Annual carbon flux from woody debris for a boreal black spruce fire chronosequence

[1] This study examined the distribution and respiration dynamics of woody debris (WD) in a black spruce-dominated fire chronosequence in northern Manitoba, Canada. The chronosequence included seven stands that burned between 1870 and 1998; each stand contained separate well-drained and poorly drained areas. The objectives of this study were to (1) quantify the distribution of WD, by diameter and decay class, in well-drained and poorly drained stands across the chronosequence, (2) measure the evolution of CO2 from WD samples and model the effects of moisture, size and decay on respiration, and (3) model annual WD respiration and compute decay constants for each site. Coarse woody debris biomass ranged from 1.4 Mg ha(-1) to 177.6 Mg ha(-1), generally declining in the older stands of the chronosequence. More decayed WD had significantly (alpha = 0.05) higher moisture, lower density, and higher respiration rates than less decayed WD. Moisture and decay class were significant predictors of respiration when moisture was below 43%. Above this level, moisture was not significant, but stand soil drainage was significant, with drier sites having higher WD respiration. Year of burn was not significant in the respiration models. Modeled annual carbon emissions from WD ranged from 0.11 to 1.92 Mg C ha(-1) yr(-1). Modeled annual decay rates, between k = 0.01 and k = 0.06, changed across the age sequence. Thus a single-exponential decay model may not be appropriate for the age sequence. Calculating k directly from wood respiration measurements, as done here, may be useful in allowing examination of year-to-year changes in k.