Differential Response of Woody and Herbaceous Species to Summer and Winter Burning in an Oklahoma Grassland

Abstract

Fire has historically been an important factor in the maintenance of tallgrass prairie vegetation. Summer fires have often been thought to be more effective than dormant season fires in controlling the invasion of woody species into prairies. However, in an Oklahoma grassland, late-winter burning (March) had a more pronounced effect in reducing the density of woody spe- cies than did summer (July) burning. This response was possibly due to both environmental and site conditions. Two woody species increased in density following both summer or late-winter burning while nine species decreased in density or were eliminated by fire. Two additional woody species exhibited varied responses depending on season of burn. Woody species density increased in the smallest seedling size class, but decreased for larger seedling and sapling size classes follow- ing both burning regimes. Finally, numbers of woody and herbaceous species decreased following both summer and late-winter burns. The importance of fire as a means of increasing production, determining community composition, and controlling the invasion of woody species has been documented in many parts of the tallgrass prairie (Gleason, 1913; Daubenmire, 1968; Peet, Anderson, and Adams, 1975; Anderson, 1976; Rice and Parenti, 1978; and others). In the absence of fire, many woody species readily invade native North American grasslands, especially in the eastern tallgrass prairie where environmental conditions are more favorable for trees than in the more arid West (Sauer, 1950; Weaver, 1968; Bragg and Hulbert, 1976). Mechanisms allowing woody species to replace grassland species or to per-