PARENT SESSION
Symposium 8: Old-Growth Savannas as Models for Management of Upland Coastal Systems: The Role of Disturbance in a Time of Global Change
Organized by: F Gilliam and W Platt
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Chatham Ballroom B.
Fire regimes and groundcover vegetation responses in longleaf pine savannas: testing old-growth hypotheses in second-growth systems.
Drewa, Paul*,1, Thaxton, Jarrod2, 1 Case Western Reserve University, Cleveland, OH2 Louisiana State University, Baton Rouge, LA
ABSTRACT- Prior to European settlement, southeastern longleaf pine savannas were frequented by lightning-initiated fires that burned large areas during the early growing season. Such natural fires have been postulated to have a negative effect on resprouting woody vegetation. It has also been proposed that anthropogenic alteration of natural fire regimes has resulted in increased abundances and expanded distributions of shrubs, as are commonly observed in fragmented old-growth savannas. We have experimentally examined the effects of fire season and intensity on shrub demography in second-growth longleaf pine savannas across the southeastern Gulf coastal plain. Our research demonstrates that anthropogenic dormant season fires result in increased stem densities of root crown-bearing shrubs. Following biennial dormant season fires in bog habitats of Florida savannas, stem densities of Hypericum spp. were seven times greater than densities prior to these fires. By contrast, densities did not change appreciably after the re-introduction of biennial, early growing season fires. Relationships between stem densities of root crown-bearing shrubs and fire intensity are likely contingent on species and fuel type. Stem densities of H. microsepalum, but not H. brachyphyllum, decreased with increases in intensity of fires. These fine fuel fires were ineffective in completely killing genets of these species. Instead, heavier fuels are needed to create fires intense enough to reduce shrub densities. In longleaf pine savannas of Louisiana, experimental additions of woody fuels to growing season fires not only reduced stem densities, but also induced genet mortality of root-crown bearing species, including Quercus spp. and Ilex vomitoria. Returning natural fire regimes to old-growth savannas will likely maintain present stem densities of root-crown bearing shrubs. Genet mortality and reductions in densities appear likely only at localized scales where woody fuels create hotspots with fire intensities comparable to those associated with treefalls in old-growth longleaf pine savannas.
Key words: fire intensity, fire season, root crown-bearing shrubs, savannas