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FOREST SOILS AND THElR RELATIONSHiP

TO‘ FGREST MANAQEMENT 5N
BRITESH CGLEEMBM

Thesis for the Degree of M. 8..
MICHIGAN STATE UNIVERSlTY
MICHAEL JAMES ROMAINE
1968

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ABSTRACT

FOREST SOILS AND THEIR RELATIONSHIP
TO FOREST MANAGEMENT IN
BRITISH COLUMBIA

by Michael James Romaine

The purpose of this presentation is to outline a
method and provide guidelines by which the forester, with
consultation of a trained soils Specialist, can readily
separate forest land areas into units for future land
management. The suggested method and guidelines are based
upon: (1) previous classification methods employed in the
Province and elsewhere and (2) field data collected and
‘observations made on forest-soil relationships, while the
author was involved with the soil capability for Forestry
Classification Program being conducted in the interior of
the Province during the 1965-1967 field seasons.

A drainage sequence develOped from glacial till was
selected in the Princeton study area, while a drainage
sequence developed from glacial lacustrine deposits was
selected in the Quesnel study area. Based upon field ob-
servations and stand measurements, a number of forest-soil
relationships were found to be influenced predominately by
the topographic position of these soils along with their

related soil drainage.

Michael James Romaine

The rapidly to well drained soils situated on convex
slopes and t0ps of knolls had a low to medium productivity
suitable for the growth of lodgepole pine (Pinus contorta).
Existing stands were either poorly or over-stocked. The
over-stocked stands had a tendency to stagnate on these soils.
The major limiting factors to forest growth were attributed
to soil moisture deficiency and restriction of the rooting
zone by the proximity to bedrock.

The moderately well to imperfectly drained soils had
a high to medium productivity for both lodgepole pine (Pinus
contorta) , and engelmann Spruce (Picea, engelmanni) and white

Spruce (P'icea glauca) . The topographic positions of the

 

well drained soils were primarily convex or flat lying areas
and upper slopes, while the imperfectly drained soils were
located predominately on concave lower slopes. The avail-
ability of seepage water and nutrients moving down slope

from adjacent upland soils, as well as the protection offered
from climatic extremes by the tOpographic position of these
soils were considered the major factors favorable to forest
growth.

The poorly drained to very poorly drained soils
generally had a low to very low forest productivity rating.
These soils were found in concave and depressional areas to
extensive flat areas with poor surface drainage. Forest
growth was predominately limited to either engelmann Spruce

(Picea engelmanni), or white Spruce (Picea glauca). Black

Michael James Romaine

Spruce (giggg mariana) predominated on the very poorly
drained soils in the northern portions of the Quesnel study
area.

Some guidelines have been discussed as to how the
landscape might be delineated into systematic units which can
serve as a base for future management interpretations and
plans. In applying the guidelines, the following observa-
tions as a minimum requirement are suggested in delineating
land units: (1) general tOpographic features, (2) natural
soil drainage, (3) parent materials, including observed vari-
ations, or closely associated different kinds of parent
materials, (4) soil classification at the subgroup level,
and (5) physical soil properties, most important of which
are effective soil depth, texture, and structure.

It is suggested that the guidelines outlined in this
thesis, or comparable methods will be more useful in determin-
ing forest productivity and will have broader application
(such as on logged and cleared areas) than the conventional
site index methods presently employed. In addition, the
guidelines will serve as a tool to have practicing foresters

take an even greater interest in their soils.

FOREST SOILS AND THEIR RELATIONSHIP
TO FOREST MANAGEMENT IN

BRITISH COLUMBIA

BY

Michael James Romaine

A THESIS

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

MASTER OF SCIENCE

Department of Resource DevelOpment

1968

ACKNOWLEDGMENTS

Various people and agencies have been helpful in
providing the author with background material which made it
possible for this thesis to be written. Thanks are extended
particularly to Mr. T. M. Lord, Pedologist, Soil Survey
Section of the Canada Department of Agriculture, Vancouver,
B. C. and to Mr. G. G. Runka, Pedologist, Soils Division,
of the British Columbia Department of Agriculture, Kelowna,
B. C.

The author is indebted to Dr. M. H. Steinmueller,
major professor and thesis advisor, whose ideas and help not
only prompted an interest in this project, but also aided in
its completion.

Thanks are also extended to the other committee
members, Dr. C. R. Humphrys and Professor I. F. Schneider
(minor professors) for their interest, comments and committee
participation.

Finally, the author wishes to extend his deep appreci-
ation to his wife; Sharyn Lynne, for her assistance in the
typing of this thesis, and for her understanding and encourage—

ment which she gave him in hours of need.

Michael James Romaine

ii

TABLE OF CONTENTS

ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . .

LIST OF TABLES. . . . . . . . . . . . . . . . . .

LIST OF FIGURES . . . . . . . . . . . . . . . . .

LIST OF APPENDICES. . . . . . . . . . . . . . . .

 

Chapter
I. INTRODUCTION . . . . . . . . . . . . . . .

Purpose and Guiding Hypothesis. . . .
Methodology . . . . . . . . . . . . .
Limitations of the Study. . . . . . .
Justification . . . . . . . . . . . .

II. REVIEW OF THE LITERATURE . . . . . . . . .

Limitations of Accepted Methods . . .
Forest-Soils Relationships. . . . . .
T0pography. . . . . . . . . . . . .
Physical Soil PrOpertieS. . . . . .
Forest Land Classification. . . . . .

III. DESCRIPTION OF AREAS AND METHODS EMPLOYED.

The Study Areas . . . . . . . . . . .
Location and History. . . . . . . .
POpulation Centers and Industries .
Climate . . . . . . . . . . . . . .
Physiography and TOpography . . . .
Forest Vegetation . . . . . . . . .
Soils . . . . . . . . . . . . . . .

Methods Employed. . . . . . . . . .
Determination of Soil Capability for

Forestry. . . . . . . . . . . . .
Selection of Soils. . . . . . . . .
Forestry Interpretations. . . . . .

iii

Page

ii

vi

vii

OEU'HP‘IP l-‘

10
15
14
17
22

24

24
24
26
29
29
35
54
36

56
58
59

TABLE OF CONTENTS - Continued
Chapter
IV. OBSERVATIONS, INTERPRETATIONS AND CONCLUSIONS.

Observations. . . . . . . . . . . . . . .
Interpretations . . . . . . . . . . . . .
Conclusions . . . . . . . . . . . . . . .

V. APPLICATION, SUGGESTED PROCEDURE AND EXTENSION
OF INFORMATION. . . . . . . . . . . . . .

Application . . . . . . . . . . . . . . .
Suggested Procedure . . . . . . . . . . .
Selection of an Area. . . . . . . . . .
Initial Survey. . . . . . . . . . .
Aerial Photograph Interpretation. . . .
Pre-mapping . . . . . . . . . . . . . .
Extension of Information. . . . . . . . .
Productivity. . . . . . . . . . . . . .
Forest Management . . . . . . . . . . .
Engineering . . . . . . . . . . . . . .
Watershed Management. . . . . . . . . .
Research. . . . . . . . . . . . . . . .

VI..SUMMARY AND FUTURE REQUIREMENTS. . . . . . . .
Summary . . . . . . . . . . . . . . . . .

Future Requirements . . . . . . . . . . .

Lack of Information . . . . . . . . . .

Lack of Suitable Research Projects. . .

Lack of Qualified Personnel . . . . . .

BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . .

APPENDICES. . . . . . . . . . . . . . . . . . . . . .

iv

Page

41
47
50

56

56
57
57
59
61

62
62
65
65
65
66

67
67
69
7O
71
72
75

85

Table

II.

III.

IV.

VI.

LIST OF TABLES

Generalized Temperature Data for Princeton and
Quesnel Study Areas. The S. W; Interior
Plateau and the Central Interior Climatic
Regions. . . . . . . . . . . . . . . . . .-. .

Generalized Precipitation Data for Princeton
and Quesnel Study Areas. The S. W. Interior
Plateau and the Central Interior Climatic
Regions. . . . . . . . . . . . . . . . . . . .

Relationship Between a Soil Catena in the
Princeton Study Area and Some Forestry Observ-
ations . . . . . . . . . . . . . . . . . . . .

Relationship Between a Soil Catena in the
Quesnel Study Area and Some Forestry Observa-
tions. . . . . . . . . . . . . . . . . . . . .

Guidelines to Identify the Major Observed Land
Units Occurring on Glacial Till and Some
Associated Forest-Soil Relationships . . . . .

Guidelines to Identify the Major Observed Land
Units Occurring on Glacial Lacustrine Deposits
and Some Associated Forest Soil Relationships.

Page

51

51

48

49

51

52

Figure

1.

2.

LIST OF FIGURES

Page

Typical Relationship Between Soil Texture and
Plant Available Water. . . . . . . . . . . . . . 20

Location of the Princeton and Quesnel Study

Areas in British Columbia. . . . . . . . . . . . 25
Generalized Climatic Regions in British

Columbia . . . . . . . . . . . . . . . . . . . . 50

The Imperfectly Drained Pefferle Soil Series on
the Lower Section of a Long Straight Slope . . . 42

Drainage Sequence of Soil Series in the
Princeton Study Area . . . . . . . . . . . . . . 45

Drainage Sequence of Soil Series in the Quesnel
Study Area . . . . . . . . . . . . . . . . . . . 44

The Well Drained Mazama Soil Series Occurring
Near the T0p of a Knoll. . . . . . . . . . . . . 46

Rapidly Drained Bankeir Soil Series Closely
Associated with Exposed Bedrock. . . . . . . . . 46

Suggested Field Card . . . . . . . . . . . . . . 60

An Even—Aged Well Stocked Stand Suitable for
Measuring Soil Productivity. . . . . . . . . . . 64

A Multi-Storied, Uneven-Aged Stand Not Suitable
for Measuring Soil Productivity. . . . . . . . . 64

vi

LIST OF APPENDICES

Appendix Page
I. Generalized Profile Descriptions. . . . . . . 84

II. Forest Capability Classes, Limitations and
PrOductiVity. O O O O O O O I O O O O O O O O 90

III. Soil Drainage Classes . . . . . . . . . . . . 91

IV. Supporting Plot Data for Determining Capa-

bility Class Rating . . . . . . . . . . . . . 94
V. Parent Materials. . . . . . . . . . . . . . . 95
Soil Texture. . . . . . . . . . . . . . . . . 97
Soil Structure. . . . . . . . . . . . . . . . 99

vii

CHAPTER I
INTRODUCTION

British Columbia's economy is closely linked to its
forest resources. The estimated net value of forest products
in 1966 was $1,057 million or approximately 55 per cent of

1 Sales of

the total net value of all commodity production.
forest products are primarily dependent upon the world
market. In 1964, for example, approximately 74 per cent of
total forest products produced were sold on the foreign
scene.2 Foreign sales therefore, are a large and important
part of the forest industries economic life and it is im-
portant that they remain competitive on the world market.
At present, the forest industries are concerned over

3

the cost-price squeeze facing them. Their costs are rising

steadily, while the ability of the industry to raise prices

 

1British Columbia, Bureau of Economics and Statistics,
Manual of Resources and_Qevelogment, British Columbia,
Department of Industrial Development, Trade and Commerce,
(Victoria B. C.: Queens's Printer, 1967), p. 15.

2The_§;itish Columbia Forest Industries 1965-66 Year-
book, (Vancouver B. C.: Mitchell Press Limited, 1966), p.
J18.

3British Columbia. Department of Industrial DeveloP-
ment, Trade and Commerce, British Columbia Business Outlook
1968, (Victoria B. C.: Queen's Printer, 1968), p. 5.

is limited by the fact that its products must compete in
world markets. A reduction in average log size, decrease

in quality of operatable timber being logged, higher wages--
while the proportional increase in output per worker has

not kept pace with other manufacturing industries, and the
move towards more distant and difficult areas in search of
merchantible forest stands have been cited as contributing
factors to this cost-price squeeze.1

As the supply of old growth timber continues to
diminish, forest industries will have to move towards more
intensive management of readily accessible and closer-to—
market lands. At this stage of forest management, it will
be necessary to take a closer look at how productivity of
the forest resource is interpretated and how it may be main-
tained or improved.

One of the fundamental factors which will require
study and research at this level of management, will be the
effect that soils have on the trees growing in it. This will
require an inventory of the kinds and extent of forest soils

in an area, and their relationships to forest growth and

related management plans.

