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80
Figure 21. Schematic of site layout for a highway site.
checked each morning. Animals trapped were removed, the greater ground cover in moister microhabitats or cool
tentatively identified to species and bagged, then positively aspects. Bluebunch wheatgrass (Agropyron spicatum), june-
identified, sexed, weighed, and measured later on the day of grass (Koeleria macrantha), arrow-leaved balsamroot (Bal-
capture. The research team completed all capture work from samorhiza sagittata), and kinnikinnick (Arctostaphylos uva-
14 through 18 June and 4 through 8 July 2005. ursi) were more commonly present in drier locations with a
The study site was within the Interior Douglas-Fir biogeo- sparse understory and less pinegrass. Small patches under
climatic zone (IDF) in the province's dry climatic region.35 dense Douglas-fir cover had essentially no understory. While
Within the IDF, six "site series" (descriptors of potential cli- downed woody debris was sporadically present, there was typ-
max vegetation and soil moisture) have been described. The ically little of this because of the relatively young forest age and
research team judged the forested portion of all sites to be its history of past disturbance. All ROWs were predominantly
composed historically of the same predominant site series: vegetated by wild and/or agronomic grasses and wild straw-
Douglas-fir (Pseudotsuga menziesii), lodgepole pine, (Pinus berry, with variable cover of other forbs, no trees or downed
contorta), pinegrass (Calamogrostis rubescens), and twinflower woody debris, and minimal shrub cover.
(Linnaea borealis). However, because of topographic variabil-
ity, past wildfires, and partial-cut logging, study sites were Data analyses. The research team compared the number
mid-seral mixes of Douglas-fir, lodgepole pine, western larch of species trapped (and abundance of each) among transects
(Larix occidentalis), and ponderosa pine (P. ponderosa), with and among treatments. Where sample sizes permitted, the re-
a minor component of trembling aspen (Populus tremuloides) search team also compared weights of adult males, weights of
and paper birch (Betula papyrifera). The research team did not adult females, sex ratios and juvenile:adult ratios among tran-
measure habitat variables, but did record general habitat con- sects and treatments using t-tests and 2 tests as appropriate
ditions subjectively. Crown closure was typically 40% to 60%, using the program JMP IN (SAS Institute, Inc., Cary, North
with portions of some sites ranging from about 10% to 80%. Carolina).
At all sites, the dominant understory plant was pinegrass with
roughly 5% to 20% cover, but up to approximately 50% cover
in some small openings of past disturbance. Other common Findings and Results
understory species in all sites included soopolallie (Shepherdia
Utah
canadensis), birch-leaved spirea (Spiraea betulifolia), common
snowberry (Symphoricarpos albus), saskatoon (Amelanchier In 2004, a total of 11 species were captured; two species
alnifolia), Douglas-fir saplings, and heart-leaved arnica (Ar- were captured exclusively in areas close to the road (rock
nica cordifolia). Tall Oregon grape (Mahonia aquifolium), squirrel [Spermophilus variegates] and sagebrush vole [Lem-
showy aster (Aster conspicuus), twinflower, wild strawberry miscus curtatus]), and two species were captured exclusively
(Fragaria virginiana), and a variety of mosses contributed to distant from the road (piñon mouse [Peromyscus truei] and
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Table 29. Species detected at different distances deer mice (Peromyscus maniculatus) had lower densities closer
from Interstate 15 in 2004. to the road (Figure 22) while Great Basin pocket mice (Perog-
nathus parvus) exhibited the opposite trend (Figure 23). Re-
Genus species No. individuals captured
sults of ShannonWiener diversity index (H) analysis revealed
Common name Close (50 m) Distant (400 m) there were variations in diversity trends in different years. Dur-
Peromyscus maniculatus ing 2004, the ShannonWiener diversity index (Table 31) was
124 120
Deer Mouse
Perognathus parvus significantly higher in areas distant from the road (Wilcoxon Z
39 54
Great Basin Pocket Mouse = -2.224, P = 0.026) as compared to results in 2005 (Table 32)
Tamias minimus
27 18 in which diversity peaked close to the road (Friedman test 2 =
Least Chipmunk
Dipodomys microps
6, P = 0.05; LSD Hclose > Hmid and Hclose > Hdistant, P < 0.05).
