Earlier fall precipitation increases the competitive advantage of non-native plant communities in a desert ecosystem

Abstract

AbstractClimate change is likely to influence competitive interactions between native and non-native plant species by altering soil resource availability. The objective of this study was to characterize how shifts in fall precipitation timing due to climate change affect plant community assembly of native and non-native plant communities. We selected common non-native annuals and native perennial species from the Great Basin Desert in western North America and grew them in native, non-native, and native + non-native mixed communities. We tested the responses of these three community types to simulated earlier fall precipitation in a full factorial design. Early fall precipitation dramatically increased the height, density, biomass, seed production per unit biomass, and carbon-to-nitrogen ratio (C:N) of both native and non-native plant communities in comparison with the late precipitation treatment. However, competition with non-native species reduced the positive benefit of early precipitation for the native plant community. When grown in a native-only community, native plant species increased in height (twofold), density (threefold), biomass (13-fold), seed production per unit biomass (18-fold), and C:N (1.3-fold)but not tissue percent nitrogen as compared to a mixed community. In contrast, non-native plant species grown in mixed communities with natives showed little to no reduction in growth and reproduction. While all species benefitted from earlier fall precipitation our data suggest that increased earlier fall precipitation will likely magnify the exclusion of native vegetation by non-native annuals, particularly Bromus tectorum L., which is largely responsible for human-grass-fire cycles in this ecoregion.