The Pattern of Influence of Individual Forest Trees on Soil Properties
Author(s): Paul J. Zinke
Source: Ecology, Vol. 43, No. 1 (Jan., 1962), pp. 130-133
Published by: Ecological Society of America
Stable URL: http://www.jstor.org/stable/1932049
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REFERENCES
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130
Ecology, Vol. 43, No. 1
REPORTS
cache of seeds which were later identified as C. album "just like a jar," according to the finders. The top of
(Fig. 1). The seeds were in a circular, straight-sided the cache was roughly level with the lower portion of the
hole about 15-17 cm wide and 20-22 cm deep that was 10- to 12-cm-deep occupation layer. The finders stated
*
0
..
-
that the soil layer over the cache was intact with no
evidence of former burrows or other disturbance. The
4-5 liters of seeds were all as clean as that in Figure 1.
Unfortunately, the finders did not recognize the possible
significance of the find and it was only as an afterthought that they retained about one cupful of the
material. There was no evidence of a container and no
photographs were obtained in situ. The seed sample
consisted of empty hulls but with vestiges of a primary
root adhering to many. The seed coats, a glossy black
color in fresh material, were dull and lusterless. Indications were that the seeds had germinated and the primary roots and cotyledons had later disintegrated, while
the hulls were preserved intact.
In view of the widespread use of C. album as a food
plant by primitive peoples, the apparent man-made characteristics of the storage hole, and the location of the
cache in relation to a former occupation site, it is suggested that this find provides further evidence of the
gathering and use of C. album by the Blackfoot Indians
in the prehistoric period.
*1
UX.
......
. ..j.............
REFERENCES
FIG.
1.
Seed of C.eonopodium
album from "Ross"
site: Top-showing condition of sample upon recovery,
and Bottom-close-up of individual seeds.
Blankinship, J. W. 1905. Native economic plants of
Montana. Mont. Agr. Exp. Sta. Bull. 56.
Budd, A. C. 1957. Wild plants of the Canadian
prairies. Can. Dept. Agr. Publ. 983.
Dempsey, Hugh A. 1960. Personal communication.
Forbis, R. G. 1957. Some late sites in the Oldman
River region, Alberta. Natl. Museum Can. Bull. 162.
Contributions to Anthropology.
Helbaek, H. 1960. Comment on Chenopodium album
as a food plant in prehistory.
Berichte, Des geobotanishen Institutes der Eidg. techn. Hochschule
31: 16-19.
Moss, E. H. 1960. Flora of Alberta. Univ. of Toronto
Press.
. 1961. Personal communication.
THE PATTERN OF INFLUENCE OF INDIVIDUAL FOREST TREES ON
SOIL PROPERTIES1
PAUL J. ZINKE
University of California, School of Forestry, Berkeley, California
INTRODUCTION
The soil under the influence of a forest develops properties that vary spatially with relation to the location of
the trees. This variation in soil properties is frequently
reflected in the distribution of the various species of the
ground flora. The amelioration or degradation of the
forest soil takes place with each tree as a center of influence. This paper reports the patterns of soil properties
which develop under individual trees with examples
drawn from work in the forested areas of California.
The literature of forestry and soil science has frequent
1 Presented at the IX International Botanical Congress, Symposium on the influence of forest vegetation on
Montreal.
the degradation and amelioration of soils.
August, 1959.
reference to the effect of different species on soil properties but there are relatively few papers dealing with
the spatial variation in these soil properties relative to
individual forest trees. Among these papers a classic is
P. E. Muller's (1887) description of the occurrence of
distinctive mull humus soils under each clump of oak
trees cn otherwise podzolized soils of heath lands in
Denmark. Jamison (1942) noted that certain soil properties varied systematically with distance from individual orange trees in orchards in Florida. Harradine
(1954) observed that in California forests where Pinus
ponderosa Laws. and Quercus kelloggii Newb. were
mixed there was less soil nitrogen in the open than under
the influence of the pines or oaks. Fireman and Hayward
(1952) found a distinctive pattern of occurrence of exchangeable sodium under various shrub species in the
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Winter 1962
Escalante desert in Utah.
Sodium was high under
Sarcobatus vermiculatus (Hook.) Torr. and low under
Arternesia trideiitata Nutt. Muller and Muller (1956)
noted that in desert areas the occurrence of herbaceous
ground vegetation was associated with the influence of
individual shrubs on the soil. The general pattern apparent from these studies is that the individual plant is
a center from which soil properties may vary in a predictable manner. This paper reports an evaluation of
these effects by sampling soils systematically with relation to individual forest trees in California and determining the properties of these soils.
VARIATION
UNDER
A SINGLE
Pinus cantorta
The effect of a single tree on patterns of soil properties was evaluated by sampling under a 45 yr old shore
pine (Pinus contorta Dougl. ex Loud) growing on a sand
dune area one mile inland from the Pacific Ocean near
Cresent City in northwestern California. The mineral
soil was sampled to a depth of 2X2 in. at distances of 1,
4, 8, 12 and 16 ft from the tree on 4 transects at right
angles to each other. The tree had a crown proj ection
radius of approximately 12 ft. Two of the sampling
transects outward from the tree were parallel to the
prevaling winds in the area which during clear weather
come from the northwest, and during storms and moist
weather come from the southeast. The other transects
were at right angles to these directions.
