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Responses of Small Mammals to Forest Riparian Perturbations1
Stephen P. Cross
2
Abstract.--Trapping studies at several mixed conifer
forest
sites in southwestern Oregon demonstrate
a
differentially high use of riparian habitat by small
mammals.
Harsh perturbations of this habitat radically
affect the presence and abundance of many species. Riparian
leave-strips were found to support small-mammal communities
comparable to undisturbed sites.
INTRODUCTION
on some small-mammal species (Gashwiler 1970,
Black and Hooven 1974, Hooven and Black 1976,
Campbell and Clark 1980).
But little attention
has been given to comparing the effects of such
perturbations on wildlife such as small mammals of
different forest vegetational zones.
Leaving a
strip (buffer) of riparian and transition zone
vegetation along the edges of streams when the
surrounding area is logged is a forest management
practice used in some areas.
There are many
potential benefits
to
this practice but
the
effects on resident wildlife populations of the
streamside leave-strip are not known.
Riparian areas have been identified as
extremely important habitat for wildlife (Johnson
and Jones 1977, Thomas et al. 1979).
Much of the
supporting data for this contention comes from
studies in arid regions where the riparian
vegetation contrasts sharply with other types and
is the only local source of some essential habitat
components such as trees and free water.
The
riparian zone in more mesic regions, although
recognizable, does not contrast as sharply with
nearby habitats.
Trees are not so limited in
distribution and free water is generally more
widely available and in less demand by wildlife.
Considering these conditions, it is appropriate to
ask if there is disproportionately high use of the
riparian zone by wildlife in mesic regions.
The studies reported here were designed to
make quantitative comparisons of the small-mammal
use of various forest vegetation zones associated
with streams.
A related objective was to assess
the impact of harsh forest perturbations and
riparian leave-strips on the resident small-mammal
communities.
Natural history information suggests that
more wildlife
species
potentially use
forest
riparian habitat than other nearby habitats.
But
quantitative assessments of species diversity and
abundance are necessary to verify the predicted
differential or disproportionate use.
GENERAL STUDY AREA AND METHODS
The studies were conducted at four sites in
southwestern
Oregon
in
the
mixed-conifer
vegetation zone (Franklin and Dyrness 1973).
The
study sites were widely separated and varied in
vegetational composition.
Streamside forest riparian vegetation is
usually distinct from nearby upland vegetation
which is upslope and not under direct influence of
the stream.
The blending of riparian and upland
vegetation often creates a
rather broad
and
distinctive ecoton~, usually referred to as the
transition zone.
This zone is particularly
important because of its potentially high value
for timber production, wildlife habitat, and as a
buffer for the riparian zone.
Small mammals were collected using three
types of traps.
Sherman live-traps (9 x 7.5 x
23.5 em) and pitfall traps (5-lb plastic food
container, 18.4-cm deep with 14.6-cm diameter
opening) were used at all the sites.
Museum
Special snap traps were used at two of the sites.
Bait consisted of rolled oats for the live-traps
and a mixture of rolled oats and peanut butter for
the snap traps.
After all traps were in place at
a given site there was a 4-5 day waiting period
before they were activated.
During this period
the pitfall traps were covered with tight fitting
lids and the other traps were prebaited.
Once
traps were activated they were checked twice
daily, during the 3-4 hours after sunrise and the
2-3 hours before dark.
Clearcutting and other harsh forest
perturbations are known to have a profound effect
1
Paper presented at the North American
Riparian Conference.
[University of Arizona,
Tucson, April 16-18, 1985].
2
Stephen P. Cross is a Professor of Biology,
Department of Biology, Southern Oregon State
College, Ashland, Oregon.
269
The transition zone, located between the
riparian and upland zones, includes a distinctive
combination of vegetative characteristics of the
other two zones.
