COS 188-4 - Fire return interval is more influential than fire seasonality on plant community similarity in pine savannas

Background/Question/Methods

Historical fire regimes are considered to be strong filters of current plant community composition, generating communities of species with life history traits linked to those regimes. If fire regimes are changed, specialized or endemic species would presumably be lost, and/or species that are not harmed by this alternate fire regime would become more frequent. Our objective was to test the influence of changing historical fire frequency and seasonality in wet-mesic and dry pine savannas of the southeastern USA, a hotspot of biodiversity in North America. We compared groundcover plant community composition at the start and finish of 20 years of biennial, seasonal prescribed fire treatments, and again 20 years after the seasonal fire treatments were abandoned, when fire seasonality and return interval became variable. Fire seasons were classified by periods of active plant growth and dormancy in the study area, and fire return interval was defined as the number of years between successive fires.

Results/Conclusions

Based on species’ frequencies of occurrence, different patterns were observed for plant communities before and after seasonal fire treatments were applied. Plant communities diverged significantly during the 20 years of fire seasonality treatments. These changes were mostly independent of fire seasonality. Minor differences were likely a result of variation at the plot level rather than between treatments. More significantly, plant communities shifted together over time. During the 20 years after fire seasonality treatments were abandoned and fire season and frequency became variable, plant communities continued to shift together, except for those plots with more than 20 years without fire. This long fire return interval resulted in lower species richness and changed community composition as compared to those plots that continued to be burned. Our results suggest that these communities are resilient to different fire seasons when applied at high fire frequency but might be more affected by large-scale, extrinsic pressures. Furthermore, pine savanna plant communities are also resilient to variation in fire frequency as long as fires are frequent.