Technical Bulletins & Special Reports

Technical Bulletin No. 0877: Dynamics of Coarse Woody Debris in North American Forests: A Literature Review

Coarse woody debris (CWD), which is commonly defined as snags, downed logs, and stumps that persist in the ecosystem for some time, has become an important consideration in forest management. Management plans for CWD should be based on sound understanding of the factors that control CWD dynamics. This report provides information on methods for assessing CWD, the processes that affect CWD inputs, outputs, and nutrient dynamics, and the range of dynamics under various situations. There is no uniform minimum size class at which woody material is considered to be CWD, and that minimum size likely depends upon the site-specific decomposition rate. Most surveys distinguish a range of decay states for downed logs and snags. The most general classification is simply “sound” versus “rotten.” A more detailed scheme defines decay classes based on characteristics such as number of branches, presence of bark, loss of top, and bole integrity. When sampling CWD, pieces of CWD encountered in plots or along transects may be collected and weighed. More generally, however, volumes are estimated and converted to mass via wood density measurements obtained from the study site or from previously published data. Regardless of the measurement scheme, the precision when projecting estimated CWD quantities to larger areas depends upon the sample size and the inherent variability in CWD quantities. Planar intercept transects appear to be a fast and reliable method for collecting data related to downed log accumulations under a variety of conditions. A triangle of transects provides good coverage and is relatively easy to set up in the field. Permanent sample plots also should include counts and diameters of snags and live trees by species. Repeated surveying of sample plots on some regular cycle (annually, every 3 years, every 5 years, etc.) would provide useful data on dynamics.