Assessment of long-term tallgrass prairie restoration in Manitoba, Canada

Ecological restoration is important in mitigating degradation and habitat loss of tallgrass prairie in North America. In 2002, we assessed the progress of a long-term tallgrass prairie restoration initiated in 1987 in southern Manitoba (Canada). Nine restoration and three reference sites were examined, as was a neighbouring site of future restoration that is now used for agriculture. Vegetation diversity, species composition, and associated soil properties were compared among restoration and reference sites, and changes associated with restoration identified. Restoration had a substantial effect on diversity and species composition, although restoration sites had significantly lower native and higher exotic diversity than reference sites. Overall and native diversity decreased over time, as both exotic and seeded native species were lost from the restoration sites. Particularly vulnerable were native forb species, which represent much of the diversity of prairie habitats. Forb presence was negatively associated with that of warm season native grasses, especially Andropogon gerardii (big bluestem). Similarity of restoration and reference vegetation increased over time, particularly for seeded native graminoids. When species that had been seeded elsewhere and had colonized restorations were examined, similarity between restoration and reference also increased with time, suggesting that older sites may be self-propagating. No significant differences in soil properties variables were observed among restoration sites, indicating that changes in these factors are slow relative to vegetation changes. Although time-since-restoration had a substantial impact on diversity and species composition, this habitat will require ongoing restoration.