MODELING AIR-TEMPERATURE GRADIENTS ACROSS MANAGED SMALL STREAMS IN WESTERN WASHINGTON

Leaving riparian strips on both sides of a stream is widely accepted t o be an effective management approach in sustaining the valuable funct ions of stream and riparian ecosystems. The authors' overall objective is to provide microclimatic information for assessing the effectivene ss of these strips. During the summer of 1993 and 1994, air temperatur es were collected across 20 small, buffered streams in western Washing ton, USA, including five streams sampled before and after harvesting o f the forest. These data were statistically analysed to examine the ef fects of adjacent harvesting with preservation of 16-72 m riparian for est strips. Regression models were developed to predict air temperatur es at the stream and buffer edges, the difference between two location s, and seasonal changes. The authors found: (1) clearcutting in winter 1993/94 increased air temperature on the stream by up to 4 degrees C, and changes in temperature variability from the stream to the upland, measured by coefficient of variation (CV), were significantly higher after harvesting; (2) forest buffers provided minimal protection for s tream air temperature during the middle of summer (July) but were more effective early and late in the season; (3) buffer width was not a si gnificant variable in predicting stream air temperature, suggesting th at even a 72 m buffer was not sufficient to maintain a stream environm ent because of greater depth of edge influences. (C) 1998 Academic Pre ss.