ABSTRACT
Most natural disturbances leave structural legacies that are used by a variety of organisms as forest regrows. Forest management prescribes retention of “wildlife tree patches” in harvested stands. Ecosystem-based management assumes that, as levels of retention move beyond natural levels, risk to biodiversity increases. This study estimates RONV for structural attributes remaining after fire, insects and wind disturbances within a variety of ecosystems of the SBS and ESSF biogeoclimatic subzones of interior BC, to allow risk assessment following a variety of management options.
We measured structural legacies (live and dead standing stems and downed wood) in 140 plots in 27 sites that had been disturbed by fire, wind and insects over the past 50 years. In the study area, fire caused the most extensive catastrophic disturbances; beetles were extensive, but often not catastrophic; wind disturbance was least common. We encountered considerable difficulty in locating unsalvaged disturbances and identified only four of wind or insect origin that were more
than 10 years old.
Immediately following disturbance, fire left the most snags, and wind created the most downed wood. Even the most severe beetle disturbances left live trees. Wind and beetles left more large than small snags and downed wood. Size-class distribution of snags following fire initially was negatively exponential, but became unimodal over time as the smallest snags fell.
A multivariate classification model was able to distinguish between the three types of disturbance. Overall, the range of natural variability was large, and covered all possible values of retention. However, the mean and standard deviation of numbers of snags and volume of downed wood left after disturbance can guide risk analyses.
