Ecological uniqueness of riparian forests in the western boreal mixed-wood

Riparian forests, those adjacent to open water, are expected to have high productivity and species richness as a result of their topographic position, proximity to water and the influence of relatively strong ecological gradients. They may also serve important ecological roles in the landscape as movement corridors for vertebrates and as a large proportion of the remaining older forest in areas subjected to timber harvesting. We examined the ecological uniqueness of riparian forests in the aspen-dominated boreal mixed-wood forest of Alberta. Using a series of paired transects we compared forest structure and composition 50 m away from the lakeside forest edge with that in the same stand of forest but 600 to 800 m into the interior. The following traits were examined: trees - size, age, density by species, canopy cover; snags - size, condition by species; coarse woody material - amount, size, condition by species; shrub and herb cover to species, litter depth, soil N and P availability. Data were analyzed by paired t-tests and discriminant analysis. Riparian habitats were characterized by more balsam fir and paper birch, less balsam poplar, larger aspen and spruce, greater soil phosphorus availability, a denser canopy and lower species diversity for herbs. The discriminant analysis showed significant differentiation between the two habitat types. Floristic similarity between paired transects showed that 70 - 75% of species were in common.