Interactive Effects of Drought, Nitrogen Deposition, and Fire on Herbaceous Communities in a Semi-Arid Savanna

Understanding the responses of savanna communities to disturbance and altered resource conditions will gain importance under climate-change induced modifications to precipitation patterns and nutrient cycling. This study investigates 1) how an herbaceous community within a semi-arid savanna will respond to drought, nitrogen deposition, and prescribed fire and 2) how these factors will interact to alter those responses. Sixty-four 5 x 5 m, herbaceous-dominated plots were established at the Texas A&M AgriLife Research Station on the Edwards Plateau, a generally rocky, shallow-soil savanna ecoregion (latitude 31°N, longitude 100° W). A prescribed drought treatment (rainout shelter or ambient), nutrient treatment (nitrogen addition or control), and fire treatment (burned or control) was assigned to each plot in a full factorial, completely randomized experimental design. Vegetation and topsoil data were collected to evaluate the treatment effects on both the vegetative community and also on the soil and vegetation chemistry. The vegetative community responded rapidly to the treatments especially in terms of drought-reduced ANPP (ANOVA p<0.05) and a shift in community composition from the full combination of treatments (PERMANOVA p<0.05) after 8 months of treatments. After 12 months of treatments, forb ANPP was reduced by fires (ANOVA p<0.01) but increased by drought (ANOVA