Final Draft Paper

Alien annual grass species have been identified as a particular threat to the vegetation types that occur within the winter-rainfall region of South Africa. However, the impact that these grasses have on plant species richness in invaded areas is not well documented. In this study the impact alien annual grass species have on the plant species richness of Hantam-Roggeveld Doelrite Renosterveld is investigated. Data on the abundance of alien grasses and plant species richness was collected at 9 sites using 32 1m2 samples at each site, giving rise to a total of 288 samples. The dominant alien annual grass species within the study area are Wild Oats, Avena fatua and Ryegrass, Lolium rigidum. Wild Oats was found to occur in 94 % of the 288 samples, while Ryegrass occurred in 48 % of the samples. Regression analysis revealed a significant relationship between both Avena and Lolium abundance and plant species richness. Although highly significant, the regression coefficients were very low, with Avena accounting for only 5 % of the variance in the data and Lolium 12%. The data set however did not include very heavily infested areas where an impact is most likely. Indeed, the data indicated that impacts on species richnes