Long-Term Effects of Aeration and Fire on Invasion of Exotic Grasses in Mixed-Brush Plant Communities

Abstract

Invasion of exotic grasses into grasslands dominated by native plants changes fire cycles and reduces biodiversity. Brush management practices that create soil disturbance, such as aeration, may potentially result in invasion of exotic grasses and replacement of native vegetation. We tested the hypothesis that a long-term effect of aeration and prescribed burning is an increase in exotic grasses. The study was conducted at the Chaparral Wildlife Management Area in the western south Texas plains where four treatments were evaluated: aeration, warm-season burn, aeration followed by a warm-season burn, and no treatment (control). The experimental design was a randomized complete block with four replicates. We estimated percentage canopy cover of exotic grasses, native grasses, forbs, litter, bare ground, and woody and succulent plants in 2007. There was a multivariate main effect among treatments for the dependent variables absolute canopy cover of exotic grasses, native grasses, forbs, litter, and bare ground (Wilks’s Lambda F15,179.8452.78, P50.001). Variables that contributed to the significant overall
effect included litter (F3,6954.32, P50.008) and native grasses (F3,6956.11, P50.001). The multivariate main effect of treatment was significant (Wilks’s Lambda F9,180.2552.04, P50.038) for the relative canopy cover of herbaceous species. Relative cover of exotic grasses was 31% higher (P 5 0.024) in control than in the prescribed burn treatment. Native grasses relative cover was 30% higher (P50.003) in prescribed burn than in the control treatment. We did not detect differences among treatments in the percentage of total woody and succulent plants canopy cover (P50.083). Under the environmental conditions at the time of the study, aeration and/or prescribed burning do not increase exotic grasses.