Abstract. The study of vegetation dynamics in tallgrass prairie in response to fire has focused on dormant season fire in late successional prairies. Our objective was to determine if late season fire of varying frequency results in divergent successional patterns in an early successional tallgrass prairie disturbed by grazing and cultivation. Specifically, we evaluated the influence of late‐summer fires of varying frequency on community composition and species richness. We collected vegetation and environmental data on two sites burned in the late growing‐season at varying frequencies. These communities differed in composition depending primarily on edaphic factors, time since the last burn, and year‐to‐year variation. We interpret the time effect as related to changes in species composition accompanying plant succession that followed disturbance either from cropping and heavy grazing on the loamy site or heavy grazing on the shallow site. Other unidentified factors also have a role in vegetation dynamics on this prairie. Community composition and species richness were not consistently responsive to frequency of growing‐season fires.

Wildfire in the growing season is relatively frequent and interest is increasing in using growing-season fm in management of tallgrass prairie. However, the influence of fue in the growing season on forage production and species composition, especially in mid-successional tallgrass prairie, is largely unknown. Our objective was to compare vegetation composition and production on Loamy Prairie and Very Shallow ecological sites in mid-successional stages in response tu late growing-season fire at different frequencies. We applied 4 burning treatments (no burn, or 1, 2, or 3 burns iu 5 years) in the late growhtg season in southern Oklahoma during a series of years of above-average precipitation. The sites were dominated at the beginning of the study by early-and mid-successional species including prairie threeawn (Aristi oligantha (Michx)), a species indicating a disturbance history. After the initial burns in 1990, tallgrasses, little bluestem, and perennial grasses were reduced by burning on the Loamy site. Forbs were more productive on burned plots (1,9&t kg ha-') than on plots that were not burned (1,290 kg ha") averaged across sites. Total production was not reduced by burning in 1990. Growing-season burns in 2 consecutive years had little influence on species composition or production as compared to a single burn ht 2 years. Warm-season perennial grasses other than tallgrasses and little bluestem increased on the Loamy site, but decreased on the Shallow site. Production of cool-season perenuial grasses increased to almost 49% of total production on twiceburned plots averaged across sites. Other than the effect on coolseason perennial grasses, 2 burns over a two-year period bad little effect beyond the fmt growing season after the second bum. Twice-burned plots and plots burned 3 times produced more forbs than either plots that were burned once or not burned. Production of perennial grasses was opposite that of forb production. Total production was not reduced on either site regardless of fw frequency. Results indicate managers may expect a short-term reduction in production of forage grasses and an increase in forbs following late growing-season fire in mid-successional Mlgrass prairies,

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