@ SOUTH
EST
FOREST SERVICE
U. S.DEPARTMEMT O F AGRICULTURE
P. 0.BOX 245, BERKELEY, CALIFORNIA 94701
NON-GRAZ NG AND GOPHERS LOWER BULK DENS
N ANNUAL-PLANT SO
Raymond D. Ratliff
USDA Forest Service
Research Note PSW-254
1971
Stanley
E. Westfall
Since the days of the early Spanish settler, the
hauences of liwstock use have altered,the character
of California's rangelm&. Native perennid bunchgasses were replaced by annuals introduced at the
Spanish missions1 and soil properties have chmgedparticularly balk density.2
Mature cattle exert static ground pressures equal
to those of h e a y wheel tractors-around 24 pounds
per square inch of hoof-bearing aream3Trampling
compacts the upper few inches of soil, increasing soil
bulk density and reducing porosity and moisture
storage capacity-especially when soils are moist.
In a study at the San Joaquin Experimental Range,
h central G&fornia, we sou&t to determhe whether
surface soil bulk densiw where grazing had been
absent for a n u m b r of years differed significantly
from that where grazing had been continued. We also
kvestigated the reaction of soil acidity under the two
con&tions. These E n & of hformation have not been
available for soil in the ganitic zone of annual-plant
rangeland. We found that the absence of livestock
grazing resulted in lower soil bulk density and lower
aci&ty in the soil.
STUDY AREA
coarse sandy loam were studied at the San Joaquin
Experimenbl Range in central California. An exclosure, on which there had been no livestock grazing for
34 years, had a lower surface bulk density and lower
acidity thm an adjacent range that had been grazed.
Bulk density averaged 1.08 gm./cc. on the ungrazed
range, and 1.43 gm./cc. on the grazed range. The pH
values were 6.15 for the ungmed mea, and 5.65 for
Oxford: 268(974): 114.464: 187 x 427.6.
Retvieval Terms: livestock influences; soil compaction;
central Sierra Nevada ecosystems; Ahwahnee coarse
sandy loans; soil pH; gophers; soil density.
Two areas-an exclosure and an adjacent area (fig.
I).-on the same site on the Experimental Range were
selected for study. Each test area was §@feet square.
%he site is classed as open-rollkg wi"ch a sora"ehern
exposure and a slope of 6.5 percent. The soil, an
bwabnee coarse smdy loam, is common on the
Experimental Range and much of the land nearby.
No livestock have grazed inside the exclosure since
1936. The exclosure also excluded squirrels but not
gophers. The adjacent area has been moderately
grazed from the first of February to early June since
1960. This is the season with adequate green forage
md abundant soil m ~ i s t u r e . ~
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Figure 1-The exclosure (fenced arm) and adjacent (lower boundary
indicated by mmker stakes) study areas on the San Joaquin Experiimental Range.
Wi& the exclosure, the vegetation was mostly
ripgut brome (momus irk'@dusj5with smaller mounts
of soft chess (mornw mollis) and slender wild oat
(Aveno barbata) mked in. O d y a few f o r b sere
present. Outside the exclosure, ripgut brome and soft
chess were preselat. We also found m n u d fescues
8 4 ; e s ~ m spJ, an abunhnce of broad-leaf B"liaree
(Erodiupipz b w s ) , an$ several other forhspecies.
Both &side and outside of the exclosure, five
equally-spaced lines were drawn. This restriction to
rmdomization was used to asmre ample Goarerage of
both areas. Nong each Ihe, 10 sampling points were
randomly selected from a possible 40, providing for
50 obsewations per area.
A soil core 08. how11 volume (1 17.3 cc.) was
removed at each point. The depth of sampling (6.5
em.) was governed by the cylinder length of our field
density sampler. The cores were dried at 1OS°C. for
24 hours md then wei&ed to the nearest one-tenth
gram. From the men-dry weights and volume, we
computed the bulk density of each core.
The pH for each core was determhed u%ing the
spot-plate technique. Values of pH were converted to
their ari thmetically equivalent values before
For both values, bulk densily m d pH, the hypothesis of equality was tested by using Student's t test
with 98"of freedom.
mS'r&JLTSAND DISCUSSION
The means in bulk densi'cy m d pH vdues and their
afferences were:
Bulk density (gll~./cc.)
Grazed
Ungazed
DSkrence
1.43
1.08
-35
pH
5.65
6.15
.50
'The Gfferences were statisticaay simiflcant at the
5 percent level of probab2ity.
We found that the sod w i ~ the
h exclosure was
soft and friable. On the gazed area it was hard,
requirhg much @eater effort to collect the cores. The
soils were also noticeably &fferent in structure. So2
~
t the hewdosure was gmular; on the gazed area
it had a coarse platy appearmce.
Hence it came as no surprise that soil bulk densiq
inside the exclosure averaged 24 percent less than on
the gazed area, These f i n h g s on b u k density
corresponds wit31 those reported by Liacos for mnud
grassland in ~ a l i f o r n i a .EIis
~ data were from the hills
east of S m Frmcisco Bay and a soil developed on
ahtone.
