Measurement of differences in snow accumulation, melt, and micrometeorology between clearcut and mature forest stands

To quantify the hydrologic response of forest harvesting, measurements of snow accumulation, melt, and micro-meteorological were taken in mature and harvested units of the Gifford Pinchot (GP) and Umpqua National Forests. Data were collected as part of the Demonstration of Ecosystem Management Options (DEMO) project. The study areas are located in the transient snow zone of the western Cascades of southwestern Washington and central Oregon, respectively. The GP site contains six units at approximately 900 meters in elevation (five mature secondary growth, 1 clear-cut). The Umpqua site contains five units at approximately 900 meters in elevation (four mature, one shelterwood), and three units at 1200 meters elevation, (two mature, one shelterwood). Data have been collected during the past three snow seasons. In the summer of 1997, each site's mature stands (excluding one control) will be harvested with varying retentions and additional seasons of data will be collected. Measurements of incoming and reflected shortwave radiation, incoming longwave radiation, windspeed, relative humidity, air temperature, and precipitation (or throughfall) were taken in the units. Snow accumulation and melt at the unit scale (10ha) was measured weekly throughout the winter and spring with snow courses taken on a twenty point grid. Point observations of snow pack outflow consisted of two non-weighing snow lysimeters (2.6 sq. m. each) in each unit. Comparison of lysimeter observations between shelterwood and mature units during the 95/96 season show a 56% increase in 3 day production of runoff and a greater than 150% increase in 3 day snowmelt (outflow-throughfall). The shelterwood also shows nearly a 50% increase in snowmelt during radiationdominated spring events. Snow course data taken at the GP before and 10 days after the rain-on-snow event of February 1996 show a decrease in the average snow water equivalent of the clearcut unit from 26 to 16 cm and a decrease in an adjacent mature stand's SWE from 21 to 18 cm.