This area is dominated by
Douglas-fir in the canopy to a greater extent than
the other zones. There are some western redcedar,
bigleaf maple, and grand fir (Abies grandis) also
present. Twenty-five species of ground cover were
recorded with whipple vine (Whipplea modesta),
twinflower (Linnea borealis), mosses, snowberry,
and grasses being the most abundant..
Widths of
the riparian and transition zones are somewhat
variable depending upon slope and aspect.
Small mammals trapped alive were identified,
sexed and aged when possible, and toe-clipped for
individual identification. Emphasis was placed on
live-trapping to minimize any increase in
immigration that might be caused by removal and to
study the influence of streams on local movements.
Data from each sample plot were placed in
contingency tables and analyzed with the
chi-square statistic. Since small-mammal trapping
is somewhat selective and may not accurately
reflect the true community structure, the
Brillouin index (log to base 2) was used as a
measure of diversity. Two quantitative values for
similarity, the quotient of similarity and percent
similarity, were used to compare small-mammal
samples from various habitats or test plots.
The
former takes into account only the presence or
absence of species, whereas the latter also takes
into account the relative abundances of the
various species. Derivation and use of the above
quantitative measures are described in Brower and
Zar (1984).
Small-mammal communities in each of the zones
were sampled in the following manner.
Two-row
belt transects were placed parallel to the stream
in each vegetative zone. Each row consisted of 20
stations divided into two separate 10-station
sections.
The resulting pattern had 40 stations
in each zone in the form of two replicate
20-s ta tion belt t ran sects.
The two rows of each
transect were 12.5-m apart while the distance
between stations within a row was 15-m.
The two
20-s tation transects within each zone were offset
from those of
the other zones to avoid
interference.
The
riparian
transect was
positioned so that the two rows of traps were on
opposite sides of the stream.
This was done in
order to stay within the relatively narrow zone of
riparian vegetation and to allow mammals utilizing
this zone equal exposure to both rows of traps, as
in the other zones.
DIFFERENTIAL USE OF RIPARIAN HABITAT - SODA CREEK
The specific objective of this study was to
compare
small-mammal
abundance,
community
composition, and diversity in a coniferous forest
streamside riparian
zone with neighboring
habitats.
Two Sherman live-traps and one pitfall trap
were placed within 2.5-m of the station marker.
The live-traps were placed on opposite s~des of
the station marker and moved roughly 90
after
each two days of trapping.
The traps were
activated on 23 June 1981 and remained in
operation for 10 days (9 nights). Total trap-days
(nights) were identical for each zone.
Study Site and Methods
The Soda Creek study site is located in an
old-growth forest in the foothills of the southern
Oregon Cascades, 23-km northeast of Ashland, T37S,
R3E, Sections 19 and 20, Willamette Meridian at
ca. 900-m elevation.
The creek flows northerly
into the south fork of Little Butte Creek, part of
the Rogue River drainage.
Although relatively
small (streambed ca. 5-m), the creek influences
the surrounding vegetation to the extent that
three typical zones (i.e. habitats) may be
recognized.
Results and Discussion
Since the small-mammal samples from the
replicate transects within each of the three
habitat zones were not significantly different (p
> 0.05) they were combined for further analysis.
The species captured and the associated measures
of abundance and diversity within each habitat
zone are shown in table 1.
The species
frequencies in the samples from the three zones
are significantly different (p < 0.001). Pairwise
comparisons of the samples indicate that the
riparian is significantly different from both the
transition (p < 0.001) and upland (p < 0.001) but
the transition is not significantly different from
the upland (p > 0.05). Sample size, an indication
of abundance, is similar in the riparian and
transition zones (106 and 102, respectively),
almost double that of the upland zone (54).
The riparian zone is dominated by Douglas-fir
( Pseudotsuga menziesii),
bigleaf maple
(Acer
macrophyllum), white alder (Alnus rhombifol~
and western redcedar (Thuja pl~) in the canopy
and understory.
