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THE RELATIONSHIP BETWEEN SOILS
AND VEGETATION
M. Hironaka
Maynard A. Fosberg
Kenneth E. Neiman, Jr.
The numerous failures suggest that a basic soil!
vegetation reI ati on shi p does not exist or something fundamental has been overlooked. The sporadic successes in
correlating soils with vegetation appear to be locally significant, but are not applicable elsewhere. Johnson and
Simon (1987) had some success in broad relational correlations; for example, Festuca idahoensis occurred on loess
soils, whereas Agropyron spicatum did not, Pseudotsuga
menziesii and Pinus ponderosa occupied soils without
Mazama ash, and Abies grandis and Abies lasiocarpa were
associated with soils without ash. Although supported with
data from 775 intensively sampled plots, they were unable
to extrapolate their correlations between soils and vegetation outside their area of study. The high number offailures that have been published is surely dwarfed by the
number of studies that were not reported. A review of
some of the basic concepts appears in order.
ABSTRACT
Numerous studies have failed to show consistent relationship between soils and vegetation. A review of basic concepts of soil and vegetation development indicates that
vegetation and soils are mutually associated with each
other, both being the product of the same environmental
variables. The mutual association is between the whole
soil and vegetation, not individual soil properties and vegetation or selected attributes of vegetation. At any scale
beyond a very localized application, a universal correlation
does not exist between soil properties and vegetation attributes. Even within very restricted geographic bounds, variation between attributes can yield untenable results. Soil
bodies, when grouped and classified at the soil series level,
should correlate reasonably well with habitat type. Conceptually, each habitat type is associated with a unique set of
soil series.
FUNDAMENTAL SOIL EQUATION
INTRODUCTION
.....
Let us start with Jenny's (1941, 1958) widely accepted
basic soil formation equation:
Numerous studies have attempted to correlate climax
vegetation and soils (Daubenmire 1970; Daubenmire and
Daubenmire 1968; Jensen and others 1990; Neiman 1988;
Sexton 1986; Tisdale and Bramble-BrodahI1983) and, in
general, the results have been disappointing. There have
been few successes demonstrating correlation between
selected soil properties and vegetation. Using factor analysis and multiple discriminant functions, Bunting (1978)
was successful in correlating selected soil properties with
major vegetation types in the Guadaloupe Mountains in
southwestern Texas. Working in an area where parent
materials were similar, Tisdale and Bramble-Brodahl
(1983) showed site variables, including soil pedon properties, discriminated between habitat types to a fair degree.
Klemmedson (1964), working with seral vegetation in a
very localized situation, demonstrated the relationship
between site factors and vegetation.
In general, studies involving soils derived from different
parent materials have done poorly (Neiman 1988; Sexton
1986). Attempts to predict tree site index using selected
soils and site properties have been inconsistent (Copeland
1958; Monserud 1990).
Soil = f(climate, parent material, relief, organisms, time)
This tells us that if the soil pedons at two different points
on the landscape have, in all details, the same kinds and
intensities of soil properties, the soils of the two places are
the same and they have had the same developmental history. Conceptually, the productivity of the soil at the two
places also would be the same, because the physical and
chemical properties of the soil at the two places would be
the same. And, should the soil pedons be classified according to conventional soil classification standards, they would
be classed as members of the same soil series, the basic
unit of soil classification.
VEGETATION-SOIL DEVELOPMENT
A less familiar concept is that each soil body is associated
with a specific climax vegetation. This is supported by
Major's (1951) deduction and rationale that the same environmental factors responsible for soil formation are also
responsible for the vegetation that is produced. The same
independent variables involved in the soil equation are
included in his equation on plant community:
Vegetation
Paper presented at the Symposiwn on Management and Productivity
of Westem-Montane Forest Soils, Boise, ID, April 10-12, 1990.
M. Hironaka is Professor, Department of Range Resources, University
ofIdaho, Moscow, ID 83843. Maynard A. Fosberg is Professor, Department of Soil Science, University ofIdaho. Kenneth E. Neiman, Jr., is
Terrestrial Ecologist, Parametrix, Inc., Bellevue, WA 98004.
=f(cl, pm, r, 0, t)
A particular climax vegetation as well as a specific soil
would result under a fixed set of independent variables.
