Composition and structure of fescue prairie respond to burning and environmental conditions more than to grazing or burning plus grazing in the short-term

Burning and grazing are key processes in the natural disturbance regime of the Fescue Prairie. Burning, grazing and their interacting effects on plant species diversity (Hʼ), species richness, and heterogeneity in species composition were studied at two spatial scales for two years in a remnant Fescue Prairie near Saskatoon, Saskatchewan. Cattle distribution in relation to plant communities was also studied. At the plot scale (100 m²), burning increased Hʼ (P<0.01) on species richness; richness varied between years (P=0.04), averaging 14.2 species m⁻² in year one versus 15.8 species m⁻² in year two (S.E.±0.65). Spatial heterogeneity (P>0.25; x=46%; S.E.±3.0) and temporal heterogeneity in species composition (P>0.21; x=42%; S.E.±3.8) were not affected by burning, grazing, or their interaction. Burning + grazing increased tiller densities in Elymus lanceolatus (68%) and those of Festuca hallii (11%) (P<0.001) compared to the control. Burning decreased total
\naboveground net primary production (ANPP) (P<0.001) (x=305 g m⁻²) compared to unburned treatments (x=500 g m⁻²; S.E.±30.8). Grazing and burning + grazing had no effect on total ANPP or graminoid ANPP (P≥0.36). At the scale of Kernen Prairie (130 ha), H' increased between 1996 (P<0.05) (x=1.10) and 2005 (x =1.40; S.E.±0.094). Species richness increased from 5.2 species 0.25 m⁻² in 1996, to 6.8 species 0.25 m⁻² in 2005 (S.E.±0.505). Heterogeneity in plant species composition tended to increase after prescribed burning was started in 1986 and
\nafter grazing began in 2006. Cattle preferred Bromus inermis- and Poa pratensis-dominated
\nplant communities, areas with intermediate amounts of total aboveground standing crop of
\nplants, and areas in which shrub densities exceeded 16 stems 0.25 m⁻². In the short term, burning
\nand environmental conditions had greater effects on species diversity, richness, and heterogeneity in species composition than grazing or the interaction of burning and grazing. Different responses may be expected with different combinations of timing, frequency, and intensity of burning and grazing at different sites under ever changing environmental conditions.

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