Can native species control the above-ground biomass and reproductive output of Urochloa decumbens, an invasive grass in the Brazilian savannas?

Abstract

The invasion of exotic species is a global problem that impacts natural ecosystems. Here, we assessed the impact of the annual grass Andropogon fastigiatus and the shrub Lepidaploa aurea, two native species commonly used in restoration projects in the Brazilian savannas, on the control of the invasive grass Urochloa decumbens. We did a plant competition experiment using 40 plots, where a single U. decumbens individual was surrounded by eight individuals of A. fastigiatus, L. aurea, or a combination of both species, along with a control treatment with only U. decumbens. After 4 months, we collected the aboveground biomass and seed biomass of focal U. decumbens individuals. Native species did not reduce the biomass or seed production of the U. decumbens. However, A. fastigiatus exhibited competitive ability similar to U. decumbens, being the only treatment where there was no increase in the invasive grass biomass. In the presence of L. aurea and when A. fastigiatus density was reduced by half, the biomass of U. decumbens was about three folds that observed in the control plots. This is likely due to a more effective use of available resources in the soil. Despite these two species being widely used in ecological restoration efforts in the Cerrado, we found that only A. fastigiatus was able to control U. decumbens biomass, but neither species could reduce the invasive grass reproductive output. Nevertheless, at high density, A. fastigiatus can be a strong competitor against U. decumbens and should be included in seed mixtures for Cerrado restoration.