Grass response to seasonal burns in experimental plantings

Abstract

A 6-year experiment examined the effects of spring and summer fires on grasses in southern Wisconsin. Synthetic communities of C3 and C4 grasses were seeded (100 seeds m-2 species-1) in 1992 and subjected to prescribed burns in May and August of 1995 and 1997, or left unburned. By 1994 all plots were virtual monocultures of the C3 reed canary grass (Phalaris arundinacea L.). By the second post-season sample in 1998, total productivity of plots burned in May was higher (781 +/- 212 se g m-2 year-1) than those burned in August (362 +/- 28 g m-2 year-1) or left unburned (262 +/- 43 g m-2 year-1) due to the incursions of either the C4 grasses big bluestem (Andropogon gerardii Vitman), switchgrass (Panicum virgatum L), or both. These large late-season grasses are much more productive per area covered than P. arundinacea or the other two C3 grasses present, Elymus virginicus L. and Poa pratensis L. Even at this early stage of succession, C4 production in plots burned in May was 5 to 6 times that in the other 2 treatments. August burns produced a mix of C3 and C4 grasses but did not strongly favor the pre-treatment C3 dominant P. arundinacea. Unburned plots most resembled those burned in August in species composition, but differed in having 4 times the accumulated litter, perhaps foretelling divergence in C3 and C4 composition as succession proceeds.