Influence of Alternative Silviculture on Small Mammals 

Background 

Small mammals are an important component of forest 

ecosystems in the Pacific Northwest and are the primary prey 

for many species of predators, such as the northern spotted owl 

and marten. In addition, small mammals play key roles in the 

dispersal of fungal spores and influence population dynamics of 

herbaceous and woody plants. 

A variety of silvicultural methods (e.g., thinning, green-tree 

retention) can be used as alternatives to traditional clearcut 

systems to promote structural diversity within forest stands and 

to provide commodity production. However, our understanding 

of the responses of wildlife in general, and small mammals in 

particular, to these methods is poorly developed. 

In recent years, there has been increased interest in retaining 

dead wood on the forest floor to promote biodiversity and other 

ecological values. Downed wood provides numerous benefits 

to small mammals, such as favorable microhabitat for dens and 

cover from predators. Research on how small mammals respond 

to downed wood in stands harvested with alternative silvicultural systems is lacking and would enable managers to better 

manage forest stands to meet multiple objectives, including 

timber and wildlife.

A recent study by CFER scientists Dave Waldien and John 

Hayes examined small mammal response to alternative silvicultural systems 8–12 years following harvest and in the first two 

years following addition of downed wood to the same stands. 

Specifically, their study objectives were to determine:

1. how populations of small mammals respond to alternative 

silvicultural treatments 8–12 years after harvest, 

2. how downed wood influences small mammals for two 

years after the addition of wood, and

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006-3100

July 2006 Printed on recycled paper

Salem

Albany

Portland

Corvallis

Eugene

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McDonald-Dunn Forest

Coast Range

Willamette Valley

3. if path selection by Townsend’s chipmunk is influenced by 

downed wood.

This study was located in the McDonald-Dunn Research 

Forest in the Oregon Coast Range (Figure 1). The Douglas-firdominated stands in this study were 30–90 years old and were 

part of a long-term research project with uncut control stands 

and replicates of three alternative silvicultural treatments implemented from 1989 to 1991. From least to most intense, the three 

treatments were small group-selection (where 33% of the stand 

volume is removed in patches), two-story (75% of the volume 

is uniformly removed), and clearcut. For their first objective, 

Waldien and Hayes sampled the small mammal population in 

two replicates of 

each stand 

type in three geographic blocks (24 stands total). Trapping sessions were conducted each year (1999 and 2000) during spring, 

summer, and fall. For the second objective, downed wood was 

added to a randomly selected group-selection stand from each 

replicate pair by felling five mature Douglas-fir trees within a 

trapping grid. Similarly, one clearcut was randomly selected 

from each replicate pair, and 11 mature Douglas-fir logs were 

placed by helicopter in a trapping grid (Figure 2). Trapping 

sessions were conducted each year (1999–2002) during spring, 

summer, and fall.

Figure 1. Location of 

McDonald-Dunn Research 

Forest.
For the third objective, Townsend’s chipmunks were trapped 

from July to September of 2001. Using the spool-and-line technique, thread was attached to each animal as it was released. At 

least four hours later, the researchers returned to the study area 

and followed the thread to measure the habitat along the chipmunk’s path (Figure 3). Habitat use was classified as arboreal 

(in trees or shrubs), subterranean (below ground), or surficial 

(on the ground surface). Use of downed wood was evaluated by 

comparing presence of wood at points along the path to presence of wood at random points next to the path. Three models 

Figure 2. Tree being felled in group-selection stand (upper) and 

Douglas-fir logs ready for placement in clearcut stand (lower).

Figure 3. Line of thread marking chipmunk’s path on the forest 

floor.

were developed to evaluate how wood availability, wood diameter, and whether the wood was elevated or not influenced path 

selection. These models were refined by examining influence of 

gender, season, or quantity of wood.

Results

Twenty-two species of small mammals were captured 

35,138 times during 91,200 trap nights (one trap night = one 

trap set). The deer mouse was the most abundant species, with 

Townsend’s chipmunk and Trowbridge’s shrew the next most 

abundant (Table 1). 

