Technical Abstract: Grazed grasslands contribute greatly to the economy and environment of the northeastern United States, though their ecology has not been extensively studied. Plant community composition was sampled in five to seven fields in each of five grazing farms: two in New York, two in Pennsylvania, and one in Maryland. A modified Whittaker plot permanently located in each field was sampled three times per year for three years, with 224 plant species identified. This sampling scheme offers multiple hierarchical spatial scales for examining beta diversity: within-field, within-farm, within-state, and overall. Few studies of beta diversity explicitly incorporate changes over time; we have both year and season of sampling as hierarchical temporal variables. Permutation-based tests of the multivariate homogeneity of group dispersions were used to compare the variance of both presence- and abundance-based dissimilarity metrics at each of these spatial and temporal scales. Within-farm beta diversity varied significantly by state and by season. Abundance-based dissimilarities were more sensitive than frequency-based dissimilarities. Grazing management tends to favor certain species, ensuring that the dominants are similar across farms, while subordinate species composition is more variable. Managed systems such as these grazed temperate pastures offer a valuable context for studying patterns of plant diversity and composition: within this region they comprise a known set of species with similar management regimes. Improved understanding of diversity may translate directly into improved management for ecosystem services that provide food, fuel, and indirect services.