Influence of partial cutting on site microclimate, soil nitrogen dynamics, and microbial biomass in Douglas-fir stands in western Washington

摘要

A study was conducted to investigate partial cutting (dispersed green-tree retention) as an alternative to clear-cutting in Douglas fir (Pseudotsuga menziesii) stands in Washington, USA, in relation to air and soil temperatures, soil moisture, surface mineral soil net ammonification, nitrification and total N mineralization rates and soil microbial biomass. The effects of tree proximity in the green-tree retention areas on these factors was also studied. The study was conducted in 60- to 70-year-old stands in the Cedar River Watershed, about 70 km southeast of Seattle, between July 1994 and August 1995. Air and soil temperatures and soil moisture in the green-tree retention treatments were generally intermediate between the uncut forest and the clearcut treatments. There were no significant differences in net ammonification, nitrification and total N mineralization rates and in soil microbial biomass between treatments. Soil moisture influenced net ammonification and total N mineralization ratesand microbial biomass. Nitrogen dynamics were generally not influenced by nearness to trees in the green-tree retention treatment. Average microbial biomass, however, was higher near to green trees (1 m) compared with further away (6 m).