5 1 For all species in 2004, the overall trend was increased
Chisel-Toothed Kangaroo Rat
Rethrodontomys megalotis
4 3 density with increasing distance from the road (Figure 24);
Western Harvest Mouse
however, the result was not statistically significant (Wald test Z
Peromyscus boylii
Brush Mouse
3 11 = -0.49, P = 0.63). However, the transects were established
Neotoma lepida
2 1
along about 20 mi (32.2 km) of habitat adjacent to Interstate
Desert Woodrat 15, and the research team noticed changes in sagebrush habi-
Lemmiscus curtatus
Sagebrush Vole
1 0 tat, especially in Area B, an area geographically between Areas
Spermophilus variegatus A and C. Area B had a noticeably different habitat (a distinct
1 0
Rock Squirrel sagebrush habitat type), so the research team conducted the
Ammospermophilus leucurus
White-Tailed Antelope Squirrel
0 4 same analysis for all species but segregated the data by three
Peromyscus truei distinct geographic areas. Different trends were found in dif-
0 2
Piñon Mouse ferent areas (Figure 25). Densities recorded in Area B were sig-
nificantly greater than in Area A for both close (Wald test Z =
-2.15, P = 0.03) and distant webs (Wald test Z = -3.07, P =
white-tailed antelope squirrel [Ammospermophilus leucurus]). 0.002), and both were significantly higher than in Area C for
The remaining seven species were captured at both distance close (Wald test Z = -2.84, P = 0.004) and distant webs (Wald
classes from the road (Table 29). During 2005, a total of seven test Z = -2.97, P = 0.003). For 2005, there was a statistically sig-
species was captured (Table 30) with three species caught nificant trend toward higher abundance near the road (Wald
exclusively close to the road (desert cottontail [Sylvilagus test Z = 3.99, P < 0.001) than distant from it (Figure 26).
audubonii], jackrabbit [Lepus californicus], and desert woodrat
[Neotoma lepida]).
British Columbia
Results from density and abundance comparisons between
different distances from the road indicate that, in most cases, The research team trapped 401 individuals, including
small sample sizes prevented a precise estimation to discern nine species of rodents and two species of shrews. The three
clear trends. Despite the lack of statistical significance, in 2004 most commonly trapped species (Table 33) were deer mice
Table 30. Species detected at different distances from Interstate 15
in 2005.
Genus species No. individuals captured
Common name Close (0 m) Mid (200 m) Distant (600 m)
Perognathus parvus
12 4 2
Great Basin Pocket Mouse
Peromyscus maniculatus
10 1 1
Deer Mouse
Dipodomys microps
8 11 2
Chisel-Toothed Kangaroo Rat
Tamias minimus
2 1 0
Least Chipmunk
Sylvilagus audubonii
2 0 0
Desert Cottontail
Lepus californicus
1 0 0
Jackrabbit
Neotoma lepida
1 0 0
Desert Woodrat
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450 Table 31. Values of ShannonWiener diversity
Density Estimates (P. maniculatus)
400 index (H) estimated for 2004 by transect in close
and distant webs in Utah.
