Long-Term Population Changes of a Fire-Adapted Plant Subjected to Different Fire Seasons.

Long-term studies of the responses of plant populations to fire can inform adaptive management of ecosystems. I present results of an analysis of responses of a fire-adapted plant, Pityopsis graminifolia (Michx.) Nutt. (silkgrass goldenaster), to season of fire from 2001 to 2005 in a longleaf pine (Pinus palustris P. Miller) sandhill community in north Florida. Replicated May-burned and January-burned plots had been burned biennially from 1986 to 2004. Previous work in the early 1990s showed that populations of this species benefited more from fires during the peak lightning fire season (i.e., May) than from January fires. In 2001, however, shoot densities in both treatments were substantially lower than in 1992 and remained relatively low through March 2005. Shoot densities were significantly higher in May-burned plots than in January-burned plots between 2001 and 2005. May fires significantly increased shoot densities in 2002 (relative to January fires), but did not in 2004. Shoot densities in January-burned plots remained remarkably stable between 2001 and 2005. As in the early 1990s, May fires were consistently more effective than January fires at stimulating flowering, which in turn produced higher seedling densities. Seedling survival was low, however, as in the early 1990s. Positive short-term effects of lightning-season fires on long-term population trends in this fire-adapted species appear to be substantially reduced by periodic population crashes, inconsistent short-term effects on clonal growth, and inherently low seedling establishment rates. [ABSTRACT FROM AUTHOR]