample soil moisture significantly increased root dry weight by 72, 106, and 25 percent at the high, moderate, and low temperatures, respectively. The response of root dry weight over time to increas- ing soil-water suction was extremely variable. Regression analysis of root dry weight over time showed that only 27 28 Table 5. Temperature and soil moisture effect on root dry weight (mg) of 10-week-old jack pine. Soil-Water Day/Night Temperature (°C) Suction 32/21 24/13 16/5 0 to 0.1 atm 31a 35a 15b 0 to 15.0 atms 18b 17b 12c aValues with the same letter in the superscript are not significantly different. to 34 percent of the variability could be accounted for by the time factor. This indicated that root dry weight was fluctuating over time in response to some other fac- tor. When root dry weight was compared to soil moisture depletion cycles, a definite relationship appeared to exist (Figure 4). This relationship is best seen under low temperatures (C) where the soil moisture depletion cycle extends over a considerable period of time. The initial decline is probably caused by the low temperature. By the end of the fourth week, available soil water had been depleted and the pots rewatered to the upper limit of 20 percent. Increase in root dry weight tends to fol- low the replenishment of moisture until the soil moisture is depleted to approximately 4.3 percent moisture content by weight. After reaching this point, the root dry weight decreases and continues to decrease for about one week after the soil water is restored to the upper limit. It appears that during the tenth week, the roots began to increase in p O O p . O 100 O O V'UVTII N O O O p N W O O I l H O Y loot Dry Weight (mg) Available liter (9) 180 I I 140 - 100 rl 60 . 20 - 401- 30 - 10 - Root Dry Weight any) Available water (9) 180 140 100 P 60 ’ 20 p O O O O 40 - 30 7 20 P 10 ' Boot Dry Height (1119) Available Water (9) Figure 4. Heek Relationship of root dry weight to soil moisture depletion cycles over ten weeks at temperatures of (A) 32°C day-21°C night, (3) 24°C day-13°C night, and (C) 16°C day-5°C night. 30 dry weight once again. This same cycling can be seen at the other temperatures, but the more rapid cycles of soil moisture plus the rigid sampling schedule may tend to mask some of the cycles in root dry weight. A decrease in root dry weight suggests the mortality and sloughing of root tissue. During at least two of the sampling periods, root mortality was noted in pots where soil water approached the lower limit. Furthermore, the decrease in root dry weight is initiated at approximately the same point on the soil moisture depletion curve for all temperatures. This point ranges from 4.3 to 5.0 percent moisture content by weight, which corresponds to soil-water suction values of approximately 3 to 3.5 atmospheres. This range of soil- water suction is very near the point on the soil moisture characteristic curve where very small changes in water content result in large differences in soil-water suction (Figure 1). Shoot/Root Ratio and Dry Weight Distribution The temperature and soil moisture treatments had little influence on the shoot/root ratio or the distribu- tion of dry weight among needles, stem, and roots. However, the shoot/root ratio was significantly reduced by increas- ing soil-water suction at the high temperature. When soil water was limiting, the shoot/root ratio at the high temp- erature was also lower than that at the low temperature (Table 6). 31 Table 6. Average shoot/root ratio over a ten-week period as influenced by temperature and soil moisture. Soil-Water Day/Night Temperature (°C) Suction 32/21 24/13 16/5 0 to 0.1 atm 1.50a 1.40a 1.55a o to 15.0 atms 1.25b 1.39ab 1.58ac aValues with the same letter in the superscript are not significantly different. The distribution of biomass into needles, stems, and roots was influenced by soil moisture only at the high temperature (Table 7). The proportion of biomass in need- les declined significantly from 50 percent to 45 percent as soil water became limiting. In contrast, 41 percent of the total dry weight was accounted for by roots where soil water was readily available as compared to 46 percent where it was limiting. Table 7. Average percent of total dry weight in needles, stems, and roots over a ten-week period as in- fluenced by soil moisture. Temperature 32°C Day - 21°C Night Soil-Water Percent Dry Weight in Suction Needles Stems Roots o to 0.1 atm 50.1a 8.1a 41.1a o to 15 atms 45.4b 8.2a 46.4b aValues with the same letter in the superscript are not significantly different. 32 The distribution of biomass was influenced by temp- erature only where soil-water suction reached 15 atms. About 8 percent of the total dry weight was accounted for by stem tissue at the high and moderate temperatures as compared to 10 percent at the low temperature (Table 8). The amount of biomass distributed to the roots was also higher in seedlings under low temperatures as compared to those under high temperatures. Table 8. Average percent of total biomass in needles, stems, and roots over a ten-week period as influenced by temperature at low levels of soil water. Percent of Total Day/Night Temperature (°C) Dry Weight in 32/21 24/13 16/5 Needles 45.4a 47.7ab 49.7b Stems 8.2a 8.6a 10.4b Roots 46.4a 43.7ab 39.9b aValues with the same letter in the superscript are not significantly different. Needle Moisture Content An attempt to relate needle moisture content to soil-water suction showed no apparent relationship between these two factors. 33 Discussion Temperature An important response to temperature is the obvious decline in all growth parameters at the low temperature, when compared to the moderate and high temperatures (Figure 5). Only four days after the seedlings had been exposed to the low temperature treatment, the cotyledons began to exhibit a purple coloration. By the end of the fourth week, the purplish cast had intensified. It was also evi- dent on all foliage of seedlings subjected to moisture stress, and on all tissue except primary needles of seed- lings with ample moisture. The cool temperatures may have triggered the formation of anthocyanin, which then persisted throughout the ten week period. Also, the uptake or trans- location of phosphorus may have been impeded by the low temperatures resulting in the purplish coloration. A sim- ilar response has been reported in ponderosa pine seedlings where air temperatures ranged from 13° to 7°C (Larson, 1967; Steinbrenner and Rediske, 1964). The influence of tempera- ture on jack pine growth was most pronounced when soil water was not limiting. Differences in growth response to temperature were greatly diminished when seedlings were subjected to soil water stress. Although no apparent difference in over-all seedling growth occurred between the moderate and high temperature treatments, a Visible decline in seedling vigor was observed ‘ 34 Inches 1A B _ _ , __ ___ 4 _ 1 L_ __ _ ,___ _ 2 i;:, ‘1 ‘E ii 0 s O 7‘ V __ I 1 . J p L _ ‘ .l, i. --' . ~' 1. a ‘ 1 \A i ' 2 ‘ t g e T ’ . 1 ‘ 6 8 Inches 1A B I _ __ 9 _. _ __ 1 M ._ — —— — —— — ,___ 2 -——*~- H I v u, (I U’ " b» V I V LL 0 v "M I If I; . ' 2 4 6 8 Inches Figure 5. Ten—week—old jack pine seedlings grown under day/ night temperatures of (from top to bottom) 24/13°C, 32/21°C, 16/5°C, and soil-water suctions of (A) 0.0 to 0.1 atm, and (B) 0.0 to 15.0 atms. 35 at the high temperature during the tenth week. The res- ponse to temperature on the basis of total dry weight indi- cates a lower rate of dry matter accumulation at the high temperature than at the moderate temperature (Figure 2). A similar decline in vigor of jack pine seedlings was also noted by Yeatman (1967) under conditions of 27°C day temp- erature and 19°C night temperature. High respiration rates stimulated by the high temperatures may have reduced the net production of photosynthate to a lower level. Yeatman (1967) also concluded that temperature was the principal factor controlling the initiation of growth in the spring. In this study, the initiation of height growth at the high temperature occurred at least ten days prior to that at moderate temperatures. Eyre and LeBarron (1944) have reported that terminal bud set in jack pine is under the control of environmental factors other than photoperiod. In this study bud set at .the low temperature appeared to be controlled by soil water. The low shoot/root ratio resulting from the