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

We quantified effects of watershed disturbance by forest fire and harvestin g on littoral benthic macroinvertebrates from 12 lakes on the Boreal Shield of Quebec and by fire on 15 lakes in the Boreal Sub-arctic Plains of Alber ta. In Quebec, water chemistry, epilithon and benthos were collected two ye ars 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, sample s 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 refe rence and harvested systems in Quebec, and greater than reference systems i n Alberta. Whereas total faunal densities did not differ among reference, h arvested or burnt systems in Quebec, total densities from burnt lakes in Al berta were twofold greater than reference lakes. Species richness did not d iffer among lake types in either Quebec 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 th an that from burnt lakes when means were adjusted for the covariate of dist urbance magnitude. Redundancy and canonical correspondence analyses, using biomass of the five most abundant taxonomic groups and selected environment al variables, showed that benthic communities on the Boreal Shield of Quebe c were strongly related with total phosphorus, epilithic chi a, dissolved i norganic nitrogen and dissolved organic carbon. Biomass of the five most ab undant taxonomic groups from sub-arctic Boreal Plains lakes were strongly r elated with color, soluble reactive phosphorus, total inorganic nitrogen an d epilithic chi a. (C) 2000 Elsevier Science B.V. All rights reserved.