Maintaining native plant diversity through fire management is challenging in the wildland-urban interface. In subtropical South Florida, fragments of fire-dependent, globally imperiled pine rockland forest are scattered throughout urban areas. To determine the effects of recent fire frequency, major soil type, and fragment size on species composition, we measured understory vascular plant presence and cover in 162 plots distributed among 16 publicly-owned pine rockland preserves in 1995 and 2003. Fragments received either 0, 1, or > 1 burn(s) between sampling periods. Native plant richness was very high overall. Major soil type, which varies regionally and is associated with latitude and elevation, strongly influenced the assemblage of species present at a given site. Native species cover was significantly different across different burn categories. Fragment size was positively associated with plant species richness, but small fragments had high variance in the total number of native plant species they supported, with some having nearly as many plant species as the largest fragment. Examining trends over time for rare native and invasive non-native plant species revealed the spread of the invasive grass Rhynchelytrum repens (Willd.) C.E. Hubb. and showed no major decreases in rare plant species. In general, this study provided encouraging results for managers of small urban forest fragments, showing that they can maintain high levels of native plant diversity, even when fire occurs infrequently.