Residence Times and Decay Rates of Downed Woody Debris Biomass/Carbon in Eastern US Forests
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A key component in describing forest carbon (C) dynamics is the change in downed dead wood biomass through time. Specifically, there is a dearth of information regarding the residence time of downed woody debris (DWD), which may be reflected in the diversity of wood (for example, species, size, and stage of decay) and site attributes (for example, climate) across the study region of eastern US forests. The empirical assessment of DWD rate of decay and residence time is complicated by the decay process itself, as decomposing logs undergo not only a reduction in wood density over time but also reductions in biomass, shape, and size. Using DWD repeated measurements coupled with models to estimate durations in various stages of decay, estimates of DWD half-life (T HALF), residence time (T RES), and decay rate (k constants) were developed for 36 tree species common to eastern US forests. Results indicate that estimates for T HALF averaged 18 and 10 years for conifers and hardwoods, respectively. Species that exhibited shorter T HALF tended to display a shorter T RES and larger k constants. Averages of T RES ranged from 57 to 124 years for conifers and from 46 to 71 years for hardwoods, depending on the species and methodology for estimating DWD decomposition considered. Decay rate constants (k) increased with increasing temperature of climate zones and ranged from 0.024 to 0.040 for conifers and from 0.043 to 0.064 for hardwoods. These estimates could be incorporated into dynamic global vegetation models to elucidate the role of DWD in forest C dynamics.
Keywordscarbon flux decomposition forest inventory forest fuels decay class coarse woody debris
This work was supported by the USDA Forest Service, Northern Research Station. We thank Lori Daniels, Alex Finkral, Ron McRoberts, Steve Prisley, and Herman Shugart for their comments that improved the content of this work.
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