Impacts of 'Hyparrhenia hirta' (L.) Stapf (Coolatai grass) on native vegetation in a travelling stock route in northern New South Wales

Abstract

'Hyparrhenia hirta' (L.) Stapf (Coolatai grass, tambookie grass) is an invasive grass from Africa and the Middle East that has infested large areas of northern New South Wales (NSW) and also occurs in other Australian states. Ten plots were set up for this monitoring study in white box/yellow box/Blakely's red gum woodland, an endangered ecological community, on a travelling stock route near Manilla. Five plots were in an area infested by 'H. hirta' and the rest were in an area where infestations had previously been controlled by spot spraying with glyphosate. Vegetation surveys were conducted in these plots in autumn 2003 and spring 2005. In both surveys 'H. hirta' dominated ground cover in all infested sites and greatly reduced the species richness of native flora, but was absent from the controlled sites. The presence of 'H. hirta' reduced native species richness by about 48% in 20 x 20 m plots and 59% in 6 x 5 m plots in 2003. Results were similar in 2005. Projected cover of 'H. hirta' greatly exceeded that of all native ground-cover species combined in the infested plots. The results are consistent with those of McArdle et al. (2004) from Kwiambal National Park and demonstrate that the impact of this weed on species richness in travelling stock routes, which are intermittently grazed, may be as severe as those in conservation reserves, where domestic livestock grazing is excluded.