This research investigated the natural recovery of upland boreal forest vegetation on a peat-mineral mix substrate in the Athabasca Oil Sands Region, Alberta. Three sites, aged 26 to 34 years, were assessed to determine effects of substrate (pH, electrical conductivity, texture), topography, slope, aspect, hummock size, litter depth, tall shrub and tree stem densities, canopy cover, and tree ages on community composition and cover of upland boreal vegetation. Environmental variables that had the most influence on the plant communities were substrate texture (clay), tree canopy cover, and tall shrub stem density. The plant communities, which likely developed from early successional lowland communities, most closely approximate an upland boreal mixedwood forest in transition from an early to mid successional stage. Community development was concluded to be a product of measured environmental variables, with unmeasured factors such as propagule dispersal, germination conditions, and initial species composition also playing important roles.