Avian Response to Old-growth Maintenance Logging in the Swan River State Forest, Montana

Abstract

Old-growth maintenance silvicultural treatment is a tool implemented to retain old-growth forest attributes, remove shade-intolerant trees, and create canopy gaps. Our objectives were to examine how these treatments affect avian diversity and density. We used a Before-After/Control-Impact Pairs study design by pairing old-growth stands proposed for harvest with nearby untreated stands, based on their pre-treatment forest structure and composition similarity. Logging reduced basal area by 40 percent (P < 0.05), overstory canopy cover by 31 percent (P < 0.05), and the density of trees >42 cm dbh (P < 0.05). No major changes in bird species composition or diversity were detected. Only the relative densities of evening grosbeaks changed (58% reduction in density, P < 0.05), likely due to the removal of insect-infested trees. All old-growth associated bird species continued to occupy treatment stands under the landscape conditions we observed. We did not evaluate avian survival or reproductive success, which would provide beneficial metrics for further interpretation of the potential effects of old-growth maintenance treatments.