Effects of experimental disturbances on a tropical freshwater marsh invaded by the African grass Echinochloa pyramidalis

Abstract

Perennial African C4 grasses are highly successful invaders in tropical and subtropical environments. One of these species, Echinochloa pyramidalis, has been introduced in the freshwater wetlands of the Mexican tropics. This alien species reduces biodiversity by replacing native species. The removal of non-indigenous species from invaded communities often requires different techniques such as physical, chemical, or biological controls. We evaluated the effects of mechanical (cutting or soil-disking) and chemical (spraying Round Up™ herbicide) disturbance treatments on the plant community of a freshwater marsh invaded by E. pyramidalis. We predicted that intense disturbance would eliminate this African grass from the experimental plots. Over a nine-month period, we analyzed species cover, richness, and diversity in experimental plots that received different disturbance treatments. Also, we measured the aerial biomass at the end of the experiment. The treatment that best reduced the dominance of E. pyramidalis and increased the diversity of native species was soil disking, but this was not enough to eliminate the grass. After nine months, E. pyramidalis recovered in all the treatments and again became the dominant species. To eliminate this species completely, it is necessary to recreate the natural topography and hydrology of the wetland and to select control mechanisms that disrupt those growth characteristics (e.g., rapid propagation from rhizomes and horizontal expansion via tillers) that make this grass more competitive than native species.