Soils were
sampled for volume weight and a bulk sample. The
bulk samples were analyzed for pH, total nitrogen
content on all transects, and exchangeable bases on one
transect.
The volume weight of soil on all 4 transects increased
with distance from the tree. It varied from 1.17-1.32
g/cm2 near the tree to 1.65 g/cm2 in the open sand
dune. The soil volume weights on the northwest transect
were 1.20, 1.27, 1.44 and 1.58 at distances of 1, 4, 8, and
12 ft from the tree trunk.
The pH as determined from saturated soil pastes with
a glass electrode is in Figure 1. The pH was lowest
(5.7) adjacent to the trunk and rose progressively with
distance from the tree to 7.2 on the open sand dune.
The high pH on the open dune is due to weathering
shell particles in the sand. There was a change in
ground flora from a single Pyrola dentata (Sm.) Piper
immediately adj acent to the tree trunk to scattered
Franscria Chamissonis Less. on the open sand dune.
These species are associated with acid and alkaline soils,
respectively. The pattern of soil pH as expressed by
the isolines of pH (Fig. 1) indicates an effect of the
southeast wind, the moisture bearing wind.
The nitrogen content of the soils declined with
distance from the tree. The highest value was 0.0286%
near the tree; the lowest was 0.0025%o in the open
sand.
Note in Figure 2 the skewed nature of the distribution of nitrogen about the tree, oriented as if by the
direction of the prevailing storm winds at the site.
The exchangeable bases were determined for the
transect extending south from the tree trunk. The exchangeable cations decreased with distance from the
tree (Fig. 3); however the divalent exchangeable cations (Ca + + + Mg++)
decreased up to the edge of
the crown canopy but then rose rapidly with increasing
distance outward into the adjacent barren dune, apparently because of the effect of shell material in the
open sand. The exchange capacity of the soil, largely
derived from organic matter in this sandy soil, declined
with distance outward from the tree, continuing low
outside the influence of the tree crown. The quantity
of exchangeable monovalent cations (K + + Na +) deSOIL
131
REPORTS
dined with distance from the tree, becoming very low
beyond the influence of the tree.
There is a distinct pattern of surface soil properties
about this tree, and it might be postulated that in the
absence of external variables such as wind or steep slope
the properties of the soil under the influence of forest
trees will develop in a symmetrical pattern around each
tree. Thus each tree has an influence circle roughly
proportional to the size of the crown area projection on
the soil surface. The tree has a maximum influence under
the crown canopy and the influence decreases outward
from the tree. To test the generality of this conclusion
transects extending radially outward from mature forest
trees in various areas in California were sampled.
Radial variation of soil properties about mature
forest trees
The general pattern of soil properties under several
mature individuals of Pseudotsuga inen-iesui (Mirb.)
*65N
70
6~ 0
062~
SNNW
FIG.
1.
The pH of surface
mineral soil under
of Pinus contorta. Isolines and recorded values
are indicated. Wind rose (arrow flying with the
indicates relative proportions of wind directions
area.
a tree
of pH
wind)
in the
'IV#,~~~~~~~~'
Ass~~~~~A
FIG.
2. The nitrogen contents (per cent by weight) of
the surface mineral soils under one Pin/us contorta tree.
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132
Ecology, Vol. 43, No. 1
REPORTS
Franco, Pinus ponderosa Laws., and Libocedrus decurrens Torr. were determined at locations throughout
Calif. The trees were all mature (approximately 200
yrs old). Sampling of soils was carried out in surface
mineral soils to a depth of 2Y2 in., usually at distances of
1, 4, 8, and 16 ft from the south side of the tree trunk.
The outer sampling point was always beyond the influence of the crown canopy, its edge being between 8
and 16 ft.
A series of relationships between soil properties and
distance from the tree were developed (Fig. 4). The
pH associated with an individual tree was almost always
lowest near the tree trunk, increasing with distance outward from the tree. The nitrogen content of the soil
under a tree was generally lowest near the tree trunk,
increasing to a maximum at 4-6 ft out, and declining
or increasing with further distance outward depending
upon the nature of the adjacent vegetation. The high
~~~~~~~~~~~Capacity
nitrogen associated with tree no. 1 was occasioned by
sampling under an adjacent Ceanothus integerrimus H.
& A. bush which is a nitrogen-fixing plant. Generally
the amount of exchangeable bases was low near the tree
trunk, increasing with distance to a maximum, declining
Q~~~~~~~'
Nat
with distance beyond the influence of the crown canopy.
The soil exchange capacity followed a similar trend.
3.0
2.0
.2
o
E
C
S_
w
0.0
,
I
*
'
Distance from tree Reet)
FIG. 3. Exchangeable cation composition of surface
mineral soil in the transact extending to the southeast
of the single Pinus contorta.