Shrub species in the understory
include California hazel (Corylus cornuta), ocean
spray
(Holodiscus
discolor),
and
ninebark
(Physocarpus capitatus). Thirty species of ground
cover plants were identified with mosses, bedstraw
(Galium sp.), thimbleberry (Rubus. parviflorus),
snowberry (Symphoricarpos albus), and grasses
occurring most frequently.
----The upland zone has a canopy and understory
also dominated by Douglas-fir with some western
redcedar and Pacific madrone (Arbutus menziesii),
and occ~sional Ponderosa pine (Pinus ponderosa)
and Cal~fornia black oak (Quercus kelloggii).
There are very few shrubs present.
Twenty-two
species of ground cover were identified but most
ground is devoid of cover.
Species richness is greatest in the sample
from the riparian zone, intermediate in the
transition zone, and lowest in the upland zone.
The computed diversity indices follow
the same
trend.
All the species captured in either the
upland or transition habitats are also present in
270
Table
1.--Small-mammal
species
abundance
and
diversity in three habitat zones adjacent to
Soda Creek.
Species and
Summary
Riparian
Deer mouse
California red-backed
vole
Trowbridge's shrew
Pacific shrew
Shrew-mole
Jumping mouse
Siskiyou chipmunk
Vole species
Total species
Total individuals
Diversity (H)
Evenness (J)
Habitat Zone
Transition
DIFFERENTIAL USE AND HARSH PERTURBATION - LOUIS
CREEK
The first objective of this study was
identical
to
that described for Soda Creek.
Another objective was to compare the small mammals
from the riparian and upland zones in an
old-growth coniferous forest to similar locations
in a neighboring clearcut.
Upland
23
14
13
24
25
13
13
6
1
1
35
43
3
7
0
0
0
18
23
0
0
0
0
0
8
106
2.39
.8524
5
102
1. 7 5
.7976
54
1.44
.9763
Study Area and Methods
The Louis Creek study site is located on the
western flank of the Cascade Mountains, ca. 470-m
elevation, 17.7-km northeast of Myrtle Creek,
T28S, R3W, sections 29 (forest) and 30 (clearcut),
Willamette Meridian.
Louis
Creek flows
southeasterly into South Myrtle Creek, part of the
Umpqua River drainage.
The creek is quite small
(streambed ca.
2-m)
and
the associated open
(non-canopied) corridor is also small, but a
riparian zone along the edges of the creek can be
recognized.
The transition and upland zones are
also recognizable although the edges are not as
clearly defined as in the more xerically situated
Soda Creek site.
3
the riparian zone sample. Conversely, five of the
species captured in the riparian zone are absent
in the samples from one or both of the other
zones.
The riparian zone sample has the highest
number of individuals for six species while the
transition zone has the highest number of
individuals for two species.
The three vegetation zones may be
distinguished on the basis of the combinations of
dominant canopy·and understory. The riparian zone
is characterized by a canopy dominated by western
hemlock
(Tsuga
heterophylla)
with
some
representation of western redcedar, Pacific yew
(Taxus brevifolia), and grand fir.
The understory
of this zone is dominated by vine maple (Acer
circinatum) with some Pacific dogwood (Cornus
nuttallii).
A few red alder (Alnus rubra) are
unique to this zone.
The transition zone canopy
is also dominated by western hemlock followed by
western redcedar, grand fir, and Douglas-fir.
The
understory is again dominated by vine maple but
also includes California hazel (Corylus cornuta)
and western hemlock. A few bigleaf maple occur in
both the riparian and transition zones.
The
upland zone canopy is dominated by grand fir and
Douglas-fir
with
western
hemlock
scarcely
represented.
The understory is dominated by
incense cedar (Libocedrus decurrens) and saplings
of Douglas-fir and grand fir.
The quotient of similarity (table 2), based
only on species composition, indicates that the
riparian and upland samples are less similar to
each other than the other combinations.
But when
the number of each species is also considered, as
in percent similarity, the transition and upland
zones are more similar to one another than the
other combinations, which agrees with the
chi-square analysis.
These data indicate differential occupancy
patterns in the three habitats sampled.