high temperature and low soil moisture treatments results pri- marily from the influence of temperature and soil water on the distribution of root biomass (Tables 6, 7, and 8). Under soil water stress, the proportion of total weight in the roots increased as temperature increased. .Corres- pondingly, shoot weight was reduced under these same 36 conditions, thereby causing a low shoot/root ratio. Simi- lar results were reported for ponderosa pine by Steinbrenner and Rediske (1964). Soil Moisture Regardless of temperature level, there was a signi- ficant increase in every observed growth parameter when soil-water suction was maintained at less than 0.1 atm. The importance of soil moisture definitely exceeded that of temperature at the moderate and high levels. At the low temperature level, the influence of soil water was diminished considerably. These results differ from those found by Steinbrenner and Rediske (1964) in ponderosa pine seedlings where temperature was the most important factor influencing growth. However, their moisture limits were set rather arbitrarily, and the relationship to soil- water suction was not defined. The extent to which soil water must be depleted before plant growth is influenced has long been a subject of controversy (White, 1958). Veihmeyer and Hendrickson (1950) have supported the view that water is equally avail- able for plant growth until very near the wilting point. On the other hand, Kramer and Kozlowski (1960) postulate that soil-water suctions above 1 or 2 atms would inhibit plant growth. Stanhill (1957) showed that in 66 studies out of 80, plant growth was apparently affected before 37 soil moisture reached the permanent wilting point. Recent work supports the idea that growth is already reduced, with soil-water suctions well below the permanent wilting point (Sands and Rutter, 1959; Stransky and Wilson, 1964; Boersma, Babalola and Youngberg, 1969; Kaufmann, 1968; and Glerum and Pierpoint, 1968). In this study, the soil-water suc- tion was allowed to remain at 15 atms for only short peri- ods of time, normally no more than a few hours. The magni- tude of the difference between seedlings at the two soil moisture treatments indicates that growth was affected at some value of soil-water suction above the 15 atm level. CHAPTER IV STUDIES UNDER FIELD CONDITIONS The planting of bare-rooted nursery stock has been the commonly used method in artificially regenerating jack pine in Michigan. This method does have several disad- vantages, however, such as: (1) the high cost of produc- ing and planting the seedlings; (2) the often excessive time lag between nursery production and operational needs; (3) the planting "shock" often exhibited by newly planted seedlings; and (4) the frequent failures of plantations on adverse sites. Direct seeding is an alternative method that can be conducted at a considerable reduction in cost while still retaining the potential of producing well-stocked stands. The success of direct seeding is diminished, how- ever, by rodents, birds, and unfavorable climatic condi- tions. The young succulent seedlings are especially susceptible to heat and drought injury. The use of container-grown seedlings is now re- ceiving widespread attention as an alternate planting method. In the modern application of this technique, conifer seedlings are raised in plantable containers 38 39 under ideal conditions for four to twelve weeks and then outplanted. In North America a small split-plastic tube has gained popular acceptance as a useable container for raising coniferous seedlings. Shortcomings Of this tube, however, have stimulated interest in seeking a container that is more suitable. Specific Objectives gt the Study The specific objectives of this portion of the study were: 1. To evaluate the response of direct seeded and con— tainer grown jack pine seedlings to site modifica- tions influencing wind, light, soil moisture, and competition. 2. To compare the performance under field conditions of seedlings raised in split-plastic tubes, Jiffy- 7 pellets, and those from direct seeding. Methods Study Area The study is located on the Mio Ranger District, Huron-Manistee National Forest, approximately ten miles southeast of Mio, Michigan. This area is typical of jack pine sites in northern Lower Michigan (Figure 6). A commer- cial pulpwood harvest was conducted in the winter of 1965- General view of study area near Mio, Michigan. Figure 6. 40 41 1966 and the area was broadcast burned with a fast moving headfire in October, 1966. The soil, Grayling sand, is a uniform glacial outwash sand (Table 9). Field capacity was 10.3 percent by weight as established in the field, while wilting point was estimated to be 3.5 percent by weight using the lS-bar pressure membrane apparatus. Ground cover was determined by randomly locating three transects over the study area (Table 10). The pre- dominant ground cover species and the prime competitors of jack pine on this site are Pennsylvania sedge (Carex penn- sylvanica) and blueberry (Vaccinium angustifolium). These two species occupy 32 percent and 8 percent of the ground surface, respectively. Occasional hardwood species found on the site are northern red oak (Quercus rubra) and black oak (Quercus velutina). The general climate in this area is characterized by warm summers and cold winters, with approximately ten days out of every growing season exceeding 32°C. Average total precipitation equals 65.5 cm, with about 63 percent of this occurring during the growing season. Information concerning the climate at the study site was obtained from a standard evaporation pan, a 3-cup anemometer, a standard precipitation gauge, and a hygrothermograph (Table 11). During this first growing season, May and June precipita- tion was higher than the long-term average, but average 42 ea mHH ma Hm ~.o n.m ccmm +mm 0 ea mHH mm mm e.o m.m ocmm mmlnm mm ea MHH om ma v.0 m.m ocmm hmnma Hammm «a mHH em OH m.o N.m comm maum uflamm em mas mm me e.m m.e seam muo Ha o: mu m m nmuwmz a AMUV . . page no m whopxma nu ma coNflHom 1 mm\ was muemenpsz.menmaem>« ucmoumm .mmnm hosum on» so csmm mafiammuo mo mmflunomonm aeom cam mHflmoum m>eumucmmmumwu d .m magma 43 Table 10. Classification of percent ground cover on a rep- resentative jack pine site in northern Lower Michigan. Ground Cover Percent of Ground Surface Occupied Carex pgnnsylvanica 32 Vaccinium angustifolium 29 Organic Matter 19 Mineral Soil 8 Logging Slash 2 Comptonia peregrina 2 Andropogon scoparius 2 Oryzopsis pungens 2 Andropogon gerardi l Panicum depauperatum l Prunus pumila < l Epigaea repens < l Actostaphylos uva-ursi < l Danthonia spicata < 1 Viola subvestita < l Pinus banksiana < l 44 .000 Beams mm3 wuzumuwQEmu Eseflcfle mmmc mo Hones: mumofip:« A y me mmsHm> m .Uomm omnwmoxm wusumuomfimu ESEHxME mast mo Honfisc mumowpcw A V ca mmsHo>N .cmmflnoez .0“: .om .oz .mmumum coves: ecu mo acmmumoumeflau .cmmflnowz .mcflmsmq ummm .smousm Honummz .m.3H me n Aevm Hm onmm «.mh ov.m mm.m mm.m mm.m Amalav umnEwumwm me oa Amvoa mm Aavbm m.vm mm.oa ma.ma vm.n ow.m Dmsms< we Ha onmH mm Aavmm N.mh Hm.ma o>.ma hm.n mm.m hand be m Amvm mm Hovma o.~m mm.mH mm.ma mm.m om.ma mash ov e Revs ma AvaH m.vm ov.aa on.m mm.m om.m AHmumHv m N mm: OOOOIOCOwOOCOOOCO .0OI...CCOOCOOOUOCCOCCCOOOCOCOO .m@\OEx OOOOOOCOOOCCOCOCEUOOIOOOOOOOOOOOO mme ommauamma mmma oomalamma mwma mmma mmmalamma mama omeIHmmH moma nucoz Eseflcw: ESEHCHZ maflmo EDEmez NHHMQ pcfiz cofluouomm>m newumufimfiomum adage mmmum>¢ Hobos Hmuoe Hmuoa NuHUHEsm m>fiumHmm musumummmms new .mmmmuw>m Hmmmlom one ImH nuwz common mcflzoum mmma ecu mcfiuso mc0flum>ummno oeumsflao mo comfiquEoo .HH manna 45 daily maximum temperature was lower. The month of August, however, received a lower than average amount of rainfall, and evaporation exceeded the norm by 5.6 cm. Throughout the 1969 growing season, prevailing southwesterly winds were comparable to those normally occurring in the area. Experimental Design The response of jack pine seedlings to modifica- tions in wind, shade, soil moisture,and competition was studied utilizing a split-plot factorial design with six replications (Figure 7). Prior to any treatment, all snags and logging slash were removed from each replication, and all competing vegetation was hand-scalped from each 1.2- meter-square experimental plot. A cut 30 cm deep was made around the edge of each plot to eliminate the influence of lateral roots from the surrounding vegetation. Treatments Wind. One-half of each replication was protected from the prevailing southwesterly wind by erecting a 1.2 meter high reinforced burlap wind barrier 2.1 meters away from the south and west sides of the plots. To allow some natural wind movement, approximately 25 percent of the total surface area of the wind barrier was removed by cutting 15.2 cm square holes in the burlap material (Figure 8). 