Pyrogenic flowering of Aristida beyrichiana following 50 years of fire exclusion

Fire-stimulated or pyrogenic flowering is one of many traits that enable plants in fire-prone ecosystems to persist or dominate following frequent fires. Obligate pyrogenic flowering has long been observed in wiregrass (Aristida beyrichiana), a foundation bunchgrass in frequently burned longleaf pine ecosystems in the southeastern United States. Widespread fire exclusion in this ecosystem has contributed to well-documented declines in plant and animal biodiversity prompting the need for restoration efforts. We studied the effect of fire reintroduction on the flowering of wiregrass in northern Florida, USA. Prescribed fires were ignited in a 50-yr unburned site and an adjacent frequently burned site in the summer of 2017. Wiregrass was measured eight months after the burns in both stands. As expected, the frequently burned stand had higher density, basal area, and percent flowering of wiregrass tussocks. Logistic regression revealed that wiregrass initiated flowering at significantly larger sizes in the long-unburned stand. Despite these differences, wiregrass size distributions were similar in both stands, with the long-unburned stand lacking tussocks in the largest (100+ cm²) size class. We did not find differences in the number of flower culms per unit of mass between the two stands. Even though diminished in nearly every measure, the ability of wiregrass to flower after five decades of fire exclusion, and presumably no sexual reproduction, provides evidence of resilience of the dominant herb of these ecosystems.