The superior re-sprouting performance of exotic grass species under different environmental conditions: the study case of Paspalum atratum (Swallen) and Urochloa brizantha (Hochst. ex A. Rich. - Stapf.)

The invasive success of exotic grass species has been linked to a better physiological performance under a variety of environmental conditions. Several studies showed that disturbances such as fire and herbivory might favor invasions by exotic grasses in detrimental of native species. However, studies comparing how native and exotic grasses respond to variation in environmental resources under natural conditions after a disturbance are scarce. A clear understanding on how disturbances and environmental resources influence plant populations’ resistance and resilience is important, and might contribute for management actions to control invasive processes in natural ecosystems. The aim of this study was to investigate how variations in light, nutrient and water availability influence the regrowth of native and exotic grasses after a simulated disturbance (defoliation). Two C4 grass species with similar morphological and physiological characteristics were selected: the native Paspalumatratum and the African exotic Urochloa brizantha. The study was set up in a Cerrado sensu stricto area that was cleared for the experiment. Biomass production was monitored at regular intervals, and absolute growth rates for both grasses were calculated. Although irrigation did not promote further growth for both grasses, U. brizantha benefited more from fertilization and shade than P. atratum, sustaining higher growth rates until the end of the rainy season. We show that under natural conditions the exotic grass presented a higher regrowth ability than the native grass species, suggesting a stronger resilience to the variation in resource availability. Thus, natural disturbances might further stimulate the invasion and dominance of this exotic grass.