LATE GROWING-SEASON FIRE EFFECTS IN MID-SUCCESSIONAL TALLGRASS PRAIRIES

Wildfire in the growing season is relatively frequent and interest is increasing in using growing-season fire in management of tallgrass pra irie, However, the influence of fire in the growing season on forage p roduction and species composition, especially in mid-successional tall grass prairie, is largely unknown, Our objective was to compare vegeta tion composition and production on Loamy Prairie and Very Shallow ecol ogical sites in mid-successional stages in response to late growing-se ason fire at different frequencies. We applied 4 burning treatments (n o burn, or 1, 2, or 3 burns in 5 years) in the late growing season in southern Oklahoma during a series of years of above-average precipitat ion. The sites were dominated at the beginning of the study by early-a nd mid-successional species including prairie threeawn (Aristida oliga ntha (Michx)), a species indicating a disturbance history, After the i nitial burns in 1990, tallgrasses, little bluestem, and perennial gras ses were reduced by burning on the Loamy site, Forbs were more product ive on burned plots (1,980 kg ha(-1)) than on plots that were not burn ed (1,290 kg ha(-1)) averaged across sites, Total production was not r educed 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 in 2 years, Warm-season perennial grasses other than tallgrasses and little bluestem increased on the Loamy site, but decr eased on the Shallow site, Production of cool-season perennial grasses increased to almost 40% of total production on twice-burned plots ave raged across sites, Other than the effect on cool-season perennial gra sses, 2 burns over a two-year period had little effect beyond the firs t growing season after the second bunt Twice-burned plots and plots bu rned 3 times produced more forbs than either plots that were burned on ce or not burned, Production of perennial grasses was opposite that of forb production, Total production was not reduced on either site rega rdless of fire frequency, Results indicate managers may expect a short -term reduction in production of forage grasses and an increase in for bs following late growing-season fire in mid-successional tallgrass pr airies.