CONTRASTING MICROCLIMATES AMONG CLEAR-CUT, EDGE, AND INTERIOR OF OLD-GROWTH DOUGLAS-FIR FOREST

Clearcut, remnant old-growth forest patch, and edge are the three primary landscape elements in northwestern North America. Microclimatic information on this forest landscape is needed for both research and resources management purposes. In this paper, seasonal summaries and diurnal changes in air temperature and moisture, soil temperature and moisture, short-wave radiation, and wind velocity are quantified for recent clearcut (10-15 years old), edge, and adjacent interior old-growth Douglas-fir forest environments in southern Washington state, USA, over two growing seasons. Influences of local weather condition and edge orientation (relationship of edge to the azimuth) are also assessed. Over the growing season, daily averages of air and soil temperatures, wind velocity, and short-wave radiation are consistently lower, and soil and air moisture are higher, inside the forest than in the clearcut or at the edge. Daily differences (i.e. maximums minus minimums) of all variables are consistently lower in the forest, The microclimates at the edge and the clearcut show a variable relationship with regard to averages and differences. Between the edge and the forest, greater differences occur under clear sky conditions for air temperature, but under partial cloudy conditions for relative humidity and soil temperature. Edge orientation is critical in assessing solar radiation, soil moisture, and relative humidity. The highest variability in microclimate exists at the edge, rather than in either clearcut or interior forest, primarily because of the influences related to edge orientation. The supposition that edge microclimates are intermediate between clearcut and interior forest is consistently true only for wind velocity and solar radiation, not for temperature and moisture.