Response to silvicultural treatment depended on the species. 

The deer mouse, dusky-footed woodrat, Oregon vole, Pacific 

jumping mouse, Townsend’s chipmunk, and vagrant shrew 

tended to be more abundant in stands 8–12 years after harvest 

than in controls (Figure 4). This likely reflects a relationship 

with the increasing understory vegetation following overstory 

removal. Although data were limited for analysis of northern 

flying squirrels and western red-backed voles, these two species 

were captured more often in control or group-selection stands 

where some forest canopy was retained, and less often or not at 

all in two-story and clearcut stands (Figure 5).

There were no clear responses by small mammals to the 

addition of downed wood. All measures for all species varied by 

season except for densities of Pacific and vagrant shrews. Lack 

of a clear response by small mammal populations to the addition of downed wood may be due to the newness of the wood 

used; the benefits of downed wood to small mammals may be 

related to how much the wood is decayed.

Forty-one chipmunks were tracked using the spool-and-line 

technique for a total of 5,093 m. The mean trail averaged 85% 

surficial, 15% arboreal, and <1% subterranean. Just over half 

of surficial trail use was associated with downed wood, and a 
Table 1. Number of individual small mammals captured for the silvicultural treatment and downed wood treatment objectives. NW=no wood added. W=wood added.

First Objective: Silvicultural Treatment Second Objective: Wood Treatment

 GroupGroup- Two- Selection Clearcut

SPECIES Control Selection Story Clearcut Total NW W NW W Total

Virginia opossum 0 0 0 0 0 0 0 1 0 1

Pacific jumping mouse 1 4 26 10 41 8 5 26 30 69

Brush rabbit1 0 0 1 0 1 3 2 1 0 6

Western red-backed vole 16 22 4 0 42 25 35 2 1 63

Oregon vole 29 83 74 137 323 64 109 79 209 461

Townsend’s vole 0 0 0 0 0 0 0 2 0 2

House mouse 1 0 0 0 1 0 1 0 0 1

Bushy-tailed woodrat 1 0 0 0 1 0 1 0 0 1

Dusky-footed woodrat 2 15 35 52 104 29 25 127 53 234

Deer mouse 910 1074 1293 1158 4435 1047 1045 1261 1012 4365

Ermine 4 8 8 11 31 8 5 9 11 33

Northern flying squirrel 27 18 0 0 45 21 36 0 0 57

California ground squirrel1 0 0 7 12 19 1 1 9 21 32

Townsend’s chipmunk 98 261 336 208 903 350 336 300 310 1296

Douglas squirrel1 0 1 0 0 1 13 1 0 0 14

Baird’s shrew 12 24 14 8 58 24 15 4 8 51

Pacific shrew 33 74 43 18 168 87 87 7 29 210

Fog shrew 17 37 23 18 95 24 30 10 13 77

Trowbridge’s shrew 195 182 145 111 633 281 251 174 242 948

Vagrant shrew 5 18 34 80 137 16 25 57 108 206

Shrew-mole 4 0 0 0 4 4 1 1 1 7

Coast mole1 0 1 0 0 1 2 1 0 2 5

TOTAL2 1355 1822 2029 1799 7005 1967 2002 2049 2005 8023

1Represents number of captures because individuals were not marked.

2Does not include captures of California ground squirrels for the silviculture treatment or captures of brush rabbits, California 

ground squirrels, Douglas squirrels, and coast moles for the wood treatment because the number of individuals of these species 

were not tracked.

Figure 4. Density of vagrant shrews by silvicultural treatment.

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Figure 5. Mean captures per season of northern flying squirrels by silvicultural 

treatment.

majority of this use was on 

top of logs. In all but one 

case, chipmunks disproportionately selected paths with 

downed wood relative to its 

availability (Figure 6). Size 

and quantity of wood also 

influenced path selection.

