Plant communities are influenced by disturbance events that alter both abiotic and biotic conditions, and the extent of the impact can be historically contingent. We hypothesized that less frequent fires would lead to less resistance and therefore greater community response to fire. Between 2011 and 2014, plots in a pyrogenic longleaf pine-wiregrass system in eastern North Carolina were burned annually, biennially, every three years, or never. In 2015, managers returned to an approximately three-year burn cycle. Leveraging herbaceous community data, we examined whether plots with a larger “fire return interval” (between the previous fire and current one) responded differently to the current fire, as captured by the change in various diversity metrics, using exponential decay models. We also asked whether plots differed in their composition after fires in 2015 or 2016 based on their previous fire histories.
Results/Conclusions
The change in richness and Shannon’s diversity due to a fire were both best predicted as exponential decay models by the length of the fire return interval (p =2.67e-08, 4.88e-07; adjusted R2 = 0.2168, 0.18; intercept = 3.07, 0.988; k = -0.00077, -0.00066), with greater fire return intervals leading to greater decreases in richness and Shannon’s diversity in response to fire. Plots burned in 2015 or 2016 grouped differently along nonmetric multidimensional scaling axes by historical fire treatment group, indicating that their compositional response to fire in those two years differed based on the fire frequency they experienced in the preceding period (PERMANOVA, p=0.024, 0.012). We also performed discriminant analysis using traits and trait variability as predictors of a species’ change in cover across a fire year. Together, these results suggest that plant communities respond with varying resistance to fire events depending on their fire history, leading to compositional differences.