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.     

Threshold effects of variable retention harvesting on understory plant communities in the boreal mixedwood forest

We studied the effects of six levels of dispersed green-tree retention (GTR) harvesting (clearcut (0%), 10%, 20%, 50%, and 75%, and unharvested reference (100%)) on understory plant communities in the 8th growing season post-harvest in the mixedwood boreal forest in northwestern Alberta. For the partial harvest treatments (10%, 20%, 50%, 75%) sample plots were located in the partially harvested (retention) strips as well as in the intervening machine corridors used by the harvesting equipment. The understory plant community was significantly influenced by the gradient of retention level. The cover of understory vegetation, especially graminoids, increased with increasing harvesting intensity for the retention strips and overall considering both plots types. Species richness was unaffected by retention level but did decrease as tree density increased. Lower levels of retention lead to increased abundance of early successional, shade-intolerant species. The results suggest a threshold in understory response to GTR harvesting between the 10% and 20% retention treatments. In terms of understory cover and composition, machine corridors within partially harvested forests resembled clearcuts. The results suggest that retaining more than 10% during GTR harvesting could have significant benefits in terms of maintaining understory plant communities more similar to unharvested reference forest.     

Influence of variable organic matter retention on nutrient availability in a 10-year-old loblolly pine plantation

The effects of varying forest floor and slash retention at time of regeneration were evaluated 10 years after the establishment of a loblolly pine plantation near Millport, Alabama. Treatments included removing, leaving unaltered, or doubling the forest floor and slash material. Forest floor and litterfall mass and nutrient concentrations, available soil N, foliar nutrient concentrations and stand yield were all impacted by the treatments. Forest floor mass and nutrient contents in the doubled treatment were significantly greater than the other two treatments. The doubled treatment accumulated 25, 45 and 350% more forest floor mass and 56, 56, and 310% more N than the control treatment in the Oi, Oe, and Oa layers, respectively. The other nutrients followed similar patterns. Potentially mineralized NO₃⁻-N in the mineral soil was also significantly higher in the doubled treatment. The positive effect of doubling the forest floor on soil N availability was reflected in greater foliage production, 30% more litterfall and 25% more stand yield for this treatment. This study shows that increasing the forest floor retention has resulted in increased nutrient availability and improved tree growth.     

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.     

Forecasting vole population outbreaks in forest plantations: The rise and fall of a major mammalian pest

Voles of the genera Microtus and Myodes feed on tree seedlings planted on cutover forest land in temperate and boreal forests of North America and Eurasia. This damage may have serious economic implications as well as limit regeneration of appropriate tree species in certain forest ecosystems. Prediction of vole population outbreaks and feeding damage to forest plantations, across even a limited geographic range, has yet to be achieved in North America. Thus, a major objective was a detailed analysis of changes in population dynamics of long-tailed voles (Microtus longicaudus), and to test three hypotheses (H) that vole populations would: (H₁) rise and fall in accordance with the abundance of herbaceous plants (grasses and forbs) during early vegetative succession after forest harvesting, (H₂) be positively associated with grass-seeded sites; and (H₃) incidence of feeding damage to seedlings would be positively associated with vole abundance. Voles were live-trapped for 6 years (2004–2009) from the time of harvesting on intensive sites, as well as surveyed over a range of extensive sites. Population numbers were related to habitat characteristics and tree damage in young forest plantations near Golden, British Columbia, Canada.