COS 113-6 - Legacies of exotic plant invasions on the northern prairies: Forty years after cattle grazing in Riding Mountain National Park, Manitoba

Thursday, August 11, 2011: 3:20 PM
10A, Austin Convention Center
Rafael Otfinowski, Western and Northern Service Centre, Parks Canada, Winnipeg, MB, Canada and Peter A. Sinkins, Riding Mountain National Park, Parks Canada, Wasagaming, MB, Canada

Biological invasions describe the establishment and proliferation of exotic species to the detriment of indigenous organisms. Despite the negative impacts of exotic invaders on native biodiversity, few studies have focused on their long-term persistence. Here, we examine the recovery of rough fescue prairie communities, 41 years after the removal of livestock grazing from Riding Mountain National Park, Manitoba. In contrast with other prairie dominants, summer grazing of plains rough fescue (Festuca hallii (Vasey) Piper) leads to its displacement from the plant community and increased dominance by exotic plant species. We apply multivariate models to vegetation data collected along permanent transects to explore changes in the structure and composition of historically grazed plant communities, examine the persistence of exotic plants, and correlate their abundance with residual, long-term changes in the soil environments.


Despite the long absence of livestock disturbance, plant communities and soil environments remained correlated with historic grazing intensities. Since 1973, heavily grazed sites shifted in composition from a mixture of exotic forbs and grasses to dominance by exotic grasses and native weedy shrubs. In addition, native species, including plains rough fescue, remained rare in these areas. Heavily grazed sites were also characterized by higher levels of macronutrients, pH, and electrical conductivity. Past grazing disturbance continued to exert a strong influence on the current species composition of rough fescue prairies, with groups of transects defined by the intensity of historic grazing remaining significantly dissimilar. Our results demonstrate that the recovery of rough fescue prairies following livestock grazing is inhibited by the presence of exotic species and that historically heavily-grazed areas can act as nuclei for the proliferation of exotic species into adjacent, native prairies.

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