An Ecological Analysis of Prairie Rehabilitation on Petroleum Well Sites in Southeast Alberta
Hammermeister, A.M. 2001. Ph.D. Dissertation. Dept. Renewable Resources, University of Alberta, Edmonton, AB
Abstract
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 Chemozemic and Solonetzic soils in Dry Mixed Grass prairie, were compared with an
undisturbed control for three years following wellsite construction and abandonment.
Surface soi1 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 biogeochemicaî cycling relative to natural recovery; natural
recovery was most effective in initiating community development towards a
predisturbance condition.
