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Abstract

Long-term effects of cattle and wildlife grazing on grassland plant community recovery in the East Kootenay region of British Columbia.

Abstract

In 1990, the East Kootenay Trench Agriculture Wildlife Committee was formed to mitigate long-standing conflicts concerning forage allocation among cattle, elk, and deer in the Rocky Mountain Trench in southeastern British Columbia. A habitat monitoring program was initiated in 1991 at Skookumchuck Prairie, Premier Ridge, and Pickering Hills, and a report summarizing 4 years of results was completed in 1997. The original sites were re-sampled in 2009 to evaluate 18 years of wildlife and cattle grazing. An ungulate exclosure was constructed at the Skookumchuck Prairie Historical Exclosure Site in 1951 and was sampled at about 10-year intervals between 1960 and 2009. In 1951, plant communities on both the grazed and ungrazed areas were dominated by early seral species. Over the 60 years of protection inside the exclosure, the plant community advanced to a stand dominated by rough fescue (Festuca scabrella) and Idaho fescue (Festuca idahoensis), whereas the plant community on the grazed area remained at an early seral stage. Bluebunch wheatgrass (Agropyron spicatum), which was virtually absent inside the exclosure in 1951, peaked in cover by 1970 and then declined from about 50% cover to less than 5% by 2009. Constructed in 1991, the Skookumchuck Prairie "Three-way Exclosure" Site was divided into three grazing treatment areas to allow differential access to cattle, wildlife, and cattle and wildlife together. An exclosure was also constructed adjacent to the grazed areas to prevent all ungulate grazing. Early seral plant communities dominated all four areas in 1991, and little change was apparent in any of the treatment areas until the site was re-sampled in 2003. After 18 years, rough fescue and Idaho fescue cover had increased significantly in the Ungulate Exclosure and Cattle Only Area, but cover of these species remained negligible on the Wildlife Only and Combined Use Areas. Vegetation changes in both the grazed areas and ungrazed exclosures at Premier Ridge and Pickering Hills were essentially stagnant for 18 years, indicating that historical grazing by cattle and wildlife had impeded recovery. Widely dispersed rough fescue plants were found on both sites, indicating that ecological potential for recovery exists. The exclosures at the Skookumchuck Prairie Historical Exclosure Site, and the Ungulate Exclosure and Cattle Only Area at the Three-way Exclosure Site, demonstrate that these rangelands can recover to higher seral stages given proper management and sufficient time. Plant communities resulting from such recovery, however, will contain a mix of native dominant species and naturalized alien species that may have reached a new "steady state" or "potential natural community." While improved livestock and wildlife management is essential for recovery and long-term sustainability of range resources, external management inputs, such as fire, chemical treatments, or mechanical treatments, may be necessary to achieve desired plant communities. Long-term exclosures provide a rare opportunity to evaluate undisturbed plant communities over extended time periods. Such information affords insight into possible end points in succession, which are valuable for assessing the effects of grazing management and other disturbance regimes. The rate of recovery provides us with a framework for management to gauge reasonable time frames for plant community change and evaluate the composition and productivity of various seral stages to supply resource values.