Tolerance to drought and flooding events provides a competitive advantage for an invasive over a native plant species

Abstract

1. Changes in precipitation patterns are one of the most pervasive components of climate change. It has been suggested that the increased frequency of extreme drought and flooding events could affect the outcome of competition between native and invasive plants. However, empirical evidence for this prediction remains scarce.

2. We combined controlled experiments and field observations in a freshwater floodplain to assess how drought and flooding events affect growth and biomass production of a native and an invasive plant species, grown in monoculture and mixed culture. We used the native Panicum dichotomiflorum and the invasive Urochloa mutica, which are two common grasses that frequently grow in natural floodplains of the Neotropics.

3. The experimental and observational data showed that biomass production, growth and relative dominance of the native species were higher under more stable water levels. By contrast, the invasive species had higher biomass production, growth and relative dominance under extreme drought and flooding conditions. Thus, extremes in precipitation can alter the relative dominance of the two species in favour of the invader.

4. Our study provides comprehensive evidence that water-level oscillations may negatively impact the performance of the native species, whereas they did not alter the biomass production and growth of the invasive species. Under stable conditions, faster growth of the native species may hinder successful establishment of the invasive species. However, under extreme drought and flooding events, the invader could be favoured. Although our findings are based on the outcome of the interaction between only one native and one invasive plant species, our results suggest that biotic resistance might be higher under stable water conditions.