Invasion of native vegetation by Coolatai Grass 'Hyparrhenia hirta': impacts on native vegetation and management implications

Coolatai Grass 'Hyparrhenia hirta' is an exotic perennial grass and environmental weed that is spreading rapidly in parts of southeastern Australia. This study examined the effects of Coolatai Grass invasion on the composition of ground strata vegetation within Kwiambal National Park in northern New South Wales. Plots that were heavily infested with Coolatai Grass together with matching control plots were surveyed. Coolatai Grass infestation reduced the richness of native ground strata plants and their projected groundcover, but did not affect the number of exotic species in plots. The control plots varied markedly in floristic composition, but infested sites were more homogenous, with Coolatai Grass clearly dominating the ground strata vegetation. Coolatai Grass appears to increase in abundance following fire; it persists under heavy grazing and is resistant to many herbicides. Spot spraying small swards and isolated tussocks with glyphosate or flupropanate provides prospects of control on a small scale, but there are no suitable methods for large-scale control. Changes to roadside management practices could help to reduce the spread of Coolatai Grass, but research into seedbank dynamics and appropriate control techniques is required, as well as increased awareness of the threat to native vegetation posed by the species.