 

1Royal Commission on Canada's Economic PrOSpects, The
Outlook for the Canadian Forest_;ndustries, John Davis,
Chairman of the Forestry Study Group. (Hull, Ont.: Queen's
Printer, March, 1968), p. 65 and 67; and Joe des Champs,
"Williston tells why Forest Taxes hiked by $5.7 Million,"
Canadian Forest Industries, LXXXVII (March, 1968), pp. 65-66.

Unfortunately, limited forest soils survey and soils
research has been conducted in the forested areas of the
Province. What surveys that do exist, have been primarily
extensions of agricultural soil surveys. Since they have
been for agricultural purposes, their use to forestry has
proven to be of limited value. On the Coast for example,
most of the soil surveys extending into forested areas are
of a very general nature and often the map units contain
uninformative terms such as "rough mountainous lands."

Much of the forest research that has been conducted
is of limited value, since it has not been conducted on
previously soil surveyed lands. AS a result, the extent and
importance of the research is unknown, and the significance
of the results obtained can only be applied with uncertainty
to other areas, where soils may be quite different.

This lack of forest soils information and its limited
direct use to foresters may account for part of the reason
why further studies into forest soils receive such low
priority. Studies from widely varied sources has Shown a
definite relationship between site quality, as measured by
tree growth, and soil characteristics. A soils investigation
program must be devised in British Columbia which is rela-
tively simple to use, is economically feasible, and from

which observations of its applicability are readily apparent.

Purpose and Guiding Hypothesis

The purpose of this study is to outline a method and
provide guidelines by which the forester, with consultation
of a trained soils specialist, can readily separate forest
land areas into units which will serve as a basis for future
forest land management.

The guiding hypothesis is: sufficient experimental
information exists for the formulation of a first approxima-
tion to a method for delineating forest land areas into more
appropriate units for determining forest productivity, for
planning reforestation programs, and for applying forest
fertilization etc., than has been heretofore used in British

Columbia.

Methodology
The suggested method and guidelines are based upon:
(1) previous classification methods emplOyed in British

1 and

Columbia by such research investigators as Lacate,
(2) field data collected and observations made on forest-soil
relationships, while the author was involved with the soil
capability for Forestry Classification Program being con-
ducted in the interior of the Province during the 1965—1967

field seasons. The soil capability for Forestry Classifi—

cation Program was carried out under the auSpices of the

 

1D. S. Lacate, Forest Land Classification for the
Universityiof British Columbia Research Forest, Department
of Forestry, Publication No. 1107 (Ottawa, Ont.: Queen's
Printer, 1965).

Canada Land Inventory, a joint Federal-Provincial program.

Some of the findings are incorporated in this study.

Limitations of the Study

This study is a prOposed guide and cannot be consider-
ed as a simple solution to a complex problem. It is not
proposed or even implied that the forester can find his
questions or problems answered on a certain page. Instead,
stress has been placed on principles and basic procedures,

a knowledge of which will hOpefully provide the tools that
can be used to study and map Specific areas, and upon which
sound procedures for forest land management can be developed.
The suggested method may be considered as a reconnaissance
survey which lacks the refinements of a detailed soil survey.
It is suggested that such a method is necessary not only to
initiate an interest in soils, but also provides a means to
cope with the magnitude of the area to be covered. The
guidelines are quite generalized however, and will require
possible modifications, delineations, and additions to each
area studied.

It is not the intent to leave the reader with the
impression that other techniques in classifying land or the
study of other effective factors influencing productivity
throughout the life of the stand should not be considered
in the overall assessment and evaluation of forest land and
related management practices. Their discussion however, is

beyond the sc0pe of this study.

Justification

The rational management of forest resources should
be preceded not only by a knowledge of the nature and extent
of the soils which trees grow in, but also by the inter-
relationships between forest and soils. A reconnaissance
survey is a means of delineating soils at a level suitable
to forest management and can be the basis for providing
additional information as well.

As outlined by Lemmon, evaluation of forest land based
on soil survey data can provide in addition to potential
soil productivity, information on Species priority, regener-
ation potential, degree of plant competition, trafficability,
and erosion, windthrow and disease hazard.1 Steinbrenner
states that once a soil survey has been completed, it should
be possible to relate problems such as brush encroachment,
insect and disease attacks and wildlife damage in surveyed
and mapped soil units.2 Steinbrenner also mentions that
follow—up studies can relate "certain forestry problems to
soil types, will provide useful management information such
as choice of appropriate techniques for silvicultural prac-

tices, forest protection and timber extraction and will

 

1Paul E. Lemmon, "Soil Interpretations for Woodland
Conservation," First North American Forest Soils Conference,
(East Lansing, Mich.: Michigan State University, Agricul-
tural Experiment Station, September 8-11, 1958), pp. 155-58.

2E. C. Steinbrenner, Ten Years of Forest Soils Re-
searchggn RetrOSpect and PrOSpeCt, (Centralia, Wash.:
Weyerhaeuser Forestry Research Center, April, 1961).

locate problem areas for concentrated research effort."1
Such broad use of soil survey information suggests that the
cost of an initial survey can be considered as economically
feasible when pro-rated over the entire management program.

In discussing the relationship between soils and
research, Scott believes it is quite possible for the future
silviculturist to control the appearance as well as the
productivity of a forest by altering the nutritional status
of an area.2 Scott continues "The exact nature of the cell
wall, both chemically and physically, is also influenced by
the nutrient status of the soil in which the tree is growing,
as is the initiation and deve10pment of floral parts. With—
in a decade it may well be pOSSible»to:COntr01 both seed crops
and wood characteristics by manipulating the characteristics
of the soil.3

The demand for sound information for forest management
is certain to increase in the future. It is suggested that
the method outlined in this study will not only aid in supply—
ing the answers, but will reduce the pressure for Speedy

results at a sacrifice of adequate scientific standards.

 

lIbid., p. 16.

2David R. M. Scott, "Silviculture in the Douglas-Fir
Region--In PrOSpect," Proceedings,Society of American
Foresters Meeting: Resources, Forestersygand Policies for
ZProgress, Washington, D. C.: Society of American Foresters,
1967), pp. 95-94.

31bid., p. 94.

In the future, a follow-up, more detailed soil survey and
classification must be used which will further aid and

will be more informative to the forest manager.

CHAPTER II
REVIEW OF THE LITERATURE

Investigators have long sought simple, precise, and
practical means of classifying and evaluating forest areas
in order that the production of a given Species in a given
area could be determined and used as a basis for management
decisions. In British Columbia, as in many other areas,
forest growth is usually determined by site index.1

For a considerable time, foresters have been inclined
to believe that classifications based on site index would
serve their purposes, and sets of Site index curves develOp-
ed from data collected for a particular Species have been
used widely.2 In addition, site-predicting equations have
been derived in certain geographical areas for certain

Species based upon information which has proven to be statis-

tically significant.

 

1Site index refers to the average height that the
dominant or dominant and co-dominant trees of a given Species,
in an even-aged stand reach at a Specified age.

2C. E. Farnsworth and Albert L. Leaf, "An Appraisal
of Soil—Site Problems: Sugar Maple-Soil Relations in
New York," Forest-Soil Relationships in North America, ed.
by Chester T. Youngberg, (Corvallis, Ore.: Oregon State
University Press, 1965), p. 285.

10

Limitations of Accepted Methods
Site index measurements have been appealing methods
for determining forest growth, but they have the following
limitations.
1. The term Site itself is vague, and is too inclu-
sive. Site has been defined by Toumey "as the sum of the
effective conditions under which the plant or (plant) com-

"1 Emphasis has been rightly placed upon the

munity live.
effective conditions, namely those factors that in some
manner support and influence the vegetation. However, Site
does not distinguish these effective factors, how signifi—
cant they are, and how they can be measured accurately.

2. The determination of site requires actual measure-
ments, and as Choate mentions the cost of intensive field
work to satisfy most present demands for site data would be
prohibitive.2

5. The use of dominant and co-dominant trees for
determining site index is not always satisfactory. Spurr

mentions the following problems:3

 

1James W. Toumey, Epundations of Silviculture Upon An
Egological Basis, (second edition: New York: John Wiley and

Sons, 1928), p. 7.

2Grover A. Choate, Estimating Douglas-Fir Site Quality

From Aerial Photographs, Pacific Northwest Forest and Range
Experiment Station, Research Paper 45, (Portland, Ore.: U. S.
Department of Agriculture, Forest Service, 1961), p. 1.

3Stephen H. Spurr, Forest Ecology. (New York: Ronald
Press Company, 1964), p. 128.

11

a) Dominant and co-dominant tree classes are sub-
jective and two foresters may differ widely in their concept
of what constitutes dominant and co-dominant trees.

b) Many of the co-dominant trees will drOp out of
the main canOpy as the stand ages and therefore, perhaps
should not be measured.

c) Thinning and other cutting Operations may arti—
ficially change the average height of the dominant and co-
dominant trees without changing the actual site quality.

d) It is often very difficult to see the t0ps of
co-dominant trees in tall and dense timber and it is there—
fore difficult to measure their heights accurately.

4. Site determination is obviously a problem on
logged over lands and as Smith and Ker mention in the Douglas
fir region little information is available concerning the
original site quality of stands that have been logged and
burned or burned.l

5. Site index does not have a perfect correlation with
productivity.2 Its use, therefore in determining the growth
of a Specified area over a certain period of time is limited.

6. The conventional use of site index curves is sub-

ject to criticism because:

 

1J. Harry G. Smith and John W. Ker, "Some Problems
and Approaches in Classification of Site in Juvenile Stands
of Douglas Fir," Forestry Chronicle, XXXII (December, 1956),
418.

2Farnsworth and Leaf, loc. cit.

12

a) Site index can be determined accurately only from
trees growing in reasonably well stocked even—aged stands.1
The height growth of open grown trees or trees growing under
conditions of suppression may reflect the influence of Spac-
ing and shade rather than basic site productivity. In addi-
tion, the stands should be old enough to reflect the full
impact of the site factors. For instance, if the depth of a
soil is limited either by physical or physiological reasons,
growth of a tree may be normal up to the point that the depth
of the soil becomes a limiting factor. On another soil, the
same Species may grow slowly until the roots reach an under—
lying enriched horizon or a deep-lying water supply, after
which growth will be accelerated.

b) The technique for using site index curves is
sound only if the average site quality is the same for each
class.2 If, however, as is often the case, younger stands
are found on generally better Sites, while the remaining old
growth stands are concentrated on the poorer sites, the
average curves will be warped upwards at younger ages and
downward at older ages.

c) A major weakness of the conventional technique

used is the assumption that the shape of the height-growth

 

1G. R. Trimble Jr., and Sidney Weitzman, "Site Index
Studies of Upland Oaks in the Northern Appalachians,"
Forest Science, II, No. 5 (September, 1956), 162.

ZSpurr, op. cit., p. 129.

15

curve is the same for all sites. Although, this generaliza—
tion gives good results in many instances, it does not hold
for all soil conditions.

d) Farnsworth and Leaf mention that methods of curve
develOpment which assumes similar forms for all curves
within a family or curves for a given Species may mask sig-
nificant effects of site and Species characteristics, and
introduce inconsistencies that reduce their validity.1

7. Site prediction equations are of limited value
since they are usually restricted to the geographical areas
in which they were derived. In addition, often the complexity
of the equations, coupled with the cost of obtaining the
individual variables severely restricts their use for prac-

tical forest management.

Forest—Soil Relationships
_As a result of the above limitations of site index as
a measurement of productivity, many foresters have sought
more precise methods of evaluating growth potential. Early
approaches to this problem were to reduce observations to
one or two measurable soil prOperties which were related to

2

tree growth in a particular area. Unfortunately, as more

information becomes available it is apparent that the growth

 

lFarnsworth and Leaf, loc. cit.

2Theodore S. Coile, "Soils and the Growth of Forests,"
Advances in Agronomy, IV (September, 1952), 550-98.

14

of a forest stand is controlled by a complexity of inter-
related factors, not only of soil but climatic and biologic
as well. In an attempt to simplify this complexing and often
confusing situation, this review will be limited to the
following easily observed soil factors in which previous
studies have shown a significant correlation with forest

growth.1

TOpography
For simplicity the approach used by Aandahl in dis-

tinguishing different topographic features is followed.2

General Setting in the Landscape.--The location of soils upon
a basis of relative elevation is a most useful and meaningful

3 The t0pographic position

criteria in site classification.
of the site is often closely related to the physical proper-
ties of the soil that govern soil moisture relationships.

Trimble, Weitzman and Doolittle have found that relative

position between ridge tOp and cove, is one of the factors

 

1Throughout the review, it will be noted that the
term site is still in vogue for want of a better term.

