How does prescribed burning in grasslands of coastal southern Texas, USA, impact butterfly populations?

Butterflies are important pollinators worldwide and are often sensitive indicators of ecosystem health. Prescribed fire is used in grassland to mimic historic wildfires, improve forage nutritional value, and increased forb production and diversity. However, there is little understanding of prescribed fire effects on butterfly populations. We evaluated effects of winter and summer prescribed burning and time since burning on butterfly population abundance, richness, and diversity in the Gulf Prairies and Marshes ecoregion of southern Texas. We evaluated these over a two-year period in both Gulf cordgrass and non-Gulf cordgrass grasslands. We hypothesized that summer burning would have greater positive impact on butterfly populations by increasing forb yields. We found no effects of winter burning on butterfly abundance, richness, or diversity. Summer burning reduced butterfly abundance during 5 months and richness during 6 months of our study, even as long as two years after burning. Abundance and richness were only increased by summer burning during one month of our study, in patches burned 6 and 18 months previously. Summer burning did not affect Shannon's Diversity Index; however, it did create differences in dominance among treatments as measured by Simpson's index during two months of our study. The presence of Gulf cordgrass did not affect butterfly populations; however, in Gulf cordgrass-dominated rangelands butterfly abundance was greater closer to woody mottes. We reject our hypothesis and recommend burning during winter months in southern Texas to avoid possible negative impacts on butterfly populations.