Heterogeneity of wood decay classes within hardwood logs

As forest floor coarse woody debris (CWD) decays, it changes from solid wood to material without a recognizable origin. Decaying logs provide a progression of woody habitat substrates that contribute to the diversity of species and ecological processes in the forest. For studies of the habitat values of logs, decaying logs typically are assigned to one of the five classes with Class V being highly decayed logs that have lost their cylindrical shape and are composed primarily of powdery wood. In a study made in Quercus hardwood and mixed hardwood stands of the University of Connecticut Forest, near Storrs, CT, we examined the range and variability in actual decay classes present within logs assigned to decay class groups I, II, III, or IV. The proportions of all the decay classes found in each of 125 logs were estimated from measurements of the length and diameters of each different sector of decay within a log. The homogeneity of within-log decay classes varied by overall decay class group with the decay class III logs and group being the most variable. We compare our results to an idealized continuum of decay and conclude that by virtue of being in the middle of the decay sequence, class III is expected to be the most variable. We recognize that although the overall pattern of our results may be considered typical relative to the idealized continuum, the specific proportion of decay class variability from any one study represents site- and time-specific conditions not likely to typify 'average' conditions in a broader geographic area. Our results indicate that variability of decay state within a given log is generally to be expected, and, from this we infer within-log variability in species and ecological functioning. (C) 1999 Elsevier Science B.V. All rights reserved.