Long-term post-fire changes in the northeastern boreal forest of Quebec

Natural dynamics in the boreal forest is influenced by disturbances. Fire r ecurrence affects community development and landscape diversity. Forest dev elopment was studied in the northeastern boreal forest of Quebec. The objec tive was to describe succession following fire and to assess the factors re lated to the changes in forest composition and structure. The study area is located in northeastern Quebec, 50 km north of Baie-Comeau. We used the fo rest inventory data gathered by the Ministere des Ressources naturelles du Quebec (MRNQ). In circular plots of 400 m(2), the diameter at breast height (DBH) of all stems of tree species greater than 10 cm was recorded and in 40 m(2) subplots, stems smaller than 10 cm were measured. A total of 380 pl ots were sampled in an area of 6000 km(2). The fire history reconstruction was done based on historical maps, old aerial photographs and field samplin g. A time-since-fire class, a deposit type, slope, slope aspect and altitud e were attributed to each plot. Each plot was also described according to s pecies richness and size structure characteristics. Traces of recent distur bance were also recorded in each plot. Changes in forest composition were d escribed using ordination analyses (NMDS and CCA) and correlated with the e xplanatory variables. Two successional pathways were observed in the area a nd characterized by the early dominance of intolerant hardwood species or P icea mariana. With time elapsed since the last fire, composition converged towards either Picea mariana, Abies balsamea or a mixture of both species a nd the size structure of the coniferous dominated stands got more irregular . The environmental conditions varied between stands and explained part of the variability in composition. Their effect tended to decrease with increa sing time elapsed since fire, as canopy composition was getting more simila r. Gaps may be important to control forest dynamics in old successional com munities.