Interspecific wood trait variation predicts decreased carbon residence time in changing forests

Abstract

Abstract Increasing disturbance will result in a significant flux in above‐ground carbon (C) from live trees to deadwood, concurrent with shifts in forest composition. While interspecific decay variation is widely reported, the implications of compositional change on ecosystem‐level deadwood decay and consequently the future of a globally significant C pool have not been previously explored. Leveraging a 25‐year treefall record for two eastern hardwood forests in central Illinois, USA, we used a chronosequence approach to estimate downed deadwood decay rates for eight common tree taxa. We hypothesized that the increasing dominance of Acer spp. in eastern forests, due to disturbance regime changes, is driving an increase in the mean species‐weighted deadwood decay rate, decreasing the total C storage capacity of regional forests. We observed significantly greater interspecific variation in deadwood decay rates than short‐term studies, with a nearly 12‐fold difference in half‐lives between Aesculus glabra (T1/2 = 6.2 years) and Quercus spp. (T1/2 = 71.1) logs. The canopy‐dominant Acer saccharum (T1/2 = 19.1) decayed significantly faster than other historically dominant eastern taxa, Quercus spp. and Fraxinus spp. (T1/2 = 41.4). Wood traits, notably taxon initial wood C:N ratio, pH and Mn concentration, outweighed local environmental factors in explaining variation in decay rates. Taken together, our findings suggest that at multi‐decadal time‐scales, species traits are the dominant controls of wood decay rates. Our findings corroborate previous studies showing species with slow‐decaying wood tend to have higher C:N ratios. Our species‐specific decay estimates highlight the importance of longer term studies for accurately assessing the decay of high C:N ratio species, as shorter term decay studies are prone to underestimating their decay rates. Our results suggest that ongoing forest compositional changes, where fast‐growing species with less‐dense wood are becoming increasingly abundant, have substantially diminished the deadwood C pool over the last century (species abundance‐weighted mean T1/2 in 1922 = 16.9; T1/2 2020 = 10.5). A free Plain Language Summary can be found within the Supporting Information of this article.