46 1.2 Meter Square 7/ I ————— 1 Plot 4% Partial Shade V M lar Cover Permittin [j Y 9 Soil Moisture Control Partial Shade and Mylar Cover '6 .0 33¢”?3 0 fs &. V633flgq€p {03“ A A -‘fi' D O Q '0 e - ro0.0:O:Q. )-———-2:—d- Wind Barrier‘--1 Figure 7. One complete replication of the design used to determine treatment effects of partial shade, wind, and soil moisture on jack pine regeneration. 47 Modifications of study area by the construction of (A) wind, (B) shade, and (C) soil moisture control structures w~0 Figure 8. 48 Shade. Randomly selected plots were covered with a shade structure consisting of camouflage netting stretched over a wooden frame (Figure 8). The covering was effective in reducing light intensity to approximately 45 percent of that in the open. The structure sloped in one direction from 1.1 meters on the high side to 0.75 meters on the low side. The shade covering extended beyond the plot edge a distance sufficient to prevent direct sunlight from reach- ing the plot at any time during the day. Soil Moisture. Randomly selected plots were as- signed either a "wet" treatment, where soil-water suction at a depth of 10 to 20 cm was maintained below 0.5 atmos- pheres, or a "dry" treatment, where soil-water suction, at this same depth, was allowed to fluctuate between 0.0 and 15.0 atmospheres. Precipitation was excluded from the dry plots by constructing a transparent mylar-covered wooden frame over them (Stransky and Duke, 1964). This frame was 1.2 meters high in the center and sloped in two directions to 0.75 meters beyond the edge of the plot (Figure 8). The transparent mylar was also placed over the shade material on one-half of the shade structure to study the interactions between soil moisture level and shade. The moisture control treatments were not initiated until after germination was complete. Direct Seed, Container Raised Seedlings, and Compe- tition. Four plots were established within each combination 49 of wind, shade, and soil moisture treatments (Figure 7). Three of these plots were randomly selected to be planted with either jack pine seed or jack pine seedlings raised in two kinds of containers. These plots were maintained weed-free by hand weeding throughout the growing season. One-half of the remaining plot was selected to be direct seeded, while the other half was planted with seedlings raised in split-plastic tubes. After the initial scalping, the competing vegetation was allowed to become re-estab- lished on this plot. Five replications were used to study the effects of competition as described above. Micro-Climatic Measurements Wind Measurements taken with 3 cup totalizing anemom- eters showed that the wind barrier was effective in reduc- ing prevailing winds by an average of 45 percent, varying from 64 percent to 26 percent at locations closest and far- thest from the barrier, respectively. Wind movement from all directions throughout the growing season was reduced by 30 percent. Temperature Air temperatures were measured 10 cm above the soil surface with mercury-in-glass maximum-minimum thermometers. Shade structures significantly lowered maximum air temper- atures by an average of 2°C from that in the open, but the 50 mylar covering had no such effect. The mylar covering did significantly raise the minimum temperatures by an average of 0.5°C, but there was no affect by the shade structure. Air temperatures were not affected by the wind barrier. Mercury-in-glass soil thermometers were used to measure temperature in the upper 5 mm of the soil surface. The presence of partial shade lowered soil temperatures an average of 3.5°C during the hottest portion of clear days. No other treatment appeared to influence soil temperature. Soil Moisture Gravimetric samples were collected at a depth of 10 to 20 cm throughout the growing season to determine the rate of moisture depletion on plots assigned the dry treat- ment. Tensiometers were randomly located on plots assigned the wet treatment to insure they did not exceed the soil- water suction limit of 0.5 atm. The presence of shade lengthened the time to reach wilting point at this sampling depth from four to nine days beyond that required for the exposed plots. Both competing vegetation and wind barrier appeared to have little influence on soil moisture depletion. Seeding and Plantipg Seeding The jack pine seed used for both the direct seeding and the container trials came from the same seed lot as that used in the controlled environment studies described in 51 Chapter III. The seed was collected in 1963 from several mature trees near the study area. The use of a North Dakota Seed Blower to sort the seed improved the germina- tion from the 74 percent reported earlier to 92 percent. Seeds were treated with a mixture of Endrin and aluminum flakes to prevent rodent and bird damage. On May 30 each scarified plot to be direct seeded was sown with 100 jack pine seeds. Seeds were evenly distributed over the mineral soil seedbed and lightly covered with soil to prevent move- ment from the action of wind and water. Container-Raised Seedlings The first type of container used in this study was a small split-plastic tube1 measuring 1.6 cm in diameter by 7.6 cm in length. Each tube was filled to within 1.5 cm of the top with a mixture of 50 percent sifted peat and seeded with one jack pine seed. The seed was then covered with a shallow layer of perlite. The tubes were then ar- ranged in shallow trays with holes in the bottom to permit subirrigation. The second type of container was a small peat pot 2 known commercially as the Jiffy-7 pellet (Hermann, 1969). This container is shipped as a small compressed disk wrapped 1Manufactured by Canada Building Products, Ltd., Micro-Plastics Div., Actin, Ontario, Canada. 2Manufactured by Jiffy Pot Ltd., Grorud, Norway. 52 in a fine plastic net. Upon wetting, the disk swells until it is approximately 4.5 cm in diameter and 4 cm high. The netting expands with the pellet and gives the saturated peat dimensional stability. Each Jiffy-7 was seeded with two jack pine seeds. The seeded containers were then placed on copper screen which covered the bottom of shallow plas- tic trays. The screen was used to inhibit root growth below the bottom of the pellets. Following germination, the seedlings were grown in their respective containers for about four weeks. During the first three weeks, the seedlings were raised under greenhouse conditions. During the last week, both con- tainers were placed outside to give the seedlings an adjust- ment period prior to outplanting. Both containers were fertilized twice by substituting a complete nutrient solu- tion for a routine watering during the second week and again just prior to outplanting. When the container-grown seedlings were about four weeks old, they were planted in the field. Trees in Jiffy- 7 pellets were thinned so that only one seedling remained for each container. The randomly selected weed-free plots received either 50 seedlings in split-plastic tubes or 36 seedlings in Jiffy-7 pellets. The remaining half of the plot used to study the effects of competition was planted with 20 seedlings in split-plastic tubes. All field plant- ing was done on May 27 and 28. 