Date of Award

5-2003

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Wildlife Ecology and Wildlife Conservation

Advisor

Daniel J. Harrison

Second Committee Member

William B. Krohn

Third Committee Member

Frederick A. Servello

Abstract

The extent of precommercial thinning (PCT) to manipulate stand density in overstocked, regenerating stands and to accelerate growth, yield, and the rate of development of crop trees has been increasing within the Acadian forest of northeastern North America. Although the silvicultural responses of crop trees to thinning are well studied, few studies have evaluated the effects of PCT on forest-dependent wildlife and their habitat. I investigated the effects of PCT and stand succession on snowshoe hares, small mammals, and forest structure on 38 stands (25 treated with PCT, 13 unthinned stands) from 1 to 16 years post-treatment within 7 townships in the commercial forests of northern Maine. Forest stands were clearcut from 1967-1983, treated with an aerial herbicide during 1977-1988, and treatment stands were manually thinned from 1984-1999. Densities of snowshoe hares were examined by establishing approximately 46 km of pellet transect across 30 stands and live-trapping a subset of 8 stands to determine the relationship between densities of pellets and estimated densities of hares. Densities of hares were linearly related to pellet densities from 0-3 hareslha (P < 0.001). Two similar pellet x hare density regressions developed outside Maine did not perform well (AICc, > 10) and predictions from these regressions underestimated densities of hares. Unthinned stands had approximately 2x greater densities of hares than similar stands treated with PCT across stand ageclasses, 2 years of sampling, and during leaf-off (October -May) and leaf-on (June - September) seasons (P < 0.10). Although densities of hares were lower in stands treated with PCT, thinned stands still maintained densities greater than stands managed using some alternative silvicultural regimes. I examined the temporal effects of PCT on small mammals by live-trapping within 37 stands (24 treated with PCT) during June-August 2000 and 2001. Thinning increased [red-backed voles (Clethrionomys gapperi), P = 0.008; masked shrews (Sorex cineus), P < 0.0011 or produced no detectable effect [deer mice (Peromyscus maniculatus), P = 0.544; short-tailed shrews (Blarina brevicauda), P = 0.5171 on the 4 - most abundant species of small mammals captured on my study areas; therefore, PCT was compatible with maintaining or enhancing densities of common species of forest-dwelling small mammals in regenerating conifer stands. ' Dominant changes in forest structure were described from 1 to 11 years post-treatment between herbicide treated clearcuts with and without PCT, to predict wildlife responses to thinning and stand succession. During summers 2001 and 2002,29 structural characteristics were quantified across 30 forest stands (17 treated with PCT). Variables with either significant effects of treatment or thinning class were incorporated into a principal components analysis (PCA) to reduce the dimensionality of data. Nearground cover, overhead cover, and understory structure described approximately 80% of variation between thinned and unthinned stands. Horizontal cover, an overstory to understory contrast, and a gradient of herbaceous vegetation accounted for 75% variation in forest structure among thinning classes of stands. Wildlife associated with dense, early successional habitat, such as snowshoe hares, have been negatively affected by PCT, but thinning could positively influence species that use more mature forest with a more open understory (i.e. red-backed voles).

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