An ecological analysis of prairie rehabilitation on petroleum wellsites in southeast Alberta

Ongoing disturbance of native prairie in Alberta necessitates understanding rehabilitation practices and their effectiveness. Observations indicate that wheatgrass (Agropyron spp.) cultivars currently used in seed mixes may suppress other typically more dominant species. High diversity seed mixes and natural recovery have been suggested as alternatives. Various plant community and biogeochemical attributes were studied in four rehabilitation treatments: three seed mixes (Current - low diversity dominated by wheatgrass cultivars, Simple - low diversity dominated non-wheatgrass perennial grasses, Diverse - high diversity) and natural recovery. Treatments, at seven petroleum wellsites on Chernozemic and Solonetzic soils in Dry Mixed Grass prairie, were compared with an undisturbed control for three years following wellsite construction and abandonment. Surface soil was stripped, stored for less than six months, and replaced as part of standard reclamation practices. Soil disturbance resulted in a 16.5 and 19% reduction in organic carbon and total nitrogen, respectively; a reduction in nutrient supplying potential and long term implications for ecosystem development were postulated. Few significant differences were found among seeded treatments. Soil disturbance increased nitrate availability relative to the control; nitrate was highest in the Natural Recovery and lowest in the Current treatment. Native wheatgrass cultivars dominated plant community development and suppressed establishment of other species. Dominance was attributed to life history strategy and high establishment rate, growth rate, competition, and reproduction. The Diverse treatment did not increase community diversity and similarity to undisturbed prairie. Natural recovery was characterized by annual forb domination and increasing perennial species. Soil nitrate was positively correlated with annual forb biomass which was negatively correlated with grass biomass. After three years, the principal conclusions were that species attributes were more important than seed mix diversity for plant community development; with relatively high nitrogen availability, wheatgrass cultivars suppressed establishment of other species; seeded treatments accelerated recovery of biogeochemical cycling relative to natural recovery; natural recovery was most effective in initiating community development towards a predisturbance condition.