53 Sampligg Procedure Germination and survival counts were taken on June 12, June 30, July 12, and September 12. Frequent checks between these dates insured that no germination or mortal- ity was overlooked between sampling periods. Percent sur- vival was determined by counting living seedlings at each sampling period and dividing by total germination or num- ber of seedlings planted. On August 15 and September 15, representative seed- lings were removed intact from each plot. Stem diameter, terminal growth, and rooting depth were measured after the soil had been carefully washed from the roots. Shoot and root dry weights were determined after drying the tissue at 70°C. Analysis gt Data Both survival and growth data were analyzed using a split-plot analysis of variance. Wide ranges in values required the use of arcsin transformations in analyzing the percent germination and survival (Steel and Torrie, 1960). Results Germination and Seedling Development tg Containers Germination in both types of containers began ap- proximately seven days after seeding. Total germination 54 over the four-week period averaged about 80 percent in plastic tubes, but only 66 percent in the Jiffy-7 pellets. The reduced rate of germination in peat pellets may have been caused by the rather large exposed surface area which resulted in rapid evaporative cooling. Temperatures in the area of seed deposition were 3° to 7°C lower than the ambient daytime temperature of approximately 29°C. Growth and development of the young seedlings were good in both types of containers (Figure 9). At outplant- ing, however, the Jiffy-7 seedlings were less well developed than those grown in the plastic tubes. The slower rate of germination in the peat pellets resulted in seedlings that were somewhat younger than those grown in split-plastic tubes. The copper screen placed beneath the Jiffy-7 pellets was effective in confining the root system to the container. While the presence of the copper screen normally resulted in the death of the primary root, a good secondary root sys- tem developed. Germination, Survival and Growth gt Seedlings From Direct Seeding Germination The first signs of germination occurred on June 22, twenty-four days after seeding. By June 30, 98 percent of the total germination was complete. No germination was ob- served after July 12. Figure 9. The planting of four-week old container-grown seedlings in (A) split plastic tubes and (B) Jiffy- 7 pellets. 56 .Hm>fl>usm cam coaumsflfinmm new» umuwm co woman mo pommmm new: .oa muzmflm some mH\m Hm mflxm Hm ma\e om ma\m H\w . r P — p p , 90 .3 a e .2 m 7 . \ \ :8 m. \ m 01 llllllllllll l0ll|0\\ 110% so... 06 E m. m m 0 .III 8 am 2 18 M QUMSW I I M. :8 m .r 1. 1 4. on: 57 The main effect of shade was a beneficial one. Average total germination was 42 percent under partial shade, but only 23 percent on plots without shade (Figure 10). The wind barrier alone had no significant effect on germination. However, the interaction between wind pro- tection and shade was significant (Table 12). The reduc- tion of air movement behind the wind barrier, combined with the lower air and soil temperatures caused by the presence of shade, probably reduced soil surface evapora- tion and provided improved moisture conditions for germina- tion. No explanation can be offered for the observed re- duction in germination with the presence of the wind bar? rier and in the absence of shade. The design of the study did not include testing the effects of soil moisture level and vegetative compe- tition on germination. Soil moisture was maintained near field capacity throughout the period of germination. Also, the re-invasion of competing vegetation had not progressed to the extent that it had any influence on germination. Survival Soil moisture and weed competition alone had no influence on survival. The presence of partial shade, however, did lower both soil and air temperatures and reduce the rate of soil moisture depletion so that by the 58 Table 12. Percent germination as influenced by partial shade and wind protection. Wind Protection Partial Shade Yes No Yes 45 18 No 39 28 Interaction significant at the 5 percent level. end of the growing season, survival was significantly in- creased by 21 percent (Figure 10). Seedlings exposed to competition and low soil moisture levels were, however, more chlorotic and of lower vigor. Survival was not in- creased by protection from wind. Growth Most of the stem and terminal growth had occurred by August 15. Total dry weight production, however, in- creased considerably between August and September, with approximately 40 percent of the total dry weight accumu- lated during this latter period (Table 13). The most predominant treatment influencing growth was control of soil water level (Table 14). When soil water was maintained near field capacity, stem diameter and rooting depth were both significantly increased by about 15 percent. Terminal growth, however, was apparently not af- fected. Dry weight showed the largest response, with in- creases of 52 and 36 percent for the roots and shoots, 59 Table 13. Growth of jack pine seedlings grown from broad- cast seed,by sampling period for all treatments. Sampling Date Characteristic Measured Aug. 15 Sept. 15 Terminal Growth (cm) 0.60 ** 0.85 Stem Diameter (mm) 0.69 ** 0.79 Rooting Depth (cm) 14.45 ** 17.32 Shoot Dry Weight (mg) 22 * 39 Root Dry Weight (mg) 15 ** 26 Total Dry Weight (mg) 37 ** 65 Shoot/Root Ratio (length) 0.19 ** 0.16 Shoot/Root Ratio (weight) 1.72 * 1.51 **Significant at the 1 percent level *Significant at the 5 percent level respectively. The lack of response in terms of shoot length, with a corresponding increase in rooting depth, produced a shoot/root ratio (length) which was significantly lower where adequate moisture was provided (Figure 11). Shade significantly increased terminal growth but tended to decrease rooting depth. These two relationships combined to produce a shoot/root ratio significantly higher if shade was provided (Table 14). The absence of competing vegetation apparently affec- ted only dry weight increment. Stem dry weight was influ- enced the most, increasing approximately 38 percent, while root dry weight increased only 18 percent. The competition X shade interaction, as measured by rooting depth, and the competition X wind interaction, as measured by stem diameter, 6O .mccfls mcwawm>mum Eoum cmuomuoum cwa3 cowufluwmsoo use .musumwoe Hfiom .mcmsm ou mmcwacwmm mcwm xomn cmcmmmluomuwo .oaouxmmzucmouusom mo uncommom .HH musmflm ll ‘Il‘l‘lul 1‘1 no» 02 mm» .1. oz 11 ”A new "A oz in» new WA oz v YR ZOHBHBMQSOU V 1 .mé o... .031} cm 1 A .mé ob .o.m 11 .o.m AEWA EDBmHOS .HHOm A . I V A 1v. no» 02 madmm AdHBMflm .Ho>ma unmouom m can um pcMOHmwcmflm moconmmwwa. .Hw>ma unmouom H on» no usmoamwcmflm mucouommwoss 61 ee.H mm.H mm.H ee.H oe.H . ~o.a om.H mm.a loomeoec oeumm poom\uoonm ma.o oH.o eH.o . 4H.o ee.o . eH.o mH.o oH.o isomooae oeomm ooom\ooozm mm .. Ne em . an mm as em He lost homeoz zoo Hobos em . mm Hm .. mm mm mm mm mm lose onoeoz zuo uoom em .. so mm . me em es mm me lose ozoeoz zuo ooozm oo.ea mo.ea oe.os . mm.ma mo.ee oo.es mo.ee mm.eH. Asov zoooo mcfluoom ee.o om.o ee.o .. em.o om.o ma.o ee.o om.o lees umpofimeo zoom me.o mm.o om.o om.o om.o . om.o om.o om.o Asov suzono Hmcflsuoe mo» oz o.mH ouyp.o m.o on o.o oz mo» oz mo» nouoeouoo coHuflummEou AmEumv cofluosm Hmumzlawom wpmnm cofluomuoum wcwz £u3ouw .mucmEumwuu an mafia xoon cocoon “condo mo uncommon use» umuwm .vH magma 62 were both significant at the 5 percent level (Tables 15 and 16). In both cases, site amelioration in the presence of competition retarded jack pine growth. It thus appears that the improved conditions favored development of compet- ing vegetation at the expense of the jack pine seedlings. Table 15. Rooting depth (cm) of fourteen-week-old jack pine seedlings as influenced by partial shade and competition. ‘7 Partial Shade (I Competition Yes No No 18.10 17.15 Yes 15.90 18.14 Interaction significant at the 5 percent level. Table 16. Stem diameter (mm) of fourteen-week-old jack pine seedlings as influenced by wind protection and competition. J1 _— f—- t Wind Protection Competition Yes No No 0.846 0.746 Yes 0.765 0.782 Interaction significant at the 5 percent level. Survival and Growth gt Container-Grown Seedlings Survival Seedlings growing in plastic tubes had a signifi- cantly higher rate of survival than those growing in Jiffy- 7 pellets (Figure 12). By the end of the growing season, an average of 94 percent of all the trees growing in plastic 100 ,‘ 90 61° 80 H g -H 70 > S to 60 100 ,‘ 90 64° 80 H m .3 > 70 H s ‘0 60 Figure 12. 63 — -- Shade — No shade 1 I J L 1 l 1 1 -- Plastic Tube - -—' Jiffy-7 l I 1 1 l 1 l J 6/1 6/15 6/30 7/15 7/31 8/15 8/31 9/15 1969 First year survival of container-grown jack pine seedlings, in the field, as influenced by (A) shade, and (B) type of container. 