Effects of fire season on flowering phenology in a pine savanna

Abstract Background Fire maintains many grasslands and savannas worldwide, including pine savannas of the southeastern US. In these ecosystems, lightning initiates fire during the spring and summer, while humans have more often managed these systems with winter burning. Changes in season of fire potentially alter ecosystem function, including flowering phenology, i.e., the seasonal pattern of flowering, which could ultimately influence species composition. On the other hand, ability to burn in different seasons increases capacity to maintain frequent fire regimes. Little research has been conducted on the effects of fire season on flowering phenology in pine savannas, and the few studies available mostly focus on the differences among winter, spring, and summer fires. In order to more fully understand the effects of season of fire, including fall fires, on flowering phenology, we compared number of species flowering, co-flowering assemblages, and month of first flowering among plots burned in each of the four seasons over the course of a year. Results We found 175 species flowering during the study, with peak flowering in September and October. There were no differences in the average number of species flowering among season of fire treatments, but there were among months. Co-flowering assemblages did not differ among season of fire treatments, but spring, summer, and winter burns showed delayed flowering of certain species. We also identified species that flowered following fire regardless of season, did not flower when burned during a particular season, reflowered if burned while flowering, or, most commonly, showed delayed flowering following the most recent burn. Conclusion Our results suggest that flowering phenology of upland pine savanna species is generally resilient to differences in season of fire, with a few exceptions mentioned above. The mostly subtle shifts in flowering phenology in response to season of fire suggest that any resulting changes to plant community composition would occur over periods much longer than this study. These results suggest that spreading prescribed burns more widely over the course of the year to achieve management objectives would have minor impacts on flowering of the plant community.