Contrasting microclimates among clearcut, edge, and interior of old-growth Douglas-fir forests.

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