1.Variable retention harvests in temperate coniferous forests provide various intensities and sizes of disturbance across a gradient, from clear-cutting to single-tree harvesting. These 'green-tree retention systems' leave large live trees after harvest (i.e. residual trees) to increase structural diversity of the regenerating stand. It is unclear what effect these harvesting patterns will have on wildlife in general, and small mammals in particular. 2.This study was designed to test the hypotheses that: (i) the abundance and diversity of forest-floor small mammals will decline with lower levels of tree retention; (ii) the abundance, reproduction and survival of Microtus spp. and southern red-backed vole Clethrionomys gapperi populations will decline and increase, respectively, with the basal area and density of residual trees after harvest; and (iii) habitat heterogeneity generated by variable retention harvesting will limit population size of Microtus , thereby reducing feeding damage to tree seedlings planted on harvested areas. 3. Small mammals were intensively live-trapped from 1996 to 1999 in replicated clearcut, single seed-tree, group seed-tree, patch-cut and uncut forest sites in mixed natural forests of Douglas fir Pseudotsuga menziesii -lodgepole pine Pinus contorta in southern British Columbia, Canada. The seed-tree harvesting system leaves a few wind-firm seed trees standing singly, or in groups, to provide seed to regenerate an area naturally. The patch-cut system harvests timber from small (< 1-ha) units dispersed over a given area of forest. 4. Contrary to hypothesis (i), the mean total abundance of small mammals was similar among sites, and mean species richness and diversity of small mammals was lowest in the uncut forest but similar across the other four treatments. 5. The overall mean abundance (ha -1 ) of Microtus spp. was higher on clear-cut (11·3) sites than single seed-tree (6·0), group seed-tree (3·9), patch-cut (1·8) or uncut forest (0·1) sites. Overall mean abundance (ha -1 ) of C . gapperi was similar in uncut forest (16·2) and group seed-tree (10·0) sites, which were both higher than patch-cut (6·4), clear-cut (4·2) or single seed-tree (2·7) sites. 6. The recruitment of new Microtus spp. differed significantly among sites, declining from clear-cut to uncut forest. The recruitment of C . gapperi exhibited the opposite trend. The mean number of successful pregnancies was similar among treatments for Microtus spp. but for C . gapperi was highest in uncut forest, group seed-tree and patchcut sites. The survival of each vole species was similar across treatment sites. 7. Hypothesis (ii) was supported. The mean abundance of Microtus spp. was inversely, and that of C . gapperi positively, related to mean basal area and density of residual trees after harvest. The mean abundance of Microtus spp. was also inversely related to percentage cover and crown volume index of residual trees, and positively related to number of lodgepole pine cones (seeds) in logging debris. 8.In terms of hypothesis (i...

