The Effectiveness of Prescribed Fire for Native Grassland Restoration and Exotic Weed Control Differs Between Soil Types

Abstract

The presence of invasive species often makes the use of prescribed fire for native grassland restoration challenging, as fire could also facilitate exotic plant invasion. The outcome of fire treatment may depend on variation in soil environments. Nutrient-rich soils that are heavily invaded by exotic plants may burn at higher temperatures and damage native plant species recovery. A high nutrient availability may also facilitate post-fire establishment of exotic species that can readily exploit available nutrients. We tested the effect of prescribed fire within a temperate grassland reserve in southeastern Australia that includes two soil types with contrasting nutrient availability—nutrient-poor red soil and nutrient-rich grey soil. A plant survey of the post-fire community showed that fire in red soil reduced the proportion of exotic cover by 39%, but fire in grey soil maintained exotic dominance and reduced native grass and forb abundance by 30% and 71%, respectively. Moreover, fire altered community composition more in red soil than in grey. Partitioning of community dissimilarity further suggested that fire in red soil created a unique native community that differed from unburnt plots, whereas fire in grey soil reduced the abundance of some species without replacing them with individuals of other species. Exotic biomass was correlated with maximum burning temperature, but variation in temperature did not explain the observed differences in native community response to fire between the soil types. Fire increased disparity in soil nutrient content between soil types, potentially making red soil more suitable for some native species. While our study was limited to a single landscape, the results suggest that fire in nutrient-poor soils could be an effective management tool for suppressing exotic plant invasion and increasing native β-diversity across the landscape. But the same practice could be ineffective, or even harmful, in nutrient-rich soils that are already heavily invaded by exotic species.