Vegetation, like soil, is the product of the same group of
29
with habitat type classification, the range site classification would be comparable to the habitat type phase,
if the phase were to be based on productivity (Hironaka
1986). If one were to group all range sites capable of supporting the same climax vegetation, the group of range
sites would be equivalent to a habitat type (Hironaka
1986). Therefore, range sites represent differences in
productivity within a habitat type. Unfortunately, the
nomenclature of the range site classification does not
identify or allude to the climax vegetation, and grouping
of range sites into habitat types cannot be easily done.
independent variables. Vegetation and soil mutually
influence each other and neither is the result of the other
(Jenny 1958; Major 1951).
The two fundamental equations show that a soil body
is associated with a specific plant community, the climax
plant community. This is an important point. This means
that all points on the landscape with the same soil are
associated with the same climax plant community, the
same plant association, and the same habitat type. The
plant association is the basic classification unit of climax
vegetation and the habitat type is the land classification
unit that supports or supported a particular plant association (Daubenmire and Daubenmire 1968).
Different soils are known to support the same climax vegetation (Daubenmire 1979; Daubenmire and Daubenmire
1968; Hironaka and others 1983; Neiman 1988). The fact
that the same aggregate of plants can grow and thrive on
different soils means the same climax vegetation can be
supported on more than one soil. This phenomenon is
explained by factor compensation of plants. Plants are
able to grow and thrive over a range of conditions, permitting the same plant community to occur on different soils.
FOREST SITE PRODUCTIVITY
The site index has been a primary means of assessing
forest site productivity. In essence, the average height of
dominant trees at age 50 or 100 years is used as the site's
index of productivity. Site index curves have been developed for various timber species for local and regional
interpolation. To estimate site index from soil and site
characteristics, attempts have been made to correlate
known index values with site and soil parameters to
develop prediction equations. Recently, using stem analysis to get direct measure of site index of inland Douglasfir, Monserud (1984) found that site index for old inland
Douglas-fir tended to drop off considerably because the
older measured trees occurred on "poorer" and more inaccessible sites. This suggested that the older trees occurred on different and less productive soils. In a followup study Monserud and others (1990) attempted to correlate site and soil factors with site index by partitioning
the habitat type series. They came to the overall conclusion that site index correlations with site and soil variables were not very reliable.
Jenny's (1941) contention that no soil property can be
universally correlated with property of vegetation and
Major's (1951) stress that mathematically there are no
universal correlations between vegetation and soil properties as neither is determined by the other have been
ignored. In a nutshell, this is the basic reason why seeking of mathematical correlation of soil properties and
vegetation has failed in the majority of cases. Only with
studies where the independent variables have been sufficiently constrained have meaningful correlations been
demonstrated. It would appear that the forest site index
would be closely predicted by the soil series. It is something to think about.
SOILS AND HABITAT TYPE
The relationship between soils and habitat type has not
been easy to demonstrate because of fuzziness of how much
variation we include in our abstract classification units of
soil and vegetation. Conceptually, the units can be defined,
but the problem is whether they are sufficiently close to
ecological reality. Because of the lack of undisturbed vegetation, we are unable to confirm whether our assumptions
about vegetation are correct.
Assuming we are correct, each soil series is associated
with a particular climax community, and in turn with a
particular habitat type. Otherwise, Major's (1951) vegetation equation is flawed. Since it is likely that more
than one soil series is associated with the same climax
community, by definition then, each habitat type is associated with a unique climax vegetation and a unique set of
soils. It also tells us that all soils included in a soil series
are associated with a single habitat type and no other.
Should this not be the case, the soil or the habitat type
is misclassified.
Not only should all soils of a soil series support the same
climax community, they should also have the same productivity. It must be kept in mind that soils of different soil
series may possess the same productivity. While differences in pedon properties or intensities justify placing
soils in different soil series, the differences may not affect
productivity because of plant compensation. That is to say,
soils of different soil series may possess the same level of
productivity.
SOIL CLASSIFICATION AND FOREST
AND RANGELAND MANAGEMENT
The practice of classifying and mapping soils at the soil
family level of classification does not work very well for
intensive land management. This is especially true when
it is not used in conjunction with the habitat type classification. The soil family class groups soil series on the
basis of broad textural, mineralogical, and soil climate
similarities. This level of classification often includes
soils of different habitat types and productivity levels,
and greatly weakens the reliability and effectiveness
of management prescriptions.
