Canadian Forest Service Publications
Does postharvest silviculture improve convergence of avian communities in managed and old-growth boreal forests? 2013. Thompson, I.D.; Kirk, D.A.; Jastrebski, C. Canadian Journal of Forest Research 43:1050-1062.
Issued by: Great Lakes Forestry Centre
Catalog ID: 35198
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Habitat change following forest management may reduce biodiversity in boreal forests, as it has done globally in many forest types. Postharvest silviculture (PHS) is implemented to improve the yield of commercial tree species and has been applied to large areas of boreal forests. PHS may also influence animal communities and so we assessed songbird responses to these treatments in stands 20–52 years old in Ontario, Canada. We expected that several old-forest species would respond positively to PHS, that avian assemblages in treated forests would be distinct from those in untreated managed forests regardless of age, and that assemblages in our oldest treated stands would begin to converge with those of mature unmanaged forests. PHS stands had higher conifer density than naturally regenerating managed stands. The avian assemblage differed between treated and untreated stands at 20–30 years but not at 31–52 years. Convergence with old-forest assemblages was incomplete at 31–52 years after harvesting, although abundances of seven of 13 old-forest species did not differ from those in unmanaged forests. Of 10 old-forest species with competitive models, only Bay-breasted Warbler (Setophaga castanea (Wilson, 1810)) responded positively to PHS at the stand level, whereas two species responded positively at the landscape scale. Brown Creeper (Certhia americana Bonaparte, 1838), Boreal Chickadee (Poecile hudsonicus Forster, 1772), and Blackburnian Warbler (Setophaga fusca (Müller, 1776)) were absent from most managed stands and so require specific attention in planning for forest management, including retention of old-forest and delaying harvest of second-growth stands to ensure their occurrence and persistence.
Plain Language Summary
We wanted to determine whether silvicultural treatments used in boreal forest management (site preparation, planting or seeding of conifers, and tending with herbicides) result in a reduction in biodiversity due to habitat change. Long-term effects of forest management on wildlife species in the boreal forest are uncertain because the oldest mechanically logged boreal forests in eastern Canada have not yet reached maturity. We examined songbird responses in stands 20–52 years old in Ontario. We compared bird populations between heavily managed stands and unmanaged stands of natural origin. We found that the avian assemblage differed between treated and untreated stands at 20–30 years but not at 31–52 years. Three species of birds (Brown Creeper, Boreal Chickadee and Blackburnian Warbler) were absent from most managed stands. We recommend that managers continue to maintain large areas of unmanaged forests (e.g., >10% of a management unit) to ensure that old-forest bird species can persist.