7
Z25 /w
_--;>
r
5
( E..~40.,
56V
4
8
8
Reasons for the characteristic pattern of soil properties
under individual trees
The major reason for these patterns is the difference
between the relative influence on soil properties of bark
2
,e8 10
16
~
0
~
12 16
0
(~
,~b
go 25
4
W1
15
E
5
noa ~'On
o
##V2
N
0
8
1
12 16
0
ale
w~~~~~~~~~~~~~
922
a
12
~~~~~.150
E
0%35
4
,'"3
j
%
i,
'
)5
~~~~~E
p
0 4 81216
p10p
0 4 81216
Distance from Tree (feet)
FIG. 4. The variation of soil properties (pH, per cent nitrogen, total exchangeable bases, and cation ex
change capacity) with respect to distance from old forest trees. Numbers 1 and 2 are Pinus ponderosa; 3 is
Libocedrus decurrens; and 4 is Pseudotsuga menziesii. The latter (3, 4) are from the Sierra Nevada just west
of Yosemite Park, 1 is from the Cuyamaca Mts., and 2 is from the San Bernardino Mountains in Calif.
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Winter 1962
133
REPORTS
litter, leaf litter, and no litter in the opening between
trees. Compared to leaf litter, bark litter is usually very
acid, low in bases and results in a mineral soil that is
acid, low in bases, nitrogen and carbon. Leaf litter is
generally higher in base content and nitrogen and results
in a soil that is higher in pH, base content, and nitrogen
content. In the adjacent opening without leaf litter the
soil becomes lower in exchangeable bases and nitrogen.
A nearby tree or bush may alter this effect by eliminating
or affecting the open area. In addition to the variation
in litter properties the quality of the rain water entering the soil may differ due to source as stemflow from
the tree trunk, drip from the foliage or unimpeded
throughfall and this would be reflected in soil property
Thus a general, predictable soil pattern
differences.
The tree is
about individual mature trees develops.
surrounded by an inner ring of bark litter, an outer
ring of leaf and twig litter, and the adj acent marginal
effects of an opening or the corresponding influence
ring of a nearby tree. A characteristic distribution of
soil properties in the forest develops from this pattern
(Fig. 5).
associated with individuals of various species must be
carried out with regard to these variation patterns.
These patterns may be as distinctive as the depth functions or profiles of soils.
Thus to demonstrate the
difference in influence of various species it is wise to
sample comparable distances from the tree trunk.
The overall effect of a unit area of the forest on soil
properties would best be determined as a summation of
the individual influence patterns which occur in the area
and the openings outside these areas. The denser the
forest becomes the more these influence patterns merge.
The older the trees the more definite the patterns will
probably be. A pattern should subsist for a period following the death of a tree. The shape of these patterns
will tend to be circular, but this will vary with steepness
of slope, direction and intensity of prevailing winds, and
shape of the tree crown. The magnitudes of the soil
properties within the patterns should be functions of the
soil forming factors-climate,
organisms, topography,
parent material and time as defined by Jenny (1941).
The development of knowledge of such patterns as they
occur in a forest as a function of the species present
when combined with percentage cover by species in the
forest should aid in determining the role of various species
mixtures in soil formation, as well as in the formation
of the soil-vegetation system.
SUMMARY
The pattern of soil properties under single forest trees
is generally developed with radial symmetry to the tree,
varying with distance from the tree trunk so that there
is a systematic change in pH, nitrogen content, exchangeable bases, and exchange capacity and volume
weights. The general pattern of this variability is due
to the difference between the effect of bark litter, leaf
litter, and the adjacent opening or neighboring tree.
The patterns obtained are predictable in a given forest
region.
REFERENCES
.open
FIG. 5. The hypothetical pattern of influence circles
on soil that would develop under an open mixed conifer
forest of Pinus ponderosa (Y), Pseudotsuga menziesii
Blank indicates
(D), and Libocedrus decurrens (I).
bark litter effect, cross hatched indicates leaf litter
effect, with properties depending upon species, and
stippled indicates open rainfall leaching effect.
DIscuSSION
The presence of distinct patterns of soil properties in
the forest centered in radial symmetry about each tree
means that sampling of soils to correlate soil properties
Fireman, M. and H. E. Hayward. 1952. Indicator significance of some shrubs in the Escalante Desert,
Utah. Bot. Gaz. 114: 2 pp. 143-155.
Harradine, F. H. 1954. Factors influencing the carbon
and nitrogen levels in California soils. Ph.D. Thesis,
Univ. of California, Soils Dept.
Jamison, V. C. 1942. The slow reversible drying of
sandy surface soils beneath citrus trees in central
Florida. Proc. Soil Science Soc. of America. 7: 3641.
Jenny, H. 1941. Factors of soil formation. McGraw
Hill, New York. xii + 281 pp.
Muller, P. E. 1887. Studien uber die natfirlichen
Humusformen und deren Einwirkungen auf Vegetation und Boden. vii + 324 pp. Julius Springer,
Berlin.
Muller, W. H. and C. H. Muller. 1956. Association
patterns involving desert plants that contain toxic
products. Am. J. Bot. 43: 354-355.
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