Biomass and carbon attributes of downed woody materials in forests of the United States

• First national inventory of down dead wood finds it is ubiquitous across US forests.
• Ecosystem processes and management/disturbance events vary dead wood resources.
• Down dead wood biomass often exceeds standing dead biomass in US forests.
• Proportion of a stand’s standing live/dead and down dead biomass invariant of climate.

Due to burgeoning interest in the biomass/carbon attributes of forest downed and dead woody materials (DWMs) attributable to its fundamental role in the carbon cycle, stand structure/diversity, bioenergy resources, and fuel loadings, the U.S. Department of Agriculture has conducted a nationwide field-based inventory of DWM. Using the national DWM inventory, attributes (e.g., carbon stock totals and biomass density) were summarized by state and common tree species along with evaluations of residue pile metrics and relationships between DWM and other stand attributes (e.g., live tree biomass, relative density, and climate). Results indicate that DWM are ubiquitous in US forests with individual components (e.g., fine woody debris and piles) varying by region as influenced by endemic ecosystem dynamics and management practices. Eastern forests, particularly in the southeast, have fine woody debris and residue piles biomass densities that often exceed those of west coast forests. Rocky Mountain forests have coarse woody biomass densities approaching those of west coast forests, which have the largest amounts nationally. There is a complex relationship between the standing dead, standing live, and down dead wood biomass densities per unit area in the context of changing stand relative densities and average annual precipitation/minimum temperatures. As evidenced by this initial exploration, a publicly available national dataset comprised of DWM attributes may inform decision makers with objective estimates of DWM resources and facilitate further DWM dynamics research.