64 tubes were still alive, as compared to 69 percent of those in peat pellets. The rate of mortality in the plastic tubes was fairly uniform, averaging 1 to 2 percent per month from June 1 to September 15. The seedlings in Jiffy- 7 pellets, however, suffered rather severe early season mortality; 27 percent of the trees died between June 1 and June 30. The principal cause of mortality in all cases was physical rather than biotic. Whereas birds seemed attrac- ted to the white plastic tube, their damage was confined to the tube itself, and the seedling was left undisturbed. The presence of partial shade significantly increased the survival of seedlings in both containers. When partial shade was provided, survival was increased 8 and 25 per- cent for seedlings grown in plastic tubes and Jiffy-7 pellets, respectively. Growth Seedlings in both containers had completed most of their diameter and height growth by August 15 (Table 17). Growth in terms of dry weight, however, increased considerably from August 15 to September 15. During this latter thirty-day period, shoot dry weight increased 54 and 89 percent, and root dry weight increased 85 and 146 percent, respectively for seedlings grown in plastic tubes and Jiffy-7 pellets. The proportionately greater increase 65 Table 17. Growth of jack pine seedlings raised in two types of containers by sampling period for all treatments. t r L 1 — m Plastic Tube Jiffy:7 Sampling Date Sampling Date Aug. 15 Sept. 15 Aug. 15 Sept. 15 Characteristic Measured Terminal Growth (cm) 2.65° 2.90b 4.3s° 5.30d Stem Diameter (mm) 0.96° 1.21b l.50° 1.98d Rooting Depth (cm) 18.85a 22.05b 23.60° 26.90d Shoot Dry Weight (mg) 110a 169b 261° 494° Root Dry Weight (mg) 66° 122b 109° 268° Total Dry Weight (mg) 177° 291b 370° 762d Shoot/Root Ratio (length) 0.28a 0.26° 0.28° 0.29° Shoot/Root Ratio (weight) 1.65° 1.41b 2.44° 1.89d aValues with the same letter in the superscript are not sig- nificantly different. in root dry weight between sampling periods reduced the shoot/root ratio (weight). On the other hand, the shoot/ root ratio based on length was relatively unaffected during this time, because of the small increase in shoot and root extension. The relatively large increase in shoot dry weight by seedlings in peat pellets was primarily in the form of lateral branches. After one growing season, the growth of seedlings raised in the Jiffy-7 pellets was significantly superior to that of seedlings in plastic tubes (Figures 13 and 14). The seedlings in peat pellets had an average of 83 percent more terminal growth, a stem diameter 65 percent larger, and roots approximately 5 cm longer than did seedlings in 66 .Eu|4:_. \ {Ii ' .m.z on .o.z 11 .o.m [ [1‘ A A . . o . . qm>mq mmDsmHoz qum 3 u o m 1 mm W. A o z momzm AaHemmm z .mccw3 mcflafim>oum scum wouoouonm cws3 mucofiumouu musumfioe Hwom cam woman on .muoHHom plummeh CH common .mmcwauoom mafia xUMm oaouxooslmuco3u mo uncommom .ma ousmwm 67 { A I III III III [1 [1 {IA \I . 0 mm 0 mm o no» oz mo» 2 onaHammzoo w z a z I I." If 1‘ I- e e e e VIA e e I! m a E ‘UGWI ) e e \ a z o» o m o m om>mq mmDsmHoz qum o m k W mos momma quamam oz .mccfl3 mcwaam>mnm on» Baum couomuonm coc3 cowufluomfioo can .ousumfloa deem .oomnm ou .monou owummam uflamm ca common .mmcflavomm scam xomn oaonxmm3lmuco3u mo uncommom .vH onsmflm 68 \ plastic tubes. Jiffy-7 seedlings had approximately four times more shoot biomass and two times more root biomass than plastic tube seedlings. The large difference in shoot dry weight resulted in a significantly increased shoot/root ratio for Jiffy-7 seedlings as compared to trees in plastic tubes (Table 17). The presence of partial shade significantly in- creased the terminal growth of all seedlings, but in- creased the shoot and total dry weight for only those seedlings growing in plastic tubes (Table 19). However, the shade X container interaction was not significant at the 5 percent level. In contrast, only trees in Jiffy-7 pellets responded to an ample supply of soil water, with significant increases shown in terminal growth, shoot and total dry weight, and shoot/root ratio. The contrasting response of terminal growth to soil moisture treatment between trees in Jiffy-7 pellets and those in plastic tubes resulted in a significant interaction (Table 20; Figures 13 and 14). The interaction between shade and soil moisture treatments as they affected terminal growth and shoot/root ratio (length) was also significant (Table 20). The pres- ence of partial shade increased terminal growth by about 9 percent when the seedlings were under soil moisture stress, but increased it 34 percent when soil moisture was readily available. Maintaining soil water near field capacity in 69 .Ho>oa unwouom .Ho>oa useouom m on» Do Dzooemezmem. H one no ozooeeecmem.. mm.o oe.o ea.o em.o om.o oa.e e~.e . mm.o ooze oeomooo loooeozc oeoom -- I- am.o ma.e me.e oo.~ mm.e oa.e e-zoeen Dooz\oooom e~.o o~.o m~.o o~.o e~.o em.o g~.o om.o ooze oeooooa looozoee oeoom I- I- em.o .. om.o mm.o om.o em.o .. om.o e-zooea Doom\oooom emo.o ..mam.o oo~.o oom.o ~m~.o . amm.o me~.o oom.o ooze oeooooa lot oooeoz I- I- mmo.o . mmm.o eme.o one.o one.o mme.o eIzooea >oo omooe aeo.o ..e~o.o aoo.o mmo.o aoo.o mme.o «Ne.o -H.¢ ooze oeomoea loo oooeoz - -- mm~.o Nm~.o omm.o omm.o oo~.o oe~.o e-zooeo zoo Doom moe.o ..aoo.o emo.o omo.o meo.o . aae.o mmo.o amo.o ooze oeomoea Ame oooeoz - - Nma.o . mmm.o Hom.o oma.o mee.o aom.o e-zooeo zoo uooom me.ao.. om.m~ mm.om me.- mm.o~ mm.- om.- oa.em ooze oeoooea 1261 ooooo - -- ma.o~ mm.o~ mm.o~ m~.e~ o~.e~ oo.m~ e-zooeo ozeuoom mo.o .. N~.o mo.o m~.o oo.o om.e ma.o mm.e ooze oeooooa lees tooosoeo I- - oa.o ao.~ aa.o ea.e oa.o aa.o e-zmmeo soom mo.m .. oa.~ oe.~ mo.m mm.~ . m~.m me.~ mo.m ooze oeooooa 1261 oosooo - - mo.a .. oa.m mm.e . me.m ma.a oo.m e-eooeo oozeEooe IOOOIOOOOOOOIIOI..00...OOOOOOOOOOOOOOmcmmz “OH“...OOOOOOOOOOCOIOIOOOOOIO no» 02 o.mH on 0.0 m.o on 0.0 oz mm» oz mow Hmcemucou Umusmmwz seeueuomEou AmEumV seeuoom Hobos-Heom wcmnm seeuomuoum use: «0 meme oeumeuouomumzu .ucoEummuu an mafia goon c3onmluocemucoo mo uncommon new» umuem .mH mange 70 Table 19. Influence of soil moisture and type of container on terminal growth (cm) of twenty-week-old jack pine seedlings averaged over all shade and wind treatments. Container _ Soil-Water Suction Plastic Tube Jiffy-7 0.0 to 0.5 atm 3.05 5.90 0.0 to 15.0 atms 2.70 4.65 Interaction significant at the 5 percent level. Table 20. Influence of shade and soil moisture on shoot/ root ratio (length) and terminal growth (cm) of all container-raised jack pine seedlings twenty-weeks old. Shade Soil-Water Yes No Yes No Suction Shoot/Root Ratio (length) Terminal Growth (cm) 0.0 to 0.5 atm .31 .27 5.15 3.85 0.0 to 15.0 atms .26 .26 3.80 3.55 Interactions significant at the 5 percent level. the absence of shade increased terminal growth only 8 per- cent. The greater increase in shoot extension under the favorable combination of partial shade and adequate soil moisture resulted in a corresponding increase in the shoot/ root ratio. The presence of competing vegetation caused a highly significant reduction in the growth of seedlings raised in plastic tubes (Table 18). The most pronounced effect was on shoot and root dry weights, which were reduced 33 and 40 percent 71 respectively. There was no significant affect on the shoot/ root ratios due to the relatively uniform reduction in both shoots and roots. In general, there was no significant difference in the growth parameters measured between trees growing with wind protection and those without (Table 18). However, protected seedlings in Jiffy-7 pellets tended to have taller shoots and shorter roots. Likewise, the shoot dry weight of protected trees in plastic tubes tended to be greater than that in unprotected trees. These relationships re- sulted in shoot/root ratios significantly higher where the seedlings were protected from the prevailing wind. Discussion Germination and Survival Improvements in germination in the presence of par- tial shade is in general agreement with the findings of other investigators (Fraser and Farrar, 1953; Beaufait, 1959; LeBarron, 1944; Fraser, 1959). The presence of shade reduces the rate of evaporation from the soil surface. Loss of surface moisture is especially severe in sandy soils, which are subject to very rapid drying when exposed to direct insolation. The observed increased survival in the presence of partial shade for all seedlings differs with the results obtained by Beaufait, 1959, and LeBarron, 1944. They report 72 a decrease in first-year jack pine survival under a level of shade very similar to that used in this study, indicat- ing an early expression of the intolerance of this species. However, neither of the above investigators attempted