FOREST SUCCESSION FOLLOWING A FIRE IN A B ALSAM FIR YELLOW BIRCH STAND IN THE BAS-SAINT-LAURENT REGION OF QUEBEC

Forest successions following a forest fire that occurred in 1932 were studied on mesic sites of the boreal mixedwood forest of the Bas-Saint -Laurent region of Quebec, Canada. Physiographic, soil and vegetation data were collected in 28 ecosystems distributed on a topographic grad ient. The vegetation composition of the main canopy, 64 years after th e fire, varied according to topographic situation, The proportion of t olerant hardwood species (yellow birch (Betula alleghaniensis Britton) , sugar maple (Acer saccharum, Marsh.), red maple (Acer rubrum, L.)) i ncreased toward upper slopes whereas it was the opposite fur coniferou s species (white spruce (Picea glauca [Moench] Voss), balsam fir (Abie s balsamea [L.] Mill.)), as their proportion increased toward lower sl opes. Intolerant hardwood species (white birch (Betula!la papyrifera M arsh.), trembling aspen (Populus tl el,tremuloides Michx.)) were abund ant in all ecosystems. The distribution pattern of regeneration densit y and stocking of tolerant hardwoods and conifers was similar to that of the main canopy. The majority of commercial species, including tole rant species, established rapidly after the fire. Only eastern white c edar (Thuya?! occidentalis L.), which is a species typical of late suc cession, did not grow back. Ten years after the fin, 78% of the sample d dominant trees were established. Competition caused by mountain mapl e (Acer spicatum Lam.) did not seem to be as important after fire comp ared with the situation after clearcutting. Results showed that after the elimination of intolerant species, the vegetation composition shou ld evolve toward the potential vegetation (climax) of the toposequence , that is, the sugar maple - yellow birch type on upper slopes, the ba lsam fir - yellow birch type on midslopes and the balsam fir - yellow birch - cedar type on lower slopes.