350
300 Diversity Index
Transect
250 Hclose Hdistant
1 0 0
200
168.3 2 0.8 1.27
150 3 0.8 1.01
100 4 0 0.3
83.9
5 0.35 0.56
50
6 0.35 1.04
0 7 1.17 1.3
close distant
8 0.43 0.6
Distance from Road
9 0.6 0.67
Figure 22. Density estimates of Peromyscus manicu- 10 0 0.5
latus in 2004 at different distances from the road. 11 0.14 0
12 0.99 0.81
70 (Table 33). Trapping problems included several brief but
heavy rains that snapped traps, larger animals stepping on
Density Estimates (P. parvus)
60
traps or otherwise snapping them, non-functional traps,
50 usually due to soil thrown up by the impact of raindrops,
and a few captures of songbirds which prevented the capture
40
of small mammals. As a result, realized trapping effort was
30 29.6 78% of attempted trapping effort. Capture rates, adjusted
for realized trapping effort (Table 33), were low and un-
20 20.2
evenly distributed spatially for most species. Total capture
10
rates were 9.8 and 12.6 captures per 100 trap-nights, in re-
lation to attempted and realized trapping effort respectively.
0 Six species were more abundant at highway sites, while five
close distant
were more abundant at transmission-line sites. Five species
Distance from Road
were present at more highway than transmission-line sites
Figure 23. Density estimates of Perognathus parvus and four were present at more transmission-line than high-
in 2004 at different distances from the road. way sites. The low sample sizes and clumpy, among-site dis-
tribution of captures prevented within-species comparisons
(Peromyscus maniculatus), southern red-backed voles of spatial distribution in relation to transect, with the ex-
(Clethrionomys gapperi), and yellow-pine chipmunks ception of deer mice (Figure 27). For this species, there was
(Tamias amoenus). True trapping effort was slightly uneven no difference in capture rate among transects for highway
among treatments, sites, and transects because of various sites (2 P = 0.93) but a difference was realized for trans-
trapping impediments that are inherent to field work in mission-line sites (P = 0.04). Comparing highway to trans-
which environmental variables are not always controllable mission-line sites for each transect, a marginally significant
Table 32. Values of ShannonWiener diversity index (H)
estimated for 2005 by transect in close, mid, and distant
trapping lines in Utah.
Diversity Index
Transect
Hclose Hmid Hdistant
1 0.67 0.69 0
2 0.64 0 0
3 1.31 0 0.64
4 1.35 1 0
5 1.04 0.45 0
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350 (2 P > 0.17 for all comparisons except highway vs. transmis-
Density Estimates (Small Mammals)
sion line for ROW transect, for which P = 0.08; Figure 30).
300
Sample sizes were relatively low, likely due to a combination
250 of a low realized trapping effort, some periods of inclement
weather that may have limited animal activity and survivor-
200
ship, and the timing of sampling effort. The field season oc-
150 148.8 curred in early June and July when recovery from the annual
115.4 winter population decline would have been incomplete for
100
some species.225 Combining all transects per site, similar pat-
50 terns of diversity and abundance were evident between trans-
mission-line and highway sites, although distribution was
0
close distant clumpy for most species. With the exception of deer mice and
Distance from Road yellow-pine chipmunks, each species occurred at fewer than
half of the sites, despite being common at some of those sites.
Figure 24. Density estimates of small mammals in
For any given transect distance, only deer mice were trapped
2004 at different distances from the road.
at more than half of the sites. This clumping suggests that
difference was evident for deer mice between treatments within the forest, microhabitat or some other localized effect
only for the 600 m transect (ROW P = 0.32, 50m P = 0.47, was stronger than any influence of distance to the highway.
