The importance of the volatile carbon fraction in estimating deadwood carbon concentrations

The volatile carbon concentration or fraction (VCF) of wood—i.e., the proportion of woody tissue which is composed of heat-sensitive volatile organic compounds (VOCs), which are lost during sample preparation—is an important contributor to wood C concentrations. Studies of live wood have shown that failure to account for the VCF of wood may result in significant errors in forest C stock estimates. However, while studies have shown that deadwood C concentrations differ from those in live wood, no study has explicitly quantified the VCF in deadwood. Here, we quantify the VCF in deadwood for the first time, using n = 400 individual deadwood samples obtained from 13 species, multiple decay classes (DC), and two primary woody tissue types (i.e., stem wood and bark), in a temperate forest. The VCF in deadwood is non-trivial, averaging ∼0.9 % and ranging widely across species and decay classes. Across both taxonomic divisions (gymnosperms vs. angiosperms) VCF is largest (1.73 %) in DC 1 but declines to 0 % in DC 5. Overall, stem wood exhibits higher VCF (1.06 %) than bark (0.64 %). Lastly, deadwood VCF appears systematically lower than that in live wood, indicating that live wood VCFs may not be good approximators of the VCF in deadwood. Our results suggest that failing to account for the VCF of deadwood in forest C estimation studies, especially in the early stages of decay, results in errors in deadwood C stock estimates of ∼0.9 % on average. Future studies focused on tree- and forest-scale C estimation should therefore account for the VCF in their analyses, in order to improve the accuracy of C stock estimates.