Management practices in tallgrass prairie: large- and small-scale experimental effects on species composition.
Abstract
The effects of contrasting management practices on the species composition of tallgrass prairie in Kansas, USA were examined at 2 spatial scales. At the larger scale, the effects of 12 years of cutting and burning on 5 soil types (reflecting a topoedaphic gradient) were examined in 45 plots of 10 000 m2. At the smaller scale, the effects of 3 years of burning, cutting and fertilizer application were examined in 64 plots of 100 m2 according to a split-plot design. Classification of the large-scale plots using TWINSPAN allowed the analytical level at which treatments could be resolved to be identified along with the corresponding indicator species. Soil type was the most important discriminator of plant communities with a separation of soil subgroups (Pachic Argiustolls and Udic Argiustolls) at the 1st level of classification. Burning separated plots at the 2nd level of classification and cutting effects were not apparent until the 3rd level of resolution. Burning and cutting differed in their effect on species richness, especially the representation and number of exotic species. Annual burning decreased the number of native species on lowland Tully soils. Cut plots had a higher cover of C3 grasses, annual grasses and annual/biennial forbs, and a greater number of annual grasses and exotic species. Species composition of the large-scale plots was affected primarily by cutting, followed by fertilizer application and then burning. Burning increased the abundance of some species (e.g. Andropogon scoparius [Schizachyrium scoparium]), and decreased species richness in interaction with cutting or fertilizers. N fertilizer decreased species richness. Cutting allowed the incursion of exotic species including Andropogon bladhii [Bothriochloa bladhii]. It was suggested that the inconsistency in the resolution of common management practices at the 2 scales in this study indicated a need to consider scale-dependent causal mechanisms in developing models of grassland structure.