2Andrew R. Aandahl, "The Characteristics of Slope
Positions and Their Influence on the Total Nitrogen Content
of a Few Virgin Soils of Western Iowa," Soil Science Society
pprmerica Proceedings 1948, XIII (1949). 449—54.

3Spurr, op. cit., p. 111.

15

closely related to site.1 One of the greatest values of
topography is that it can be quickly recognized and evalu—
ated.2 Topographic differences can be easily distinguished

and delineated on aerial photographs viewed steriosc0pically,

ASEeCt.--A8pect is universally considered as having an impor-
tant effect on tree growth.3 In temperate latitudes the cool
moist north and west SlOpes have been found to be more favor-
able for growth of many coniferous Species than the hotter

and drier south and east lepes.

Gradient.--The effect of lepe gradient and length not only

can have an influence on soil depth, but also is of utmost

4

importance in soil moisture relationships. This partly is

5 Slope

attributed to the resulting climatic conditions.
gradient also influences productivity in another manner.
Since the greater the lepe, the greater is the surface area

per acre or other area measured horizontally. For this reason,

 

lTrimble and Weitzman, op. cit., p. 167: and Warren T.
Doolittle, "Site Index of Scarlet and Black Oak in Relation
to Southern Appalachian Soil and TOpography," Forest Science,
111. No. 2 (June, 1957), 123.

2Spurr, loc. cit.

3Choate, 0p. cit., p. 6.

4James D. Curtis, Silvicultpgal Limitations of Shallow
Soils, Intermountain Forest and Range Experiment Station,
Miscellaneous Publication No. 24, (Ogden, Utah: U. S. Depart-
ment of Agriculture, Forest Service, 1961).

5Choate, loc. cit.

16

good forest sites of moderate lepe usually contain more
trees and produce greater yields per acre (horizontally as

it always is) than do comparable level sites.1

Curvature.--Tarrant has shown the effects that curvature of
the land has on site quality.2 In his studies, site index
has been found to be significantly greater on the concave
terrain characteristics of lower s10pes, valleys, and basins
than on the convex situations associated with upper lepes,
hilltops, and ridges. Upper s10pes lose moisture and solu-
able salts through drainage and are depleted of fine material
and humus by erosion. Also, they are generally more exposed
to winds and lose a greater amount of moisture by evapora-
tion than do lower lepes. Conversely sites on lower lepes
benefit from deposition of fine material, soluble salts and
water.

Horizontal or contourwise configuration is important
because it affects the duration or frequency of exposure of
the site to wind and sun, and also because it influences
drainage. Choate states that a site in a depression such
‘as a draw is usually more moist and hence more productive

3

than one on a Spur or the end of a ridge. The former is

 

1Robert F. Tarrant, "Forest Soils of the Pacific
Northwest," Proceedings, Society of American ForesterspMeet—
ing: Converting the Old—Growth Forest, (Washington, D. C.:
Society of American Foresters, 1956), pp. 75-76.

2Spurr, loc. cit.

3Choate, loc. cit.

17

more sheltered from the drying effects of wind and sun and,
furthermore, is frequently the location of a stream or in-

termittent drainageway.

Physical Soierroperties
In a comprehensive review of the factors that influ-
ence tree growth, Gaines concluded that physical soil charac-

1 He found that chemical

teristics are of primary importance.
characteristics are also important, but are generally related
to the physical characteristics. Of the individual physical

characteristics, effective soil depth, soil textures and soil

structure and the type of parent materials are listed as the

most important factors in influencing forest growth.

Effective Soil Depth.--Lemmon listed effective soil depth

as the most important factor in determining the productive

2

capacity of a site. Steinbrenner has found a positive rela-

tionship between effective soil depth and site index.3

 

1E. M. Gaines, Soil Factors Related to the Local De—
termination of Forest Site Quality, A Review of literature,
Southern Forest and Range Experiment Station, (Asheville,
N. C.: U. S. Department of Agriculture, Forest Service,
1949).

2Paul E. Lemmon, "Factors Affecting Productivity of
Some Lands in the Willamette Basin of Oregon for Douglas-fir
Timber,“ Journal of Forestry, LIII, No. 5 (May, 1955), 526.

3E. C. Steinbrenner, "The Influence of Individual Soil
and Physiographic Factors on the Site Index of Douglas-fir in
Western Washington," Forest-SoilpRelationships in North Ameri-
.g§, ed. by Chester T. Youngberg, (Corvallis, Ore: Oregon
State University Press, 1965), p. 265.

18

Effective soil depth being defined as that depth of the
portion of the soil that is either occupied or capable of
being occupied by the roots of the tree for which the site
index is desired. Choate states that effective soil depth
is closely related to the internal water relationship of the
profile which in turn influences plant growth.1 In converse,

the limitations of shallow soils are pointed out by Curtis.2

Soil Texture and Structure.--Soil texture affects site qual-
ity. It influences the chemical properties of the soil,

soil moisture and air relations, and root development.3
Physically, the texture of the soil regulates the pore Space
and consequently both the water and the air-holding capacity
of the soil. Coarse textured soils have large pore Space.

As a result, they are easily drained, and are apt to be
excessively dry. Carmean mentions that Site quality decreases
with an increase in the percentage of gravel in the soil pro-
file.4 The best conditions for absorption and retention of
available water for plant growth are those soils having a

loam to silt loam texture.5 The relationship between texture

 

1Choate, op. cit., p. 8.

2Curtis, loc. cit.

3Spurr, op. cit., p. 112.

‘Willard H. Carmean, "Suggested Modifications of the
Standard Douglas-fir Site Curves for Certain Soils in South-

western Washington," Forest Science, II, No. 4 (December,

5Spurr, 0p. cit., p. 115.

19

and plant available water is shown in Figure 1.

The texture of a soil has a direct influence on soil
structure. Structure is most important in soils with a high
silt and clay content.1 The development of a granular
structure in such soils permits good percolation of both
water and air, reduces erosion, and results in a soil that
has many of the desirable physical properties for forest
growth. Studies such as that of Steinbrenner has found that
soils with a dense impermeable structure and on the other
extreme, soils with a porous single grained structure limit
forest productivity; the optimum forest growth, being found

on soils whose porosity lie within these two extremes.2

Soil Parent Material.--The prOperties of soils are function-

3 One of these

ally related to the soil forming factors.
factors is parent material. The texture, structure, or
fabric and mineralogical and/or chemical composition of the

parent materials predetermine or at least strongly influence

the properties of soils formed from them.4 The kind of

 

lIbid., p. 114.
2Steinbrenner, 0p. cit., p. 268.

3Hans Jenny, ggctors of SoilpFormationl A System of
Qpantitative;§edoloqy, (New York: McGraw-Hill Book Company,
1941).

4E. P. Whiteside, "Some Relationships between the
Classification of Rocks by Geologists and the Classification
of Soils by Soil Scientists," Soil Science.Society_p§ America
Proceedings, XVII (1955), 158-42.

20

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21

deposit often imparts a definite Shape or form and other
characteristics such as drainage pattern to the landscape.

A landscape in which coarse outwash deposits are the major
parent material may be expected to impart different prOper-
ties to the soils and will reSpond to management differently

than a landscape developed from a fine textured glacial till.

Soil Drainage.--Soil drainage reflects the natural water
table and to some extent available soil moisture for plant
growth in a soil. Unfortunately, the measurement of avail-
able soil moisture is still a difficult and laborious task.
However, available soil moisture can be interpreted indirect-
ly through soil texture. Auten, Coile and Young have shown
the thickness of the solum is a good guide to forest growth
in areas where soil moisture is a dominant growth factor.1
In his discussion on soil drainage, Lacate mentions the
"soil drainage can be assessed on the basis of differences
in soil color, depth to mottling or gleying, depth to im-
permeable material, tOpographic location, size of watershed,

length of slope, depth to existing water table, and the

 

1John T. Auten, "Some Soil Factors Associated with
Site Quality for Planted Black Locust and Black Walnut,"
Journal oprorestpy, LXII, No. 8 (August, 1945), 592-98:
Theodore S. Coile, Relation ofpSoil Characteristics to Site

Index of Loblolly and Short Leaf Pinespin the Lower Piedmont

gegign of North Carolina, Duke University Forestry School
Publication No. 15 (Durham, N. C.: Seeman Printery, 1948):

and Harold E. Young, "Forest Soils-Site Index Studies in
Maine," SoilpScience Society of America Proceedings, XVIII
(January, 1954), 85-87.

22

texture, structure and permeability of the solum."1

Forest Land Classification

In the field the above soil factors and their contrib-
uting influences are all interrelated. To be of use then,
these factors must be recognized, combined, or separated in
some manner which will allow grouping into identifiable and
reoccurring land units.

Such a method has been employed by Lacate in British
Columbia.2 Lacate's method (using aerial photographs and
field checks) delineates land into divisions or units that
are relatively homogeneous with reSpect to the more stable
features of landform, surficial geology, soil and vegetation.
Lacate states such a division of landforms into land units
"provides a framework to which forestry information and
estimates of potential for forestry purposes can be related
and subsequently extended over adjacent landscapes using air-

"3 Reports by Lacate

photos and airphoto interpretations.
and others contain interpretations and grOUpings of soils

on the basis of mapping units applicable to forest

 

1D. S. Lacate, Fprest Land Classification for the Uni-
yggsity of British Columbia Research Fogest, Department of
Forestry, Publication No. 1107 (Ottawa, Ont.: Queen's
Printer, 1965).

2Ibid.

31bid., p. 5.

25

management.1 A review of other approaches used to classify
land, soils, and forest sites have been prepared by Rowe
and Lacate.2

The recent study by Keser is highly significant and
will warrant close consideration in future forest management
considerations once it becomes operational. The objective of
his study is to “develOp a system providing a basis for pre-
dicting the characteristics of a stand at a given time for a
desired set of conditions that can be imposed Upon the soil

or stand at a Specific time or stage of the development."3

 

1Ibid.; and D. S. Lacate, et al., "Forest Land Classi-
fication and Interpretations for Management in the Spruce
Working Circle, Tree Farm License No. 9, Okanagan Valley,
B. C.," B. C. Department of Agriculture, Co-Operative Interim
.Report, (Kelowna, B. C.: July, 1965); and P. N. Sprout, D. S.
Lacate, and J. W. C. Arlidge, Eprest Land Classification Sur-
vey and Ipterpretations for Management of a Portion of the
Niskonlith_grovincial ForestL_Kam100pS District, §4_C., De-
partment of Forestry Publication No. 1159 (Ottawa, Ont.:
Queen's Printer, 1966).

2J. Stanley Rowe, "Soil, Site and Land Classification,"
Forestry Chronicl§_XXXVIII, No. 4 (December, 1962), 420-52;
and D. S. Lacate, "Wildland Inventory and Mapping,“ Forestry
Chronicle XLII, No. 2 (June, 1966), 184-94.

3British Columbia, Forest Service, The Forest Research
Review, (Victoria B. C.: Queen's Printer, 1967), p. 15.

CHAPTER III
DESCRIPTION OF AREAS AND METHODS EMPLOYED

The Study Areas
Location and History

The two studied areas lie within the central and south-

'western regions of the interior of the Province. The boundar-

ies of the study areas are outlined in Figure 2. The study

area in the central region of British Columbia will be called

the Quesnel area, while the study area in the southwestern

;portion of the Privince will be called the Princeton area.1

'The Quesnel area was chosen in order to gather soils informa-

‘tion which will aid in finding a solution to the developing

eagricultural forestry fringe conflicts. The Princeton area

xmas selected because the area has a wide diversity in land-
ifiorm and soil features which provided an ideal Opportunity
tc: test the mapping procedures used.

During glacial times, British Columbia, except for the

hi4gher elevations was completely covered by ice. Both the

Qtuesnel and Princeton areas were covered by the Cordilleran

_ J'Designated names, Quesnel and Princeton refer to
majcar settlements within the study areas.

24

25

   

Quesnel§§

 

I I I I j

o 100 200

. [E Princeton
Miles

GID Princeton Study Area

€23 Quesnel Study Area

Figure 2. Location of the Princeton and Quesnel
Study Areas in British Columbia

26

ice sheet.1 AS a result, much of these areas are covered
by glacial till, varying in thickness and composition.
During the glacial period, glacial lakes also formed, and
the old glacial lake beds, with their deposits of silt and
clay can be observed over a considerable part of the Quesnel
area. Glacial lake deposits in the Princeton area, by com-
parison are minor, and occur in the northerly portion of

the study area.

Coarse sediments carried by glacial meltwaters have
been deposited in the form of sands and gravels in both of
these areas. In the Princeton study area, the most notable
gravel and sand deposits is in the form of a large glacial
delta, which lies just to the west of the village of Prince-
ton. In the Quesnel area, glacio-fluvial deposits, consist-
ing primarily of terraces and beach ridges are associated
with the upper elevational limits of the glacial lacustrine

deposits.

