Forest-floor Small Mammal Community Research Articles

Woody debris structures on large clearcut openings: Oases for small mustelids and prey species?

Restoration structures such as post-harvest woody debris piles on large clearcut openings may provide habitat for many mammal species. Mustelids such as the American marten (Martes americana) and several weasel (Mustela spp.) species are important furbearers in temperate and boreal forests and are negatively affected by clearcutting. We ask if constructed piles of woody debris on large (e.g., 30–50 ha) openings will be used by these mustelids and their small mammal prey species? We tested the hypotheses (H) that (H1) the presence (index of activity patterns) of small mustelids, (H2) abundance, species richness, and species diversity of the forest-floor small mammal community, and (H3) reproduction of the major species: southern red-backed vole (Clethrionomys gapperi), long-tailed vole (Microtus longicaudus), and deer mouse (Peromyscus maniculatus), would be greater on sites with woody debris piles than on sites with dispersed debris. A fourth hypothesis (H4) predicted that the above response variables would be similar across a linear configuration of debris piles on the large openings. Mustelid presence and populations of forest-floor small mammals were sampled on four replicated (n = 4) large (30–50 ha) clearcut sites from 2017 to 2022 in south-central British Columbia, Canada.Mean presence of mustelids was significantly higher (4.5 to 8.0 times) in piles than dispersed sites during the first four post-harvest years, thereby supporting H1. Mean index of mustelid activity per line was similar among pile index-lines across these clearcut openings. Mean abundance of C. gapperi was similar statistically between treatment sites but with numbers 3 to 10 times higher, on average, in the piles than dispersed sites and was likely biologically important. Mean abundance of M. longicaudus was significantly higher (1.2–4.4 times) in the piles than dispersed sites. Mean abundance of P. maniculatus and Sorex spp. were similar between treatment sites. Mean abundance of total small mammals, including the less common species, was significantly higher (1.4–1.9 times) in piles than dispersed sites. Similarly, mean species richness and diversity were both significantly higher in piles than dispersed sites. Mean number of total recruits was higher in piles than dispersed sites for M. longicaudus and P. maniculatus, but most measures of reproductive attributes were similar, thereby providing only partial support for H3. As per support for H4, response variables were similar across a linear array of debris piles on large openings. Our study is the first to measure responses of small mustelids and forest-floor small mammals to constructed piles of woody debris as a means of habitat restoration on relatively large (mean area 40.5 ha) openings created by conventional clearcutting. Piles of debris seem to act as oases for mustelids and their prey species in ecological restoration of cutover forest land.

Long-Term Changes in Abundance and Composition of Forest-Floor Small Mammal Communities in a Landscape with Cumulative Clearcutting

Responses of forest-floor small mammals to clearcutting are species-specific with generalists occupying a range of habitats, and specialists persisting on clearcuts for variable periods. We investigated the responses in abundance and species composition of small mammal communities to cumulative clearcutting of coniferous forests on a landscape that had four independent clearcutting events (Periods 1 to 4) over a 42-year interval from 1979 to 2020 in south-central British Columbia, Canada. We ask if the small mammal communities have changed significantly over these decades owing to removal of old-growth forest by clearcut harvesting. Hypotheses (H) predicted that the small mammal community would (H1) increase in abundance, species richness, and diversity on new clearcuts owing to the availability of early seral post-harvest habitats from cumulative clearcutting; and (H2) have higher mean abundance, species richness, and species diversity in clearcut than uncut forest sites, owing to availability of vegetative food and cover. A third hypothesis (H3) predicted that abundance of (i) early seral vegetation (herbs and shrubs) and (ii) small mammal populations, will be greater in ungrazed clearcut sites than in those grazed by cattle (Bos taurus). Mean total numbers of small mammals on new clearcuts declined in Periods 3 and 4, and hence did not support the abundance part of H1. Much of this decline was owing to low numbers of the long-tailed vole (Microtus longicaudus) and meadow vole (M. pennsylvanicus). Two generalist species: the deer mouse (Peromyscus maniculatus) and northwestern chipmunk (Neotamias amoenus), contributed to high mean species richness and diversity in Periods 2 and 3 before these metrics declined in Period 4, and hence partly supported H1. The similarity in mean total numbers of small mammals in Periods 2 to 4 did not support the abundance prediction of H2 that total numbers would be higher in clearcut than uncut forest sites. Higher mean species richness (Periods 2 and 3) and diversity (Period 3) measurements on clearcut than forest sites, particularly in the early post-harvest years, did support these parts of H2. The vegetation part (i) of H3 was not supported for herbaceous plants but it was for shrubs. The small mammal part (ii) of H3 that populations would be higher in ungrazed than grazed clearcut sites was supported for abundance but not for species richness or diversity. The decline and near disappearance of both species of Microtus was possibly related to the reduction in plant community abundance and structure from grazing (at least for shrubs) and potentially from drought effects associated with climate change. Loss of microtines from these early seral ecosystems may have profound negative effects on various ecological functions and predator communities.

