Effects of partial harvesting on vertebrate species associated with late-successional forests in Ontario’s boreal region

Abstract

In the boreal forest region, partial-harvest silviculture has been garnering increasing interest as a means of maintaining wildlife species and habitat structure associated with late-successional forests. If late-successional species can find suitable habitat in partially harvested stands with a given level of structural retention, then partial harvesting might represent a viable silvicultural tool for maintaining wildlife dependent on mature or old-forest habitat within managed stands over time. Here we summarize literature on the responses of late-successional amphibians, birds, and mammals in Ontario’s boreal region to various intensities of partial harvesting. We assess species responses from comparisons of habitat use in harvested and unharvested stands; we do not explicitly consider impacts of partial harvesting applied over large areas across the landscape. At the stand scale, light-intensity harvesting (70% retention) negatively affects several passerine birds, as well as spruce grouse winter habitat, but most late-successional species (including all mammals and amphibians considered) appear to be tolerant of this level of habitat alteration. Moderate-intensity harvesting (50% retention) was found to reduce the abundance of about 40% of the species considered, particularly cavity- and snag-dependent species (martens, northern flying squirrels, owls) and passerine birds that forage or nest in the canopy and understory. High-intensity (30% retention) partial harvesting was found to provide unsuitable habitat for about one quarter of all late-successional species, including most forest raptors, pileated and black-backed woodpeckers, brown creepers, northern flying squirrels, and woodland caribou. Also, studies indicate that additional passerine bird species would decrease in abundance, as would small, moisture-dependent, terrestrial species such as short-tailed shrews, red-backed voles, and eastern red-backed salamanders. There is a need to strengthen our understanding of responses to partial harvesting for nonpasserine birds and large mammals, and to verify species responses through experimental studies within Ontario’s boreal region. Key words: structural retention, selection, shelterwood, seed tree, cavities, snags, downed woody debris, habitat suitability, amphibians, birds, mammals, biodiversity, review