Morphological attributes and snag classification of four North American boreal tree species: Relationships with time since death and wood density

Snag degradation classification systems based on external morphological attributes are widely used in ecology but have rarely been related to elapsed time since death (TSD) or wood density. Furthermore, these classification systems rely on the overall aspect of snags, and the predictive ability of specific attributes has rarely been investigated. We examined which morphological attributes best predicted TSD and wood density in snags of four major boreal species in eastern North America: trembling aspen (Populus tremuloides Michx.), balsam fir (Abies balsamea [L] Mill.), jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] BSP). We also investigated how a commonly used snag degradation classification system relates to TSD and wood density. Sampling was conducted in northwestern Quebec, Canada. For each species, 37-65 snags were sampled and TSD was determined using dendrochronology. Bark cover was the only morphological attribute common to models of all species and was the sole predictive variable of TSD in balsam fir. As for TSD, the combination of predictors for wood density was species-specific and wood penetrability was a common predictor in all species. Degradation stages provided rough approximations of TSD and wood density. This study shows that the degradation classification system used can be helpful when rough estimates are needed. However, species-specific models built according to significant morphological attributes do not represent more time- and resource-consuming field assessments and they provide more precise measurements of TSD and wood density. (C) 2011 Elsevier B.V. All rights reserved.