Decadal dead wood biomass dynamics of coterminous US forests

Abstract

Due to global change, temperate forests are expected to face growing threats to forest health (e.g. insects/disease) and increasing probabilities of severe disturbances (e.g. wildfires), which may result in amplified tree mortality against a backdrop of a changing climate and associated ecosystem/atmospheric feedbacks (i.e. increased rates of dead wood decay/combustion). Despite these expectations, we lack a fundamental understanding of current forest biomass trends among live and dead components across large spatial and temporal domains. The goal of this study was to examine changes in forest biomass components (downed dead wood (DDW), standing dead trees (SDs), and live trees) across coterminous US forests using a nation-wide, multi-decade (∼2006-2010 to ∼2015-2019) repeated forest inventory at the scale of regional ecosystems. It was found that the total biomass stocks of DDW, standing dead, and live trees all increased (18.3%, 14.7%, and 3.9%, respectively) with biomass accumulation in large live trees coupled with increases in the biomass of smaller sized down dead wood illustrating the influence of stand development across US forests at the scale of individual forest ecosystems (i.e. self-thinning). Coupled with this observation, tremendous positive skew of biomass change across all biomass components and size classes demonstrates the ability of severe but episodic disturbance events to produce substantial biomass inputs to SD and DDW pools with legacy effects exceeding the period of this study. Overall, against a backdrop of expected future global change and growing interest in the maintenance of the terrestrial forest carbon pool, the incorporation of dead wood-focused analytics such as decay-related functional traits, microbial/fungal community assessments, or dead/live biomass relationships into broader forest carbon/biomass monitoring efforts is essential.