The Soda
Creek riparian zone appears to support a more
diverse small-mammal fauna
than
the
adjacent
forested habitats.
Most species also occur in
greater abundance in this habitat, but a high
number of two species in the transition zone makes
it comparable in total abundance to the riparian
zone.
Riparian zone ground cover has the highest
density and the greatest number of unique species.
The upland zone ground cover has lower density and
few unique plant species while the transition zone
has moderate density and virtually no unique
species.
Table 2. --Community comparisons of small mammals
in' the three zones adjacent to Soda Creek
(R = riparian, T = transition, U = upland).
Characteristic
Total species
Species in both
Quotient of similarity
Percent similarity
A clearcut, located to th~ immediate west of
the forest study area was used for another study
plot.
The site was logged, prepared and replanted
during the summer and fall of 1977.
It was
sprayed with herbicides each year from 1978
through 1981 to reduce competition with conifer
seedlings.
Habitats Compared
R x T
R x U
T x U
8
5
.769
69.8
8
3
.545
67.9
5
3
.750
89.2
The trap transect pattern for sampling small
mammals in the forest was similar to the one used
at Soda Creek. The interstation distance was 10-m
between rows and 12-m within each row. Two
271
additional transects, similar in relative location
and interstatioP distances to the riparian and
upland zones in the forest, were placed in the
clearcut. Trapping regimen was identical to Soda
Creek.
Trapping began on 18 August and was
completed on 28 August 1981.
low quotient of similarity (table 4).
But when
the numbers of each species are also considered,
the two zones show a relatively high percent
similarity, a reflection of the equally high
numbers of three species.
The frequencies of small mammals in the
samples from the ripar·ian zone of the forest and
the clearcut are significantly different (p <
0.001).
This is also true for the upland region
of the forest and the clearcut.
Species richness
and other measures of diversity are higher for the
forest riparian than in the clearcut riparian
samples.
But sample size, an indication of
density, is greater in the clearcut. To a lesser
degree, this also holds true for the forest and
clearcut upland samples but they are comparable in
richness and other measures of diversity. Species
composition within a given zone is quite different
(tables 3 and 4) in the forest and clearcut
samples.
Only six of 12 species occurred in both
riparian zones and only four of 10 occurred in
both upland zones. This results in relatively low
quotients of similarity.
The percent similarity,
however, indicates that the respective riparian
zones of the forest and clearcut are more similar
to one another than the riparian and upland zone
of the forest. The composition and frequencies of
species from the upland zone of the forest and
clearcut are very dissimilar~
Results and Discussion
The frequencies of small mammal captures from
the replicalc transects within each of the habitat
zones of both the forest and the clearcut were not
signifi,..:::ucly different (p ) 0.05) so those
samples were pooled.
The capture frequencies,
total individual captures, and sample diversity
are shown in table 3.
Within the forest, the
capture frequencies of the samples from the three
habitat zones are significantly different (p <
0.001).
Also, when the samples from the habitat
zones are compared in a pairwise fashion, they are
significantly different (p < 0.01).
Sample size indicates that small mammals are
somewhat more abundant in the forest riparian zone
than in the other two forest zones.
Species
richness is highest in the riparian and transition
zone samples.
The diversity indices grade from
highest in the riparian to lowest in the upland.
The greatest similarity of species occurs between
the riparian and transition zones (table 4). When
numbers of each species are also considered, as in
percent similarity, it is evident that the
riparian and upland zones are the least similar.
Individual species patterns in the three
Louis Creek forest habitat zones are similar to
those observed at Soda Creek.
The jumping mouse
(Zapus sp.) is almost completely restricted to the
riparian habitat in both forests.
Other species,
such as the northern flying squirrel (Glaucomys
sabrinus) and shrew-mole (Neurotrichus gibbsii),
show preference tendencies for the conditions
found in the riparian zone.