Population Centers and Industries
In the Princeton area, the village of Princeton with

a 1966 population of 2,151 persons is the largest population

 

1J. D. Chapman et al., editors, British Columbia
Atlas of Resoprces, British Columbia Natural Resources Con-
ference, (Vancouver B. C.: Smith Lithograph Company, 1956),
pp. 9-100

27

1 The village was an important min-

center in the study area.
ing center during the early decades of the present century,
but with the closing of the main mine at COpper Mountain,

the village has continuously declined in population and im-
portance. Numerous other small communities in the area have
suffered the same fate. Forestry and agriculture are the main
remaining industries. There are two main sawmills in the
area, while ranching is the primary agricultural activity.

The area is hOping for renewal mining activity to improve its
economy, but its greatest potential may well be in the field
of recreation. The area has several small lakes and is well-
known as a paradise for "rock hounds." It's proximity to

the Hozameen and Okanagan mountain ranges offers potential
attraction for hunters, hikers and sight-seers.

In the Quesnel area, the town of Quesnel, with a 1966
pOpulation of 5,725 persons, is the largest pOpulation center
of the study area and is an important trade, tranSportation,
administrative, and service center for the surrounding area.2
Numerous small communities are found north and south of
Quesnel strung along the Cariboo highway.

The economy of the area is closely linked with forestry,

eSpecially sawmilling, planing, and plywood manufacture.

 

1British Columbia, Bureau of Economics and Statistics,
Facts and Statistics, Department of Industrial DevelOpment,
Trade and Commerce, (Victoria B. C.: Queen's Printer, 1967),
p. 62.

21bid., p. 61.

28

‘With the near completion of a pulp mill in the area, it can
be expected that there will be more stability and eXpansion
of the forest-based industries. Agriculture is second in
economic importance. Virtually all of the cultivated land

is in the immediate vicinity of Quesnel at lower elevations
of the Fraser Plateau. Agriculture is limited to hardy field
cr0ps, dairying and ranching. Surplus products, both wood

and agriculture, are shipped from the area by rail and truck.

Climate
The study areas can be placed in two broad climatic

regions.1

These regions are very broad and do not reflect
local topographic and latitudinal influences or differences.
Within each of these regions, important climatic elements
have essentially similar values although the great variety

of tOpography and range of elevations may produce unex-

pected extremes in individual localities.

\

Princeton area.—-This area lies in the southwest interior
climatic region. Climatic values refer to the plateau area
only, since this was the area in which the soils were
studied.2 Here, annual precipitation everywhere exceeds 12

inches and reaches 25-50 inches towards the western limits

 

11bid., pp. 21-22.

2A fuller discussion on the physiography of the areas
is given in the following section entitled Physiography and
TOpography.

29

of the region. This region includes the driest and hottest

parts of the Province.

Qppsppl area.--The study area lies in the transition zone
between the southwest interior region to the south and the
central interior region to the north. The generalized cli-
matic regions are outlined in Figure 5. The change to the
central interior region is quite distinguishable through
vegetational changes north of the Cottonwood river. The
central interior region is characterized by having generally
humid conditions (the result of reduced temperatures and
somewhat increased precipitation in comparison with the south-
west interior). Here, winters are cold and the summers are
cool and short. Four to five months have mean temperatures
below 52°F.

Tables I and II summarize temperature and precipita-

tion data for these two regions.

Physiography and TOpography
Both study areas possess a great diversity of land-
forms and topography. In the discussion that follows only
the major physiographic subdivisions as outlined by Holland

are described.1

 

1Stuart 8. Holland, Landforms of British Columbia,
A Physiogpaphic Outline, British Columbia Department of Mines
and Petroleum Resources, Bulletin No. 48 (Victoria B. C.:
Queen's Printer, 1964), p. 44.

5O

      

I
\ \

'| s
\ s
\ \
\ \ ‘
I
I 1, \ ‘
I I \

   

,-,_Quesne

'O.
O “- I
‘ \

 

I) 106 280

Miles

’\

I \ .

\_/ Coast
I

\

GID r S d 7‘ ' ’
P inceton tu y Area ‘IISOUthWESt Interior

I \

I A

\.’Central Interior
1’, ‘

MpiNorthern Interior

as

l x
\_ I Northeast

Figure 3. Generalized Climatic Regions in British Columbia

51

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52

Princeton area.--This area lies in the southern portion of
the Thompson Plateau, and includes the eastern portion of
the Hozameen Range and the northern portion of the Okanagan

1 There is a complete transition between the plateau

Range.
area and the adjoining mountain ranges because the rise

of the plateau surface towards the mountains is gradual
with progressively higher summit levels and greater dissec-
tion of the plateau surface. The Thompson Plateau is a
gently rolling upland of low relief, with prominences of
more restricted rock rising above it to 6,768 feet at Look-
out Mountain, and 5,702 feet at Wilbert Hills. Glaciation
has produced many drumlins and drumlin-like forms oriented
southeastly and southerly. Between drumlins, in old melt-

water channels, and along the river and creek valleys,

stratified sands, and gravel have been deposited.

Quesnel_pppg.--The Quesnel area contains portions of both
the Fraser Basin and the Fraser Plateau.2 The Fraser Basin
is an irregularly shaped area of low relief surrounding the
main river valleys. Its surface lies for the most part
below 5,000 feet and is covered with lacustrine clays and
silts and glacial-fluvio and alluvial deposits.

The Fraser Plateau is generally a flat to gently

rolling country, with prominences of more resistant rock.

1Ibid., p. 44.

2Ibid., p. 67 and pp. 69-71.

55

The glacial till and glacial-fluvio outwash deposits, which
cover the plateau surface, are evident by the occurrence of
drumlins, and drumlin-like forms and by meltwater channels

and stream deposits.

Forest Vegetation
In the discussion on forest vegetation, the forest

regions as described by Rowe have been elaborated on.1

Pginceton area.--The plateau area is classified as the
Ponderosa Pine and Douglas Fir Section (M.I.) of the Montane

2 The area of concern in this study (the

Forest Region.
higher elevations of the plateau) is covered with a mixture
of Douglas fir (Ppeudotsugamenziesii) and lodgepole pine
(Pinus contorta), the latter forming a relatively permanent
type over large areas because of the frequency of fires.

Engelmann Spruce (Picea engelmanni) mixes with Douglas fir

and lodgepole pine on cool, north—facing slopes.3

‘Quesnel area.--The study area contains part of two Forest
Regions. The Central Douglas Fir Section (M.2) in the south,

and the Northern ASpen Section (M.5) in the north.‘

 

1J. Stanley Rowe, Forest Regions o§_Canada, Canada De—
partment of Northern Affairs and National Resources, Forestry
Branch, Bulletin No. 125 (Ottawa, Ont.: Queens's Printer,1959).

21bid., pp. 57-58.

3Canada, Department of Forestry, Native Trees of Canada,
.Bulletin No. 61 (Sixth edition: Ottawa, Ont.: Queen's
Printer, 1961).

4Rowe, 0p. cit., p. 58.

54

Douglas fir is common in the southern portion of the study
area but thins out northward. Only scattered stands occur
north of the Cottonwood river. Lodgepole pine occurs on
most of the soils encountered. Exceptions are the very
poorly drained soils. Black Spruce (Picea mariana) occur to
a limited extent (in depressional areas) on very poorly
drained soils. Engelmann Spruce and white Spruce (Pigpp
glauca) are common throughout the north and eastern parts of
the area, with the best stands occurring in the Fraser

Plateau, east of the Fraser and Quesnel rivers.

Soils
Soil surveys have been conducted in both study areas.
The kinds and extent of soils occurring in the Princeton
study area are described in detail in soil survey reports
by Green and Lord.1 Similar information for the Quesnel
study area can be found in the soil survey reports by Farstad

and Laird; and by Mackintosh, Sneddon, and Farstad.2

 

v—

lAlix J. Green and Terry M. Lord, "Soil Survey of the
Princeton Map Area, British Columbia," Canada Department of
Agriculture, Research Station, Vancouver B. C. (In prepara-
tion): and Terry M. Lord and Alix J. Green, "Soil Survey of
the Tulameen Map Area, British Columbia," Canada Department
of Agriculture, Research Station, Vancouver B. C. (In prepara-
tion .

2L. Farstad and D. G. Laird, Soil Survey of thepgpesnel,
Nechako, Francois Lake andpPulkley-Tgrrace Areas in thpp
Central Interior of British Columbia, Report No. 4, of the
British Columbia Soil Survey, (Victoria B. C.: Queen's Printer,
1954); and E. E. Mackintosh, J. I. Sneddon, and L. Farstad,
"Soil Survey of the Quesnel Area in British Columbia," Canada
Department of Agricu1ture, Soil Survey Report No. 10, of the
British Columbia Soil Survey (In preparation).

55

Generalized profile descriptions of the soils studied can be
found in Appendix I.

The basic unit in the soil classification system used
in these surveys is the soil series. A soil series consists
of soils that are develOped on Similar parent material and
under Similar environmental conditions, particularly drainage
and vegetation. Any significant variation in one or more of
the soil forming factors results in dissimilarities of pro-
file features and the soil is classified as a different
series. In some cases, individual soil series occupied large
continuous areas but more commonly, they occur as soil associ-
ations. Continuously eroding lacustrine deposits adjacent
to streams, are delineated as eroded land types and rock
land areas represent rock land types.

While series was the basic unit used in the field
classification of soils, other categories were used to group
soils into broader classes. In the classification system
adOpted by the National Soil Survey Committee, there are six
levels at which soils may be separated or grouped together.1
These are: order, great groups, subgrOUp, family, series
and type. In the three upper categories of order, great

groups and subgroups divisions are based on major differences

 

1National Soil Survey of Canada, Report on the Sixth
Meeting of the National Soil Survey Committee of Canada,
(Laval University, Que.: [n.p.], October, 1965).

56

in morphological features exhibited in the soil profile. In
the lower three categories of family, series and type,
divisions within any one subgroup are based on soil varia-
tions resulting from differences in composition, texture of
the parent materials, drainage, and difference in thickness
and degree of develOpment of soil horizons.

In the mapping of soils, the soil association was
commonly used, particularly in upland areas, where soil
capabilities for agriculture were rated as low, and where
further refinements for forestry purposes did not warrant the
expenditure of additional time and effort which would other-
wise be required to separate these mapping units at the
series level. The drainage association is a group of soils,
consisting of different series, developed under various drain-
age conditions on similar parent material. Each soil series
in the drainage sequence occuPies a different position in
the landscape and differs in profile characteristics due to

the local influence of drainage and vegetation.

Methods Emplpyed
Determination of Soil Capability for Forestry
The first step was examination of the areas using
aerial photographs and a stereoscope in an attempt to pick
out suitable forest stands for measurement. Stands were
selected and marked on the airphotos on the basis of their
apparent uniform age and composition growing on uniform

materials and in a specific t0pographic position. An attempt

57

was also made to get a sequence of plots growing either on
different materials or in a different t0pographic location
within Specified areas.

The second step was the location and examination of
the plot in the field. In general, the stands selected for
measurement were even-aged, close to rotation age (80-100
years), thrifty, fully stocked and were predominantly of one
Species. One-fifth acre plots within the stands were marked
for measurement if the plot could be located in a uniform
area and if the trees were growing in a soil, representative
of the major soil series identified during the soil survey.
Observed features of soil profile, soil depth, soil drainage,
and landform were recorded.

Plot measurement was the third step. One-fifth acre
square or rectangular plots were laid out, the shape se-
lected being dependent upon the uniformity of the area and
the stand conditions. For example, a rectangular 2 chain by
1 chain plot was frequently used on rapidly drained ridges
which were less than 2 chains wide but were more than 2
chains long. Square plots were employed wherever uniformity
of soils and stands were greater than 2 square chains. On
each plot, all trees were tallied in one-inch diameter
classes. Five sample trees of the calculated average plot
diameter were measured for height and age. Volume of the'
plot, on the basis of these sample trees and, using the

British Columbia Forest Service standard cubic-foot volume

58

tables wasidetermined.l Mean Annual Increment (M.A.I.) was
then derived by dividing the total volume of the plot con-
verted to a per acre basis by the average stand age. The
M.A.I. was then adjusted by the use of Site index curves to
a rotation age of 100.2 M.A.I.'s were then grouped into

the 7 class forest capability system outlined by McCormack.3

Selection of Soils

In this study, two soil catenas have been selected,
one from each area to Show the general forest-soil relation-
ships found. A catena being defined as a sequence of con-
trasting soil series develOped from similar parent materials,
but differing_in SlOpe and drainage.

