Environmental effects of partial-harvest logging in riparian reserves of Boreal Shield streams

A large-scale field project was conducted on the Boreal Shield near White River, Ontario, to investigate the ecological implications of forest watershed disturbance by logging on stream habitat conditions, benthic invertebrate communities, and leaf litter breakdown processes.;In the comparative study, there were no significant differences between logged and reference watersheds in stream habitat measurements or riparian conditions, but there were significantly lower decomposition rates of leaf litter in streams of logged watersheds. This was accompanied by significant differences between logged and reference watersheds in the community structure of aquatic invertebrates on leaf packs. These differences were largely the results of significantly lower abundances of two leaf-shredding caddisfly taxa, and a detritivorous mayfly in streams of logged watersheds. Effects on litter decomposition and leaf-pack invertebrate communities were linked to upland logging disturbances because riparian areas were undisturbed. The mechanisms or pathways by which upland logging disturbances were conveyed to instream processes and biota were not directly measured but may be related to peak flow increases from logged watersheds.;In the experimental study, the partial harvest in riparian buffers resulted in 10, 20 and 28% average basal area of riparian forest removed at the three logged sites. At the two more intensively logged sites, there were small (<10%) reductions in canopy cover and no significant changes in solar radiation at stream surfaces. There were no measurable impacts on stream temperatures at two of the three logged sites. At the most intensively logged site, daily maximum temperatures were significantly higher (∼4° C) for about 6 wks in the first summer after logging than in pre-logging years or at reference sites. Temperature increases were attributed to a logging-induced temporary disruption of cool water inputs from ground disturbance in a lateral-input seep area. No significant differences from sedimentation patterns at reference sites were detected for two of the three logged sites. At the site with the more intense riparian logging, significant increases of about 3-5 times higher than pre-logging or reference levels were detected in fine inorganic sediment (250 mum--1 mm) load and accumulation, but not in fine organic sediments or very fine sediments (0.5--250 mum), in the first year after logging. The increased inorganic sediment deposition at that site was temporary with no significant differences from reference or pre-logging levels detectable by summer of the second post-logging year.;Post-logging leaf litter decomposition rates at the experimentally-logged sites were not significantly different from pre-logging or reference rates. This is in contrast to the findings from the comparative study, and plausible reasons for this discrepancy are discussed. At the two sites with the more intensive riparian logging, no significant postlogging differences from reference streams were detected among a suite of invertebrate community metrics and composition measures. At the 3rd logged site, there were significant post-logging differences from reference and pre-logging measures of invertebrate communities, and these were largely the result of increases in some leaf-shredding stoneflies, and a detritivorous mayfly, concomitant with decreases is some chironomid groups in fall samples 2-4 years alter logging.;Overall, the project demonstrated and explored ecological linkages between boreal forest streams and their adjacent terrestrial environment by disturbing the riparian and upland forests and measuring responses in streams. Land/water linkages between forest streams and their catchments have been explored extensively before, but very few studies of this nature have occurred in the boreal forest, especially on the Boreal Shield. Significant year-to-year fluctuations among our various response measurements across experimental sites and the significant differences among the comparative sites indicated that catchment-wide influences (i.e., upland logging, interannual climate conditions, watershed runoff) had a greater bearing on litter decomposition and invertebrate community structure than the reach-level disturbance created by riparian logging. Partial harvesting at up to 50% tree removal (10-30% average removal but up to 50% at any one spot) in riparian buffers of boreal forest streams is not likely to adversely affect over-stream canopy cover, solar radiation inputs, temperature patterns, sediment deposition rates, leaf litter decomposition or associated aquatic invertebrate communities. This novel riparian harvesting approach could be a viable riparian management strategy for boreal forest streams. (Abstract shortened by UMI.)...