Responses of mustelids and small mammal prey to combined retention on clearcuts: Woody debris, green trees, and riparian structures

Small mustelids such as the American marten (Martes americana) and short-tailed weasel (Mustela erminea) are important furbearers in temperate and boreal forests and are negatively affected by clearcutting. A major prey species, the southern red-backed vole (Myodes gapperi), also disappears from clearcuts and does not return to abundance levels of uncut forest for many decades. We tested the hypotheses (H) that on newly clearcut sites, (H1) the presence of small mustelids, (H2) abundance, species richness, and species diversity of the forest-floor small mammal community, and (H3) reproduction of the major species: M. gapperi and the deer mouse (Peromyscus maniculatus), would be greater on sites with combined retention treatments of woody debris piles, riparian, and green-tree retention than on sites with no retention. A fourth hypothesis (H4) predicted that the above response variables on sites with combined structural retention would be comparable to or higher than those in uncut old-growth forest. Mustelid presence and populations of forest-floor small mammals were sampled on five replicated (n = 4) treatment sites from 2017 to 2020 in south-central British Columbia, Canada.Mean presence (index of activity patterns) of mustelids was statistically similar among sites but in the combined treatments was 1.4 to 2.9 times higher than that in the dispersed (no retention) and uncut forest sites and was likely biologically important. Mustelid presence was particularly evident in the debris piles and riparian sites. Mean abundance of M. gapperi was 11.1 to 16.6 times higher in the combined retention and uncut forest sites than the dispersed sites. Mean abundance of P. maniculatus was higher in the dispersed than uncut forest, but similar in the combined retention to these treatments. Mean total abundance, species richness, and species diversity of eight small mammal species were all higher (1.3 to 1.6 times) in the combined retention sites than the dispersed and uncut forest sites. Although not formally significant (P = 0.08), results for mustelid presence tended to support H1 that these small carnivores would occur more frequently on sites with combined structural treatments than the dispersed and uncut forest sites. The overall high total numbers (and species richness and diversity) of small mammal prey species supported H2 that abundance would be greater on sites with the combined retention than on the dispersed sites with no retention. Reproduction and survival followed the pattern of abundance for the major species, and hence H3 was supported. Higher mean total abundance in combined retention sites than in uncut forest supported H4 in 2017–2018 but not in 2019–2020 when an influx of generalist species increased total abundance in the dispersed sites. This study is the first to measure the responses of small mustelids and small mammal prey species to combined structural retention. One or more of these retention treatments is highly recommended during most harvesting regimes in these forests.

Similarity in occupancy of different-sized forest patches by small mammals on clearcuts: conservation implications for red-backed voles and small mustelids