Management of forested landscapes for biological diversity is a major objective across North America. Perhaps the greatest potential to diversify future forests lies in the vast areas of young second-growth stands which may be managed silviculturally to accelerate ecosystem development. This study was designed to test the hypotheses that large-scale precommercial thinning, at ages 17-27 yr, to various stand densities would, over the 10-yr period since treatment, enhance: (1) productivity of lodgepole pine (Pinus contorta) crop trees, (2) stand structure attributes, and (3) species richness and diversity of forest floor small-mammal communities. Study areas were located near Penticton, Kamloops, and Prince George in south-central British Columbia, Canada, in three forest ecological zones. Each study area had three stands thinned to densities of ϳ500 (low), ϳ1000 (medium), and ϳ2000 (high) stems/ha, with an unthinned juvenile pine and old-growth pine stand for comparison. Understory vegetation was measured in all stands in 1990, 1993, and 1998, and coniferous tree layers were measured in 1998. Small-mammal populations were sampled intensively in 1990, 1991, and 1998. Mean diameter increments of trees in the low-density stands were significantly higher than those in the medium-and high-density stands at all study areas. Mean height increments of trees were similar in the medium-and high-density stands and significantly higher than that in the low-density stands at Penticton and Prince George. Crown volume index (biomass) of herbs was highest in the thinned stands by 1998, but there was no difference among stands for shrubs and trees; volume of mosses was highest in the old-growth stands. Mean species richness and diversity of herbs, shrubs, and trees were similar among stands at 2, 5, and 10 yr after thinning. However, mean species diversity and structural diversity of coniferous trees were significantly higher in the low-and medium-density stands than in the high-density and unthinned stands 10 yr after thinning. Total structural diversity of all vegetation in the low-density stands was significantly greater than that of the mediumdensity, unthinned, and old-growth stands in 1998.Mean total abundance of all small mammals was similar among stands in 1990-1991, but the low-density and old-growth stands had the most mammals in 1998. Mean abundance of southern red-backed voles (Clethrionomys gapperi) was consistently higher (2.1-3.3 times) in the old-growth stands than in unthinned stands. In seven of nine cases, mean abundance of red-backed voles was similar among old-growth and thinned stands. Mean species richness and species diversity of small mammals were highest in the low-density and medium-density stands. Heavily thinned lodgepole pine stands developed structural attributes such as large diameter trees, large crowns, and structurally diverse vegetative understories. Forest floor small-mammal communities reflected the compositional and structural diversity of these managed stands.

No abstract

We investigated plant community responses (abundance, species diversity, and structural diversity) to a range of precommercial thinning densities in young lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) stands 12 to 14 years after thinning, with both unthinned and old-growth stands for comparison. Abundance of understory plants, especially herbs, appeared to increase dramatically in the thinned stands. The moss layer was significantly more abundant in old-growth stands than in the young pine stands. Of a total of 108 species sampled, only three were introduced species, all of which occurred more frequently in the low-density stands than in any of the other stands. Thinning treatments appeared to increase the abundance of late-seral species. Our results suggest that by disrupting canopy closure, thinning decreased the dominance of tall trees and increased the abundance of herbs, shrubs, and trees in the understory height classes. As a result, thinning to low densities significantly increased the structural richness of the tree layer and caused an increase in total structural diversity, which, although only marginally significant (p = 0.06), was likely biologically important. Our results suggest that thinning will enhance the abundance, species diversity, and structural diversity of the plant community 12 to 14 years postthinning.

Summary 1.Variable retention harvests or 'green-tree retention systems' are important to the management of coniferous forests in the temperate zone. Green-tree retention leaves large live trees after harvest (i.e. residual trees) to increase structural diversity of the regenerating stand and provide mature forest habitat that develops sooner than in typical even-aged management by clear-cutting. The seed-tree system is one method of harvesting that leaves a few wind-firm seed trees standing singly, or in groups, to provide seed to regenerate an area naturally. Green-tree retention may increase biological diversity and help to enhance functional links among forest structures or ecological processes. 2. This study was designed to test the hypothesis that the abundance (e.g. basal area and density of residual trees and amount of vegetation) and diversity (e.g. species diversity and structural diversity of the herb, shrub and tree layers) of various aspects of stand structure will decline with lower levels of tree retention. In particular, abundance and diversity should be greater in sites with green-tree retention than in clear-cut sites. 3. Stand structure attributes were measured from 1996 (immediately after harvesting) to 1999 in replicated clear-cut, single seed-tree, group seed-tree, patch-cut and uncut forest sites in mixed forests of Douglas fir Pseudotsuga menziesii -lodgepole pine Pinus contorta in southern British Columbia, Canada. 4. In terms of abundance, clear-cut, single seed-tree and group seed-tree sites had similar mean basal areas of residual trees, ranging from 0·1 to 2·5 m 2 ha -1 , with significantly higher levels on patch-cut (23·4 m 2 ha -1 ) and uncut forest (39·0 m 2 ha -1 ) sites. Mean densities of residual trees also followed this pattern, ranging from 0·7 to 16·3 stems ha -1 on the clear-cut to group seed-tree sites, to 769·4 and 2050·0 stems ha -1 on the patch-cut and uncut forest sites, respectively. However, mean volume (m 3 ha -1 ) of fallen wood (i.e. dead wood or woody debris) was similar among sites, ranging from 116·7 in the single seedtree to 210·2 in the patch-cut sites. Contrary to our hypothesis, the mean index of total crown volume of herbs, shrubs, mosses and lichens was similar among sites. 5. Mean species richness of herbs, shrubs and total plants was similar among sites. Mean richness of trees in seed-tree sites was similar to that in uncut forest in three of four post-harvest years. The mean species diversity of herbs was similar among sites, but that of shrubs and trees was generally lowest in the patch-cut sites and similar among the other sites. 6. The mean structural richness and diversity of herbs was lowest in the uncut forest and similar at the other sites 3 and 4 years post-harvest. The mean structural richness of trees and total plants in the patch-cut and uncut forest sites had more vegetation layers than the other sites. 7. Our hypothesis was partly supported in terms of basal area and density of residual trees and structural richness of total vegetation laye...

