Response of an Astrebla Spp. grassland to heavy grazing by cattle and light grazing by sheep in North-west Queensland.

Abstract

Botanical changes were measured in a semi-arid, Asrrebla lappacea (Mitchell grass) dominant grassland in the summer rainfall region of north-west Queensland that has been grazed traditionally by Merino sheep. Cattle have been introduced recently in large numbers and the effects of heavy grazing by cattle on these pastures in the dry season is unknown. A paddock v\as sub-divided and t\%o grazing treatments were applied in 1971. For seven consecutive years, steers were grazed at 70 to 141 beast grazing days per hectare per annum in the late dry season and compared with sheep grazing at equivalent to 17 to 37 beast grazing days per hectare per annum. Compared with light grazing, the heavy grazing treatment caused: an increased number but smaller Astrebia spp. plants; lower basal cover; reduced standing dry matter yield; reduced root yield; increased annual grass population and yield; reduced Aris- rida lar[f?jlia (feathertop) population; and an increased number of forbs.