Plant species richness in relation to pasture position, management, and scale

The objective of this research was to describe how landscape position, grazing management, and scale affected overall plant species richness and species richness per functional group in temperate pastures located in the central United States. The effects and interactions of summit, backslope, and toeslope positions and continuous, rotational, and nongrazed stocking systems on species richness were examined at sample scales of 0.18 m2and 4.5 m2. Landscape position explained 40–63% of species richness variation at 0.18 m2 compared to 3–26% at 4.5 m2 for overall, perennial, perennial grass, vegetative-spreading grass, perennial herb, and perennial N2-fixing herb (legume) functional groups. Grazing management, in contrast, explained 22–35% of species richness variation for overall, perennial, annual–biennial, perennial grass, and perennial bunchgrass functional groups at 0.18 m2 compared to 30–43% of their variation at 4.5 m2. Landscape position and stocking system mostly did not interact. Overall species richness averaged 11.7, 14.3, and 10.3 on summits, backslopes, and toeslopes, respectively, and 14.8, 12.9, and 8.7 within the continuous, rotational, and nongrazed systems, respectively, at the 4.5 m2-scale. Backslope positions supported more species than summits and toeslopes regardless of scale, with differences that appeared related to total vegetation production and aboveground competition. Continuously and rotationally stocked pastures also supported more species than nongrazed pastures, effects that were consistent across functional types and scales. Increased scale enabled detection of a greater number of species per unit area but reduced the percentage of species richness variation explained by pasture position and management.