Many mammalian species decline on forest sites that are harvested by clearcutting because of a loss of food, cover, and other components of stand structure. Small mustelids are impacted negatively as is the southern red-backed vole (Myodes gapperi), a principal prey species, that disappears from clearcuts within a year of harvest. These effects may be potentially ameliorated by aggregated retention harvests that leave unlogged patches on clearcuts. We tested three hypotheses (H) that (H1) abundance, reproduction, and survival of M. gapperi populations, (H2) total abundance, species richness, and diversity of the forest-floor small mammal community, and (H3) the presence of small mustelids would be greater in large than small patches of retention forest on new clearcuts. We measured demographic responses of M. gapperi, total small mammals, and the presence of small mustelids (American marten, Martes americana, and small weasels (Mustela spp.)) from 2014 to 2016 in replicated treatments of four sizes (ha) of retention patches (means of 0.53, 1.50, 4.13, and 18.73) near Elkhart in south-central British Columbia, Canada. Mean abundance, reproduction, and survival attributes of M. gapperi were similar among treatment sites over the 3-year study. Overall mean abundance ranged from 3.5 to 5.3 voles per line in patches while this microtine was extirpated on clearcut sites (i.e., no forest patches). The similarity in population dynamics among the various forest patches across a gradient of increasing patch size of 4.5 to 35.3 times did not support H1. Mean abundance, species richness, and diversity of total forest-floor small mammals were similar among treatment sites, and hence did not support H2. Although not formally significant, mean species diversity did show a consistent increase from the largest (0.82) to the smallest (1.11) patch size, owing primarily to the presence of several generalist species such as Neotamias amoenus, Microtus, and Sorex in nearby early successional habitat. Small mustelids were present at similar levels among patch sizes, presumably in response to abundance of small mammal prey, and hence did not support H3. Although our results were relatively short-term, the detailed assessment of population dynamics of M. gapperi indicated that habitat quality was sufficient to maintain this species regardless of patch sizes, ranging from 0.3 to 20.0 ha. Similarly, the total forest-floor small mammal community and presence of small mustelids also followed this pattern. All sizes of forest patches have conservation value and will help to maintain abundance and diversity of forest mammals, both predator and prey species, on clearcuts. Longer-term studies (e.g., at 5- to 10-year intervals) are essential to determine if our results are sustainable in augmenting forest restoration.

Long-term functionality of woody debris structures for forest-floor small mammals on clearcuts

Restoration practices are much needed on clearcut openings in commercial forest landscapes where some mammal species have declined in abundance from a loss of preferred food, cover, and other components of stand structure. Retention of excess woody debris in piles and windrows provides habitat for forest-floor small mammals and some of their predators such as small mustelids. However, it is unknown if these retention habitats are used over longer periods (>10 years) as new forests grow and develop on harvested sites, or do they become unoccupied? We tested the hypotheses (H) that (H1) abundance, species richness, and diversity of the forest-floor small mammal community, and (H2) reproduction and survival of the southern red-backed vole (Myodes gapperi), long-tailed vole (Microtus longicaudus), and deer mouse (Peromyscus maniculatus) would decline on sites with woody debris structures, compared with sites of dispersed woody debris or uncut forest, up to 12 years post-construction in south-central British Columbia, Canada.Woody debris structures provided habitat on new clearcuts for M. gapperi at comparable or higher abundance than in uncut forest and 5.0 to 7.6 times higher than on dispersed sites in the first 5-year period. Although numbers declined after the initial three years, populations of M. gapperi in debris structures recovered to earlier abundance levels at 11–12 years post-construction. Mean abundance of M. longicaudus was consistently higher (2.8 to 3.5 times) in piles and windrows than in sites with dispersed woody debris over the first 5-year period. Populations of M. longicaudus were high in all three treatment sites at 11 years post-construction reaching mean annual peak numbers of 24, 42, and 36 voles per ha in the dispersed, piles, and windrow sites, respectively. Mean abundance of P. maniculatus was similar among treatment sites and consistent over time. Mean abundance of total small mammals was consistently higher (1.8 to 2.4 times) in piles and windrows than dispersed or forest sites in the first 5-year period and this pattern was continued at 11–12 years post-construction. At 11 years post-construction, all treatment sites had the highest peak numbers per ha in the study: dispersed (40.3), piles (64.1), windrows (56.1), and forest (29.0). Our results did not support H1 as abundance, species richness, and diversity were increased or maintained in the debris structures over the 12-year period. Reproduction and survival followed the pattern of abundance for the major species, and hence H2 was not supported. Our study is the first to measure long-term (up to 12 years) responses of forest-floor small mammals to constructed piles and windrows of woody debris as a means of habitat retention on clearcuts. These mammalian species, particularly voles, may then serve as prey for marten and other mustelids. This relationship provides further support for piles and windrows to act as baseline trophic structures in ecological restoration of cutover forest land.