The conservation of biological diversity (biodiversity) is becoming an integral part of the sustainable management of forest- and agro-ecosystems. A vital part of these systems is weed control, or vegetation management, to enhance crop production. Because of its widespread use and environmental compatibility, this review was designed to evaluate glyphosate herbicide in terms of: (i) its role as a disturbance agent and (ii) a measure of its impact on species diversity of terrestrial plants and animals. Our analyses were based on 60 published studies of terrestrial plants and animals in temperate zone forest- and agro-ecosystems. Species richness and diversity of vascular plants was either unaffected or increased, particularly herbaceous species, in response to glyphosate. Responses of plant species in forest ecosystems differ from those in agro-ecosystems where glyphosate is used to repeatedly reduce non-crop vegetation in most situations. Richness and diversity of songbirds appeared little affected by glyphosate-induced habitat alteration. In studies on small mammal communities and glyphosate use, none found significant reductions in species richness or diversity. As for avian responses, some small mammal species declined temporarily whereas others increased in abundance. The impact of glyphosate on large mammalian herbivores was measured by abundance of animals and food plants and by habitat use. Hares (Lepus spp. L.) and deer (Odocoileus spp. Rafinesque and Capreolus capreolus L.) were little affected, whereas reductions in plant biomass and related moose (Alces alces L.) forage and habitat use generally occur for 1–5 years after treatment. Studies on terrestrial invertebrates covered a wide range of taxa with variable responses in abundance to glyphosate treatments. The magnitude of observed changes in mean species richness and diversity of vascular plants, birds, and small mammals, from the effects of herbicide treatment, were within the mean values of natural fluctuations of these variables. The biological significance of this impact is limited to shifts in species composition based on changes in floral composition and structure of habitats. Management for a mosaic of habitats within forest and agricultural landscapes, which provide a range of conditions for plant and animal species, should help ameliorate the short-term changes in species composition accompanying vegetation management with glyphosate.Key words: agro-ecosystems, forests, glyphosate, plants and animals, species richness and diversity, vegetation management.

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If food is in short supply, then provision of addition food should increase the density of Douglas squirrels. A squirrel population was supplied with extra food during the summers of 1977 and 1978 and winter of 1978-1979 in coastal coniferous forest at Maple Ridge, British Columbia. Food produced a 5-to 10-fold increase in squirrel density compared with control populations. Control densities generally varied from 3 to 10 squirrels per trapping area with the experimental population increasing to 65 animals during the winter feeding. This irruption was produced by immigration, more reproduction in females, and increased survival. After the food was withdrawn, the population declined to a level comparable with the controls. We conclude that Douglas squirrel populations fluctuate in accordance with the abundance of food. Territorial behavior may space individuals within populations of Tamiasciurus douglasii but to density levels determined by the available food supply.