Effects of repeated burning on species richness in a Florida pine savanna:A test of the intermediate disturbance hypothesis

We studied the effect of burning frequency on the density and species richn ess of understory flowering stems in a Florida sandhill. Flowering stems we re censused weekly for 54 weeks in six sites that had been burned one to si x times in the previous 16 years. We concurrently measured overstory charac teristics such as species composition, density and basal area. We used maxi mum likelihood and Akaike's Information Criterion to compare linear, quadra tic, saturating, and null models of community response to repeating burning . We did not find a relationship between species richness, diversity or flo wering stem density and fire frequency. Tree density was related to fire fr equency and may represent an indirect pathway for fire effects on understor y characteristics. While we found no support for the Intermediate Disturban ce Hypothesis, an analysis of our experimental design indicated that we had low statistical power. We develop the hypothesis that a saturating model o f response to fire best describes understory species richness in our system . We test this hypothesis using the most extensive published fire data set we are aware of and find support for a saturating model.