Evaluating the effects of forest harvesting on littoral benthic communities within a natural disturbance-based management model

Abstract

We quantified effects of watershed disturbance by forest fire and harvesting on littoral benthic macroinvertebrates from 12 lakes on the Boreal Shield of Québec and by fire on 15 lakes in the Boreal Sub-arctic Plains of Alberta. In Québec, water chemistry, epilithon and benthos were collected two years after five of the watersheds burned (mean = 87% of the watershed burned) and four were harvested (mean = 59% of the watershed harvested), with the remaining three watersheds acting as reference systems. In Alberta, samples were collected one year after eight of the watersheds burned (mean = 90% watershed area burned). Total macroinvertebrate biomass from burnt lakes was greater than from reference and harvested systems in Québec, and greater than reference systems in Alberta. Whereas total faunal densities did not differ among reference, harvested or burnt systems in Québec, total densities from burnt lakes in Alberta were twofold greater than reference lakes. Species richness did not differ among lake types in either Québec or Alberta. Analyses of covariance tests showed that neither total macroinvertebrate nor Chironomidae biomass from Boreal Shield lakes differed between harvested and burnt systems when means were adjusted for differences in percent watershed disturbance among lake types, whereas oligochaete biomass from harvested lakes was greater than that from burnt lakes when means were adjusted for the covariate of disturbance magnitude. Redundancy and canonical correspondence analyses, using biomass of the five most abundant taxonomic groups and selected environmental variables, showed that benthic communities on the Boreal Shield of Québec were strongly related with total phosphorus, epilithic Chl a, dissolved inorganic nitrogen and dissolved organic carbon. Biomass of the five most abundant taxonomic groups from sub-arctic Boreal Plains lakes were strongly related with color, soluble reactive phosphorus, total inorganic nitrogen and epilithic Chl a.