Saproxylic Coleoptera are diverse insects that depend on dead wood in some or all of their life stages. In even-aged boreal forest management, remnant habitats left as strips and patches contain most of the dead wood available in managed landscapes and are expected to act as refuges for mature forest species during the regeneration phase. However, use of remnant habitats by the saproxylic fauna has rarely been investigated. Our objective was to characterize the saproxylic beetle assemblages using clearcuts and forest remnants in western Québec, Canada, and to explore the effects of forest remnant stand characteristics on saproxylic beetle assemblages. We sampled both beetle adults and larvae, using Lindgren funnels and snag dissection, in five habitat locations (clearcuts, forest interiors of large patches, edges of large patches, small patches and cut-block separators) from three distinct landscapes. Adult saproxylic beetles (all feeding guilds combined) had significantly higher species richness and catch rates in small patches compared to forest interiors of large patches; the phloeophagous/xylophagous group had significantly higher species richness only. Small patches, cut-block separators and edges of large patches also had the highest snag density and basal area, increasing habitat for many saproxylic beetles. No significant differences in density of saproxylic larvae were found between habitat patches, but snag dissection nevertheless suggests that snags in forest remnants are used by comparable densities of insects. Saproxylic beetles appear to readily use habitat remnants in even-aged managed landscapes suggesting that forest remnants can insure the local persistence of these species, at least in the timeframe investigated in our study.

Abstract

I examined saproxylic beetle responses in two silvicultural systems of the eastern mixedwood boreal forest of Quebec. I first investigated habitat-use and aspen-host use of saproxylic and bark and wood-boring beetles in remnant forest patches (cut-bock separators and small patches) left after harvest, theorized to resemble natural post-fire residual trees and snags. A second study focused on effects of partial cutting, a method that may serve to imitate natural succession dynamics.

Remnant forest patches had the highest saproxylic and bark and wood-boring beetle species richness and relative abundance. Although non-significant, higher larval densities were also collected from remnant forest patches. In the second study, partial cut patches had an intermediate saproxylic beetle assemblage compared to uncut forest and clearcuts.

This research has brought new information on the effects of alternative harvesting practices on saproxylic beetles, supporting the hypothesis that biodiversity is best preserved based on forest management that is diversified and based on natural disturbance dynamics.

Résumé

J'ai examiné la réponse des Coléoptères saproxyliques à deux systèmes de sylviculture utilisés en forêt boréale mixte d’Abitibi, Québec. En premier lieu, j’ai étudié l'utilisation de peuplements et de chicots de peuplier faux-tremble par les Coléoptères saproxyliques dans les habitats résiduels laissés après coupe à blanc (séparateurs secs et îlots de rétention). Une deuxième étude s'est concentrée sur les effets de la coupe partielle. Dans une optique d’aménagement émulant les perturbations naturelles, les séparateurs et îlots correspondent aux arbres verts laissés à la suite d’un feu de forêt, alors que les peuplements à rétention variable correspondent à different stades successionels.

Une richesse spécifique et une abondance d’insectes plus élevées ont été observés dans les habitats résiduels. Des densités larvaires plus élevées, bien que non-significatives, ont également été collectées dans ces habitats. Dans la deuxième étude, les coupes partielles ont montré des assemblages saproxyliques intermédiaires aux peuplements témoins et aux coupes à blanc.

Cette recherche apporte de nouvelles informations sur les effets des pratiques de coupes alternatives sur les Coléoptères saproxyliques, soutenant l'hypothèse que la biodiversité est mieux préservée quand la gestion de forêt est diversifiée et basée sur la dynamique de perturbation naturelle. © 2006 McGill tous droits réservés.