Maintenance of small mammals using post-harvest woody debris structures on clearcuts: linear configuration of piles is comparable to windrows

Management of post-harvest woody debris structures (e.g., piles and windrows) may help conserve mammal diversity in commercial forest landscapes. A windrow (continuous woody debris) provides a linear habitat to connect patches and reserves of uncut forest and riparian areas to maintain forest-floor small mammals and allow some of their avian and mammalian predators to access and traverse clearcut openings. However, most post-harvest residues are arranged in independent piles of woody debris (separated by 20–30 m, on average) and we asked if a linear configuration of piles would provide similar habitat conditions for small mammals as that achieved by a windrow of continuous woody debris. We tested two hypotheses (H) that piles of woody debris arranged in a linear configuration, on newly clearcut sites, would (H1) enhance (a) abundance of the major small mammal species (Myodes gapperi and Microtus spp.), and (b) total abundance, species richness, and species diversity of the forest-floor small mammal community; compared with dispersed (conventional) treatment of woody debris. H2 predicted that, because of the continuity of habitat, responses of small mammals in windrows would be greater than those in piles of woody debris. Three study areas were monitored in southern British Columbia, Canada, and each had three treatments of woody debris: dispersed, in a linear set of piles, and as a windrow. Forest-floor small mammals were sampled by live-trapping in spring and fall periods from 2010 to 2012. Woody debris in a linear configuration of piles and in windrows enhanced mean abundance of the southern red-backed vole (M. gapperi), total voles, and total abundance of small mammals compared with the dispersed treatment. Small mammal responses were variable between spring and fall periods, but overall mean values ± 95% CIs indicated that abundance of M. gapperi, total voles, and total small mammals were reasonably similar in piles and windrows.

Mammalian responses to windrows of woody debris on clearcuts: Abundance and diversity of forest-floor small mammals and presence of small mustelids

Forest harvesting often leaves excess woody debris on the forest floor that could provide habitat for small mammals and mustelid predators. A windrow or series of piles constructed from woody debris may connect patches of mature forest and riparian areas to allow small mammals and some of their predators to use clearcut openings. We tested two hypotheses (H) that woody debris arranged in windrows connecting reserves of uncut forest, on newly clearcut sites, would increase (H1) abundance of the major vole species and total abundance, species richness, and species diversity of the forest-floor small mammal community, and (H2) presence of small mustelids in response to abundance of small mammal prey; compared with sites of dispersed woody debris or uncut forest. We measured abundance and diversity of small mammals and the presence of small mustelids (American marten, Martes americana; short-tailed weasel, Mustela erminea; long-tailed weasel, M. frenata) from 2012 to 2016 in replicated treatments of woody debris in windrow and dispersed sites compared with uncut forest sites at two study areas near Elkhart and Golden in south-central British Columbia, Canada.At Elkhart, mean abundance of total voles and total small mammals per index-line were higher in the windrow than dispersed sites, and higher or similar to forest sites. At Golden, mean abundance of total voles was similar, but the dispersed and windrow sites had higher numbers of total small mammals than the forest sites. Mean species richness and diversity were highest in the windrow sites at both study areas. Thus, the predictions of H1 were supported, except for total voles at Golden. Mean abundance of the southern red-backed vole (Myodes gapperi), a principal prey species for mustelids, was higher in windrow than dispersed sites, and similar or lower than forest sites. M. gapperi, along with the long-tailed vole (Microtus longicaudus) dominated the overall vole population in windrows at Elkhart. M. longicaudus dominated the windrows and dispersed sites at Golden. Deer mice (Peromyscus maniculatus) and northwestern chipmunks (Neotamias amoenus) were at similar numbers in dispersed and windrow sites, but shrews (Sorex spp.) showed a positive response to windrows. Overall mean presence by marten and small weasels were, on average, 3.3–4.8 times higher in windrow than dispersed sites, and higher or similar to forest sites, which supported H2. Our study is the first to connect windrows to patches and larger units of uncut forest and to cover a 5-year period since harvest. Responses in mean total abundance, species richness, and diversity of small mammals in windrows were maintained throughout the 5-year period. This consistent result was likely related to the connectivity between windrows and uncut forests. Strategic management of post-harvest woody debris in a network of windrows or piles will help to maintain abundance and diversity of forest mammals, both predator and prey species, on clearcuts.

Green-tree retention and recovery of an old-forest specialist, the southern red-backed vole (Myodes gapperi), 20 years after harvest

