Carbon concentration of standing and downed woody detritus: Effects of tree taxa, decay class, position, and tissue type

► Angiosperms had a significantly lower carbon concentration than gymnosperms. ► Carbon concentration of gymnosperms increased by ∼10% as decomposition proceeded. ► Angiosperms showed no change in carbon concentration as decomposition proceeded. ► Standing dead wood had higher carbon concentration than downed dead wood. ► Errors of up to 14% could be introduced by assuming a 50% concentration. The degree to which carbon concentration (CC) of woody detritus varies by tree taxa, stage of decay, tissue type (i.e., bark versus wood), and vertical orientation was examined in samples of 60 tree species from the Northern Hemisphere. The mean CC of 257 study samples was 49.3% with a range of 43.4–56.8%. Angiosperms had a significantly lower CC than gymnosperms, with means of 47.8% and 50.6%, respectively. For whole-stems (i.e., wood and bark), the CC of gymnosperms significantly increased from 49.3% to 53.5% with decomposition, while angiosperms had no significant change. The CC of bark was higher than wood across all stages of decay by an average of ∼1.0%. A similar magnitude of difference was found for standing versus downed dead wood in the later stages of decay, with the former having a higher CC than the latter. Differences between angiosperms and gymnosperms are hypothesized to be associated with initial lignin concentrations as well as subsequent decomposition by white- versus brown-rot fungal functional groups. The higher abundance of brown-rots in decomposing gymnosperms may lead to an increase in lignin concentrations, a compound that has higher CC than cellulose. As a result of these findings, uncertainties associated with forest carbon inventories may be reduced by using detrital CC specific to general taxa (angiosperms versus gymnosperms) and stage of decay rather than a single assumed value of 50% as commonly practiced.