Decomposition of woody debris in a regenerating, clear-cut forest in the Southern Appalachians

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Abstract
Mass losses were estimated for coarse (>5 cm) and fine (≤5 cm) woody debris (CWD and FWD, respectively) during the first 7 years following clear-cutting of a mixed hardwood forest at the Coweeta Hydrologie Laboratory in the Southern Appalachians of North Carolina. Estimates were based on (i) precut forest biomass, (ii) volume and density of CWD and mass of FWD at year 1, and (iii) wood density changes of CWD by year 6 and mass changes of FWD by year 7. Mass estimates of CWD at years 0, 1, and 6 were 91.2, 74.8, and 53.0 Mg/ha, respectively. Mass estimates of FWD at years 0, 1, and 7 were 30.3, 21.3, and 7.8 Mg/ha, respectively. Decay constants (k) for mass losses were relatively high compared with other studies of wood decomposition, 0.083 and 0.185 year−1 for CWD and FWD, respectively, and 0.108 year−1 for total (CWD + FWD) debris. Mass loss of CWD occurred largely through wood density decreases and bark fragmentation. CO2−efflux estimates accounted for over 90% of the CWD density loss and for two-thirds (40.4 Mg/ha) of the total debris mass loss. The remaining mass loss of total debris (20.3 Mg/ha) is a source of large, organic matter inputs to the forest floor via solution fluxes and fragmentation of CWD bark and FWD. The large variation in wood-density loss among logs was examined statistically as a function of various decay factors. Density loss varied by more than 10-fold among tree species. Density loss rates were 40% higher in logs on the ground versus those off the ground, 100% higher in logs with observable fungi versus those without fungi, and 40% higher in logs that occurred in plots with south and east aspects versus those in plots with west aspects.