Factors controlling the fire-induced flowering response of the federally endangered Schwalbea americana L. (Scrophulariaceae)1

Abstract

NORDEN, A. H. AND L. K. KIRKMAN (J. W. Jones Ecological Research Center, Rt. 2 Box 2324, Newton, GA 39870-9651). Factors controlling the fire-induced flowering response of the federally endangered Schwalbea americana L. (Scrophulariaceae). J. Torrey Bot. Soc. 131:16-22. 2004.-The fire-maintained longleaf pine ecosystem of the southeastern Coastal Plain harbors nearly 200 rare and endangered plant species, many of which depend on frequent fire for persistence. One such fire-dependent species is the federally endangered hemiparasite, Schwalbea americana L. (Scrophulariaceae). Regardless of season of burn, fire stimulates flowering and subsequent seed production in this species, but the specific mechanisms involved in this fire-induced flowering response are unknown. The purpose of this study was to determine the factors controlling the flowering response to fire. Using experimental treatments in the field and greenhouse, we examined the effect of variables associated with fire that may influence flowering of S. americana. Our field treatments included fire, shading immediately following fire, stem clipping plus competing vegetation exclusion, and mowing plus raking. Greenhouse treatments consisted of a gradient of light levels plus stem clipping. Our findings indicate that flowering, and subsequent viable seed production, is stimulated by a combination of clipping and increased light. These results suggest alternative management options for S. americana during years in which prescribed fire is not feasible. If prescribed fire is not an option, we suggest that mowing plus raking could be used as a temporary means to stimulate flowering and promote seed production and future seedling establishment.