In the Princeton study area, a catena containing four
soil series develOped on a sandy loam till has been chosen.
This catena occurred over extensive areas and in a number of
locations. However, the data included in this study refers
to the plateau area only, in an attempt to keep the climate

and forest vegetation variables as constant as possible.

 

1British Columbia, Forest Service, Standard Cpbic-Foot
Volume Tables: plnterior Species, Forest Surveys and Inven-
tory Division, Vol. II (Victoria B. C.: Queen's Printer, 1962).

2Forest capability classes and their limitations to
forest growth are shown in Appendix II.

3R. J. McCormack, Land Capability for Forestry: Out-
line and Guidelines for Mapping, Prepared for Canada Land
Inventory of ARDA, Rural Development Branch, (Ottawa, Ont.:
Queen's Printer, 1967), pp. 4-6.

59

A soil catena on fine—textured glacial lacustrine
deposits was chosen in the Quesnel area. Observations are
limited to the three main soil series found to reoccur on
these lacustrine deposits, under similar climate and forest
vegetation conditions.

The two different catenas were chosen to see what
apparent forest-soil relationships did exist and to observe
if any factors appeared to have an overriding influence upon
forest productivity. In both cases, the same Species were
selected and measured on each soil series present. Observa-
tions as to soil development, soil drainage and topographic

position was observed and recorded.

Forestry Interpretations

Wherever possible, a single forest capability rating
was applied to each soil series. However, two or more
classes were assigned to some soils whose productivity ranged
over more than one capability class because of minor varia-
tions in soil prOperties.

Observed limiting factors were assigned to each soil
to indicate the nature of the limitations to forest growth.
Major limitations on the studied soils were soil moisture
deficiency or excess and soil permeability or effective
depth of rooting zone.

Tree Species were rated in three categories-—suitable,
not suitable, and limited suitability for each soil series

according to the characreristics of each soil, the silvics

40

of each tree Species, and their observed occurrence and
growth. Only those tree Species of present commercial value
occurring or expected to occur on each soil series were

considered.

CHAPTER IV
OBSERVATIONS, INTERPRETATIONS AND CONCLUSIONS

Obsprvations
In both catenas studied, the imperfectly drained soil

members were found to be the best suited for the growth of

1 Trees grow-

lodgepole pine and white and engelmann Spruce.
ing on these soils are able to utilize seepage water and
nutrients moving down sloPe from adjacent upland soils.
Because of their topographic position, these soils are not
subject to extremes in temperature or evapotranSpiration.

The limitations to forest growth are not easily identified

on the medium textured till, while rooting depth restrictions
due to the soil structure appear to be the limitation on the
fine textured lacustrine deposits. The topographic positions
of the imperfectly drained soils studied were similar. They
occurred on the lower sections of long straight slopes and
on Shorter lepes with a concave curvature (Figure 4). The
drainage sequence of the soils studied in the Princeton and

the Quesnel study areas are shown diagrammetrically in Figures

5 and 6.

 

1Soil drainage classes are defined in Appendix III.

41

42

 

: “HI-OI '3 l1? :

.. - .11 ‘ 9 .

g 41‘ ‘I Luv}

 

Figure 4. The imperfectly drained Pefferle
.soil series on the lower section.of.aw
long straight slope.

The moderately well drained and well drained catena
members, generally had a lower forest capability than the
imperfectly drained soil series. This is due to a moisture
deficiency that exists in these soils. On the glacial
lacustrine deposits, soil structure also restricted rooting
depth. In regards to growth and establishment, lodgepole
pine appeared to be best suited to these soils. Upper and
middle s10pes with a straight to slightly convex topographic

position were the predominant places where these soils were

found. However, moderately well to well drained soils also

occurred near the tops of knolls where their limited areal

45

H
V'
' 8
0-0
2 m I r-I
-~ 2 a 1‘
‘3' " «4 0 us 8
a) O a! II I: I‘ a ‘0
H o "4 H (a
o H 0 O 0-: II a,
0.. o H o m I
a) H O H m o
m . 0a ' '4 O t: o
'0 d C) H O H g: o
o . m 0 0a 0 n H
t-I S g 4 a) H 5 ,
o m o H
3 z r; .
lid 2

 

 

 
    

\\..:.:.':' \

\
\\\\\\\

10

\
\ \
‘3 \\ \

\
\\

\\
\
’\

Depth in inches

20

I
2.,

 

PO

 

 

 

 

 

 

 

 

.Bankeir -Mgzama __Ee££erle___s___Erzis_____
Rapidly Well to Imperfectly Poorly

to well mod. well drained drained
draingd __idrained_

 

Figure 5. Drainage Sequence of Soil Series
in the Princeton Study Area

 
 

44

l‘
3 °:>
I
o <-
2 53 a 1w
-H 'H
a. n n. u 3
o o S
,3 g H o H
o H 0 PI 04
0‘ . a. o It)
0 H d) H
aw - 0‘ ' '*
'u g '§ ‘3 3
o . °
,4
A 2: 2: m

 

 

 

 

  
 
 

 

 

 

 

 

 

 

 

 

 

Depth in inches

 

 

 

 

 

 

 

 

 

 

"Beavegly .Pineview_ 1Moxel¥
Moderately Imperfectly Very poorly
.well drained drained drained

 

 

 

Figure 6. Drainage Sequence of Soil Series
in the Quesnel Study Area.

45

extent was too small to allow seepage water to collect in
the rooting zone (Figure 7). In the Princeton area, the
rapidly to well drained soil series was closely associated
with exposed bedrock (Figure 8).

At best, these soils have a capability rating of class
5 for lodgepole pine. .Few stands of established Douglas fir
were found. Their convex or upper SlOpe position often
associated with ridges and rock outcrOp made for their easy
.identification, both on airphotos and in the field.

On the poorly drained soils in the Princeton area,
excess soil moisture was the only observable limitation to
forest growth and Species suitability. .Solitary lodgepole
pine occurred occasionally within the otherwise predominant
engelmann Spruce stands. This soil series occupied flat or
concave low-lying areas and *was: commonly found in swales
associated with stream channels.

Extensive flat-lying areas with a poorly established
surface drainage pattern and enclosed depressional areas were
typical of the very poorly drained soil series in the Quesnel
area. The high water table severely limits forest growth and
Species suitability. Forest vegetation varied from mixtures
of black Spruce, engelmann Spruce, and white Spruce to open

areas.1

 

1In the Quesnel area, no distinction has been made
between engelmann and white Spruce and their intergrades.

 

 

 

46

 

Figure 7. The well drained Mazama soil series
occurring near the top of a knoll.

a

‘s
I'IJ 9"

i "I‘ ‘4“:

I
Q

\

9

 

 

Figure 8. Rapidly drained Bankeir soil series
closely associated with exposed bedrock.

47

The relationship between the two studied soil catenas
and some forestry observations are summarized in Tables III

and PV.

lpperpretations

Comparable land classification methods and studies
have been described by Christian and Lacate.l Both systems
divide the land surface into land units, on the basis of the
major observable features, topography, surfacial geological
deposits, drainage patterns and vegetation. (Land Units as
defined by Lacate "are the relatively small, homogeneous seg-
ments of the land surface which have a characteristic topo—
graphic form and internal geologic structure and with which
are associated distinctive types of soils and vegetation."2

Reports by Lacate and others indicate a significant

relationship between forest capability and the delineated

land units.3

 

1C. S. Christian, "The Concept of Land Units and Land
Systems," Proceedings of the Ninth Pacific Science Copgress,
Vol. XX (Bangkok, Thailand: Organizing Committee, 1957), pp.
74- 81, and D. S. Lacate, Forest Land Classification for the
University of British Columbia Research Forest, Department of
Forestry, Publication No. 1107 (Ottawa, Ont.: Queen's
Printer,.1965).

21bid., p. 8.

3Ibid.; and D. S. Lacate et al., "Forest Land Classifi-
cation and Interpretations for Management in the Spruce Work-
ing Circle, Tree Farm License No. 9, Okanagan Valley, B. C.,"
B. C. Department of Agriculture, Co-Operative Interim Report,
(Kelowna, B. C.: July, 1965); and P. N. Sprout, D. S. Lacate,
and J. W. C. Arlidge, ForestpLand Classification Survey and
Interpretations for Management of a Portion of the Niskonlith
Provincial Forest Kamloops Districty B. fC., Department of
Forestry Publication No. 1159 (Ottawa, Ont.: Queen's Printer,

1966)-

48

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49

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50

Using land units as a basis of delineation, and expand-
ing from the relationship found to exist between t0pographic
position, soil drainages and forest productivity, it is
possible to develop generalized guidelines which will assist
in_identifying and delineating similar segments of the land-
scape.

The guidelines shown in Tables V and VI represent the
most common land units found to occur on the selected glacial
till and lacustrine deposits. In addition, some anticipated
forest-soil relationships are shown.

It should be noted however, that each area studied will
have a distinctive land pattern of its own, and may or may not
contain all or some of the major land units listed here.

Also, soils will certainly differ as to development, texture,
structure, productivity and Species suitability.

Additional descriptions of parent materials and soil

texture and structure can be found in Appendix V.

Conclusions

Based upon field observations, a number of generalized
conclusions about the two drainage sequences in the Princeton
and Quesnel study areas can be stated. Some of the conclusions
might apply to other soils occurring under similar conditions
but in different areas. First, rapidly to well drained soils
are best suited for the growing of lodgepole pine. Existing
stands studied were either poorly or over-Stocked. The over-

stocked stands of lodgepole pine have a tendency to stagnate

51

 

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55

on these soils. If artificial regeneration is required,
the feasibility of direct seeding versus planting should be
investigated. Seedlings resulting from reseeding will not
be subject to the planting shock experienced by planting
stock, particularly if they are planted in a dry year.
Although reseeding makes it difficult to obtain prOper
Spacing, subsequent thinnings could be conducted to Obtain
a fairly wide Spacing which would allow for optimum wood
production. These soils, because of their proximity to bed-
rock, Or because of their topographic position have a low
trafficability rating and are susceptible to erosion.
Trafficability ratings are based on permanent physical
features principal of which are Slope, soil drainage, soil
texture, and incidence and depth to bedrock. The traffic-
ability rating can be used as a guide for assessing ease or
difficulty of movement of heavy machinery. Erosion hazards
are based upon soil permeability, texture, stoniness and
lepe Of the area. Consideration to these factors should
be given in determining road layouts, and building and
maintenance costs. In addition, under proper management,
Open grown stands would contribute little slash on harvesting;
considering this and the fact that these soils are often
shallow and susceptible to erosion, any future plans for
slash burning should be carefully investigated.

Second, the moderately well and imperfectly drained

soils have the highest forest productivity and are also

54

suitable for the growth of the widest range of Species in
the study areas. The determination of the factor or factors
limiting forest growth on these soils is most difficult,

and is assumed to be due to a minor accumulation of adverse
factors. These soils, because of their high productivity
and unknown limitations, are the ones which Should warrant
first priority in future silvicultural and research projects
such as thinnings, prunings and fertilization. Because of
their inherent productivity, moderately well and imperfectly
drained soils also support prolific ground vegetation which
competes with the regeneration of tree seedlings. Scarifi-
cation should reduce this weed competition for the first

few years following harvesting. If artificial regeneration
must be resorted to, it is suggested that "jumbo size" plant-
ing stock (2 + 1 or larger) be used which can compete more
effectively with the ground vegetation.

Third, poorly drained and very poorly drained soils
were best suited for the growth of Spruce in the study areas.
The very low rate of growth obtained on very poorly drained
soils does not warrant their inclusion in any management plan
at present. The greater management problem expected on these
soils is regeneration.

-Where excess in soil moisture is already a limiting
factor to forest growth, the influence one harvesting method
has on the position of the water table as compared to other

harvesting methods should be thoroughly investigated before

a single cutting policy is adopted.

55

Trafficability is a problem on soils with a high
water table, which can be overcome to a certain extent by
managing these stands during the winter months when the
soils are frozen. The development of all weather roads may
be quite costly, but will vary, with the extent of the area
to be considered the availability of fill, and the feasi-

bility of drainage.

CHAPTER V

APPLICATION, SUGGESTED PROCEDURE AND

EXTENSION OF INFORMATION

Application

The delineation of land units on the basis of their
general tOpographic features and eXpected soil drainage at
best serve only as rough guides as to where and to what
extent succeeding field studies should be directed.

