Gap dynamics and replacement patterns in gaps of the northeastern boreal forest of Quebec

The northeastern boreal forest of Quebec is characterized by a humid climate. Consequently, fires are less frequent and small-scale disturbances play an important role in forest dynamics. Natural mortality and nonfire disturbances such as insect outbreaks and windthrow lead to gap-driven processes. Changes in structure and species composition can result from gap dynamics. The objectives of this study were to characterize gaps and examine patterns of species replacement in gaps in old conifer stands. Line intersect sampling was used to sample stands dominated by balsam fir (Abies balsamea (L.) Mill.) and (or) black spruce (Picea mariana (Mill.) BSP). Results show that 54% of the forest was in expanded gaps and that canopy gaps are relatively small, since 87% of them were smaller than 100 m2. The majority (94%) of the openings were caused by the mortality of less than 10 gap makers. Replacement probabilities show self-replacement of A. balsamea in Abies stands and of P. mariana in Picea stands. However, in Abies-Picea stands, there seems to be a reciprocal replacement of the two species. These results provide knowledge of the disturbance dynamics of the region as a basis for development of silvicultural practices that preserve the structural components of older forest stands.