Context <p>Fire is a fundamental ecological process in the Great Plains rangelands. While it is well-established that dynamic mosaics created by fire and grazing are essential for maintaining biodiversity of grassland systems, how fire affects plant diversity in spatially heterogeneous savanna landscapes of the Southern Great Plains remains poorly understood.</p> Objectives <p>The objective was to explore how spatially heterogeneous fire affects plant α- and β-diversity and their spatial patterns, the possible mechanisms, and the regulating roles of precipitation and soil in the Great Plains savanna systems.</p> Methods <p>We collected prefire and postfire data of plant species composition and abundance data from 288 plots stratified by soil types and generated a fine-resolution (21-cm) burn map using aerial imagery and machine learning. These data were analyzed to quantify the effect of heterogeneous fire on plant α- and β-diversity measures and their spatial patterns, and the influence of soils with distinct water-holding capacity, in a mesquite-oak savanna landscape.</p> Results <p>Prescribed fire promoted α-diversity while it reduced β-diversity, with the effects mediated by patterns of soil moisture availability and fire heterogeneity. Differential changes in species composition and relative abundance of forbs and grasses in response to fire contributed to reductions in both incidence- and abundance-based β-diversity. Significant associations between the spatial patterns of the burn and postfire α- and β-diversity underscores the role of fire heterogeneity in shaping the spatial pattern of plant diversity.</p> Conclusions <p>The findings demonstrate that spatial patterns of fire heterogeneity and temporal patterns of precipitation significantly influence plant diversity and its spatial pattern, which should be a critical consideration in developing management strategies for sustaining biodiversity and other ecosystem services within these rangeland landscapes of the Southern Great Plains.</p>