The marsh shrew
( Sorex bendirii) is represented by only one
capture in the riparian zone at Louis Creek but,
Frequencies of small mammals in samples from
the two zones of the clearcut are
also
significantly different (p < 0.001).
Species
richness, abundance, and diversity are highest in
the riparian zone sample.
Although 10 species
were captured in the clearcut, only five of them
were found in both zones, producing a relatively
Table 3.--Small-mammal species abundance and diversity
in three habitat zones adjacent to Louis Creek.
Species and
Summary
Riparian
Deer Mouse
California red-backed vole
Trowbridge's shrew
Pacific shrew
Townsend's chipmunk
Pacific jumping mouse
Creeping vole
Northern flying squirrel
Shrew-mole
Other (2 species)
California ground squirrel
Dusky-footed woodrat
Other (2 species)
Total species
Total individuals
Diversity (H)
Evenness (J)
Forest
Transition
Upland
so
0
1
1
0
0
0
0
0
56
0
24
10
8
36
39
0
0
0
5
0
2
7
92
1.99
.763
8
180
2.39
.831
7
125
2.10
• 7 58
18
11
26
16
8
25
3
3
1
1
0
0
0
20
25
19
12
3
1
3
1
1
1
0
0
0
9
31
33
6
10
112
2.60
.841
10
86
2.30
• 7 57
272
Clearcut
Riparian Upland
11
0
19
0
6
0
37
0
0
0
4
8
1
Table
4.--Community comparisons of small mammals in the
various habitat zones at Louis Creek (R = riparian, T =
transition, u = upland, ClC = clearcut, For = forest).
Areas and Habitats Compared
Characteristic
Rx T
Total species
Species in both
Quotient of similarity
Percent similarity
11
9
.900
71.3
Forest
R X U
10
7
.824
58.7
T
X
U
Clearcut
R xU
10
7
.824
7 3.1
10
5
.667
73.3
For x ClC
R
u
12
6
.667
63.9
10
4
.571
30.9
EFFECT OF A RIPARIAN LEAVE-STRIP - MIDDLE AND
SOURGRASS CREEKS
based on life history information (Maser et al.
1981), it is likely to be restricted to that zone.
With the exception of one individual of one
species, a mole ( Scapanus sp.), all species that
were sampled in the transition and upland zones
were also sampled in the riparian zones..
This
finding is important when considering the relative
value of the different zones as travel corridors
or permanent living space.
The objective of these studies was to assess
the effect of leaving a strip of forest riparian
and transition vegetation, when the neighboring
area ls harshly perturbed, on the resident
small-mammal community.
Study Area and Methods
Clearcutting and the other associated harsh
perturbations had some striking affects on the
zonally associated small-mammal communities. Some
species, such as the deer mouse (Peromyscus
maniculatus) and creeping vole (Microtus oregoni),
appear to be more abundant in both the riparian
and upland zones of the clearcut than in the
forest.
The jumping mouse also occur in larger
numbers in the riparian zone of the clearcut than
in the forest.
Some species, such as the
California
ground
squirrel
(Spermophilus
beecheyi),
dusky-footed
woodrat
(Neotoma
fuscipes), Townsend's vole (Microtus townsendii),
and house mouse (Mus musculus) occur only in the
clearcut samples.
Effects on other species, such
as Townsend's chipmunk (Eutamias townsendii) and
Trowbridge's shrew (Sorex trowbridgii) seem to be
minimal.
---
Middle Creek
The Middle Creek study site is located in the
Klamath Mountains, ca. 12.5-km west of Glendale,
T31S, R7W, Section 25, Willamette Meridian at ca.
457-m elevation.
This moderate-sized (streambed
ca. 6-m) creek flows westerly into Cow Creek, part
of the Umpqua River drainage.
The local forest is dominated by Douglas-fir
and grand fir.
Oregon ash (Fraxinus latifolia),
vine maple, and red alder are abundant in the
riparian zone.
Salal (Gaultheria shallon) is a
common groundcover.
