A comparative study of long-term stand growth in eastern Canadian boreal forest: Fire versus clear-cut

Abstract

Clear-cutting and fire are the two main disturbances affecting the boreal forest of eastern Canada. These two disturbance types exert different effects on forest dynamics, which can have major implications in terms of economic and ecological sustainability. This study compared the long-term effects of these two disturbance types on stand composition, stand density, and merchantable volume on eastern Canadian mesic boreal forests dominated by black spruce and balsam fir. We used 157 permanent sample plots (PSP), 41 of which originated from fire and 116 were from clear-cuts. Model selection with finite-sample corrected Akaike Information Criterion (AICc) was used to understand which factors had the greatest influence on relative stand density and merchantable volume. Our results indicate that merchantable volume was positively influenced by stand density, which in turn was primarily influenced by disturbance origin, with post-cutting stands being denser than post-fire stands. These results indicated that an increase in stand density is an important mechanism through which disturbance acts upon merchantable volume. We also found differences in forest composition between stand-origin categories, with balsam fir being more abundant post-clearcutting; this was likely because advance regeneration was mainly composed of balsam fir, whereas post-fire stands are dominated by black spruce. Differences in merchantable volume between post-fire and post-clearcut stands become non-significant with time, likely because of higher tree growth and lower mortality in the dominant canopy of clearcut-origin stands. Overall, the results indicate that stand origin is an important determinant of stand composition and stand yield, but that the latter effect tends to disappear after a few decades. The higher balsam fir content generally observed in naturally regenerated, clear-cut origin stands could have potentially negative economic and ecological impacts at the landscape scale, which may call for mitigation strategies.