The study of a species at its range limits allows the factors associated with its presence on the landscape to be determined. This study examines the distribution and dynamics of jack pine (Pinus banksiana), a fire-adapted boreal tree species, in two sectors of its longitudinal distribution limits. We studied jack pine's western range limit in the Northern Boreal Forest (NBF) study area, east of James Bay, and its eastern limit in the Lower St.-Lawrence (LSL) study area, which is part of the boreal and the Great Lakes-St. Lawrence forest regions. Six and twenty-four sampling stations were selected in the NBF and the LSL, respectively, in different habitats to describe jack pine stand structure and dynamics and to obtain additional information on its regional extent. For all the stations, reproduction and growth variables were compared to test for differences in the species' reproductive capacity by study area and habitat. In addition, summary statistics were calculated to describe the fire regime from mapped fires in NBF and LSL from 1952 to 1998. We found striking differences in the distribution patterns of jack pine between the study areas. The species is widespread in the NBF landscape, whereas in the LSL it typically appears in isolated patches across the landscape in less favorable habitats where it exhibits continuous regeneration. Tree and seedling growth and germination rates were higher in the LSL than the NBF. The number of seeds per cone did not differ significantly between study areas, but there were more cones per tree in the NBF, making the number of viable seeds per dominant tree 2.6 times higher in the NBF than in LSL. The LSL individuals have a higher proportion of in vivo open cones than NBF; however, serotiny levels in the NBF were lower at experimental heating temperatures of 41 and 60 °C than for LSL. Our results suggest that at its western range limit, where large fires are common, the distribution of jack pine is mainly a function of the fire regime. At its eastern range limit, by contrast, aging jack pine populations become senescent and scattered on their preferred habitat (glacial deposits) and in the absence of large, moderately frequent fires this species tends to occupy sub-optimal habitats (rocky outcrops and drained bogs) as refuges. © 2004, Tall Timbers Research, Inc.