Residence Times and Decay Rates of Downed Woody Debris Biomass/Carbon in Eastern US Forests

Abstract

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.

Environmental drivers of deadwood dynamics in woodlands and forests

“…The decomposition of deadwood is considered a knowledge gap (Birdsey et al 2006), whose importance is clearly linked with the possibility for instance to better predict ecosystems responses to global change derived from a more precise understanding of the variability of deadwood decomposition rates and associated C flux (Weedon et al 2009). Few studies investigated the temporal dynamics of deadwood, particularly of downed woody debris, and fewer quantified mass loss through time (Russell et al 2014). A recent investigation by Russell et al (2014) provided estimates of down woody debris half-life, residence time and decay rate for 36 tree species of eastern US forests, coupling repeated measurements with models.…”

“…Few studies investigated the temporal dynamics of deadwood, particularly of downed woody debris, and fewer quantified mass loss through time (Russell et al 2014). A recent investigation by Russell et al (2014) provided estimates of down woody debris half-life, residence time and decay rate for 36 tree species of eastern US forests, coupling repeated measurements with models. This approach could provide new insights for the quantification of ecosystem functions related to deadwood dynamics.…”

Illinois Forests 2015

“…Beyond transition of dead wood carbon to other pools, these carbon stocks may be reduced due to increased rates of decay if future temperature and precipitation patterns change (Russell et al 2014a(Russell et al , 2014b. This is an important consideration because of the reduced amount of coarse woody debris in Illinois.…”

Delaware Forests 2013

“…Although the carbon stocks of down woody materials are relatively small compared to those of soils and standing live biomass across Delaware, down woody material is still a critical component of the carbon cycle as a transitory stage between live biomass and other detrital pools such as the litter. Beyond the transition of dead wood carbon to other pools, if future temperature and precipitation patterns change, there is a potential for a reduction in these stocks due to increased rates of decay (Russell et al 2014a(Russell et al , 2014b. The loss of dead wood carbon stocks could indicate the reduction of other pools in the future.…”