Since this is a comparison
study of two similarly vegetated sites, a
description
of
other
distinctive
zonal
characteristics is unnecessary.
Two plots were used for study. The upstream
(full-forest) plot
is largely undisturbed
old-growth forest with attendant vegetative zones
on the south side of the stream.
The north side
of the stream is variously disturbed, with a dirt
road running parallel to it about 25-m away.
The
downstream
(leave-strip)
plot,
located
approximately • 5-km to the west, is essentially a
streamside strip or corridor of forest vegetation.
The north side of the strip is formed by the road
described above and the south side is bordered by
another road on the edge of a clearcut plantation
containing ponderosa pine saplings.
The major
difference between the two plots is that the south
side of the full-forest plot blends into upland
forest whereas the south side of the leave-strip
plot is an abrupt forest edge bordered by a road
and clearcut.
The small-mammal samples from both
sites were collected from the south side of the
creek in the riparian and transition vegetation
zones.
The average width of the leave-s trip on
the south side of the experimental site is 67-m.
A species very closely tied to the riparian
zone of the forest, the Pacific jumping mouse, was
not lost in the clearcut. Other species, such as
the California red-backed vole
(Clethrionomys
californicus),
northern
flying
squirrel,
shrew-mole, and thr~e others that occur in the
forest, were not found in the clearcut.
The
Pacific _shrew ( Sorex pacificus), found in all
three zones of the forest, is only present in the
riparian zone sample from the clearcut.
These findings suggest that the majority of
small
mammals
residing
in
mixed-conifer
communities in southwestern Oregon are capable of
living in the riparian zone. Some species survive
even when this zone is harshly perturbed, while
others are exterminated or have
populations
reduced.
Riparian leave-strips or buffers have
been suggested as a means of mitigating losses and
providing
connections
between
forest
habitat
islands.
273
Table
Two parallel rows of 20 stations, with 10-m
spacing, were placed 5-m and 15-m, respectively,
from the south edge of the creek in each plot.
One live-trap, one snap trap, and one pitfall trap
partially filled with water were placed within
2.5-m of each station marker.
Traps were tended
for ten consecutive days, 7-16 July 1980.
5 .--Small-mammal abundance, diversity, and
similarity in full-forest and leave-strip
plots at Middle Creek.
Species
Full-forest
Deer mouse
California red-backed vole
Trowbridge's shrew
Siskiyou chipmunk
Jumping mouse
Pacific shrew
Northern flying squirrel
Long-tailed vole
Bushy-tailed woodrat
Shrew-mole
Sourgrass Creek
Sourgrass Creek is located in the Klamath
Mountains, approximately 12. 9-km west of Galice.
It is a relatively small (streambed ca. 3-m)
stream which flows into Silver Creek, a tributary
of the Illinois River.
The study sites w~re
located in T35S, R9W, sections 2 and 3, Willamette
Meridian at ca. 1050-m elevation.
Total species
Total individuals
Diversity (H)
Evenness (J)
Vegetatively, the general area is dominated
by Douglas-fir and western hemlock in the
overstory
and
Port-Orford-cedar
(Chamaecyparis
lawsoniana) and grand fir in the understory.
Western azalea
(Rhododendron occidentale)
and
salal are common ground cover.
The riparian zone
is narrow but distinguishable by some unique
vegetation, including red alder in the understory.
The vegetation was judged to be similar in the
various study plots.
Species in both
Quotient of similarity
Percent similarity
Leave-strip
13
5
12
6
6
18
11
6
8
2
1
0
0
4
1
1
0
0
2
1
8
53
2.27
.853
8
44
2.16
.827
6
• 7 50
74.9
for the two plots and the community similarity
indices are high.
Two species are unique to the
samples from each plot, but sample sizes for these
four species are low.
The jumping mouse, Pacific
shrew, and shrew-mole, species closely tied to the
riparian zone, were found in the leave-strip. The
California red-backed vole, an apparent forest
obligate,
was
also
found
in
the
forest
leave-strip.
