| Abstract: | Abstract. Plant species richness and species-area relations were examined for three landscapes (toposequences), each with a summit or upland, a midslope and a toeslope or lowland, in a shortgrass steppe in Colorado. The number of plant species in the largest plot size (0.16 ha) varied from 38 to 53. Neither the exponential relationship: s = a + b log A, nor the power function: S = cAz fit the data equally well in all situations. The processes acting upon species diversity here seem to operate at two spatial scales. The number of species in plots smaller than 3 m2 was independent of the total number of species in the 0.16-ha plots and was constrained by the presence of the dominant bunchgrasses. Beyond 3 m2, species number in each plot size was a function of the total number of species in the 0.16-ha plot. |
