Pattern and process in forest bird communities on boreal landscapes originating from wildfire and timber harvest

Abstract

Policy direction to emulate natural disturbance in managed boreal forests has spurred a need to contrast the dynamics of biota on landscapes originating from timber harvest and from wildfire (hereafter, “managed” and “natural”). Typically, emphasis is on pattern emulation, and less on processes, such as competition, predation or habitat selection. Knowing how communities in the boreal forest assemble can provide further insight to the effects of anthropogenic disturbance on the processes responsible, permitting assessments about whether forestry practices emulate processes as well as patterns. We contrasted variation in species richness among forest types, with stand area, and between local (forest stand) and regional (landscape) scales on managed and natural boreal landscapes in NW Ontario. Species richness varied more among forest stand types than between landscapes, or with stand area, on either landscape. On both landscapes, mean local species richness was 1/3 of regional richness, consistent with the hypothesis that competition structured stand-level assemblages regardless of stand origin. We further compared the structure of stand-level assemblages from randomized null models using presence/absence and abundance data with observed assemblages on each landscape, while controlling for variation in habitat structure among stands. Local bird assemblages were over-dispersed in niche space relative to random assemblages, also consistent with the competition hypothesis, regardless of stand origin. We found no evidence that patterns of variation in diversity of songbirds and woodpeckers, nor the processes that govern them, differed between managed and natural boreal forest landscapes. Our results suggest that past forest practices in this region, if by default, nevertheless emulated natural patterns of variation in diversity and species assembly of bird communities. Key words: boreal forest, songbirds, woodpeckers, community assembly, null models, natural disturbance emulation, forestry, Ontario