revert forest stands to their original state, as aspen and birch are generally sufficiently abundant-even in older stands-to enable the return to intolerant hardwood stands Jack pine can also form pure or mixed stands on these sites after fire but we will concentrate here on secondary succession involving hardwoods as it is clearly more important.
Overlaying this post-fire compositional change is the effect of spruce budworm outbreaks As outbreak severity increases with the proportion of fir in stands softwood stands are most affected. Average fir mortality may exceed 80% in softwood standsover 200 years old Abundant advance softwood regeneration may permit an immediate return to a softwood-dominated stands. However, advanced softwood regeneration is usually insufficient Kneeshaw and Bergeron, 1990, and softwood stands are replaced by mixedwoods Above-ground biomass decreases as stands pass from hardwood to softwood dominance The superior height of the aspen in the younger stands. plus the presence of a