Effects of reduced-impact logging on physical habitat and fish assemblages in streams of eastern Amazonia

Abstract

1. Reduced-impact logging (RIL) has been considered as the main activity of forestry management inthe Amazon. However, little is known of the effects of RIL on the region’s ecosystems or in theirbiodiversity, and such information would be useful to inform forest management. Accordingly, thisstudy aimed to investigate the effects of RIL on physical habitat and fish assemblages in EasternAmazonia streams. We predicted that changes caused by RIL affect stream habitat, leading to a lossof diversity and changes in species composition with a predominance of generalist species. 2. We sampled 13 streams in basins dominated by native vegetation without evidence of loggingactivity (unlogged areas) and 23 in areas that had been logged at different times between 2001 and2011. Stream physical habitat structure was characterized using a standardized protocol, and theabundance, richness and composition of fish assemblages were assessed. 3. Biotic and abiotic data were compared between unlogged and logged areas, and among streams inareas with different logging years. The relationship between the stream habitat structure and fishassemblages was assessed using a distance-based linear model using a forward procedure, followedby application of the Akaike information criterion. 4. Variations in tree canopy cover, channel morphology, water temperature and dissolved oxygenand conductivity accounted for most of the differences in habitat characteristics between unloggedand logged areas. A total of 53 fish species was collected, belonging to 20 families and 6 orders. Fishabundances did not vary consistently between streams in unlogged areas and those that hadundergone RIL, and showed minor evidence of species-specific changes in response to logging years.Likewise, there were no obvious differences in species richness, composition and biomass betweenlogged and unlogged sites, regardless of logging years.5. RIL in Eastern Amazonia is performed in compliance with technical guidelines, but this practicehas resulted in changes in stream physical habitat. Nonetheless, in the headwater streams that wesampled, the effects of RIL on fish assemblages were minor.