1273 INTRODUCTION Livestock grazing is one of the most extensive land uses on Earth and an important biotic process affecting plant and animal communities and ecosystem functions. The economies of many people, particularly from rural areas, depend on the provision of goods and services such as milk, meat, wool, and hide derived from livestock. The economic importance of grazing and the reports of pos- itive or neutral effects of grazing on species richness in specific studies (e.g., Socher et al. 2013, Fensham et al. 2014, Kimuyu et al. 2014) has led some to suggest that introducing or reintroducing commercial herds of live- stock to intermittently grazed or ungrazed areas (e.g., alpine high country of Australia; Williams et al. 2006) might have benefits for biodiversity and ecosystem func- tioning (Lunt et al. 2007, Williamson et al. 2014). The notion of using livestock grazing to enhance eco- system functions contrasts markedly with the extensive body of literature on the negative effects of grazing on soil, plant, and animal attributes worldwide. Grazing- induced habitat modification alters species composition by reducing the diversity of plants and terrestrial inver- tebrates, small mammals, birds, reptiles, and soil crusts (e.g., Williams et al. 2008, van Klink et al. 2014). Grazing also alters community structure by influencing, for example, the return interval of wildfires and the accumu- lation of flammable fuel (Kimuyu et al. 2014) or plant community composition (Lunt et al. 2012, Fensham et al. 2014). These direct structural and compositional shifts have often large, indirect effects on ecosystem func- tions. The most obvious functional effect is a direct reduction in net primary productivity through herbivory (Milchunas et al. 1988), resulting in reduced decompo- sition and changes in the amount and distribution of litter and dung. Grazing also compacts soils, increases erosion, and alters soil hydrological processes (Lunt et al. 2007). Together these direct and indirect effects of Ecosystem structure, function, and composition in rangelands are negatively affected by livestock grazing DAVID J. ELDRIDGE, 1,2,4 ALISTAIR G. B. POORE, 1 MARTA RUIZ-COLMENERO, 1 MIKE LETNIC, 2 AND SANTIAGO SOLIVERES 3 1 Evolution and Ecology Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052 Australia 2 Centre for Ecosystem Science, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052 Australia 3 Institute of Plant Sciences, University of Bern, Altenbergrain 21, 3013 Bern, Switzerland Abstract. Reports of positive or neutral effects of grazing on plant species richness have prompted calls for livestock grazing to be used as a tool for managing land for conservation. Grazing effects, however, are likely to vary among different response variables, types, and intensity of grazing, and across abiotic conditions. We aimed to examine how grazing affects ecosystem structure, function, and composition. We compiled a database of 7615 records reporting an effect of grazing by sheep and cattle on 278 biotic and abiotic response variables for published studies across Australia. Using these data, we derived three ecosystem measures based on structure, function, and composition, which were compared against six contrasts of grazing pressure, ranging from low to heavy, two different herbivores (sheep, cattle), and across three different climatic zones. Grazing reduced structure (by 35%), function (24%), and composition (10%). Structure and function (but not composition) declined more when grazed by sheep and cattle together than sheep alone. Grazing reduced plant biomass (40%), animal richness (15%), and plant and animal abundance, and plant and litter cover (25%), but had no effect on plant richness nor soil function. The negative effects of grazing on plant biomass, plant cover, and soil function were more pronounced in drier environments. Grazing effects on plant and animal richness and composition were constant, or even declined, with increasing aridity. Our study represents a comprehensive continental assessment of the implications of grazing for managing Australian rangelands. Grazing effects were largely negative, even at very low levels of grazing. Overall, our results suggest that livestock grazing in Australia is unlikely to produce positive outcomes for ecosystem structure, function, and composition or even as a blanket conservation tool unless reduction in specific response variables is an explicit management objective. Key words: ecosystem function; grazing; livestock; plant composition; plant production; structural metrics. Ecological Applications, 26(4), 2016, pp. 1273–1283 © 2016 by the Ecological Society of America Manuscript received 3 July 2015; revised 9 October 2015; accepted 5 November 2015. Corresponding Editor: D. Brunton. 4 E-mail: d.eldridge@unsw.edu.au source: https://doi.org/10.7892/boris.84542 | downloaded: 20.7.2017