Variation in carbon and nitrogen concentration among major woody tissue types in temperate trees

Quantifying variation in the wood chemical traits of trees is critical for parameterizing forest biogeochemical budgets and models. Available data on wood chemical traits are based largely on samples taken from main stems; few studies have evaluated how wood chemical traits vary among major woody tissue types. We examined variation in wood carbon (C) and nitrogen (N) concentrations in 17 temperate tree species across five woody tissue types: sapwood, heartwood, small branches, coarse roots, and bark; analyses were corrected for losses of volatile C. Both C and N varied significantly among tissue types, but differences were driven mainly by high C and N in bark, a pattern observed for nearly all species. Among nonbark tissue types, bivariate correlations among sapwood, heartwood, small branches, and coarse roots were highly significant and positive for wood C (r = 0.88-0.98) and N (r = 0.66-0.95) concentrations. We suggest that intraspecific variation in C across tissue types is less important than interspecific variation for assessment and modeling of forest-level C dynamics. In contrast, differences in N among tissue types were larger and appeared to be more important to incorporate into forest-level nutrient assessments and models. Our results suggest that, with the exception of bark, wood chemical trait values derived from stemwood can be used to accurately represent whole-tree trait values in models of forest C and N stocks and fluxes, at least for temperate species.