• Fraver, Sean
  School of Forest Resources, University of Maine
  
• Milo, Amy
  George Washington University
  
• Bradford, John
  Southwest Biological Science Center
  
• D'Amato, Anthony
  Dept. of Forest Resources, University of Minnesota
  
• Kenefic, Laura
  US Forest Service
  
• Palik, Brian
  US Forest Service
  
• Woodall, Christopher
  US Forest Service
  
• Brissette, John
  US Forest Service
  

Woody debris decay rates have recently received much attention because of the need to quantify temporal changes in forest carbon stocks. Published decay rates, available for many species, are commonly used to characterize deadwood biomass and carbon depletion. However, decay rates are often derived from reductions in wood density through time, whichwhen used tomodel biomass and carbon depletion are known to underestimate rate loss because they fail to account for volume reduction (changes in log shape) as decay progresses. We present a method for estimating changes in log volume through time and illustrate the method using a chronosequence approach. The method is based on the observation, confirmed herein, that decaying logs have a collapse ratio (cross-sectional height/width) that can serve as a surrogate for the volume remaining. Combining the resulting volume loss with concurrent changes in wood density from the same logs then allowed us to quantify biomass and carbon depletion for three study species. Results show that volume, density, and biomass follow distinct depletion curves during decomposition. Volume showed an initial lag period (log dimensions remained unchanged), even while wood density was being reduced. However, once volume depletion began, biomass loss (the product of density and volume depletion) occurred much more rapidly than density alone. At the temporal limit of our data, the proportion of the biomass remaining was roughly half that of the density remaining. accounting for log volume depletion, as demonstrated in this study, provides a comprehensive characterization of deadwood decomposition, thereby improving biomassloss and carbon-accounting models.