Context Populations of many mammalian species are reduced as a result of clearcutting, despite the concurrent objectives of wood production and conservation of mammal diversity on cutover forest land. To help ameliorate this decline, green-tree retention (GTR) leaves large live trees after harvest to provide mature forest habitat and increase structural diversity of the regenerating stand. Aims To test the hypotheses (H) that, at 20 years after harvest, (H1) abundance, reproduction and survival of the southern red-backed vole (Myodes gapperi), as well as (H2) abundance and species diversity of the forest-floor small mammal community, would increase with the basal area (BA) and density of residual trees after harvest. Methods Small mammals were live-trapped in 2015–16 in replicated clearcut, dispersed retention, aggregated retention, patch cut and uncut forest sites in mixed forests of Douglas fir (Pseudotsuga menziesii var. glauca) and lodgepole pine (Pinus contorta Dougl. var. latifolia) in southern British Columbia, Canada. Key results Mean BA and density of overstory coniferous trees were significantly different at 20 years post-harvest, being higher on patch cut and uncut forest sites than on the clearcut and GTR sites. M. gapperi populations were significantly greater in aggregated retention and uncut forest sites than in the other sites, but demographic parameters were similar among sites, and therefore H1 was partly supported. Mean total abundance of small mammals differed significantly among sites, with the highest overall numbers occurring in the aggregated retention (16.2), clearcut (13.6) and uncut forest sites (11.9). Mean species richness and diversity were highest in the GTR and clearcut sites. Thus, H2 was not supported. Conclusions Recovery of M. gapperi in aggregated retention sites with 10m2 ha–1 BA of residual trees, as a group, occurred at 20 years post-harvest. Implications Aggregated retention of residual trees should help provide some habitat to conserve forest mammals on harvest openings, but successional development up to 20 years post-harvest may be required.

Diversifying clearcuts with green-tree retention and woody debris structures: conservation of mammals across forest ecological zones

We tested the hypotheses (H) that on newly clearcut-harvested sites, (H1) abundance and species diversity of the forest-floor small mammal community, and (H2) abundance, reproduction, and recruitment of red-backed voles ( Vigors), would increase with higher levels of structural retention via green-tree retention (GTR) and woody debris (dispersed and constructed into windrows). Study areas were located in three forest ecological zones in southern British Columbia, Canada. For H1, mean total abundance did generally increase with the gradient of retained habitat structure. Mean species richness and diversity were similar among treatment sites but did show an increasing gradient with structural compexity. For H2, mean abundance, reproduction, and recruitment of were higher in GTR and windrow sites than those without retained structures. There was a positive relationship between mean abundance of and total volume of woody debris across treatments. This study is the first investigation of the responses of forest-floor small mammals to an increasing gradient of retained habitat structure via GTR and woody debris on clearcuts. Our assessment of a combination of these two interventions suggested a potentially strong additive effect that could be cautiously extrapolated across three forest ecological zones. With the advent of low levels of GTR on clearcuts, woody debris structures should help provide some habitat to conserve forest mammals on harvest openings.Myodes gapperiM. gapperiM. gapperi

Influence of repeated fertilization and cattle grazing on forest ecosystems: Abundance and diversity of forest-floor small mammals

Intensive silvicultural practices such as pre-commercial thinning (PCT) and repeated fertilization have the potential to provide a diversity of forest habitats and wildlife to meet biodiversity conservation goals while maintaining wood production. Silvopasture combines livestock with trees in some managed forests, but the impact of grazing on biodiversity is unclear. Forest-floor small mammal communities may serve as ecological indicators of changes in forest structure and function, and hence biodiversity. This study was designed to test the hypotheses (H) that in young (13–23years) even-aged lodgepole pine (Pinus contorta) stands, (i) abundance of understory herbaceous vegetation and (ii) abundance and diversity of forest-floor small mammals would be: (H1) enhanced in fertilized stands, and (H2) reduced in stands with cattle grazing. Study areas were located near Kelowna (lightly grazed) and Summerland (heavily grazed) in south-central British Columbia, Canada. Each study area had four pairs of PCT stands thinned to a range of densities with one stand of each pair fertilized four times at 2-year intervals. Herbaceous vegetation and forest-floor small mammal communities were sampled from 1993 to 2002.Mean abundance of total herbs, total grasses, and fireweed (Epilobium angustifolium) all increased dramatically with fertilization in the lightly grazed stands, and hence part (i) of H1 seemed to be supported. Mean total abundance of small mammals was higher in fertilized than unfertilized stands in two years but not overall. Species richness and diversity of small mammals were similar between unfertilized and fertilized stands, and hence part (ii) of H1 was partially supported for abundance, but not for richness or diversity. Lightly grazed fertilized stands had low abundance of Peromyscus maniculatus and Tamias amoenus, but high abundance of Microtus pennsylvanicus, Sorex monticolus, and Sorex cinereus. Phenacomys intermedius and Myodes gapperi also seemed to decline in fertilized stands. Mustela erminea, a principal predator of microtines, was captured more frequently in the lightly grazed fertilized than unfertilized stands.Cattle grazing reduced the abundance of herbaceous vegetation, at least in the fertilized stands at Summerland where they consumed a significant proportion of the biomass, and hence part (i) of H2 was supported. However, this premise did not hold for the unfertilized stands where grazing had little effect on the three plant groups. Part (ii) of H2 was not supported as cattle grazing did not reduce total abundance and species diversity of forest-floor small mammals. Grazing in fertilized stands did limit population fluctuations and dynamics of M. pennsylvanicus and abundance of the two insectivores during certain years. Forest-floor small mammal communities and their myriad ecological functions should be maintained, at least in some years, in those stands intensively managed for wood, biomass, and livestock production.

