COARSE WOODY DEBRIS AND FOREST FLOOR RESPIRATION IN AN OLD-GROWTH CONIFEROUS FOREST ON THE OLYMPIC PENINSULA, WASHINGTON, USA

Carbon dioxide evolution rates for downed logs (coarse woody debris) a nd the forest floor were measured in a temperate, old-growth rain fore st in Olympic National Park, Washington, using the soda lime trap meth od. Measurements were taken every 4 weeks from October 22, 1991, to No vember 19, 1992. Respiration rates for Douglas-fir (Pseudotsuga menzie sii (Mirb.) France) and western hemlock (Tsuga heterophylla (Raf.) Sar g.), logs were deter mined for decay classes 1-2, 3, and 5 in two diam eter classes. Overall, western hemlock logs respired at a rate class 1 -2 logs of both species were similar to decay class 5 logs (4.46 and 4 .07 g CO2.m(-2).day(-1), respectively), but decay class 3 logs respire d at a lower rate (3.23 g CO2.m(-2).day(-1)). Seasonal patterns of res piration rates occurred, particularly for decay class 1 and 2 western hemlock logs where monthly averages ranged from a low of 2.67 g CO2.m( -2).day(-1) in February 1992 to a high of 8.30 g CO2.m(-2).day(-1) in September 1992. Rates for decay class 1-2 western hemlock logs were gr eater than those from the forest floor, which ranged from 3.42 to 7.13 g CO2.m(-2).day(-1). Respiration rates were depressed in late July an d August compared with fall and spring owing to the summer drought cha racteristic of the Pacific Northwest. Large-diameter western hemlock l ogs in decay class 1-2 had higher respiration rates than small-diamete r logs, whereas large-diameter decay class 3 western hemlock logs had lower respiration rates than small-diameter logs.