Does postharvest silviculture improve convergence of avian communities in managed and old-growth boreal forests?

Abstract

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.Résumé : La modification de l'habitat provoquée par l'aménagement forestier peut entraîner une réduction de la biodiversité comme cela a été le cas dans plusieurs types de forêt à travers le monde. La sylviculture pratiquée après la coupe (SPC) est utilisée pour améliorer le rendement des essences commerciales et a été appliquée sur de vastes superficies de forêt boréale. La SPC peut aussi influencer les communautés animales et nous avons donc évalué les réactions des oiseaux chanteurs à ces traitements dans des peuplements âgés de 20 à 52 ans situés en Ontario, au Canada. Nous nous attendions à ce que plusieurs espèces associées aux vieilles forêts réagissent positivement à la SPC, que les assemblages aviaires dans les forêts traitées soient différents de ceux rencontrés dans les forêts aménagées non traitées peu importe l'âge et que les assemblages dans les peuplements traités les plus vieux commencent à se rapprocher de ceux des forêts matures non aménagées. Les peuplements traités avaient une plus forte densité de conifères que les peuplements aménagés qui se régénéraient naturellement. L'assemblage aviaire était différent dans les peuplements traités et non traités âgés de 20 à 30 ans mais pas dans les peuplements âgés de 31 à 52 ans. La convergence avec les assemblages des vieilles forêts était incomplète 31 à ...

Effects of natural resource development on the terrestrial biodiversity of Canadian boreal forests

“…In Eurpean boreal forests, Andren (1994) found no evidence for isolation effects on forest birds, but Mönkkönen et al (2000, cited in Schmiegelow andMönkkönen 2002) found that species richness and abundance of resident old-forest species in northern Finnish reserves declined with distance from continuous forests. Other studies have found much weaker effects of landscape variables than stand-level variables that explained numbers of boreal birds in Ontario (Venier and Pearce 2007;Thompson et al 2013). With most of these landscape-level variables, the evidence suggests that there are weak (relative to standscale influences), species-specific effects resulting from changes in habitat configuration related to increased isolation, edge density, and composition at the landscape scale.…”

“…Further, it is important that the forests in the boreal zone are generally being maintained as forest, unlike agricultural areas with true fragmentation and habitat loss (Hobson and Bayne 2000b). Nevertheless, long-term effects on old-forest species remain uncertain (e.g., Venier and Pearce 2007;Thompson et al 2013).…”

“…Immediately after fire or harvesting, bird communities tend to be most divergent (Schieck and Song 2006;Thompson et al 2013;Simon et al 2002). Post-fire stands are generally dominated by cavity nesters (Imbeau et al 1999) where the presence of large dead and dying trees results in a high abundance of saproxylic beetles for prey as well as cavity trees for nesting (Hobson and Schieck 1999;Hoyt and Hannon 2002).…”

“…Studies to date suggest that convergence is incomplete, unknown for old-forest age classes and that differences in species composition occur between mature fire-and harvest-origin stands. For example, songbird communities differ between 50-and 100-yearold forests of all types (e.g., Drapeau et al 2000;Thompson et al 2013), and there is little evidence that woodland caribou can persist in second-forest landscapes (Environment Canada 2011). Further, for forest types that have recovered to altered states after harvesting, convergence is unlikely to occur.…”

Site preparation severity influences lodgepole pine plant community composition, diversity, and succession over 25 years

“…Our second hypotheses, H2, posited that more severe site preparation would accelerate plant community succession relative to less severe treatments by increasing tree growth rates, speeding crown closure and increasing competition for light and other resources, thereby favouring shade-and stress-tolerant late seral plants (Grime 1979) over intolerant, resource-demanding early seral species (cf. Thompson et al 2013).…”