Sideoats grama responded positively to sulfonylurea herbicides, whereas switchgrass and western wheatgrass were adversely affected. Switchgrass cover was reduced by application of either sulfonylurea or auxin herbicides. Blue grama and sand dropseed were least affected by herbicide treatment. Plant diversity was reduced under sulfonylurea treatment. Auxin herbicide treatment increased plant diversity for seeded species and total plant community over sulfonylurea treatment, which was primarily attributable to increased frequency of annual forbs. Secondary successional status for non-seeded species was dramatically accelerated under sulfonylurea herbicide treatment, however, because of increased frequency, cover and live standing crop of perennial forbs, grasses, and half-shrubs.