Lilles, E. B., Purdy, B. G., Chang, S. X. and Macdonald, S. E. 2010. Soil and groundwater characteristics of saline sites supporting boreal mixedwood forests in northern Alberta. Can. J. Soil Sci. 90: 1-14. The influence of salinity on boreal forest plants is of growing concern today because oil sands mining and other energy-related industrial activities in northern Alberta and elsewhere produce large areas of salt-affected soils that require reclamation and revegetation. We characterized soils (salinity, pH, and nutrient and moisture availabilities) and groundwater at six naturally saline sites in northern Alberta which were occupied by boreal mixedwood forests dominated by aspen (Populus tremuloides Michx.) and white spruce [Picea glauca (Moench) Voss]. Salinity increased with depth in the soil profile and decreased with distance away from adjacent non-forested saline wetlands. In areas where forest vegetation existed, the electrical conductivity (ECe) of the surface soil (0-20 cm depth) was always below 4 dS m-2; chemical properties of the lower subsurface soil (50-100 cm depth) and groundwater ranged well above what has been conventionally considered to be suitable for tree growth: EC e ranged from 4 to 23 dS m-2, sodium adsorption ratio ranged from 13 to 70, and the pH of some soil horizons was above 9.0. These sites had relatively high soil moisture and nutrient availabilities, and we hypothesize that these facilitate survival of forest vegetation on these sites, despite the high levels of salinity.