Hoverfly (Syrphidae) Communities Respond to Varying Structural Retention After Harvesting in Canadian Peatland Black Spruce Forests

Abstract

Variable retention harvesting (VRH), in which trees are removed at variable intensity and spatial configuration across the landscape, retains greater forest structural heterogeneity than traditional clear-cut harvesting and is being recommended as an alternative for sustainable management of the boreal forest. Little is known about its effects on forest fauna; thus, we studied the influence 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 configuration. However, a landscape level effect was evident, suggesting that syrphids may be useful in reflecting changes in stand structure at the landscape scale.

Distribution of Syrphidae (Diptera) across northern Ontario

“…Although the number of species caught in this study was similar to those caught in studies from more southerly regions of Ontario, fewer specimens were caught (Deans et al 2007: Lake Abitibi Model Forest, 105 species, 3209 specimens; Proctor et al 2012: Algonquin Park, 141 species, 7992 specimens). Thirty-eight species caught in northern Ontario were not reported in the Lake Abitibi Model Forest or Algonquin Park studies.…”

“…Often, the distribution of syrphid species is determined by larval habitat, especially for the slow-dispersing specialist species (Schweiger et al 2007;Aguirre-Gutiérrez et al 2016). This variability of life history makes syrphids potentially ideal bioindicators, particularly for tracking landscape changes, changes to forests (Sommaggio 1999;Deans et al 2007;Sommaggio and Burgio 2014), and environmental changes (Danks 1992).…”

Disturbance‐mediated heterogeneity drives pollinator diversity in boreal managed forest ecosystems

“…, Deans et al. , Pengelly and Cartar ), which provide disturbance legacies in the form of increased floral and habitat resources.…”

Land‐use change has no detectable effect on reproduction of a disturbance‐adapted, hawkmoth‐pollinated plant species

“…Many pollinators are adapted to naturally heterogeneous landscapes and therefore they (and the pollination services they provide) may not experience the negative impacts of land-use change, especially when such changes result in more open or early successional habitats ( Michener, 2007 ;Deans et al, 2007 ;Winfree et al, 2011 ). On the other hand, movement patterns may be altered or restricted such that some pollinators are less likely to travel across openings or spend time in edge habitat, or may spend more time in the "matrix" (developed areas, with a higher density of artificial lights, cars, predators, etc.…”