Management 

Implications

Forest managers often 

strive to balance timber revenues and forest biodiversity. 

Studies that investigate wildlife responses to alternative 

silvicultural practices help 

managers make informed 

decisions on how best to 

achieve this balance. This 

study suggests that groupselection and two-story harvesting are viable alternatives 

to clearcutting. These alternative silvicultural practices 

leave behind overstory that 

is important to some small 

mammal species, while creating gaps that allow early-successional species to increase 

in abundance. Of the three 

harvest systems examined, 

group selection is the method 

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Control GroupselectionTwo-story Clearcut

Treatment

Density (no./ha)
most likely to maintain populations of northern flying squirrels and western red-backed voles and allow some intermediate 

levels of timber harvest. This could potentially benefit northern 

spotted owls, which feed on these species.

The addition of downed wood to group-selection and clearcut stands may have been functionally redundant to the high 

levels of understory vegetation present in these stands, thus 

leading to no significant response by small mammals. However, 

Townsend’s chipmunks disproportionately selected plots with 

downed wood. These seemingly contradictory findings may be 

explained in part by the high variability in chipmunk populations, making it difficult to measure the benefits of downed 

wood at the population level in field settings. Further studies 

are needed at individual and population levels to examine the 

importance of downed wood across multiple spatial scales.

Figure 6. Percentage of wood on used paths vs. wood off of paths 

for Townsend’s chipmunks. Values located above the line indicate a 

greater preference for paths with downed wood.

Contributing Scientists

Dr. David L. Waldien received his doctoral degree from Oregon State 

University in February 2005. Currently he is a conservation scientist 

and co-director of programs for Bat Conservation International.

Dr. John P. Hayes is a wildlife ecologist for the CFER program. He 

also serves as the Associate Dean of International Programs for the 

College of Forestry and as a professor in the Department of Forest 

Science at Oregon State University. 

Research Highlights

• Species associated with open forest canopies were similarly abundant in all three silvicultural treatments and control stands.

• Species associated with closed overstory forest canopies tended to 

be captured less often in harvested stands.

• Group-selection stands appear to provide habitat for northern flying 

squirrels and western red-backed voles while still allowing for timber 

harvest.

• Chipmunks disproportionately selected paths with downed wood–54% 

of the average path was within 50 cm of downed wood and only 29% 

of the nearby area not selected by chipmunks had downed wood. 

For Further Reading

Bunnell, F.L., L.L. Kremsater, and R.W. Wells. 1997. Likely consequences 

of forest management on terrestrial, forest-dwelling vertebrates in 

Oregon. The Centre for Applied Conservation Biology, University of 

British Columbia, Vancouver, B.C., Report M-7. 130 pp.

Hayes, J.P., and S.P. Cross. 1987. Characteristics of logs used by western 

red-backed voles, Clethrionomys californicus, and deer mice, Peromyscus maniculatus. Canadian Field-Naturalist 101:543–546.

Manning, J.A., and W.D. Edge. 2004. Small mammal survival and downed 

wood at multiple scales in managed forests. Journal of Mammalogy 

85:87–96.

Waldien, D.L. 2005. Population and Behavioral Responses of Small Mammals to Silviculture and Downed Wood Treatments in the Oregon Coast 

Range. Ph.D. thesis. Oregon State University, Corvallis, Oregon.

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Wood Off Path (%)

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For more information contact:

CFER

301M Richardson Hall, OSU

Corvallis, OR 97331-5752

541-737-7612 • cfer@fsl.oregonstate.edu

http://www.fsl.orst.edu/cfer

This fact sheet 

is one in a series of information products developed by the Cooperative 

Forest Ecosystem Research (CFER) program on the biotic 

responses to change in stand structure of young forests in 

western Oregon. Funding for this research was provided to the 

CFER program by the USGS Forest and Rangeland Ecosystem 

Science Center, the Oregon Department of Forestry, and 

Oregon State University.