The role of woody detritus in biogeochemical cycles: past, present, and future

Woody detritus (WD), created by mortality of trees and their associated parts, is an important component of forested ecosystems with roles in energy flow, hydrologic and geomorphologic processes as well as in carbon and nutrient cycling. Although likely to be increasingly important as forest systems respond to climatic and other human induced changes, WD-related science is just beginning relative to other aspects of forested ecosystems. WD differs from other litter forms and soil in key ways (i.e., size range, rigidity, and heterogeneity) that limit the application of many paradigms currently used in studying and modeling decomposition. Thus, while temperature and concentrations of lignin and nitrogen are important controls, others factors related to moisture and its interaction with canopy openness, WD size, position relative to the soil surface, and decomposers need to be better understood. Moreover, the unique attributes of WD decomposers need to be acknowledged as they have evolved over hundreds of millions of years to efficiently process this high lignin, low nutrient substrate. Given the heterogeneity within and among WD entities, WD behavior can be extremely non-linear, often resulting in cascades of activity rather than all or nothing behavior. Substantial improvements in understanding and modeling the respiration, fragmentation, leaching, and burial involved during WD decomposition are required to accurately assess the impact of global increases in tree mortality. Additionally understanding how the perception of WD-related processes changes with scale and organizational level is required to fully understand WD’s role in past, present, and future biogeochemical cycling.