Climate-driven ecological thresholds in China's drylands modulated by grazing

Degradation of ecosystems can occur when certain ecological thresholds are passed below which ecosystem responses remain within 'safe ecological limits'. Ecosystems such as drylands are sensitive to both aridification and grazing, but the combined effects of such factors on the emergence of ecological thresholds beyond which ecosystem degradation occurs has yet to be quantitatively evaluated. This limits our understanding on 'safe operating spaces' for grazing, the main land use in drylands worldwide. Here we assessed how 20 structural and functional ecosystem attributes respond to joint changes in aridity and grazing pressure across China & PRIME;s drylands. Gradual increases in aridity resulted in abrupt decreases in productivity, soil fertility and plant richness. Rising grazing pressures lowered such aridity thresholds for most ecosystem variables, thus showing how ecological thresholds can be amplified by the joint effects of these two factors. We found that 44.4% of China's drylands are unsuitable for grazing due to climate change-induced aridification, a percentage that may increase to 50.8% by 2100. Of current dryland grazing areas, 8.9% exceeded their maximum allowable grazing pressure. Our findings provide important insights into the relationship between aridity and optimal grazing pressure and identify safe operating spaces for grazing across China's drylands. Understanding the synergistic effects of aridity and grazing on dryland ecosystem attributes can be important for identifying 'safe operating spaces' for grazing under an increasingly arid climate. This study uses two-dimensional ecological threshold models to assess this in China's drylands.