Follow-up studies upon which to base forestry deci-
sions should include at a minimum the following Observations:
(1) Parent materials, including observed variations; or
closely associated different kinds of parent materials,

(2) Soil classification at the subgroup level and (5) Physical
soil properties, most important Of which are effective soil

1 Additional inter—

depth, texture, structure and drainage.
pretations for management such as erosion hazard, traffic-
ability ratings, seedling mortality and vegetation competi-

tion can be carried out concurrently or subsequently.

1Descriptions of soils at the subgroup level are pre-
sented by the National Soil Survey of Canada, Report on the
§lxth Meeting of the National Soil Survpy Committee of
_Canada, (Laval University, Que.: [n.p.], October, 1965)

56

 

57

Suggested_Procedure
Outlined below is a suggested procedure which could
be used by a forester planning to initiate a survey on his

forested lands.

Selection of an Area
Before selecting an area for study, consideration
should be given to available airphoto coverage; existing soil F
and surficial geology information: access and existing forest 2

cover 0

 

Aerial photogrpphl.--Aerial photographs are a prerequisite
to this type of survey. They not only Show the access roads,
but they aid in the location Of Specific areas in the field.
Furthermore, they are an absolute necessity for mapping the
area. The scale chosen will depend upon airphotos available,
the detail required and the size of the area eXpected to be
covered.

Airphotos of a scale of 1:15,000 or 1/4 mile to the
inch, are excellent for soil mapping, but also have disad-
vantages. They require intensive airphoto interpretation,
and in areas of pronounced relief, considerable distortion
can exist. In a reconnaissance survey of this kind, a map-
ping unit may cover an extensive area, and carry over more
than one airphoto. This makes it difficult to maintain con-
tinuity as one shifts from photo to photo. If the area to

be surveyed is quite large, considerable time is required in

58

the checking, joining and transferring of boundaries. Photos
with a 1:15,000 scale are ideal, however for the selecting
Of suitable forest stands for measurement.

Airphotos of a scale of 1:50,000 or 1/2 mile to the
inch, permit easy identification and delineation of the more
observable landscape features and are well suited for this

kind of survey.

SOils andggeological maps.—-Existing soil and surficial
geology boundaries can be redrawn on the airphotos. Such
boundaries will aid the uninitiated in recognizing the soils
and their parent materials in the field. Furthermore, those
boundaries will serve as ready reference in identifying

similar areas in the field and on the airphotos.

Access and eXisting forest cover.--Good access will reduce
field time and will allow for a greater number of field
checks. Exposed road cuts are ideal for making observations
on the soils. Landform features are usually easier identi-
fied on cleared areas which are not masked by forest vege-
tation. However, on alluvial and flood plain deposits,
forest vegetation Often serves as a useful guide in the map-
ping of different drainage patterns. Areas having stands
suitable for productivity measurement are obviously more

desirable than those that have not.

 

59

Initial Survey

Before beginning a survey, a Specialist in soils and
land classification should be consulted. The Specialist can
point out mapping techniques which can be employed both in
the field and on airphotos. He can also assist in identify-
ing the major landforms, parent materials, and soils,
encountered in the field and can point out those features
which will serve as useful criteria in mapping.

Before mapping, it is suggested that the major access
roads are driven, in order to get an idea of the kind of
soils which will be encountered. Frequent stops should be
made, particularly when observable changes in topography,
parent materials or soils are noted. Observable correSpond-
ing breaks in the landscapes at these points should be drawn
on the airphotos to aid in future airphoto interpretation.

.A suggested field card shown in Figure 9 could be used to
record all pertinent and observable information noted at this
time. Each stOp number should be recorded both on the field
card and the airphoto. A number of st0ps being homogenous
as to their observed features can then be assigned a symbol
‘which will represent a Specific land unit which will encom-

3pass all soils and landform features within a defined range.l

 

1The major criteria for separating one land unit from
another will usually be: (1) kind of parent material,
(2) effective soil depth, (5) soil develOpment, and (4) soil
‘texture and structure.

 

6O

 

FIELD CARD
Photograph NO. By

Stop NO. Date

 

.Soil information

Assigned Land Unit Soil description

Soil Classification

 

Parent Material
Soil Depth
Soil Drainage

 

 

 

Soil Structure

 

Soil Texture

 

TOpography
Surface Litter

 

.Forestry interpretations
Estimated Productivity Low Medium High
Actual Productivity Species sampled

Limiting Factors to Forest Growth

 

 

 

Erosion Rating Low .Medium High
Vegetation Competition Low Medium High
Seedling Mortality Low Medium High
Trafficability Rating Poor Fair Good

 

 

Additional Comments:

 

 

 

 

Figure 9. Suggested Field Card.

61

All future stOpS falling within the limits of each land unit
should be designated on the photos and the field card by

the appropriate selected symbol.

Aerial Photograph Interpretation

Using the information collected at the various stops,
boundary lines outlining the apparent differences between
land units should be drawn. Often two or more land units are
too closely interrelated or are too small to be easily
separated either on the airphotos or on the ground. In such
cases, these land units can be grouped into what Lacate has
termed a land association. Land association as defined by
Lacate "is an aggregation of geographically associated
Land Units."1 Estimated percentages of each land unit
(totalling a 100 per cent) from ground and airphotos observa-
tions Should be noted in each land association mapped.

In mapping, it is easiest to begin separating those
units which are most easily identified. This not only re-
duces the area left to be interpreted, but gives the inter-
preter confidence in his work. For example, areas of rock
outcrOp and swamps could first be mapped out.

Once the area has been mapped, re-checking of the
'boundaries should be undertaken in the field.

_L

1D. S. Lacate, Porest Land Classification for the
:gpiversity of British Columbia Resepggh Forest, Department
(Of Forestry, Publication No. 1107 (Ottawa, Ont.: Queen's
Printer, 1965).

 

62

Pre-mapping
Once the interpreter has gained confidence and experi-
ence in this procedure, he will be able to extend his mapping
to adjacent areas. Field work will entail only checks as to
‘prevmappedgiboundaries, percentage estimates of land units
within each mapped land association; and the continuity of

similar parent materials and soils into the extended area.

Extension of Infopmation

Good forest management today includes the consideration
of other land uses as well as that for timber production.
Therefore, when forest lands are managed for maximum produc-
tion, watershed and engineering needs must be taken into
account.1 Some of the information gathered in this kind of
survey would apply to the management of other resources as
well.

Productivity

Productivity depends on the ability of a soil to supply
the necessary tree growth requirements for each species.
.A knowledge Of the Species needs and of the importance of
various factors affecting growth will require further research

and is necessary in obtaining maximum use of the survey data.

 

1F. Gehrke, "Forest Soil Surveys-«Methods, Status,
Resulting Information and Use in Management,“ Mposium of
:Foreet Watershed Management, Sponsored by Society of American
Foresters, and Oregon State University, (Corvallis, Ore.:
(Iregon State University, March, 1965), p. 185.

 

65

However, at the present stage of development in British
Columbia, the suggested survey procedure outlined will supply
data about the nature of the physical and physiographic soil
factors on which productivity is greatly dependent and the
extent of each kind of soil present.

Unproductive areas, such as swamps and rock outcrOps
can be easily delineated and their acreages determined. This
information, combined with productivity figures for the
remaining areas will aid in assigning best land use and
establishing management priorities. Soil productivity in
terms of forest growth can be determined following a method
similar to the one outlined in Chapter III on pages 56-58.
Figures 10 and 11 Show the comparison between a suitable and

a not suitable stand to be selected for measurement.

Forest Management

Information on erodibility and compaction will enable
the manager not only to choose logging methods and equipment
that will do the least damage to the soil, but also will
allow the method most conducive to the establishment and
growth of regeneration to be chosen. Soil depth, physical
composition, and type Of terrain can influence the location
of cutting boundaries so as to produce areas Similar for
future management practices. The nature of the soil can be
used in estimating logging costs and breakage can be related
to the kind and degree of rockiness. Correlations between

volume losses due to insect and decay and seedling mortality

 

64

1,- “'3 d

. ' ‘1 A'_'hQ»AC:f‘“’.U'

--V fl 7
' = \r‘. .‘~: _,-". ,1 _ _
‘ l‘ I ‘7 II. ‘ '.- fl .3 n v r. ‘ z :33”
‘Na'--" Mfm’i'dfm.

 

 

Figure 10. An even-aged well stocked stand suitable
for measuring soil productivity.

 

Figure 11. A multi-storied, uneven-aged stand
not-suitable for measuring soil productivity.

 

65

due to drought conditions and vegetation competition can
easily be determined through follow-up studies using the
original survey as a base.

The field card on page 60 has a place for additional
information. Interpretations such as erosion hazard and
trafficability can be determined from the characteristics
associated with each land unit. As an initial rough guide, F
such interpretations can be rated simply as low, medium or

high.

 

Engineering

The survey will provide information useful in the
establishment of possible problem areas where soils with poor
drainage, unstable properties, extensive rock outcrOppings,
and steep SlOpes may affect road location. This knowledge Of
position and extent will help the engineer in choosing the
best among several alternatives.

The availability of road surface materials can be
easily determined from the resulting survey map. Drainage
patterns and their related landscape features can be used in

determining culvert size and Spacing.

Watershed Management
Information about soil-moisture relationships will be
required to evaluate water production and quality. Certain
physical characteristics of the soil influence its ability to

absorb and store water. Soil depth, to a large degree,

66

controls the amount of water that can be temporarily stored
and later released to the streams. Texture, structure and
organic matter content affect the soils porosity, infiltration
capacity, and storage Space while the depth and nature of the
surface litter aid in estimating erodability.

Some of the data collected during this survey will
have future use when correlated with water management studies.
At a minimum, the survey will provide a map showing the kinds,
extent and locations of parent materials, and their related
soil depth, texture and structure. In addition, major drainage
channels and seepage lepes may be inferred from the observed

drainage patterns and associated land units.

Research
The resulting information from such a survey will pro-
vide the research scientist with knowledge about the location
and extent Of the important soils and the problem soils.
Investigations can then be established which will yield results

of the widest possible application.

 

CHAPTER VI

SUMMARY AND FUTURE REQUIREMENTS

 

Summary
Two soil catenas, one occurring on glacial till, and p
the other on glacial lacustrine deposits were selected in two *fl
different areas of the interior of the Province. A relation- 1:
ship was found to exist between tOpographic position and '

resulting soil drainage and forest productivity.

In both study areas, stands having the highest produc-
tivity, as determined by their mean annual increment at 100
years of age, occurred on imperfectly drained soils whose
tOpographic position Offered protection from extremes in
evapotranSpiration and exposures. These soils also receive
seepage water from adjacent upland soils in quantities that
does not impede forest growth.

Based upon these observations and previously devised
land classification methods, it is suggested that forest
productivity can be determined more effectively and has
broader application by the method outlined than by the con-
ventional site index methods. Cleared forest land can be
assigned a relative productivity rating while actual produc-
tivity rating can be assigned on forested areas as mensura-

tional data becomes available. Such information can then be

67

68

extrapolated to adjacent cleared, but otherwise similar
areas.

Based upon the land classification method devised by
Lacate, some guidelines have been proposed which it is hoped
will aid the practicing forester in separating his forest land
into systematic units which can serve as a base for future

1 In initiating a survey,

management interpretations and plans.
a specialist in soils and land classification should be con-
sulted to get the survey started on the right track.

A reconnaissance survey is not meant to take the place
of more detailed soil surveys. However, such a method, as
discussed in this study provides initial information in other-
wise unknown areas. It will also facilitate in the location
of follow-up detailed soil surveys and research projects in
those areas having the greatest interest to forest managers.

The primary purpose of this study was to outline a
method which practicing foresters will find not only useful,
but will also lead them to take an even greater interest in
their soils. It is hoped that consultation with a soils
Specialist will follow. A co-Operative study can have a dual

benefit. First, the forester will have an opportunity to

study soils and to learn techniques for mapping, which he may

 

1D. S. Lacate, Forest Land Classification for the Uni-
versity of Pgitish Colpmbia Research Forest, Department of
Forestry, Publication No. 1107 (Ottawa, Ont.: Queen's
Printer, 1965).

 

69

then be able to apply elsewhere unaided. The Specialist can
learn the difficulties and problems facing the forester and
can then devise methods Of interpretating soils more tailored
to the foresters needs. In sum, it is hoped that such a pro—
cedure will have positive consequences, which will be felt at
the administrative level.

The findings and procedures discussed in this thesis
are not to be considered as a simple solution to a complex
problem, but it is hoped that they will stimulate a greater

demand for surveys of forest lands.