300m P = 0.83, 600m P = 0.05). Species diversity was lowest in ROW transects than any
For both male and female deer mice, animal weights did other transect. However, there is no strong evidence to suggest
not differ among transects for highway or transmission-line that this observation was related to anything beyond a shift
sites (ANOVA P > 0.44 for all comparisons; Figure 28). Com- from native forest at 50, 300, and 600 m transects, to the less
paring highway to transmission-line sites for each sex and complex structure and vegetation of the disturbed habitat in
transect, no differences in weight were evident (t-test P > 0.24 the ROW. For example, optimal habitat for yellow-pine chip-
for all comparisons) with the possible exception of males on munks appears to be open forest with abundant woody debris;
the 600 m transect (P = 0.06). southern red-backed voles are most common in mature
There was no difference in sex ratio among transects for forests with abundant shrub and ground cover; heather voles
highway sites (2 P = 0.88), but there was some evidence of a are associated with a dense shrub layer and abundant woody
difference among transects for transmission-line sites (P = debris; and in the dry interior of British Columbia where this
0.07; Figure 29). Comparing highway to transmission-line study area was located, long-tailed voles are associated with
sites for each transect, there was weak evidence of a difference shrub thickets.178 Thus, ROWs with no forest or downed
between treatments only for the 600 m transect (ROW P = woody debris and few shrubs would be expected to have fewer
0.92, 50 m P = 0.79, 300 m P = 0.32, 600 m P = 0.09). of these species, independent of the presence of a highway
Juvenile:adult ratios did not vary significantly among tran- nearby. The only species trapped more often on ROW tran-
sects for either treatment, or among transect for any treatment sects was the western jumping mouse, consistent with its
1200
1000
Density Estimates
800
600 593.6
400
272.5
200
81.3 31.7 53.5
36.2
0
close distant close distant close distant
Area A Area B Area C
Distance from Road (per geographic areas)
Figure 25. Density estimates of small mammals in
2004 at different distances from the road in three
distinct geographic areas.
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180
160
Estimated Abundance (N)
140
120
100
80
60 57.35 59.05
40
20
7.27
0
close mid distant
Distance from Road
Figure 26. Density estimates of small mammals in 2005 at
different distances from the road.
preferred habitats, which are more typically associated with were more common in the transmission-line ROW than in the
ROWs than forest (i.e., rich meadows with abundant forbs).178 highway ROW with the exception of the aforementioned
Had there been a strong effect of highway proximity, differ- western jumping mice, which were found at only two sites sep-
ences between the highway and transmission-line sites should arated by 1.5 km. Interestingly, no presence was detected at a
have been found for the ROW transects. In fact, no species site between the two, which appeared to be largely identical
Table 33. Small-mammal species trapped in British Columbia on transects within high-
way and transmission-line rights-of-way (ROWs) or at varying distances from the ROW
centerlines.
Highw ay Transmission Line
(no. animals/no. sites) (no. animals/no. sites ) Grand
Species
In 50 m 300 m 600 m Hwy In 50 m 300 m 600 m Tr Ln Total
ROW Out Out Out Total ROW Out Out Out Total
Sorex cinereus
1/1 1/1 1/1 1/1 2/2 3/3
Common Shrew
Sorex monticolus
0/0 2/2 2/2 2/2
Dusky Shrew
Glaucomys sabrinus
Northern Flying 1/1 1/1 0/0 1/1
Squirrel
Tamias amoenus
Yellow-pine 1/1 9/4 3/3 4/2 17/6 3/3 3/1 3/2 9/4 26/10
Chipmunk
Clethrionomys
gapperi
16/2 8/2 9/3 33/3 1/1 10/2 11/3 44/6
Southern Red-
Backed Vole
Microtus longicaudus
1/1 1/1 3/2 1/1 2/2 6/3 7/4
Long-Tailed Vole
Microtus
pennsylvanicus 1/1 1/1 3/2 5/3 1/1 1/1 2/1 7/4
Meadow Vole
Phenacomys
intermedius 1/1 2/2 6/5 9/5 2/2 1/1 3/2 12/7
Heather Vole
Mus musculus
1/1 1/1 0/0 1/1
House Mouse
Peromyscus
maniculatus 28/8 29/6 34/8 35/8 126/8 41/8 29/8 34/7 57/8 161/8 287/16
Deer Mouse
Zapus princeps
Western Jumping 0/0 7/2 2/1 2/1 11/2 11/2
Mouse
Note: Blanks indicate no captures for that species.
