Widely-held, untested assumptions in many prairies are that high-intensity fires conducted during droughts will decrease native herbaceous species richness and lead to rapid invasions by alien species. We compared native and exotic herbaceous species richness and aboveground herbaceous biomass one year following the application of high-intensity growing-season fires in Texas coastal prairie. Fires were conducted in June 2008, when precipitation was 96% below the long-term monthly average, at the end of a severe 5-mo drought, resulting in high fire intensities within treatment units. Native forb species richness was greater in burned than unburned areas. In contrast, species richness of native grasses, exotic forbs, and the frequency of King Ranch (KR) bluestem [Bothriochloa ischaemum (L.) Keng.] did not significantly differ between burned and unburned treatments. The potential to use prescribed extreme fire to maintain native herbaceous species richness while not increasing KR bluestem provides preliminary evidence that growing season fires conducted during droughts can be a viable management strategy in coastal prairies.
Nomenclature: King Ranch bluestem, Bothriochloa ischaemum (L.) Keng.
Management Implications: King Ranch (KR) bluestem is an invasive C4 grass introduced from Europe and Asia that has led to declines in the richness of plant, avian, and arthropod species in prairie ecosystems. Managers in Texas Gulf coastal prairies are concerned that using fire to manage woody plant encroachment will trigger rapid invasion by KR bluestem and decrease native herbaceous species richness. The objective of this study was to compare the rapid responses of native and exotic herbaceous species in burned and unburned treatments in a huisache–mesquite-invaded coastal tallgrass prairie. In this study, prescribed fires were conducted in the growing season with special permission during a county-mandated burn ban initiated by a severe, prolonged drought that caused considerable grass curing and the potential for high fire intensities (referred to as prescribed extreme fire). Our results counter previously unsubstantiated assumptions in coastal tallgrass prairies and show that prescribed extreme fire increased native forb species richness while maintaining the richness of native grasses, and not increasing King Ranch bluestem significantly. Because other research has shown burning in the dormant season is more likely to facilitate rapid invasion by KR bluestem, prescribed extreme fires in the growing season might be more effective at maintaining herbaceous species richness in coastal prairies prone to KR bluestem invasion.