Future Requirements

The management of forest lands is dependent upon both
the administrative framework, and the technical capabilities
to execute these decisions. At the technical level, the
present state of the arts is quite adequate to provide methods
and information to aid in the development of management plans.
The literature on forest—soils relationships is voluminous,
and several techniques have been devised and used to separate
these significant features in the field. So why is it that
soils still have such a low priority in forest management
plans?

The answer must lie with the level of importance soils have
'been granted up to the present time. Soils as yet, have not
‘been recognized as the base on which to make decisions. It
appears that before soils are elevated to a position of pri-

ority they deserve, several difficulties must be overcome.

 

70

Lack of Information

The present lack of soils information is apparent in
the absence of past and current soil studies, which could
serve as a management tool. Soil studies cannot be expected
to be conducted in these forested areas until there is a
demand for them.

This cycle of waiting for a soil or land survey to
prove its worth, which in turn, depends upon 'a demand for such
surveys must be broken. To trust that one part of the cycle
will accelerate the other is to take an unacceptable risk
that nothing, or too little will happen. A co-pperative
demonstratable project involving both private and public
organizations may be a solution to this dilemma. The univer—
sity of British Columbia Research Forest is suggested as a
suitable place for such a project. The area already has been
mapped and classified by Lacate and it would be worthwhile to
see some use made of his survey, if nothing else but to make
suggestions as to Where refinements are necessary for particu-
lar purposes.1 The Research Forest could serve as a valuable
place to bring all agencies involved in managing the
Province's forest together, to exchange information among the
disciplines involved. Previous experiences of soil scientists
and foresters working together has resulted in a better

understanding of soil and plant relationships.

 

1Ibid.

 

71

Furthermore, the Research Forest would be an ideal
place to conduct research projects tailored to the numerous
unsolved problems that still face the forest industry.
Examples of research projects might be: (1) studies on which
tree Specie or Species should be planted on what kinds of r
soils, in.grder to obtain Optimum seedling survival and future
growth, (2) which soils Should receive tOp priority in ferti—
lization projects and other silvicultural treatments, and at
what stage of the stand history, and (5) on what kinds of
soils is slash burning most detrimental or beneficial and
investigations into what alternatives can be used to diSpose

of slash on those soils where burning has an adverse effect.

Lack of Suitable Research Projects

As mentioned earlier, much of the past research con-
ducted on forest soils has limited value since there were no
previous soil surveys to act as a guide. The extent of the
studied soils is unknown therefore, and may not be repre-
sentative of the area in general.

Before future research is conducted, a second look
should be given as to the kind of research being conducted.
The value of pure research should be carefully weighed in
comparison to applied research. At present, the need is
greatest for solving the routine problems Of soil classifi—
cation and interpretation, and use and management of forest
lands. Without seeking the adequate basic information supplied

‘by a suitable survey! the manager may become completely

 

72

frustrated by the limited benefits of the data obtained from
a costly research project. In the future, considerable
preliminary screening should be done to ensure that the
important soils and plant Species are being tested for yield
and performance. It is more important to limit testing to a
few key soils whose characteristics and responses are widely
different than to test a number of nearly similar soils or

soils of minor importance.

 

Lack.of.Qualified.Personnel

 

The limited number of trained soil Specialists presently
employed in the Province is also part of the problem. Because
of their absence, projects SO necessary for creating a greater
interest in soils are not undertaken. Training of personnel
qualified in another discipline to be a jack-of-all-trades is
not recommended, nor is the tailoring of a simple approach to
a complex problem the solution. Success in understanding the
importance of soils and having trained personnel to conduct
apprOpriate research can only be obtained by creating a demand
for them.

It is hOped that once such a demand exists, it will be
reflected in the curricula of the reSpective universities.

These three main obstacles, (1) lack of information,
(2) lack of suitable research projects ready for implementa-
tion, and (5) lack of qualified personnel, must be overcome
before the Province can be considered ready to plan for a

program of more intensive forest management.

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Chronicle, XLII, No. 2 (June 1966), 184-94.

Lemmon, Paul E. "Factors Affecting Productivity of Some
Lands in the Willamette Basin of Oregon for Douglas-fir
Timber." Journal of Forestry, LIII, No. 5 (May 1955),
525-50..

Rennie, P. J. "Methods of Assessing Forest Site Capacity.“
Forest Research Branch, Contribution No. 545,
Commonwealthtgorestry Review, Vol. XLII, No. 4 (December

Rowe, J. Stanley.r "Soil, Site and Land Classification."
Forestry Chronicle, XXXVIII, No. 4 (December 1962),
420-52.

Smith, J. Harry G., and Ker, John W. "Some Problems and
Approaches in Classification of Site in Juvenile Stands
of Douglas Fir.“ Forestry Chronicle, XXXII, No. 4
(December 1956), 417-28.

Tackel, David. Silvips of Lodgepole Pine. Intermountain
Forest and Range Experiment Station, Miscellaneous
Publication No. 19. Ogden, Utah: U. S. Department of
Agriculture, Forest Service, May 1959.

Trimble, G. R. Jr., and Weitzman, Sidney. "Site Index Studies
of Upland Oaks in the Northern Appalachians." Forest
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White, Donald P., and Heiberg, Svend O. "A Site Evaluation
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1965), 7-10.

Zahner, Robert. "Site-Quality Relationships of Pine Forests
in Southern Arkansas and Northern Louisiana." Forest
Science, IV, No. 2 (June 1958), 162-76.

Zumberge, J. H. Field Procedures fQEfSoil-Site Classification
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Southern Forest Experiment Station, Occasional Paper
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82

Unpublished Material

Ainscough, G. L. Personal Letter. Assistant Chief Forester,
MacMillan Bloedel Limited. Forestry Division.
Vancouver, B. C., March 13, 1968.

Burch, W. G. Personal Letter. -Chief Forester, British
Columbia Forest Products Limited. Vancouver, B. C.,
February 14, 1968.

Green, Alix J., and Lord, Terry M. "Soil Survey of the
Princeton Map Area, British Columbia." Canada Depart-
ment of Agriculture, Research Station. Vancouver, B. C.
(In preparation).

Lacate, D. S.; Arlidge, J. W. C.: Sprout, P. N.; and Moss, A.
"Forest Land Classification and Interpretations for
Management in the Spruce Working Circle, Tree Farm
License No. 9, Okangan Valley, B. C." B. C. Department
of Agriculture, Co-operative Interim Report. Kelowna,
B. C.: July 1965.

 

Lord, Terry M. and Green Alix J. "Soil Survey of the Tulameen
Map Area, British Columbia." Canada Department of
Agriculture, Research Station. Vancouver, B. C. (In
preparation).

Mackintosh, E. E.; Sneddon, J. I.; and Farstad, L. “Soil
Survey of the Quesnel Area in British Columbia."
Canada Department of Agriculture, Soil Survey Report
No. 10 of the British Columbia Soil Survey (In prepara-
tion .

Spilsbury, Richard H. Personal Letter. Forester i/c.
Research Division, B. C. Forest Service, Victoria, B. C.
February 9, 1968.

 

APPENDICES

85

APPENDIX I
GENERALIZED PROFILE DESCRIPTIONS

Princeton Study Area
Bankeir Series

Bankeir sandy loam is a rapidly to well drained Orthic
Acid Brown WOOded soil that has develOped on non-calcareous
sandy loam till. These soils occupy bedrock ridges, upper
valley slopes and crests of rock-cored drumlins. Topography
is moderately and strongly SIOping on units of rock outcrOp
and strongly and very steeply SIOping on valley steeplands.
The slope gradient varies from 15-60 per cent.

The relatively thin mantle of till comprising the sola
of Bankeir soils is derived mainly from volcanic rock types,
but frequently overlies granithcintruSions. This soil has
thin litter horizons (L-F), and brownish colored Bf horizons
that grade into sandy loam or loam BC horizons. The BC
horizons break into shattered bedrock, usually at a depth of
24 inches or less. A generalized profile of the series if

described below:

Horizon Depth Description
L §'- é-inches Fresh grass, leaves, and twigs.
F-H -§ - 0 inches Partially decomposed litter with some

bleached mineral grains scattered
through the lower boundary zone.

84

85

Bfl O - 4 inches Pale brown and dark yellowish brown
sandy loam; fine granular and weak,
fine subangular blocky; very friable,
slightly plastic; gradual boundary.

Bf2 4 - 11 inches Pale brown and dark yellowish brown
loam; medium and coarse subangular
blocky; firm, plastic, slightly
sticky; gradual boundary.

BC 11 - 24 inches Brown and dark brown to dark yellowish
brown sandy loam; medium and coarse
subangular blocky; very firm, plastic,
slightly sticky; abrupt lower boundary.

R -24 inches plus Smooth, slightly weathered andesitic
rock.

 

Mazama Series

Mazama sandy loam is a well drained to moderately well
drained Degraded Acid Brown Wooded soil that has develOped on
non-calcareous sandy loam tills. These soils occupy upper
and middle valley slopes and sides of drumlins. Topography
is moderately 310ping. The lepe gradient varies from 6-9
per cent.

The glacial till comprising the sola of Mazama soils
is derived mainly from volcanic rock types. This soil has a
thin litter horizon (L-F), a thin light colored Ae horizon,
a brownish colored Bf horizon that grades into sandy loam BC
horizons. The C horizon is a brownish sandy loam. A general-

ized profile of the series.is described below:

Horizon Depth Description
L §'- fi'inches Fresh grass, leaves, and twigs.
F—H §-- 0 inches Partially decomposed litter with some

bleached mineral grains scattered
through the lower boundary zone.

86

Ae §-- 1 inch Pale pink, sandy loam; granular and
weak, very friable, abrupt lower
boundary.

Bf 1 - 12 inches Pale brown, and dark yellowish brown,

sandy loam to loam; medium sub-
angular blocky, friable, plastic,
slightly sticky; gradual boundary.

BC 12 - 26 inches Brown, and dark brown to dark yellow-
ish brown sandy loam; medium and
coarse subangular blocky; very firm,
plastic, slightly sticky; gradual
boundary.

C -26 inches plus Brownish sandy loam.

Pefferle Series
Pefferle series is a imperfectly drained Gleyed Cutanic
Podzo Regosol that has develOped on non-calcareous sandy loam
till. Topography is gently to moderately sloping. The s10pe
gradient varies from 2-9 per cent.
The soil has a thin litter horizon, a light gray Ae
horizon, a gleyed Btj horizon and a Cg horizon at a depth of

26 inches. A description of Pefferle series is given below:

Horizon Depth Description

L-H 1 - 0 inches Pine needles and litter partially
decomposed.

Ae O - 5 inches Light gray and brown sandy loam,
granular, very friable; abrupt
boundary.

Btj 8 - 15 inches Light gray and grayish brown loam
‘with few, fine and faint, brown and
yellowish brown mottles; medium
subangular blocky; firm; many fine
roots; clear boundary.

Btjg 15 - 24 inches Light gray to grayish brown loam

with fine, distinct brown and dark
yellowish brown mottles; subangular
blocky; gradual boundary.

87

BCg 24 - 26 inches Light gray and grayish brown to
light olive brown loam with many fine,
prominent brown and yellowish brown
mottles; medium subangular blocky;
gradual boundary.

Cg -26 inches plus Light gray and grayish brown sandy

loam; fine, distinct olive brown
mottles; medium blocky; few roots.

Erris Series
Erris series is a poorly drained orthic Gleysol occur—
ring on gentle to moderately leping tOpography. The lepe

gradient varies from 2-9 per cent.

A description of Erris series is given below:

Horizon Depth Description
L-H 2 - 0 inches Decaying leaves and needles.
Ah 0 - 6 inches Black mucky loam; coarse granular

structure, friable; abundant fine
and coarse roots; clear boundary.

Aejg 6 - 17 inches Variegated colors, loamy sand and
gravel, single grain structure;
loose, few roots; clear boundary.

Btjg -17 inches plus Olive gray loam with medium,
prominent mottles of brown to dark

brown, medium subangular blocky
structure; very few roots.

Quesnel Study Area

Beaverly Series
The Beaverly series are moderately well drained and
are classified as Orthic Gray Wooded. These soils, develOped
on glacial lacustrine deposits, occur on convex slopes and
knolls of undulating topography. The SIOpe gradient varies

from 6-9 per cent.

 

88

This soil has thin litter horizons (L-F), a light
brownish colored Ae horizon and a grayish brown Bt horizon
that grades into a gleyed Cg horizon at a depth of 27 inches.

A generalized description follows:

Horizon Depth Description
L-F 1 - 0 inches Grass and needle litter.
Ae O - 7 inches Light brownish gray, and dark

grayish brown, silty clay; moderate,
medium, platy structure.