to control soil moisture levels. The means by which they pro- vided the shade may have intercepted or utilized the natural precipitation to such an extent that mortality due to soil moisture stress resulted. Failure of the soil moisture treatment to influ- ence mortality in the field agrees with the results found in the study conducted under controlled conditions (Chapter III). In the growth chamber, pots were not allowed to remain at a soil-water suction of 15 atms for more than a few hours, while in the field this period normally lasted no more than two days. The fluctuation of soil water be— tween soil-water suctions of 0.0 and 15.0 atms apparently did not create a drought stress of sufficient intensity to influence mortality. This was true despite the exclusion of natural precipitation from the field plots for as long as 15 days during critical portions of the growing season. The increased mortality of seedlings raised in Jiffy-7 pellets was probably caused by their slower initial germination and, therefore, younger age at the time of out- planting. A longer period of growth and conditioning prior to outplanting may be required to offset this delay, caused 73 primarily by the lower temperatures resulting from the evaporative cooling of the wet peat surface. Growth Shade and Soil Moisture Seedlings in both containers as well as those from direct seeding responded in about the same way to the en- vironmental modifications imposed. The younger seedlings from direct seeding appeared to be affected by the soil moisture treatment to a greater extent than the container- grown seedlings. The large difference in root dry weight of those seedlings because of imposed soil moisture treat- ment indicates that the small immature root is especially susceptible to fluctuations in soil water. These field results agree with the laboratory study, indicating that soil water fluctuations indeed influence root system development (Chapter III). For all seedlings, the presence of partial shade was beneficial, primarily to shoot growth. For container- grown seedlings, however, the benefit from shade in terms of terminal growth was much greater when ample soil water was available. This contrast in response resulted in a significant interaction (Table 20). Apparently the stress created by fluctuating soil water content was only par- tially alleviated by the presence of shade. When partial shade was removed but soil water remained at field capacity, 74 resulting higher air and soil temperatures probably reduced growth. When ample soil water was combined with partial shade, terminal growth increased considerably. A compar- able interaction was observed in the growth chambers, where the effect of temperature was greatly increased when soil water was not limiting (Chapter III). Competing Vegetation The growth of seedlings from both the direct seed- ing and those raised in plastic tubes was significantly reduced when competing vegetation was allowed to re-invade the plots. This was especially true for growth in terms of dry weight where reductions owing to competition aver- aged between 20 and 35 percent. In the case of direct seeding, the competition seemed to utilize the ameliora- tion of the site to a greater extent than the smaller jack pine seedlings. This was demonstrated by the significant shade X competition and wind X competition interactions (Tables 15 and 16). Wind In general, there was no significant difference in the growth parameters measured during the first growing season between trees growing with wind protection and those without. The relative lack of response by the seedlings to wind protection may have resulted from the low stature of the young seedlings in comparison to the surrounding 75 vegetation. Thus, differences between protected and unpro- tected seedlings may become more important as the trees grow older. The fact that there was a tendency for the shoots of protected seedlings to be larger, which resulted in significantly higher shoot/root ratios, is evidence that there was some response to protection. Bud Set An attempt was made to evaluate the treatment in- fluence on terminal bud set. By September 15, only 100 trees had set bud. Sixty four of these were found on plots subjected to soil water stress. This effect of soil mois- ture was significant at the 5 percent level using a Chi- square test. There was only a small difference in bud set between the other treatments. These results tend to sup- port observations in the growth chamber where terminal bud set appeared to be controlled by soil water level under the low temperature treatment. Comparison of Containers Seedlings in both containers responded similarly to the treatments imposed. However, the maintenance of soil water near field capacity was only beneficial to those seed- lings grown in Jiffy-7 pellets (Table 19). While rooting depth averaged about 27 cm, most of the lateral root system extening from the Jiffy-7 pellet was concentrated in the upper 5 to 10 cm of soil. Thus, the bulk of the roots were 76 susceptible to severe fluctuations in soil moisture content. In contrast, the roots of seedlings in plastic tubes were primarily confined to their container, and did not come into contact with mineral soil until they were approximately 8 cm below the soil surface. Therefore, they were not exposed to the rapid moisture depletion which occurred in the sur- face 8 cm of soil. Nevertheless, seedlings in Jiffy-7 con- tainers had an average shoot growth of 4.65 cm, as compared to 2.70 cm for seedlings in plastic containers when both were grown under conditions of fluctuating soil water levels. A comparison of growth performance after one grow- ing season indicates that seedlings grown in Jiffy-7 pel- lets are clearly superior to those in plastic tubes. This increased growth is probably related to an unrestricted and prompt development of lateral roots and a subsequent» penetration of a larger volume of soil. During the first year of establishment, the root system of trees in plastic tubes is primarily vertically oriented, resulting in a smaller total root system. Comparison of Containers and Direct Seeding One major advantage of container-grown seedlings over direct seeding is that the germination and early growth of the seedling can be initiated under controlled conditions. In this study, both the planting of seedlings 77 grown in containers and the direct seeding was completed the last week in May. Cool temperatures throughout June delayed germination for twenty-four days following seeding. During this period, seedlings in containers were growing and were already seven weeks older by the time the broad- cast seed had germinated. By the end of the first grow- ing season, this advanced start had produced trees con- siderably larger and more vigorous than trees resulting from direct seeding (Figures 11, 13 and 14). CHAPTER V SUMMARY AND CONCLUSIONS Attempts to regenerate jack pine naturally have generally been disappointing. This is due primarily to the existence of serotinous cones and the necessity of a mineral soil seedbed for adequate germination and survival. Although the planting of nursery-grown seedlings has been used with considerable success, the high cost of this method has stimulated interest in alternative methods. Direct seeding and the planting of container- grown seedlings are two such alternatives. However, both of these methods expose a vulnerable seedling to unfavor- able climatic conditions. Before either of these methods can be successfully employed, we must have a more complete understanding of the environmental factors affecting germ- ination, survival, and growth of young jack pine seedlings. In this study, the affects of several environmental factors on jack pine germination, survival, and growth were investigated under both laboratory and field conditions. Field comparisons were made between direct seeded and con- tainer-grown seedlings and between seedlings raised in two types of containers. 