Partial and clearcut harvesting of dry Douglas-fir forests: Implications for small mammal communities

Dry Douglas-fir ( Pseudotsuga menziesii) forests offer a wide range of timber and non-timber values, which may benefit from a balanced timber harvest by variable retention systems with conservation of biodiversity. A major component of biodiversity are forest floor small mammal communities whose abundance and diversity serve as ecological indicators of significant change in forest structure and function from harvesting activities. This study was designed to test the hypotheses that abundance, reproduction, and survival of (i) the southern red-backed vole ( Myodes gapperi, formerly Clethrionomys gapperi), will decline; (ii) the deer mouse ( Peromyscus maniculatus), will be similar; and (iii) the meadow vole ( Microtus pennsylvanicus) and northwestern chipmunk ( Tamias amoenus), will increase, with decreasing levels of tree retention. Small mammal populations were live-trapped from 1994 to 1997 in replicated sites of uncut forest, 20% and 50% volume removal by single tree selection, 20%, 35%, and 50% patch cuts based on openings of 0.1–1.6 ha, and small 1.6 ha clearcuts in Douglas-fir forest near Kamloops, British Columbia, Canada. M. gapperi dominated the small mammal community, starting with an abundance of 74–98 animals/ha with mean values ranging from 33 to 51 animals/ha. In the two post-harvest years, abundance, reproduction, and survival of M. gapperi populations were consistently similar among uncut forest and the various levels of tree retention. Thereafter, M. gapperi was seldom found on the small clearcuts. M. pennsylvanicus, T. amoenus, and P. maniculatus occurred predominantly in clearcut sites. As with other types of forest disturbance, responses to our treatments were species-specific. The most striking result was the high abundance and productivity of M. gapperi populations in a dry forest ecosystem, a novel result for this bio-indicator species of closed-canopy forest conditions. At least with respect to small mammals, the retention systems studied seem to enable timber extraction and maintenance of mature forest habitat in these dry fir ecosystems.

Long-term responses of ecosystem components to stand thinning in young lodgepole pine forest: II. Diversity and population dynamics of forest floor small mammals

A variety of silvicultural practices may be used to diversify second-growth forests that have regenerated from clearcut harvesting. These young stands are structurally simple and amenable to practices such as variable-density and conventional thinnings to accelerate ecosystem development. This study was designed to test the hypotheses that (i) abundance and diversity of forest floor small mammals, and (ii) population dynamics (reproduction, recruitment, and survival) of the southern red-backed vole ( Clethrionomys gapperi) would be maintained at levels recorded in old-growth forest, by large-scale thinning to various densities in young lodgepole pine ( Pinus contorta) forest. Replicate study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada. Each study area had three stands thinned to densities of ∼500 (low), ∼1000 (medium), and ∼2000 (high) stems/ha, with an unthinned young pine and old-growth pine stand for comparison. Forest floor small mammal communities were sampled intensively in 2000, 2001, and 2002 at 12–14-years after the pre-commercial thinning treatment. Mean total abundance of small mammals was similar among stands with the highest overall numbers recorded in 2002. Mean species richness and diversity of small mammals were similar among stands. Mean abundance of C. gapperi was similar among stands and increased significantly with time. This pattern of abundance of C. gapperi will likely be consistent except perhaps in years of high numbers when productivity of this species may be highest in old-growth forest. Reproduction, recruitment, and early juvenile survival of C. gapperi was similar among stands; Jolly–Seber summer survival was higher in the thinned than unthinned stands with no difference in winter survival among stands. Our results supported hypotheses (i) and (ii) that abundance and diversity of forest floor small mammals and the demographic attributes of C. gapperi populations would be maintained in young managed lodgepole pine stands (thinned or unthinned) at levels recorded in old-growth forest.