Bt 7 - 27 inches Grayish brown and very dark grayish
brown, clay; coarse prismatic
structure; faint mottling along root
channels in lower part of horizon.

Cg -27 inches plus Light gray to light olive gray clay;
yellowish brown mottles; stratified.

Pineview Series
The Pineview series are imperfectly drained and are
classified as Gleyed Gray Wooded. These soils, develOped on
glacial lacustrine deposits, occur on concave and lower slopes
of undulating topography. The slope gradient varies from 6-9

per cent.

A generalized description follows:

Horizon Depth Description
H 2 — 0 inches Forest litter.
Aeg O - 5 inches Light gray to light brownish gray,

silty clay; moderate medium platy
structure; roots abundant.

Btg 5 - 12 inches Grayish brown to dark yellowish
brown, clay; coarse, prismatic
structure; roots common.

 

89

Btgj 12 - 25 inches Light gray to brownish gray, clay;
coarse prismatic; distinct mottles
with small pockets of gray gley;
occasional roots; clear boundary.

Cg -25 inches plus Light gray to light olive gray, clay;
yellowish brown to brown mottles;
stratified.

Moxely Series
The Moxely series are very poorly drained and are
classified as Orthic Humic Gleysols. These soils occur in

enclosed depressions or relatively flat lying areas. The lepe

 

gradient varies from 0-5 per cent.

A generalized description follows:

Horizon Depth Description
L-H 2 - 0 inches Decaying leaves and needles.
Ah 0 - 11 inches Black mucky loam; granular structure,
friable; abundant fine and coarse
roots.

Btjg 11 - 29 inches Olive gray, clay; prominent mottles
of brown to dark brown; coarse
prismatic structure.

Cg -29 inches plus Olive gray, clay; yellowish brown
to brown mottles; stratified.

APPENDIX II

FOREST CAPABILITY CLASSES, LIMITATIONS
AND PRODUCTIVITY
In the classification system outlined by McCormack
(1967) pages 4-6, all mineral and organic soils are classi-
fied into one of seven classes based upon their inherent
ability to grow commercial timber. Class 1 represents the
best lands for commercial tree growth, while Class 7 represents

the poorest.

 

 

 

 

 

 

 

 

Capability Limitations to growth Productivity
class of commercial forests cubic feet/acre/year

1 No important limita- 111+
tions

2 Slight limitations 91-110

5 Moderate limitations 71- 9O

4 Moderately severe 51- 7O
limitations

5 Severe limitations 51- 50

6 Severe limitations 11- 50

7 Limitations of such a _O- 10
severe nature as to
preclude the growth of
commercial forests

 

 

 

 

 

90

APPENDIX III
SOIL DRAINAGE CLASSESl

Soil drainage classes are defined in terms of (1) actual
moisture content in excess of field moisture capacity, and
(2) the extent of the period during which such excess water is
present in the plant-root zone.

It is recognized that permeability, level of ground

 

water and seepage are factors affecting moisture status.
However, because these are not easily observed or measured in
the field, they cannot be used generally as a criteria of
moisture status.

Topographic position and vegetation as well as soil
morphology are useful field criteria for assessing soil mois—

ture status.

Rapidly drained.--Soil moisture content seldom exceeds field
capacity in any horizon except immediately after water addi-
tions.

Soils are free of any evidence of gleying throughout
the profile. Rapidly drained soils are commonly soils of

coarse texture or soils on steep s10pes.

 

1Source: National Soil Survey Committee, Report on the
Sixth Meeting of the National Soil Survey Committee of Canada,
(Laval University, Que.; [n.p.], October, 1965), pp. 125-24.

91

92

Well drained.--Soil moisture content does not normally exceed
field capacity in any horizon (except possibly the C) for a
significant part of the year.

Soils are usually free of mottling in the upper three
feet, but may be mottled below depths of three feet. B hori—

zons, if present, are reddish, brownish, or yellowish.

Moderately well-drained.-—Soil moisture in excess of field
capacity remains for a small, but significant period of the
year.

Soils are commonly mottled in the lower B and C hori-
zons or below a depth of two feet. The Ae horizon, if
present, may be faintly mottled in fine-textured soils or in
medium—textured soils that have a slowly permeable layer below

the solum.

Imperfectly drained.--Soil moisture in excess of field capa-
city remains in subsurface horizons for moderately long
periods during the year.

Soils are commonly mottled in the B and C horizons;
the Ae horizon, if present, may or may not be mottled. The
matrix generally has a lower chroma than in the well-drained

soil or similar parent material.

Poorly drained.--Soil moisture in excess of field capacity
remains in all horizons for a large part of the year.
Soils show evidence of strong gleying. -Except in high

chroma parent materials, the B, if present, and upper C

 

95

horizons have matrix colors of low chroma. Faint mottling

may occur throughout.

Very poorly_drained.--Free water remains at or within 12
inches of the surface most of the year.

Soils show evidence of very strong gleying. .Subsurface
horizons are of low chroma and yellowish to bluish hues.
Mottling may be present, but at depth in the profile. Very
poorly-drained soils usually have a mucky or peaty surface

horizon.

 

APPENDIX IV

SUPPORTING PLOT DATA FOR DETERMINING
CAPABILITY CLASS RATING

Princeton Study Area

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

No. of Plots Species Range in Capa-
Soil Name Classification Sampled Sampled M.A.I.100 bility
Class
Bankeir Orthic Acid 5 IP 51-41 5
Brown Wooded
IMazama Degraded Acid 7 IP 50-69 4
Brown Wooded
Pefferle Gleyed Cutanic 4 lP 77-91 5
Podzo Regosol
Erris Rego Gleysol 1 e5 66 4
Qgesnel Study Area
No. of Plots Species Range in Capa-
Soil Name Classification Sampled Samples M.A.I. bility
100
#7 Class
Beaverly Orthic Gray 4 1P 51-69 4
Wooded
Pineview Gleyed Gray 4 1P 64-87 3,4
Wooded
IMoxely Peaty Gleysol 6 b8 7-29 6-7

 

 

 

 

 

 

 

94

APPENDIX V

PARENT MATERIALS

Parent material refers to the initial state of the soil
system, and includes the C horizon and other materials above
the C from which the soil develOps.

A brief description of the main parent materials occur-

ring in British Columbia follows.

Alluvium.-—Refers to those materials moved and redeposited by
water. It may occur in terraces well above present streams
or in the normally flooded bottoms of existing streams.
Texture can vary from fine silty materials deposited in quiet
waters to coarse deposits, often consisting of large boulders.
Stones and rock fragments are rounded and well worked. Sort-

ing is usually evident.

Colluvium.--Is the unsorted or slightly sorted material at

the base of slopes, accumulated largely as rock fragments

that have fallen down the slope under the influence of gravity.

In its extreme form, this material is called talus. Rock
fragments are angular in contrast to the rounded, water-worn

cobbles and stones in alluvial terraces and glacial outwash.

95

 

 

96

Glacial till.--Glacial till is generally an unstratified,
unconsolidated, heterogeneous mixture of clay, silt, sand
and gravels, and sometimes boulders. Unworked till is often
very compacted, eSpecially when it is dry. Rock fragments

are usually angular in shape.

Glaciofluvialydeposits.--These deposits are made up of materi-
als produced by glacier and carried, sorted and deposited by ”I

water that originated mainly from the melting of glacial ice.

 

Such deposits can often be found at elevations considerably i

above present stream channels.

Lacustrine deposits.--These deposits consist of materials that
have settled out in the quiet water of lakes. These deposits
with a predominate silt and clay texture are usually stone—

free and are stratified.

Loess.--These are wind deposits consisting of silts or very
fine sands. Such deposits in British Columbia often exist

as a thin capping over another parent material.

Marine sediments.--These sediments have been reworked by the
sea, and later exposed through surface uplift following the
retreat of glaciation. .These deposits resemble lacustrine
deposits, are fine textured and may or may not contain remi-

nants of marine shells.

97
SOIL TEXTUREl

In the field, soil texture is determined by the feel
of moist soil when it is rubbed between the thumb and fingers.
Since sand particles feel gritty, silt particles have a
smooth velvety feel and clay is both sticky and plastic,
an estimate of the relative proportions of the separates may
be made. This procedure, of course, will not give the exact
percentage of sand, silt, and clay; but, with a little prac-

tice on samples of known composition, the relative prOportions ‘ ‘

 

of the individual separates can be closely estimated. Practice
with known samples is the only way to acquire this facility.
The ability to determine texture in the field by this method
is one of the most valuable practical skills a student of
soils can possess.

The outstanding physical characteristics of the main
textural grades as determined by the feel of the soil are

described below.

Sandy soil.--Sandy soil is loose and single grained. The

individual grains can be seen readily or felt. Squeezed in
the hand when dry, it will fall apart when pressure is re-
leased. Squeezed when moist, it will form a cast, but will

crumble when touched.

 

1Source: U. S. Department of Agriculture, Handbook on
Soils, Forest Service, ([n.p.], 1961, plus 1965 and 1966
Amendments), pp. 87-88.

 

98

Sandy loam soil.--Sandy loam soil contains much sand, but

has enough silt and clay to make it somewhat coherent.
Individual sand grains can be easily seen and felt. Squeezed
when dry, it will form a cast which will readily fall apart;
but if squeezed when moist, a cast can be formed which will

bear careful handling without breaking.

Loam soil.--Loam soil is about an equal mixture of the sands
and silt with the clay content being between 7 and 27 per

cent. A loam_is mellow with a somewhat sandy feel, yet fairly

 

smooth and slightly plastic. Squeezed when moist, it will

form a cast which can be handled freely without breaking.

Silt loam soil.—-Silt loam soil, when dry, may appear cloddy,
but lumps are readily broken, and when pulverized, it feels
soft and floury. When wet, the soil readily runs together.
Either dry or moist, it will form casts which can be handled
freely without breaking, but when moistened and extruded be-
tween the thumb and fingers, it will not form a ribbon, but

will give a broken appearance.

Clay loam soil.—-Clay loam soil is fine-textured soil which
usually breaks into clods or lumps that are hard when dry.
When moist soil is extruded between thumb and fingers, it
will form a thin "ribbon" which will break readily, barely
sustaining its own weight. The moist soil is plastic and

will form a cast that will bear much handling. When kneaded

99

in the hand, it does not crumble readily, but tends to work

into a heavy, compact mass.

Clay soil.--Clay soil is a fine-textured soil that usually
forms very hard lumps or clods when dry and is plastic and
sticky when wet. 'When the moist soil is ribboned out between
the thumb and the fingers, it will form a long flexible strip.
A clay soil leaves a "slick" surface on the thumb and fingers
when rubbed together and tends to hold the thumb and fingers

together due to the stickiness of the clay.
SOIL STRUCTURE1

The sand, silt, and clay particles of soils rarely
exist as discrete units or single particles but usually as
aggregates of particles. These aggregates are collectively
called soil structure. Since this soil characteristic is
not easily measured and there are no precise, single-valued
expressions for structure, descriptions must be used. There

are four basic geometric forms of structure.

Platy.--Platelike or flat with one dimension (the vertical)

being much shorter than the other two dimensions.

Prismatic.--Prismlike with the vertical dimension being sever—

al times greater than the two horizontal dimensions. Vertices

 

lSource: U. S. Department of Agriculture, Handbook on
Soils, Forest Service, ([n.p.], 1961, plus 1965 and 1966
Amendments), p. 90.

 

 

100

are angular. There are two varieties of prismatic structure:
(1) columnar when the t0p of the prism is rounded and

(2) prismatic when the tOp of the prism is flat.

Blocky.—-Cube1ike or blocky when the three dimensions are of

about the same size. The surface of blocky peds are casts

of molds formed by faces of the surrounding structural peds.
There are two varieties of blocky structure: (1) angu-

lar blocky--faces flat, most corners are sharply angular and

(2) subangular blocky--faces mostly rounded, corners mostly

 

rounded.

Spheroidal.--Rounded or Spherelike with all axes equal and
having curved surfaces that are not related to the faces of
surrounding units. These units are often referred to as

granules.

Structureless.--That condition in which there is no definite

 

arrangement of the primary particles. When the particles
are coherent they are called massive; when non-coherent, they
are called single grain.

The size of the individual structural units is indie
cated by the terms "very fine," "fine," "medium," "coarse,"
and "very coarse." The size limitations of these categories
vary with the structural type. The grade of the soil struc-
ture may be expressed as weak, if the structural units are
not very evident in the soil mass; moderate, if they are evi-

dent but not distinct; and strong, if very evident in the soil.

II.
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