Technical Abstract: The plant species composition and diversity of pastures can affect the total and seasonal production of that pasture, its drought resistance, and its nutrient cycling. Diversity in plant communities is in part determined by the species that are planted, but many other species can also be found. We sampled 125 pastures on 42 farms for pasture plant diversity and composition. Information about topography, soils and surrounding land use was also collected. The pastures sampled were highly diverse; the average pasture had 31 species, and the maximum number was 66 species. The percentage of the surrounding land in agricultural use was negatively correlated with species richness and total plant cover, as well as cover of grasses and forbs. Legume cover was unrelated to land use, but decreased with increasing elevation. Total species richness was positively correlated with elevation, but unrelated to slope or aspect. The composition of a pasture is determined by seeding and management, but is also affected by factors beyond the control of the producer, especially surrounding agricultural use and elevation. Management strategies must be chosen to succeed within the constraints imposed by land use and topography.