Stream Temperature Response to Forest Thinning With No Riparian Buffer in Headwater Catchments of the Coastal Pacific Northwest

Over the last few decades, forest thinning has been increasingly applied in the Pacific Northwest to increase habitat diversity in extensive second-growth stands that have developed following historic clearcut logging. However, there are concerns that thinning near streams may result in increased water temperature. This study documented the first two years' post-harvest response of headwater stream temperature in coastal British Columbia, Canada, to thinning treatments with no riparian buffer. The study included three treatment and three control streams. Following a pre-treatment calibration period, approximately 40% of each treatment catchment was harvested by removing 50% of the basal area in a cut block that spanned the stream channel. Significant warming occurred for two of the treatment streams; maximum daily stream temperature increases were similar to those recorded at streams within clear cuts with no buffer in an earlier study. Warming was greatest from May to August and for daily maximum temperature. A third stream, which was spatially intermittent at lower flows, exhibited weak and marginally significant warming. The influences of meteorological and hydrological conditions on the magnitudes of the treatment effect were assessed using both statistical modelling and energy-budget analysis.