Print PageGulf coastal prairies were once highly diverse ecosystems maintained by fire but the few remaining remnants are being threatened by the encroachment of woody plants and the invasion of King Ranch bluestem (Bothriochloa ischaemum) and other exotic species. Much of the native herbaceous species richness has subsequently been lost due to woody encroachment. Fire was critical to the maintenance of coastal prairies historically and prescribed extreme fires are beginning to be used in many grassland restoration efforts. However, coastal prairie managers are concerned that prescribed extreme fires will decrease native species richness, either directly or by facilitating invasions of alien invasive grass and forb species. We compared native and exotic herbaceous species richness and total live and dead herbaceous biomass one year following fire treatments in plots established at the Welder Wildlife Refuge near the southern boundary of Texas coastal prairie. Fire treatments were conducted in June 2008, when precipitation was 96% below the long-term monthly average, at the end of a severe 5-month drought, resulting in extreme fire intensities within treatment units.
Results/Conclusions
Ground surface temperatures averaged 933 ± 18 oC in burned plots. Total species richness was significantly greater in burned treatments (t = 2.00; P < 0.10) as a result of significantly greater richness of native forbs (t = 2.97; P < 0.05). Alternatively, exotic species richness and the frequency of King Ranch bluestem did not differ between burned and unburned treatments (t = 1.05; P = 0.32 and t = 1.11; P = 0.29, respectively). Non-metric multidimensional scaling (NMS) ordination revealed an inverse relationship between total live and dead herbaceous biomass and species richness along a burned-unburned gradient, suggesting that heavy litter accumulation is a primary, negative constraint on species richness in coastal prairie. These findings did not support concerns that extreme fires decrease herbaceous species richness nor did they increase the abundance of undesirable exotic herbaceous species. Coupled with the benefits achieved by reducing woody plant encroachment, the results from this study suggest that prescribed extreme fires (i.e. high intensity prescribed fires conducted during dry conditions) in the growing season can be a viable restoration strategy in coastal prairie ecosystems.