The
northern
flying
squirrel,
another forest obligate, was not found in the
leave-strip.
This may be because of inadequate
sampling (only one was caught in the full-forest
area) or lack of minimum area for home range.
Four streamside plots were used for study.
These plots are designated A to D from upstream to
downstream.
Plots A and D were in relatively
undisturbed forest.
Plots B and C were streamside
leave-strips resulting from recent (one year old)
clearcuts on one side of the creek and a road and
partial cutting on the other.
Plot B had
leave-strips approximately 9-m wide on the
clearcut side and slightly larger and more
variable on the road side.
Plot C had a
leave-strip approximately 12-m wide on the
clearcut side and variably about 20-m wide on the
road side.
These leave-s trips form corridors of
forest vegetation between relatively undisturbed
areas.
Sourgrass Creek yielded similar results.
Since the species frequencies of small mammals
captured within the two full-forest plots (A and
D) and within the two leave-strip plots (B and C)
were not significantly different (p ) 0.05) each
type was combined (table 6) for further analysis.
Capture frequencies in the full-forested and leave
strip plots are not significantly different ( p >
0.05).
Measures of diversity and community
similarity also show the two types of plots to be
very similar.
Of interest is the maintenance of
the high numbers of California red-backed voles, a
forest obligate, in the leave-strips.
To sample each of these plots two parallel
rows of 10 stations were placed on opposite sides
of the creek. The stations within a row were 10-m
apart and each station was 2.5-m from the edge of
the creek.
In most instances the stations were
within or next to the riparian zone.
One
live-trap, one snap trap, and one pitfall,
partially filled wj. th water, were placed within
2-m of each station marker. The traps were tended
for 10 consecutive days, 7-16 October 1980, and
the pitfall traps were left in place for an
additional five days.
Although the Middle Creek and Sourgrass Creek
sites differ in location, size of stream and
associated riparian zone,
and size of
leave
strips, they yielded similar results.
It appears
that many small-mammal species are able to utilize
forest riparian leave-strips to the extent that
their composition and abundance are maintained at
normal levels.
However, much remains
to be
learned about the effects of variations in such
vegetation strips.
Size, both length and width,
and degree of connectivity with similar habitat
are variables that undoubtedly affect some
species.
Results and Discussion
Frequencies of small mammals in the samples
from the Middle Creek full forest and streamside
leave-strip plots were not significantly different
(p > 0.05).
Examination of table 5 indicates
that sample size, an indication of abundance, is
slightly lower in the leave-strip plot but that
species composition is very similar in the two
plots. Species richness and diversity are similar
274
Table
6.--Small-mammal abundance, diversity, and
similarity in full-forest and leave-strip
plots at Sourgrass Creek.
resident and
determined.
transient
wildlife
remains
to
be
ACKNOWLEDGEMENTS
Full-forest
Species
Deer mouse
California red-backed vole
Trowbridge's shrew
Pacific shrew
Creeping vole
Siskiyou chipmunk
Shrew-mole
Total species
Total individuals
Diversity (H)
Evenness (J)
Species in both
Quotient of simi~arity
Percent similarity
Leave-strip
10
32
18
4
0
12
36
20
4
2
0
0
6
66
1.69
• 712
5
74
1.67
This project was supported by the Bureau of
Land Management, Oregon State Office.
Bureau
personnel participating directly in the study
included Dave Montgomery, Joe Lint, Cliff Oakley,
and especially Jerry Mires and Joe Witt.
Bill
Neitro provided direction and support throughout
the study.
Student field assistants included
Scott Peets, Jeff Henry, Dianne Seymour, Joe
Beech, and Les Mayer.
Claire Farrell, Russell
Davis, and Bill Gaud, who also aided with the
statistics, reviewed drafts of the manuscript.
.773
LITERATURE CITED
4
.727
96.1
Black, J. C., and E. F. Hooven.
1974.
Response
of small-mammal communities to habitat
changes in western Oregon. p. 177-186. In H.
