Respiration from coarse woody debris as affected by moisture and saprotroph functional diversity in Western Oregon

Decomposing coarse woody debris (CWD) is a conspicuous and important compon ent of forest ecosystems. Seasonal temperature and precipitation patterns i nfluence heterotroph activity, which determines the rate of CWD decompositi on. We tested the hypothesis that moisture content and heterotroph communit y composition influence carbon flux in freshly-cut Douglas fir (Pseudotsuga menziesii) logs. To evaluate the effects of physical penetration of bark a nd wood and transmission of basidiomycete compared with ascomycete fungi by insects? 360 experimental logs were assigned to five replicate sites, each with 12 heterotrophXmoisture treatment combinations in 1995. Half of the l ogs in each heterotroph treatment received normal rainfall and half were pl aced individually under elevated clear plastic tents to reduce water inputs . Respiration was measured every 1-3 months. In 1996 and 1997 a different l og representing each treatment combination was harvested from each replicat e and analyzed for the presence of inoculated and colonizing fungi. Logs in oculated with decay fungi had higher respiration than uninoculated logs but this effect only approached significance (P=0.08) during the first season. Respiration was significantly higher in sheltered than in exposed logs. Ou r results indicate that respiration and wood decomposition rates may be dep ressed by high moisture content in the wet forests of the coastal Pacific N orthwest.