In fire-dependent ecosystems, it is increasingly recognized that spatial heterogeneity in fire severity, including the occurrence of unburned patches, drives important natural ecosystem processes. In longleaf pine savannas of the southeastern U.S. Coastal Plain, where most common fire return intervals were 1-2 years, unburned patches are thought to be important for longleaf pine regeneration, wildlife cover, and plant and microbial diversity, with possible influences on pollinators and other organisms. Refugia could be important for broadening the phenological range of flowering, with benefits to pollinating insects, given that some plant species respond to fire by increasing and synchronizing their flowering. The application of prescribed fire with the intention of mimicking natural fire regimes often does not take into account the possible benefits of unburned patches, making the understanding of their effects an important conservation consideration for sustainable management of longleaf pine savannas. For this study, we asked how flower abundance and flowering phenology differ between burned plots and unburned refugia for specific species and the overall plant community. To test these questions, we surveyed the number of flowers or capitula for 84 species in paired burned and unburned plots for 7 months after a spring prescribed fire.
Results/Conclusions
To capture flowering for all of the 84 species surveyed, we visited plots twice a week from May to September, and once a week from September to November. We found that flowering communities were different between burned and unburned plots, though they become more similar as time since fire increased. Overall, flowers were more abundant in burned plots than unburned plots. Fire did affect flowering phenology, usually by delaying and synchronizing flowering in burned areas. This effect varied by species, with some species responding more strongly to fire than others, including at least one species (Tephrosia virginiana) that only bloomed in burned areas. Other species, particularly flowering plants in the genus Rubus, were only recorded blooming in unburned plots, and at least one species (Penstemon australis) had two flowering peaks, blooming first in unburned areas and then blooming again later in the season in burned areas. These differences between fire refugia and the burned matrix could be important for organisms, such as pollinators, that rely on the resources that the flowering community provides, particularly because fire refugia provide flowering resources while the plant community in the burned matrix recovers.