Impacts of grazing by kangaroos and rabbits on vegetation and soils in a semi-arid conservation reserve

Abstract

Overgrazing by introduced herbivores is widely recognized as a threatening process in Australia's semi-arid rangelands. Comparatively, grazing by native herbivores is generally considered to have benign effects. Populations of introduced herbivores are controlled in conservation reserves, but populations of native kangaroos and wallabies are seldom subject to control. We investigated the impacts of rabbit and kangaroo grazing on vegetation and soils at Yathong Nature Reserve in semi-arid Australia during the dry conditions that prevailed in 2019. We conducted spotlight and dung surveys to measure the relative abundance of kangaroos and rabbits, and assessed understorey biomass, woody plant density, soil bulk density and water infiltration rates in selective herbivore exclosures that had been established in 1979, and nearby controls that all herbivores could access. Kangaroos were the dominant herbivores at the time of our study. Grazing by kangaroos decreased grass biomass, increased soil density and reduced the rate of water infiltration. Rabbits reduced woody plant density but had no detectable effect on understorey vegetation cover or soil attributes. Our findings question the existing paradigms about how grazing by kangaroos should be viewed and prompt the question: should kangaroo populations be managed within conservation reserves to reduce their impacts on ecosystems?