'Hyparrhenia hirta' (L.) Stapf (Coolatai grass) is a summer active, C4 perennial grass, native to southern Africa and the Mediterranean region. In recent years its range has expanded rapidly and there are now populations of H. hirta in all states and Territories of Australia except Tasmania. It invades native grassy and open woodland communities, including roadsides and travelling stock routes, national parks and pastures. There is little published information on the biology and ecology of 'H. hirta' in the summer rainfall environment of northern New South Wales. This study aimed to increase our understanding of key aspects of the ecophysiology, population dynamics and community ecology of 'H. hirta' to assist in control and management.