Influence of conventional and chemical thinning on stand structure and diversity of plant and mammal communities in young lodgepole pine forest

Silvicultural practices that provide a wide variety of vegetative composition and structure (habitats) in young stands should help manage for biological diversity across forested landscapes. This study was designed to test the hypotheses that: (i) abundance and diversity of stand structure attributes (species diversity and structural diversity of herb, shrub and tree layers) and forest floor small mammal communities, and (ii) relative habitat use by large herbivores, will increase from unthinned to conventionally thinned to chemically thinned stands of young lodgepole pine ( Pinus contorta) forest. Replicate study areas were located near Summerland, Kelowna and Williams Lake in south-central British Columbia, Canada. Each study area had three treatments: a conventionally thinned, a chemically thinned and an unthinned stand. Pre-commercial thinning was conducted in 1993. Coniferous stand structure and understory vegetation were measured prior to thinning in 1993 and 5 years later in 1998. Small mammal populations were sampled intensively from 1993 to 1998. Relative habitat use by large herbivores was sampled in 1998. Our results indicate that chemical thinning of young lodgepole pine stands produced an aggregated pattern of crop trees compared with stands subjected to conventional thinning. Diameter growth of crop trees in the chemically thinned stands was similar to that in the conventionally thinned, but also to that in unthinned stands. Although horizontal stratification (aggregates of trees) was enhanced, vertical stratification (structural diversity of vegetation) was less in the chemically than conventionally thinned stands. Abundance and diversity of understory vegetation and small mammal communities were generally unaffected by stand thinning in these particular installations. Relative habitat use by mule deer ( Odocoileus hemionus) occurred in a gradient from highest in the conventionally thinned stand to lowest in the unthinned stand. Habitat use by snowshoe hares ( Lepus americanus) tended to have the opposite trend. Moose ( Alces alces) exhibited no difference in habitat use among stands. Thus, although there were few differences among treatment stands, chemical thinning could be used to develop an aggregated pattern of crop trees in pre-commercially thinned stands to maintain habitat for herbivores such as snowshoe hares and mule deer. Understory plant and forest floor small mammal communities would be maintained in these stands as well.

SMALL MAMMALS AND STAND STRUCTURE IN YOUNG PINE, SEED-TREE, AND OLD-GROWTH FOREST, SOUTHWEST CANADA

Alternative silvicultural systems to clearcutting are receiving considerable attention in Pacific Northwest forests of North America. Understanding the implications of these harvesting systems on stand structure and biodiversity through time is a fundamental aspect of forest ecosystem management. This study was designed to test the hypothesis that diversity of stand-structure attributes and forest floor small-mammal communities will increase from young pine to seed tree to old-growth forest. The study area was within mixed Douglas-fir (Pseudotsuga menziesii)–lodgepole pine (Pinus contorta) forests within the Montane Spruce biogeoclimatic zone near Summerland in south-central British Columbia, Canada. This retrospective study had three replicate stands each of 17-yr-old “young pine” (clear-cut harvested), “seed tree” composed of young pine with Douglas-fir seed trees, and uncut “old-growth” composed primarily of Douglas-fir and lodgepole pine. Stand-structure attributes (coniferous tree layers and understo...

Competition and Habitat Selection in a Forest-Floor Small Mammal fauna

In a study of habitat exploitation in a forest-floor small mammal community, we have collected habitat and population data for Peromyscus leucopus (white-footed mouse), Ochrotomys nuttalli (golden mouse) and Tamias striatus (eastern chipmunk). Using multiple regression analysis, we estimate the effects of habitat selection and competition on the local distributions of these species during three seasons. Each of the partial regression coefficients relating the density of an independent species to the density of the dependent species is negative. This result indicates that competition (i.e., mutual inhibition) is pervasive among these species. Competitive ability and habitat selectivity both increase in the order PeromyscusTamiasOchrotomys. Peromyscus is a poorly competitive habitat generalist, Ochrotomys is a strongly competitive habitat specialist, and Tamias is intermediate in both respects. The competitive hierarchy is stable between seasons. These results both confirm the conclusions reached in previous studies of this small mammal community and suggest the design of experiments to further clarify the mode and consequences of interaction between these species.