Abstract:
Agriculture and urban development has reduced tallgrass prairie to less than 1% of its original land cover in southern Manitoba, Canada. Although much of the remaining tallgrass prairie in Manitoba is protected within a single Preserve, it continues to be degraded by the invasion of exotic and woody species, fire suppression, and overgrazing. My overall thesis objective was to assess the role of rehabilitation in tallgrass prairie restoration and more specifically to examine the relative effects of disturbance, soil fertility, and seeding. Two field studies were conducted within the St. Charles Rifle Range (SCRR) and Manitoba Tall Grass Prairie Preserve (MTGPP) to assess these objectives. The impacts of burn-season were examined on a high quality tallgrass prairie located within the SCRR. This four-year study found burn-season to have a substantial impact on diversity and species composition. Fall-burn had the most desirable effect, increasing native graminoid and forb diversity, regardless of time-of-flowering. Summer-burn increased both native and exotic graminoid cover. Spring-burn had relatively no effect on species composition and was characterized by woody species. All burn-seasons, except fall-burn, became increasingly similar in species composition to the control over time. Spring-, summer-, and fall-burns had varied but desirable effects on diversity and species composition. In 1999, a long-term experiment was initiated within the MTGPP to assess the role of disturbance (glyphosate, mowing, and fire), soil fertility (ammonium nitrate), and interseeding in rehabilitating degraded tallgrass prairie. Glyphosate had the greatest impact on diversity and species composition. Exotic and weedy native species increased and desirable native species (e.g. Andropogon gerardu) were adversely affected in glyphosate-treated plots. Mowing and fire had less of an effect, in large part because of long-term haying on this site. Fertilizer increased native forbs and graminoids, whereas exotic graminoids decreased. Interseeding with native tallgrass prairie species increased native graminoids and decreased exotic graminoids, but had no effect on forbs. Species composition of glyphosate-treated plots became more similar to the unsprayed and control plots over time, whereas effects of fertilizer and other disturbance factors showed little change. Rehabilitation of tallgrass prairie shows great potential for southern Manitoba. Disturbance and fertilization can have desirable effects, but only when seedbank, above ground vegetation, and site-specific constraints have been identified. Effective techniques in rehabilitation are required if the degradation of remnant and restored tallgrass prairie is to be mitigated.
