Net carbon flux of dead wood in forests of the Eastern US

Abstract

Downed dead wood (DDW) in forest eco- systems is a C pool whose net flux is governed by a complex of natural and anthropogenic processes and is critical to the management of the entire forest C pool. As empirical examination of DDW C net flux has rarely been conducted across large scales, the goal of this study was to use a remeasured inventory of DDW C and ancil- lary forest attributes to assess C net flux across forests of the Eastern US. Stocks associated with large fine woody debris (diameter 2.6–7.6 cm) decreased over time (-0.11 Mg ha-1 year-1), while stocks of larger-sized coarse DDW increased (0.02 Mg ha-1 year-1). Stocks of total DDW C decreased (-0.14 Mg ha-1 year-1), while standing dead and live tree stocks both increased, 0.01 and 0.44 Mg ha-1 year-1, respectively. The spatial distribution of DDW C stock change was highly heterogeneous with random forests model results indicating that management history, live tree stocking, natural disturbance, and growing degree days only partially explain stock change. Natural disturbances drove substantial C transfers from the live tree pool (≈-4 Mg ha-1 year-1) to the standing dead tree pool (≈3 Mg ha-1 year-1) with only a minimal increase in DDW C stocks (≈1 Mg ha-1 year-1) in lower decay classes, suggesting a delayed transfer of C to the DDW pool. The assessment and management of DDW C flux is complicated by the diversity of natural and anthropogenic forces that drive their dynamics with the scale and timing of flux among forest C pools remaining a large knowledge gap.