Postfire black spruce establishment in subarctic and boreal Quebec

Abstract

Forest regeneration in areas burned during the 1950s in northern Quebec was studied along topographic and climatic gradients, from the northern Boreal Forest to the northern Forest–Tundra. Regenerated plant communities are mostly dominated by Cladinamitis in well-drained uplands and by hygrophilous shrub species in moister lowlands. The age structure of 23 stands, as they were immediately before and about 30 years after the 1950s fires, was used to analyze the patterns of establishment and development of black spruce (Piceamariana (Mill.) B.S.P.) populations associated with fire disturbance. Postfire black spruce establishment was active during the first 20 years of vegetation recovery, then it decreased rapidly. Three older populations originating from 1936 and 1922 fires showed a rapid postfire tree establishment, whereas a long delay of recolonization was observed in the 1906 fire. Along the topographical gradient, postfire regeneration was more rapid in hill sites, whereas spruce recruitment was more abundant in lowland sites. Along a northward latitudinal gradient, prefire populations showed an increasing trend in age range, mean age, and mean age of youngest individuals. This gradient coincided also with an increasing fire rotation period from south to north. The proportion of stunted individuals in postfire populations was often more important than in prefire populations on the same sites, suggesting more rigorous growth conditions associated with forest removal. Because most black spruce seedling establishment is occurring during a short period in this area, it is suggested that stand density is determined by regeneration conditions, including seed input and seedbed quality, soon after the fire. Therefore, comparisons between prefire and 30-year-old postfire populations can be used as an index to evaluate fire impact on stand density.