Estimating the quadratic mean diameters of fine woody debris in forests of the United States

Most fine woody debris (FWD) line-intersect sampling protocols and associated estimators require an approximation of the quadratic mean diameter (QMD) of each individual FWD size class. There is a lack of empirically derived QMDs by FWD size class and species/forest type across the U.S. The objective of this study is to evaluate a technique known as the graphical estimation (GE) method for estimating FWD QMDs across forests of the U.S. Results indicate tremendous inter- and intra-specific variation in small FWD diameters. In addition, GE model fitting results demonstrated a lack of substantial difference in FWD QMDs between common forest types. It is postulated that the mixing, fracturing, and decay of both tree and shrub downed woody debris in diverse forest types across the U.S. can homogenate FWD QMDs at state/national levels. In the absence of site-specific empirical measurement of FWD QMDs, it is suggested that a general national set of FWD QMDs derived from the GE method be adopted for large-scale FWD monitoring efforts.

Research highlights▶ Our study found that the intraspecific variation in fine woody debris quadratic mean diameters can often meet or exceed the interspecific variation across the U.S. ▶ It is postulated that the mixing, fracturing, and decay of both tree and shrub downed woody debris in diverse forest types across the U.S. can homogenate fine woody debris quadratic mean diameters at state/national levels suggesting that a general national set of fine woody debris quadratic mean diameters be adopted for large-scale FWD monitoring efforts. ▶ As explored in this study, the graphical estimation method offers an objective method for broadly approximating regional/national fine woody debris quadratic mean diameters.