Mmy &verse but co-acting factors were responsiMe for loosenkg the sod inside the exclosure. They
hclude: (a) freezing m d thawkg of the soil surface,
(6)residues md mechanical effects of plant roots, Qc)
the byproducts and activities of the soil microflora
m d fauna, and (dl the presence of a thick mdch
layer to break the force of r~ndrops.But probably
the most hportant factor was the cultivation of the
soil md resultmt m k b g of mhnaeral partides and
o r g ~ matter
c
by gophers.
h o n g the rodent species on the Experimentd
Range, the pocket gopher (nomomys bottae mewa)
is the most important soil c ~ l t i v a t o r .In
~ spring,
gophers work the upper soil layers, extending their
burrow systems w&ch are usuaDy 6 to 8 inches below
the surface. Nomdly they will throw up one or more
mounds M y , md in a singe year gophers may turn
over large portions of the s ~ r f a c e Thus
. ~ their effect
on bulk density is lagely a mechanical loosenkg of
the soil.
Gophers had equd access to both the u n g u e d
md gazed areas. However, the period when gophers
we most active near the surface is &so when the sod
is most. easiiy compacted. Tramplhg by cattle recompacts the mounds, m d their hoofs may break
into the surface burrows. Therefore, t r m p l k g offsets
so3 cultivation by gophers. No trampling by cattle for
the past 34 years combined with the cumdative
effects of gopher a c t i ~ t ywas, therefore, the p r i m w
reason for the difference in soil structure and lower
b u k density wit~uinthe ewelosure. ,
Sod wi"c9ain the exclosure averaged three times less
acid than on the grazed area. However, both the
lowest (pH 7.8) and the &&est (pH 4.7) ad&ty were
found on the gazed area. The lesser variation and less
add con&tion witkn the exclosure were l i k l y the
combined resul"cof: (a) the absence of grzing which
unevenly removes the gredomhantly basic grass
residues; md (b) the absence of uneven fertiGzing
effects resulthg from cattile feces m d urine.
Bow rapidy soil is loosened in the absence of
livestock a d how rapidy soil becomes compacted
after livestock are allowed to graze r e m ~ nto be
learned. We dso need to learn whether &fferernt
gazing mmagement practices and range ferfdization
affect gopher populations.
'lkalbot, M.W.,and A. W. Sampson. m e range in California.
In, The yeabook of ~ i c u l b r e .Washington, D. C. p.
575-582. 1948,
'~iacos, Leonidas 6. Wafer yields as influencedby degree of
gazing in the California winter g@ssIonds. J . Range Manage.
15(1): 3442. 196%.
Hehick, D. W.m e mulch layer of California annualranges.
J. Range Manage. Il(1): 22-25. 1948.
'LUU, Howad W.Soil competion on forest and mnge hnds.
U.S. Dep. AD. Misc. Publ. 768, 33 p. 1959.
"~entley,J. R., and M. W. Talbot. Efficient use of annual
plants on ml-Pleranges in the Glifornia foothills. U.S. Dep.
Ag.Circ. 870, 52 p. 1951.
'~ciermt~cplane names follow Mum, P. A., and D. D. Keck.
A &'ca&ifomiaflora. Berkeley: Univ. Calif. Press. 1959.
'~aubenrnke, R. F. Plants and environment-a textbook of
plant autecolsgy. New York: John W2ey and Sons, Inc., p.
45-59. 1953,
' ~ o r n , E. E., and H. S. Fitch. Interrelations of rodents and
ofher wiEBbife of the range. Calif. Agr. Exp. Sta. Bull. 663. g.
113-115. 1942.
"tor ex, Tracy ]I. Conllpolling fieldrodents in Califimcic. Calif.
Agr. Exp. Sta. Ext. Sew. Ckc. 434, p. 27. 1953.
The Auaolis
are msiped to the Station's range-w3dHe environmental research,
M n O N D D. MTILIFP is headquxtered in Fremo, CdS. He earned
bachelor's ((1959) and master9s ((11 961) degrees in range management at the
UniversiQ of bldifornia. He joined the Station staff in 1961. STANEY E.
WSmALL is headquartered at the Station's San Joaquk Experimentd
Range, Coapsegold, Calif. He earned a B.S. degree in anirnd husbandry at
Fresno State College. He has been a membr of the S t a ~ o nstaff dnce
1960.
GPO 981-629
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The Station's range-wddlge envhonmenlal! r e s i ~ ~ cunit,
h
headqumtered at Fresno, California, is developing the scientific base for m u l ~ p l e u s emmagernent of centxal CaMornia
ecosystems. This report adds a facet of knowledge for the
ecosystem of the Sierra Nevaha foothills.
The Forest Service of the U.S. Depadment of Agricaoltwe
. . . Conducts forest and range research at more than 75 locations from Pue&o Rico to
Alaska and Hawaii.
. . . Pa~eicipateswith all State foresthy agencies in cooperalive pmgrams to protest and improve the Nation's 395 million acres of State, local, and private forest lands.
. . . Manages and protects the 187-milllora-acre National Forest System for sustained yield
of its many products and services.
The Pacific Southwest Forest and Range Experiment S$a&~n
represergts the research brmch of the Forest Service in California and Hawaii.