Effects of Selective Forest Harvesting on Organic Matter Inputs and Accumulation in Headwater Streams

Abstract

Abstract Organic matter inputs and accumulation were measured in streams of low-order forest watersheds across a gradient of selective harvesting with no protective riparian buffers assigned. Comparisons were made among sites in selection-cut (average 29% basal area removal), shelterwood-cut (average 42% basal area removal), diameter limit-cut (average 89% basal area removal), and undisturbed tolerant hardwood catchments. The diameter limit harvest was an intentionally high-disturbance treatment and is not a normal silvicultural prescription for tolerant hardwoods in Ontario. Time trend analyses were conducted to examine differences among sites over a pre- and postharvest experimental period. Selection-based harvesting at up to 42% basal area removal with no riparian buffers did not significantly alter average over-stream canopy cover, leaf litter and other organic matter inputs, benthic particulate organic matter accumulation, or woody debris abundance. Harvesting impacts on over-stream canopy cover and organic matter inputs appeared to be minimized by natural crown architecture (overlap in crowns of over-stream trees, residual mid-crown canopy) and by careful logging practices including retention of many immediate streamside trees (within a few meters of the stream channel) and avoidance of felling directly into the streams. Dissolved organic matter fluxes increased slightly for 1 year after harvest and were associated with increased water yield. At the diameter limit harvesting intensity (about 89% basal area removal), significant effects on organic matter inputs and accumulation in streams were detected. The results indicate that selective harvesting of hardwood forests at up to about 42% basal area removal can be conducted without causing significant reductions in organic matter inputs and accumulation in headwater streams, even without prescribed streamside buffer strips.