Wood Carbon Fractions Influence Deadwood Carbon Stock Estimates

Studies quantifying deadwood carbon (C) stocks are prone to major sources of errors owing to the use of generic conversion factors when converting deadwood biomass to C stocks (that is, wood “carbon fractions” [CFs]). Generally, studies assume that 50% of dead wood is comprised of elemental carbon, though analyses have shown this is a poor approximation of dead wood chemistry. We quantify the degree to which wood CFs influence our understanding of deadwood C stocks, by (1) estimating deadwood biomass from a complete inventory of 3,820 deadwood pieces in a 13.5 ha temperate mixed-species forest and (2) integrating site- and species-specific wood CFs with deadwood biomass, to (A) estimate total deadwood C stocks, (B) assess the magnitude of errors which occur when generic wood CFs are used to estimate deadwood C stocks, and (C) quantify the volatile C stock, that is, the quantity of the overall C stock that is ‘lost’ or unaccounted for when studies employ wood CFs that do not include volatile C compounds (also called the “VCF”). Deadwood accounted for 13.42 Mg of C ha−1, with the VCF accounting for ~4% of total deadwood C stocks. A 50% wood CF underestimated forest-scale C stocks by ~ 3.6%, with these errors increasing over larger spatial scales. Our work contributes both a better understanding of how dead wood chemical traits of individual trees scale-up to influence rates of ecosystem functioning, alongside insights into the role volatile compounds play in forest chemical ecology.