The effects of grazing and aridity on multiple ecosystem functions and services in the semi-arid woodlands of eastern Australia

Dryland makes up 45% of the global land mass and supports almost 40% of its human population. Drylands are used for grazing, but declining rainfall and increasing temperatures are likely to make grazing unsustainable into the next century. Understanding how climate change and grazing, a form of land use intensification, affects the provision of ecosystem services is critical if we are to manage the effects of climate change and grazing on human well-being. In my thesis I examined how grazing by different herbivores (livestock, rabbits, and kangaroos) influenced infiltration (water flow into the soil) and five ecosystem services associated with the cycling of nutrients in wooded drylands in eastern Australia. My results demonstrate that microsites dominated by trees, shrubs and grasses had a greater effect on infiltration than grazing. Grazing effects on ecosystem services ranged from positive to neutral or negative, and depended on herbivore type. Cattle grazing suppressed infiltration, while sheep, and to a lesser extent cattle, were associated with greater soil N availability. Rabbit grazing had a greater effect on P availability than changes in climate, which were assessed as increases in aridity. Increasing aridity suppressed C storage, N availability, decomposition and plant biomass, but not P availability. Effects of aridity were greater than any effects due to grazing. Overall the results indicate that the services are likely to decline most with increases in aridity, but that grazing will also have negative effects. Overgrazing is likely to lead to long-term reductions in infiltration by removing grasses and therefore the highly conductive pores that they produce around their roots. Grazing is also likely to lead to increases in N availability