Variable retention harvesting (VRH), in which trees are removed at variable intensity and spatial conÞguration across the landscape, retains greater forest structural heterogeneity than traditional clearcut harvesting and is being recommended as an alternative for sustainable management of the boreal forest. Littleis known aboutits effects on forest fauna; thus, we studied theinßuence of one type of VRH (harvesting with advanced regeneration [HARP]) on the Syrphidae (Diptera) community in northern Ontario forests of peatland black spruce (Picea mariana). We examined the effects of varying structural retention (from unharvested through partial retention to clear-cut) on syrphid species richness and abundance, and abundance of functional assemblages. Greater species richness and population abundances were found generally in harvested than in unharvested forests. Overall species richness and the abundance of four species (Platycheirus rosarum, Toxomerus marginatus, Xylota annulifera, and X. tuberculata) and larval predators were all higher in both clear-cut sites and those with structural retention than in unharvested sites. Similarly, overall species richness and the abundance of nine species were higher in clear-cut than in unharvested sites. Species responses are discussed in an ecological context. Differences among the levels of forest retention harvesting were relatively minor compared with those of the clear-cut and unharvested area, suggesting that local habitat characteristics may play a more important role in determining the syrphid community than the landscape conÞguration. However, a landscape level effect was evident, suggesting that syrphids may be useful in reßecting changes in stand structure at the landscape scale.

Syrphidae, species richness, functional assemblages, variable retention harvesting, boreal forest