78 79 Growth Chamber Expgriment Jack pine seedlings were grown in plastic pots for ten weeks under six combinations of three temperature and two soil moisture treatments. Day and night temperatures were controlled at 32°C and 21°C, 24°C and 13°C, and 16°C and 5°C, respectively. Soil-water suction was either main- tained below 0.1 atm or allowed to fluctuate between 0.0 and 15.0 atms. All other factors were held constant at levels which simulated natural conditions. The response to treatment was determined by destructively sampling one- tenth of the trees each week over the ten-week period. No mortality was recorded for any trees under any of the above treatments. Temperature and soil moisture treatments had a pronounced affect on seedling growth. The soil moisture X temperature interaction was highly significant for every growth parameter measured. With adequate soil moisture, seedlings at the high and moder- ate temperatures had over two times more dry matter than those at the low temperature. By the tenth week, seedlings at the moderate temperature appeared to be larger and more vigorous than those at the high temperature. At the high and moderate temperatures, the presence of ample soil water increased total dry weight by more than two times. At the low temperature, however, the increase was only 32 percent. Trees under conditions of moisture stress showed little response to temperature differences. 80 The dry root weight appeared to be greatly influ- enced by fluctuations in soil water. Root tissue mortality occurred when moisture levels were low and a resumption of root growth took place following rewatering. Root mortality and a resultant decline in dry weight seemed to occur con- sistently between soil-water suctions of 2 to 3.5 atms. At the low temperature, terminal bud set and the resumption of growth appeared to be influenced by soil moisture content. Field Experiment Germination, survival, and growth of direct seeded and container—grown jack pine seedlings were investigated on modified sites in northern Lower Michigan. The study area is located on the Mio Ranger District, Huron-Manistee National Forest, approximately ten miles southeast of Mio, Michigan. The site is typical of the sand plains that sup- port stands of jack pine throughout Michigan. The first-year response of jack pine seedlings to site modifications influencing wind, light, soil water, and competition was examined using a split-plot design with six replications. The basic experimental unit for this design was a 1.2 meter square plot which was cleared and scalped to mineral soil prior to planting. 81 Seedlings were raised in either split-plastic tubes or Jiffy-7 pellets for comparison with each other and with seedlings from direct seeding. All the seed used in the study was collected from mature trees near the study area. The following treatments were arranged factorially in order to determine the significance of factor interactions. 1. Wind barriers, which reduced the prevailing south- westerly wind by an average of 45 percent, were randomly assigned to one-half of each replication. Shade structures which reduced average light in- tensity to 45 percent of that in the open were ran- domly assigned and constructed over one—half of the plots. These structures also reduced maximum air temperatures by 2°C, soil temperatures by 3°C, and lengthened the time for the soil to reach wilt- ing point by four to nine days beyond the time re- quired for exposed plots. Soil-water suction on one-half of the plots was continuously maintained below 0.5 atm, while on the remaining it was allowed to fluctuate between 0.0 and 15.0 atms. Four experimental plots were included within each combination of the above treatments. Three of the plots were randomly assigned to be planted with either 50 seedlings in plastic tubes, 36 seedlings in Jiffy-7 pellets or 100 jack pine seeds. These 82 plots were maintained weed-free throughout the growing season. One-half of the fourth plot was planted with 20 seedlings in plastic tubes; the other half was seeded with 100 jack pine seeds. The competing vegetation was allowed to reinvade this plot after the initial scalping. Germination and survival counts were taken four times and growth measurements were made twice during the first growing season. Growth and development prior to planting was gener- ally good in both types of containers. However, germination was slowed to some extent by evaporative cooling of the ex- posed wet peat in Jiffy-7 pellets. A somewhat longer growth period under controlled conditions is therefore recommended when using this container. Germination and Survival First-year results indicate beneficial effects of partial shade on germination and survival. Germination was increased by an average of 19 percent where shade was pres- ent. Shade increased survival by 21, 25, and 8 percent for direct seeded, Jiffy 7, and plastic tube seedlings, respec-' tively. Natural shade provided by logging Slash, micro-~ topography, and standing.trees should therefore be utilized to increase germination and initial survival of young seed- lings. 83 Growth The presence of shade also benefited terminal growth for all seedlings. However, for container-grown seedlings, the benefit from shade was much greater when ample soil water was available. The soil moisture treatment had its greatest affect on the growth of direct seeded and Jiffy-7 seedlings. The lack of response to moisture treatment by the seedlings in plastic tubes resulted in a significant container X soil moisture interaction. The presence of competing vegetation reduced the dry weight of direct seeded and plastic tube seedlings an average of 20 and 35 percent, respectively. Competing vegetation appeared to benefit more than’jack pine from the amelioration of the site by shade and wind protection. This resulted in a significant treatment X competition interaction. The results of this study indicate that first-year jack pine growth was improved by partial shade, ample soil water and the removal of competition. Although soil mois- ture is not subject to direct control under natural condi- tions, the presence of shade and the absence of competition would indirectly improve soil water conditions. In the past, emphasis has been placed on mechanical scarification as a means of controlling competition and exposing mineral soil. In this study, competing vegetation was allowed to 84 re-establish itself to the extent that growth was impaired, even though plots were initially scalped to a depth of 5 to 8 cm before planting. In general, there was no significant difference in growth parameters measured during the first growing season between trees growing with wind protection and those with- out. Differences may become more apparent as the height of the trees exceeds that of the surrounding vegetation. During the first year, seedlings in Jiffy-7 pellets produced 160 percent more total biomass than plastic tubes. This increased growth is probably related to the unrestric- ted and prompt development of lateral roots extending into the soil from the peat pellet, and a subsequent penetration of a larger volume of soil. One major advantage of container-grown seedlings over direct seeding is that germination and early growth can be initiated under controlled conditions. In this study, delayed germination of direct seeded plots due to cool temperatures gave the container-grown seedlings a seven-week advantage. By the end of the growing season, this advanced start resulted in container-grown seedlings which averaged eight times more total biomass than direct seeded trees. Although direct seeding should not be dis- counted as a regeneration method, the advantages offered by container-grown seedlings certainly merit attention. LITERATURE CITED Ackerman, R. F. and J. L. Farrar. 1965. The effect of light and temperature on the germination of jack pine and lodgepole pine seeds. Univ. Toronto, Fac. Forestry. Tech. Rep. 5. 41 pp. Alm, A. A. and R. Schantz-Hansen. 1970. Planting pine tubelings in Minnesota. J. For. 68(6):353-357. Babalola, 0., L. Boersma, and C. T. Youngberg. 1968. Photosynthesis and transpiration of Monterey pine seedlings as a function of soil water suc- tion and soil temperature. Plant Physiol. 43(4):515-521. Beaufait, W. R. 1959. Studies of fire and other fac- tors related to jack pine regeneration in northern Lower Michigan. Ph.D. Dissertation, Univ. of Mich." 179 pp. Benzie, John W. 1968. Regeneration of cutover jack pine stands. USDA, For. Ser., Nor. Cent. For. Exp. Sta., Res. Note NC-49. 4 pp. Blyth, James E. 1967. Pulpwood production and consump- tion in the North Central region by county, 1966. USDA, For. Ser., Nor. Cent. For. Exp. Sta., Resource Bull. NC-3. 27 pp. Brown, R. T. 1967. Influence of naturally occurring compounds on germination and growth of jack pine. Ecology. 