Do native grasses emerge and establish in areas rehabilitated using vetiver grass?

Abstract

Species-rich grasslands provide important ecosystem services, and in South Africa, approximately 40% of these grasslands are degraded.  Vetiver grass (from India) is often used during rehabilitation efforts to restore soil function without a thorough understanding of the  potential negative ecological impacts. Hence, a study was initiated to investigate vetiver’s ecological impacts during grassland  rehabilitation. Firstly, a field survey was conducted using a contiguous quadrat method to evaluate the extent of grass secondary  succession in these rehabilitated sites. Secondly, the effect of vetiver competition and seed sowing method on the recruitment of two  native grasses (Eragrostis curvula and Megathyrsus maximus) was examined using pot trials. The field survey results showed no evidence  of grass secondary succession, but rather the abundance of bare ground around vetiver, and a marked increase in grass  species richness with increasing distance from planted vetiver. Subsequently, in the pot trial, vetiver facilitated emergence in both native  grasses, and soil surface sowing of indigenous grass seeds showed greater emergence than other sowing methods. However, vetiver  inhibited native grass seedling establishment, even when root competition was excluded. This study suggests that areas rehabilitated  using vetiver are unlikely to become productive grasslands with good grazing, because vetiver inhibits colonisation by native grasses.