Residual-tree mortality following partial harvesting in the boreal forest of Ontario: Rate, time course, and spatial predictors

Partially harvested stands are likely to maintain natural forest structure and function more successfully than do clear-cut stands. However, a major concern with partial harvesting is the potential for elevated rates of post-harvest mortality, which cause losses both of timber and live-tree habitat. Few studies have quantified the level of, or causes for, post-harvest mortality following partial cutting. We used a dendrochronological approach to determine the rate and time course of post-harvest mortality across a decade-long chronosequence of partially harvested stands in the boreal forest of northeastern Ontario, Canada. Immediately following harvest, residual-tree mortality was elevated up to 10 times above background levels. These rates declined exponentially and had returned to pre-harvest levels within a decade. The probability of mortality increased with presence of harvest-induced damage, decreasing tree size, decreasing distance to cut stumps, and increasing numbers of proximal stumps. Windthrow was an important cause of mortality, but in contrast to previous studies, nearly half of all encountered dead trees remained standing. Thus mechanisms such as fungal infection or physiological shock may be important in driving the pattern of elevated residual-tree mortality at this site. These findings represent an important step towards developing quantitative models that more accurately predict forest structural and dynamic characteristics in partially harvested stands.