Who Eats the Grass? Grazing Pressure and Interactions Between Wild Kangaroos, Feral Goats and Rabbits, and Domestic Sheep on an Arid Australian Rangeland

This study examined the grazing pressure and interactions between four species of wild kangaroos (Red Kangaroo Osphranter rufus, Common Wallaroo O. robustus, Eastern Grey Kangaroo Macropus giganteus, Western Grey Kangaroo M. fuliginosus), free-ranging feral goats (Capra hircus) and European rabbits (Oryctolagus cuniculus), and stocked Merino sheep (Ovis aries). The study site comprised two contiguous pairs of stocked and unstocked paddocks, one a sloping run-off zone, the other a flat run-on zone, covering a total area of 2158 ha. These paddocks on Fowlers Gap Station in far north-western New South Wales, Australia, are representative of the arid chenopod (Family: Chenopodiaceae) shrublands stocked with sheep. Sheep and red kangaroos dominate the mammalian herbivores by biomass. The study examined the relative grazing pressure exerted by the seven species of mammalian herbivores in stocked and unstocked conditions, where only sheep were confined, across a three-year period that included rain-deficient (drought) months. The effects of climate (especially rainfall and temperature) and herbivore density on the standing biomass of pasture were teased out at a macro-scale. Herbivory at a micro-scale was examined using open and exclosed plots with detection of herbivore species by fecal deposition and time-lapse videography. Sheep exerted the highest grazing pressure and there was no compensatory increase in grazing pressure by other herbivores in unstocked paddocks. Rainfall was a key driver of pasture biomass and condition and loss by senescence typically outweighed grazing pressure. Grazing effects at a micro-scale were plot-specific and complex. The results are discussed in relation to the sustainable management of rangelands for production and wildlife.