Bird communities are affected by amount and dispersion of vegetation retained in mixedwood boreal forest harvest areas

Abstract

We evaluated bird community response to type, amount, and dispersion of trees, snags, and shrubs that were retained at harvest in mixedwood boreal forests of Alberta, Canada. We also evaluated whether the degree of similarity between bird communities in harvest and old-growth areas was related to the type and amount of materials retained at harvest. We combined data from three separate studies to generate a large data set covering a wide range of cut-block structures. Birds were surveyed using point counts and line transects. Residual vegetation was surveyed partially on the ground, and partially from aerial photographs. Bird species commonly associated with parkland and open country habitats had high densities in harvest areas that contained abundant shrubs and few residual trees or snags. Within harvest areas where more trees, particularly large deciduous trees, were retained, and when those trees were retained in clumps, bird communities were more similar to those found in old-growth forests. Thus, by retaining clumps of large trees and snags in harvest areas managers may be able to create habitats that are used by old-growth forest bird species. However, for many forest birds, density was lower in cut-blocks with residual trees and snags than it was in old-growth forest. Results should be interpreted cautiously because survival and reproductive success of forest birds in cut-blocks with residual trees and snags was not determined.