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Long-term responses of ecosystem components to stand thinning in young lodgepole pine forest: II. diversity and population dynamics of forest floor small mammals
Sullivan, Thomas P.
Perhaps the greatest opportunity to diversify forests for the future lies in the vast areas of young second-growth stands, primarily lodgepole pine (Pinus contorta) in the southern interior, which are amenable to silvicultural practices to accelerate ecosystem development. Pre-commercial thinning is a silvicultural tool which can enhance productivity of crop trees and stand structure. There are indications that some old growth structural attributes may develop sooner in young stands, particularly at densities < 1000 stems/ha, rather than waiting many decades for these features to appear in unmanaged or high-density stands. Development of such structures may be crucial for some old-growth dependent mammal species. Examples include mule deer (Odocoileus hemionus), red-backed voles (Clethrionomys gapperi), red squirrels (Tamiasciurus hudsonicus), and northern flying squirrels (Glaucomys sabrinus). This project was designed to determine (1) the population responses of redbacked voles, red squirrels, and flying squirrels to low, medium, and high densities of lodgepole pine compared with unthinned young pine and old-growth pine; (2) species diversity of the forest floor small mammal communities in these stands; and (3) relative habitat use by mule deer, moose (Alces alces), and snowshoe hares (Lepus americanus) in these stands during summer and winter periods. This report outlines results from the third year of a 4-year project (2000-2003) leading up to a 15-year remeasurement in 2003 of diameter and height growth increments of crop trees and coniferous stand structure. Stand structure attributes (species diversity and structural diversity of herb, shrub, and tree layers), and abundance of arboreal and forest floor small mammals 3 were sampled during 2000 to 2002, and relative habitat use by deer, moose, and snowshoe hares in 2000-2001, in the five stand treatments at each of three replicate study areas. These areas were near Penticton, Kamloops, and Prince George in three different ecological zones. Crown volume index (biomass) of herbs was highest in the thinned stands, but there was no difference among stands for shrubs and trees. Mean species richness and diversity of herbs, shrubs, and trees were similar among stands. Total structural diversity of vascular plants appeared highest in the thinned stands. Mean structural diversity, in terms of richness of height classes (or layers of vegetation), was greatest for shrubs in the young pine stands and for trees in the thinned and old-growth stands. Mean abundance of red-backed voles appeared highest in the old-growth stands. Mean abundance of red squirrels was similar among stands overall, but at Penticton and Kamloops was highest in the old-growth stands. Flying squirrels were at highest numbers in the high-density stands followed by the medium-density and old-growth stands. Abundance of this sciurid was lowest in the low-density and unthinned stands. This project is designed to be completed in 2003. Our comprehensive investigation will determine if old-growth structural attributes in managed stands provide functional habitat for these wildlife species while providing a continuing flow of wood products. This relationship has clear implications for sustainable management, annual allowable cut levels, and related harvest schedules and plans Thomas P. Sullivan...[et al.]
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