Flammability of the keystone savannah bunchgrass Aristida stricta
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Understanding the flammability of species in fire-prone or fire-dependent ecosystems is necessary for modeling and predicting ecosystem dynamics. Wiregrass (Aristida stricta syn. A. beyrichiana), a keystone perennial bunchgrass, is a dominant groundcover species in southeastern United States pine savannas. Although wiregrass flammability as a driver of pine savanna fire regimes is a fundamental paradigm in pine savanna dynamics, no studies have quantified its fuel structure and flammability at the individual bunchgrass level. We studied wiregrass flammability at the Aiken Gopher Tortoise Heritage Preserve in Aiken County, South Carolina, USA. We linked tussock fuel structure characteristics (total biomass, live:dead biomass,mass of perched litter and pine needles, moisture content, and bulk density) to flammability (flaming duration, smoldering duration, and flame length). Flame length was strongly and positively related to wiregrass biomass. Pine needles and other litter fuels perched on wiregrass tussocks were not related to flame length, but increased the duration of flaming and smoldering. Within the ranges evaluated, neither fire weather (relative humidity, wind speed, and air temperature) nor fuel moisture significantly affected tussock flammability. Our results indicate that different fuel structural properties drive separate aspects of wiregrass flammability. Together with litter from pines and other groundcover shrubs and trees, wiregrass modifies fire behavior locally, potentially influencing ecosystem dynamics at larger scales. These results have strong implications for southeastern pine savannas and more broadly where grass-dominated vegetation influences fire regimes.