48(4):542-546. Carman, R. D. 1967. An industrial application of the container planting technique. Pulp Paper Mag. Can. 68(4):WR181-l88. Cayford, J. H. 1958. Scarifying for jack pine regener- ation in Manitoba. Can., Dept. Nor. Affairs and Nat. Res., For. Br., For. Res. Div., Tech. Note 66. 14 pp. 85 10. V 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 86 . 1959. Seeding jack pine on the Sandilands Forest Reserve, Manitoba, 1925-1955. Can., Dept. Nor. Affairs and Nat. Res., For. Br., For. Res. Div., Tech. Note 79. 16 pp. . 1961. Broadcast seeding jack pine at weekly intervals in Manitoba. Can., Dept. For., For. Res. Br., Tech. Note 106. 12 pp. . 1963. Some factors influencing jack pine regeneration after fire in southeastern Manitoba. Can., Dept. For., Publn. 1016. 16 pp. . 1966. Operational trials of regeneration methods for jack pine in southeastern Manitoba. Can., Dept. For., Publn. 1165. 23 pp. and R. M. Waldron. 1966. Storage of white spruce, jack pine and red pine seed treated with Arasan, Endrin and aluminum flakes. USDA, For. Ser., Tree Plant. Notes. No. 77: 12-16. , Z. Chrosciewicz and H. P. Sims. 1967. A review of silvicultural research in jack pine. Can., Dept. For. and Rural Deve1., For. Br., Dept. Publn. 1173. 255 pp. Caveney, E. W. and V. J. Rudolph. 1970. Reproducing jack pine by the Shelterwood method. Mich. State Univ. Ag. Exp. Sta. Res. Rep. 110. 12 pp. Chase, Clarence D., Ray E. Pfeifer and John S. Spencer, Jr. 1970. The growing timber resource of Michigan, 1966. USDA, For. Ser., Nor. Cent. For. Exp. Sta., Resource Bull. NC-9. 62 pp. Chrosciewicz, Z. 1959. Controlled burning experiments on jack pine sites. Can., Dept. Nor. Affairs and Nat. Resources., For. Br., For. Res. Div., Techn. Note 72. 19 pp. Cooley, John H. 1970. Site preparation for jack pine on Grayling sands. Paper presented at the Mich. Acad. Sci. Arts, and Letters, Detroit, Mich., April 3, 1970. Day, M. W. 1964. Results of study on direct seeding. Quart. Bull. Mich. Agric. Exp. Sta. 46(3): 412-415. 87 21. Eyre, F. H. 1938. Can jack pine be regenerated with- out fire? J. For. 36:1067-1072. 22. and R. K. LeBarron. 1944. Management of jack pine in the Lake States. USDA Tech. Bull. 863. 66 pp. 23. Fowells, H. A. 1965. Silvics of forest trees of the United States. USDA Handbook 271:338-354. 24. Fraser, J. W. 1959. The effect of sunlight on the germination and early growth of jack pine and red pine. Can., Dept. Nor. Affairs and Nat. Res., For. Br., For. Res. Div., Tech. Note 71. 6 pp. 25. and J. L. Farrar. 1953. Effect of watering, shading, seedbed medium, and depth of sowing on jack pine germination. Can., Dept. Res. and Devel., For. Br., For. Res. Div., Silv. Leafl. 90. 4 pp. 26. Glerum, C. and G. Pierpoint. 1968. The influence of soil moisture deficits on seedling growth of three coniferous species. For. Chron. 44(5): 26-29. 27. Hellmers, H. 1962. Temperature effect on optimum tree growth, p. 275-288. tg T. T. Kozlowski (Ed.), Tree growth. Ronald Press Co., New York. 28. Hermann, Richard K. 1969. Growth of seedlings in peat pellets. USDA, For. Ser., Tree Plant Notes. No. 20(1):8-10. 29. Huuri, O. 1966. A new investigation result in the use of peat pots for the planting of pine. Finn. Pap. Timb. 17(11):148-152. 30. Jameson, J. S. 1961. Observations on factors influ- encing jack pine reproduction in Saskatchewan. Can., Dept. For., For. Res. Div., Tech. Note 97. 24 pp. 31. Jarvis, J. M. 1966. Seeding white spruce, black spruce, and jack pine on burned seedbeds in Manitoba. Can., Dept. For., Publn. 1166. 8 pp. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 88 Kaufman, C. M. 1945. Root growth of jack pine on several sites in the Cloquet Forest, Minnesota. Ecology 26:10-23. Kaufmann, M. R. 1968. Water relations of pine seed- lings in relation to root and shoot growth. Plant Physiol. 43(2):281-288. Kramer, Paul J. and Theodore T. Kozlowski. 1960. Physiology of trees. McGraw-Hill, New York. 642 pp. Laitinen, Juhani. 1965. Finns plant pine in peat pots. Finn. Pap. Timb. 5:94-97, 100. Larson, M. M. 1967. Effect of temperature on initial development of ponderosa pine seedlings from three sources. For. Sci. l3(3):286-294. LeBarron, R. K. 1944. Influence of controllable envi- ronmental conditions on regeneration of jack pine and black spruce. J. Agr. Res. 68(3): 97-119. Lewis, H. S. 1954. Forest plantations in Newfoundland. Can., Dept. Nor. Affairs and Nat. Res., For. Br., For. Res. Div., S. & M. 54-3. 15 pp. Logan, K. T. 1966. Growth of tree seedlings as affec- ted by light intensity. II. Red pine, white pine, jack pine, and eastern larch. Can., Dept. For., Publn. 1160. 19 pp. McLean, M. M. 1958. Experimental planting of tubed seedlings. Ontario Dept. Land. and For. Tech. Res. Report 39. 13 pp. Mueller-Dombois, D. 1964. Effect of depth to water table on height growth of tree seedlings in a greenhouse. For. Sci. 10(3):306-316. Pinchot, Gifford. 1909. Jack pine. USDA, For. Ser., Silv. Leafl. 44. 4 pp. Roe, Eugene I. 1963a. Direct seeding of conifers in the Lake States. USDA, For. Ser., Lake States For. Exp. Sta., Res. Pap. LS-3. 16 pp. . 1963b. Seed stored in cones of some jack pine stands, northern Minnesota. USDA, For. Ser., Lake States For. Exp. Sta., Res. Pap. LS-l. 14 pp. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 89 Rudolf, P. O. 1958. Silvical characteristics of jack pine (Etnus banksiana). USDA, For. Ser., Lake States For. Exp. Sta., Sta. Pap. 91. 13 pp. and R. L. Schoenike. 1963. Botanical and commercial range of jack pine in the Lake States. USDA, For. Ser., Lake States For. Exp. Sta., Res. Note LS-15. 4 pp. Sands, K. and A. J. Rutter. 1959. Studies in the growth of young plants of Pinus sylvestris L. II. The relation of growth to soil water tension. Ann. Bot. N. S. 23(90):269-284. Scott, J. D. 1966. A review of direct seeding proj- ects carried out by the Ontario Department of Lands and Forests from 1956 to 1964. Ontario Dept. Lands and For., Timb. Br., Silv. Sec., Silv. Note 5. 48 pp. Schneider, G., Donald P. White and Randall Heiligmann. 1970. Growing coniferous seedlings in soil- less containers for field planting. (In press, Tree Planters Notes, summer, 1970.) Steinbrenner, E. C. and J. H. Rediske. 1964. Growth of ponderosa pine and Douglas fir in a con- trolled environment. Weyerhaeuser For. Pap., Centralia, Wash., No. l. 31 pp. Sims, H. P. and Mueller-Dombois. 1968. Effect of grass competition and depth to water table on height growth of coniferous tree seedlings. Ecology 49:597-603. Shirley, Hardy L. 1945. Reproduction of upland coni- fers in the Lake States as affected by root competition and light. Amer. Midland Nat. 33: 537-612. Stanhill, G. 1957. The effect of differences in soil moisture status on plant growth. A review and analysis of soil moisture experiments. Soil Sci. 84:205-214. Steel, Robert G. D. and James H. Torrie. 1960. Prin- ciples and procedures of statistics. McGraw Hill, New York. 481 pp. Stoeckeler, J. H. and G. A. Limstrom. 1942. Ecologi- cal factors influencing reforestation in north- ern Wisconsin. Ecol. Mono. 12(2):l91-212. 56. 57. 58. 59. 60. 61. 62. 63. 64. 90 and G. A. Limstrom. 1950. Reforestation research findings in northern Wisconsin and Upper Michigan. USDA, For. Ser., Lake States For. Exp. Sta., Sta. Pap. 23. 34 pp. Stransky, John J. and William B. Duke. 1964. Shelter for testing drought~hardiness of planted south- ern pine seedlings. USDA. For Ser., South. For. Exp. Sta., Res. Note 80-11. 4 pp. and D. R. Wilson. 1964. Terminal elongation of loblloly and shortleaf pine seedlings under soil moisture stress. Proc. Soil Sci. Soc. Amer. 28(3):439-40. U. S. Forest Service. 1937. Heat more injurious than lack of moisture during drought. USDA, For. Ser., Lake States For. Exp. Sta., Techn. Note 126. l p. . 1948. Woody-plant seed manual. USDA, For. Ser., Misc. Publn. 654. 416 pp. Veihmeyer, F. J. and A. H. Hendrickson. 1950. Soil moisture in relation to plant growth. Ann. Rev. Plant. Physiol. 1:285-304. Walters, John. 1969. Synthetic ball planting on the University of B. C. research forest, Haney, B. C. USDA, For. Ser., Tree Plant Notes. No. 20(1):10-13. White, Donald P. 1958. Available water the key to forest site evaluation. Proceedings First North American Soils Conference, Michigan State University, East Lansing, Michigan. p. 6-11. Yeatman, C. W. 1967. Geographical variation in jack pine (Pinus banksiana Lamb.) seedlings. Ph.D. Thesis. 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