SOILS AND RANGE SITE
The concept that soil series and productivity go together
in wildland management is the basis of the range site classification (Shiftlet 1973). Here each unit includes soils of
several soil series of similar productivity that support or
supported the same climax vegetation. For those familiar
30
For intensive management of forests and rangelands,
a baseline soil map at the soil series level of classification
is something to work toward. Used in conjunction with
habitat type, community type, and topographic maps (GIS
overlays), much could be known about any piece of land
before leaving the office. Supported by an information
storage/retrieval system based on habitat type, community
type, and soil series and soil series phase, much detailed
management information could be made available concerning any piece of inventoried landscape. More important, it
would provide a means whereby new information relating
to land treatment and responses can be inputted and retrieved for later use by the next generation ofland managers. The new generation of land managers need not
reinvent the wheel as we have repeatedly done in the past.
Jenny, H. 1941. Factors of soil formation. New York:
McGraw-Hill. 281 p.
Jenny, Hans. 1958. Role of the plant factor in the pedogenic functions. Ecology. 39: 5-16.
Johnson, C. G.; Simon, S. A. 1987. Plant associations of the
Wallowa-Snake Province, Wallowa-Whitman National
Forest. R6-ECOL-TP-255a-86. Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific Northwest Region. 400 p.
Klemmedson, James O. 1964. Topofunction of soils and
vegetation in a range landscape. In: Forage plant physiology and soil-range relationships. American Society of
Agronomy Spec. Publ. 5. Madison, WI: American Society
of Agronomy: 176-189.
Major, Jack. 1951. A functional, factorial approach to plant
ecology. Ecology. 32: 392-412.
Monserud, Robert A. 1984. Height growth and site index
curves for inland Douglas-fir based on stem analysis data
and forest habitat types. Forest Science. 30: 943-965.
Monserud, R. A.; Moody, U.; Breuer, D. W. 1990. A soil-site
study for inland Douglas-fir. Canadian Journal of Forest
Research. 20: 686-695.
Neiman, Kenneth E., Jr. 1988. Soil characteristics as an
aid to identifying forest habitat types in northern Idaho.
Res. Pap. INT-390. Ogden, UT: U.S. Department of Agriculture, Forest Service, Intermountain Research Station.
16 p.
Sexton, William T. 1986. Selected forest soil-parent material relationships in the Clearwater and Nez Perce National Forests. Moscow, ID: University of Idaho. 85 p.
Dissertation.
Shiftlet, Thomas N. 1973. Range sites and soils in the
United States. In: Hyder, D. N., ed. Arid shrublands.
Proceedings 3rd workshop ofU.S'/Australia Rangelands
Panel. Tucson, AZ. Denver, CO: Society for Range
Management: 26-33.
Tisdale, E. W.; Bramble-Brodahl, Mary. 1983. Relationships of site characteristics to vegetation in canyon
grasslands of west central Idaho and adjacent areas.
Journal of Range Management. 36: 775-778.
REFERENCES
Copeland, o. L., Jr. 1958. Soil-site index studies of western
white pine in the northern Rocky Mountain region. Soil
Science Society of America Proceedings. 22: 268-269.
Daubenmire, R. 1979. Steppe vegetation of Washington.
Tech. Bull. 62. Pullman, WA: Washington Agricultural
Experiment Station, Washington State University.
131 p.
Daubenmire, R.; Daubenmire, Jean B. 1968. Forest vegetation of eastern Washington and north Idaho. Tech.
Bull. 60. Pullman, WA: Washington Agricultural Experiment Station, Washington State University. 104 p.
Hironaka, M. 1986. Habitat type, range site, and community type. In: McArthur, E. D.; Welch, B. L., compilers.
Proceedings-symposium on the biology of Artemisia and
Chrysothamnus. Gen. Tech. Rep. INT-200. Ogden, UT:
U.S. Department of Agriculture, Forest Service, Intermountain Research Station: 15-18.
Hironaka, M.; Fosberg, M. A.; Winward, A. H. 1983.
Sagebrush-grass habitat types of southern Idaho.
Bull. 35. Moscow, ID: University of Idaho, Forestry,
Wildlife and Range Experiment Station. 44 p.
Jensen, M. E.; Simonson, G. H.; Dosskey, M. 1990. Correlation between soils and sagebrush-dominated plant
communities of northeastern Nevada. Soil Science Society of America Journal. 54: 902-910.
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