| Summary: | Disturbance is important in maintaining the open structure of savannas. Frequent fires (every 1-3 years) limit the growth of woody plants, and prevent the transition from savanna to forest by maintaining open space for grasses, herbs, and fire-tolerant longleaf pine. Fires are not the only disturbances in southeastern pine savannas, which also experience hurricanes. Hurricane winds mainly affect the overstory, causing treefalls, increasing light, and adding litter to the understory. Hurricane effects were documented after Hurricane Gustav in 2008. More trees fell where the overstory was present, and produced localized effects on the ground below. Increase in light transmittance was similar across different overstory treatments, and responded to scattered treefalls across wide areas of the study site. Defoliation also added pine needles to the groundcover. Increases in fuels may increase fire intensities following hurricanes. I hypothesized that pine needles would augment fires, and therefore decrease survival of woody plants in the understory. The presence of small amounts of pine needles beneath understory hickories led to greater temperatures during fire, longer durations of heating, and more complete combustion of hickory fuels. All hickories survived fire by resprouting, but when pine needles were absent most resprouted from buds aboveground along the stem, rather than from the belowground root crown. These stems may more quickly reach a size that can withstand fire. Therefore, understory woody plants should be larger, and more fire-resistant, away from overstory pines, such as in gaps created by hurricanes. I expected greater numbers and sizes of woody plants in plots where the overstory was experimentally removed. Woody stems were taller in gaps, but there was no increase in species or density. Instead, after the overstory remains absent for several decades, the number of species and density decline. Moreover, woody plants in gaps do not reach a size resistant to fire, and repeated fires continue to top-kill stems. Resprouting stems may be competing with other understory species. Furthermore, many woody plants are dispersed by birds beneath trees. Repeated fires, increased competition, and lack of recruitment may lead to a decline of woody plants in gaps, opening space for longleaf recruitment.
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