Abstract: Drylands are increasingly vulnerable to climate change and overgrazing, where rising aridity and grazing pressure can trigger abrupt, nonlinear shifts in ecosystem structure and function once critical levels are crossed. Yet such thresholds, though central to predicting ecological collapse, remain largely absent from conservation planning. This disconnect arises because thresholds are typically defined as singular breakpoints rather than spatially explicit regions that can guide management. Here we introduce the concept of threshold zones: aridity ranges within which ecosystem properties (e.g., biodiversity, aboveground productivity, soil organic carbon, and soil pH) undergo rapid transitions. Using data from 683 field sites (including grassland and scrubland sites) encompassing 43,708 species occurrences and 26,650 spatially remote-sensing points across Inner Mongolia, we identify two critical zones: a biodiversity-rich zone (aridity 0.50-0.57) and a functional collapse zone (0.80-0.84), where grazing amplifies aridity-driven degradation. Despite their ecological importance, national protected areas encompass less than 5% of these sensitive regions. Climate projections under SSP1-2.6 indicate a twofold expansion of threshold zones by 2100, predominantly within heavily grazed grasslands. Our framework connects theoretical thresholds with actionable conservation strategies, offering a pathway to safeguard dryland biodiversity and resilience under accelerating global change.

Key words: Aridity threshold zone, Dryland ecosystem, Biodiversity, Ecosystem multifunctionality, Grazing, National Nature Reserves