Protection and management of tallgrass prairie remnants are critical to the continued existence of this rare ecosystem. While effects of individual management events (especially fire and grazing) are understood relatively well, their combined, long-term effects are more difficult to predict. We examined how a large (283 ha) tallgrass prairie remnant in Texas responded to changes in management. Previously, the site had been hayed annually for ∼100 y. In 1987, management changed to prescribed fire in multiple seasons (average fire return interval of 3.5 y) and occasional grazing and haying. From 1996 through 2020, native species richness increased from 39 ± 3 to 47 ± 1 species on slopes and from 33 ± 5 to 44 ± 4 species on summits (mean ± standard error, 7.5 m² sample area). The number of specialist species (coefficient of conservatism ≥7) remained stable (slopes: 7 ± 0.4 to 10 ± 1; summits: 5 ± 1 to 8 ± 1). Forb cover increased dramatically (slopes: 44 ± 3% to 66 ± 5%; summits: 39 ± 7% to 65 ± 6%). While overall graminoid cover remained similar, cool-season graminoid cover increased (slopes: 4 ± 2% to 14 ± 2%; summits: 12 ± 9% to 18 ± 2%) and warm-season graminoid cover decreased (slopes: 49 ± 4% to 35 ± 3%; summits: 30 ± 6% to 26 ± 3%). Tree and shrub cover remained low (<3%). The site's large size and the repeated use of prescribed fire likely contributed to these outcomes. Because fire seasonality can favor either grasses or forbs, burning in multiple seasons can increase forb cover and diversity while still maintaining grass cover. Prairie remnants should be actively managed to avoid woody encroachment and to maintain diversity.