Canada's oil sand industry produces substantial quantities of oil sands process-affected material (OSPM) including composite tailings (CT) and tailings sands (TS) that need to be reclaimed on site. This work evaluated the establishment of a pioneer plant species, alder, inoculated with a nitrogen-fixing actinomycete, Frankia. The main objectives were to evaluate alder performance in OSPM and its impact on soil characteristics and microbial community structure and function. This project was divided into two phases: a field study and a greenhouse trial. The greenhouse trial tested 2 alder species, Alnus glutinosa and A. crispa, in CT and TS. In addition to Frankia inoculation, a tripartite association with a mycorrhizal fungus, Glomus intraradices was evaluated. The field study consisted of a 2 year monitoring of Frankia-inoculated alders (A. crispa (Ait.) Pursh.) planted in TS capped with overburden material and peat moss. The parameters tested were the following: plant biomass and nitrogen content; soil chemical characteristics; microbial biomass; microbial petroleum hydrocarbon mineralization capability; and microbial community diversity and composition using the molecular techniques, PCR and DGGE. Alders performed well in OSPM and Frankia inoculation improved biomass acquisition. Frankia-alders improved a number of soil quality parameters such as pH, sodium content, and CEC. Frankia-alders presence modified soil microbial activity and diversity. Alder rhizosphere sustained more microbial biomass than unplanted soil, whereas the tripartite association did not provide additional benefits. Overall, Frankia-inoculated alders are an interesting biotechnological approach for the reclamation and revegetation of oil sand process-affected materials. Abbreviation: PCR (polymerase chain reaction), DGGE (Denaturating Gradient Gel Electrophoresis), CEC (Cation Exchange Capacity), TS (Tailings Sands), CT (Composite