Response of vegetation cover to climate variability in protected and grazed arid rangelands of South Australia

Large-scale drought and wet phases, via ecosystem responses, can significantly influence the global atmospheric carbon budget. Australian landscapes, dominated by arid and semi-arid rangelands, play an important role in this regard. In this study, temporal variation of monthly Normalised Difference Vegetation Index (NDVI) of two rangelands with different grazing intensity were analysed against monthly precipitation and Gravity Recovery and Climate Experiment (GRACE) total water storage (TWS). The results show that regardless grazing regime, over 55% temporal variation of monthly NDVI anomaly can be explained by structured cumulative antecedent precipitation. It appears that the antecedent precipitation forms better predictor variables than GRACE TWS for this study area. The results also show that both grazing and drought reduce vegetation cover, and its response to precipitation. Drought exacerbates the grazing impact on NDVI-precipitation response. These results imply that grazing in arid and semi-arid rangelands can reduce the capacity of ecosystems to assimilate atmospheric CO₂ during wet years and episodic wet events. It is important to incorporate temporal structures of intra- and inter-annual antecedent precipitation in investigating vegetation dynamic responses to precipitation. By doing so, it is possible to predict monthly vegetation dynamics to support grazing management.