C. Black, ed.
Wildlife and reforestation in
the Pacific Northwest.
236 p.
School of
Forestry, Oregon State University, Corvallis,
Oreg.
Brower, J. E., and J. H. Zar.
1984.
Field and
laboratory methods for general ecology.
266
p. Wm. C. Brown Co., Dubuque, Iowa.
Campbell, T. M., and T. W. Clark.
1980.
Short-term effects of logging on red-backed
voles and deer mice.
Gr. Basin Nat.
40(2):183-189.
Franklin, J. F.,
and C. T. Dyrness.
1973.
Natural vegetation of Oregon and Washington.
USDA For. Serv., Gen. Tech. Rep. PNW-8 •.
417
p.
Pac. Northwest For. and Range Exp. Stn.,
Portland, Oreg.
Gashwiler, J. S.
1970.
Plant and mammal changes
on a clearcut in western Oregon.
Ecology.
51:1018-1026.
Harris,
L.
D.
1984.
The
fragmented
forest--Island biogeography theory and the
preservation of biotic diversity.
211 p.
Univ. Chicago Press, Chicago, Ill.
Hooven, E. F., and H. C. Black. 1976. Effects of
some clear-cutting practices on small-mammal
populations in western Oregon.
Northwest
Sci. 50(4):189-208.
Johnson, R. R., and D. A. Jones, tech. coord.
1977.
Importance,
preservation,
and
management of riparian habitat:
A symposium.
[Tucson, Ariz., July 9, 1977.]
USDA For.
Serv., Gen. Tech. Rep. RM-43, 217 p.
Rocky
Mt. For. and Range Exp. Stn .. , Fort Collins,
Colo.
Maser, C., B. R. Mate, J. F. Franklin, and C. T.
Dyrness.
1981.
Natural history of Oregon
coast mammals.
USDA For. Serv., Gen. Tech.
Rep.
PNW-133,
496p.
US
Print.
Off.
Washington, D.C.
Thomas, J. W., C. Maser, and J. E. Rodiek.
1979.
Riparian zones.
Pp. 40-47.
In J. W. Thomas,
ed.
Wildlife
habitats
in
managed
forests--The Blue Mountains of Oregon and
Washington.
USDA For. Serv., Agric. Hndbk.
No. 553. US Print. Off. Washington, D.C.
DISCUSSION AND CONCLUSIONS
Streamside riparian zones of low to
mid-elevation
mixed-conifer
forests
of
southwestern Oregon are inhabited by small-mammal
communi ties that are more diverse and generally
more dense than in neighboring habitats.
The
riparian
habitat
contains
virtually
all
the
small-mammal species that are present in the
neighboring transition and upland zones, but the
reverse situation is not true.
A streamside
vegetative
leave-strip appears
to maintain
riparian communi ties of small mammals at levels
comparable to nearby undisturbed areas.
Forest riparian corridors have been suggested
as a means of linking forest habitat islands such
as old-growth Douglas-fir (Harris 1984).
Evidence
from this study indicates that such a management
strategy might serve small mammals very well.
But
terrestrial small mammals are relatively sedentary
compared to other wildlife, and it is likely that
larger leave-strips might be required to satisfy
the requirements of permanent living space for
more vagile species.
Nevertheless, judging by
these
small-mammal
studies,
even
small
leave-strips that include riparian habitat have
greater potential •tor serving as travel or
dispersal corridors between larger habitat islands
than leave-s trips in other zones.
This is
certainly not unexpected since the riparian zone
is more environmentally diverse and
can,
hypothetically, provide habitat requirements for a
greater variety of wildlife than other forest
habitats.
The fact that streamside leave-s trips
maintain populations of several types of small
mammals indicates that a variety of food niches
are also maintained. The small mammals themselves
may serve as food for larger predatory wildlife
that use the strip for travel from one large
habitat area to another.
Optimum or minimum size
of streamside
leave-strips
that are
selfmaintaining and can provide habitat for both
275