Global potential for regime shifts among shrubland, grassland, and forest

Grassland, shrubland and forest can form alternative biome states (ABSs), and regime shifts among them usually lead to abrupt alterations in ecosystem structure and function that are critical to environmental health and human well-being. However, the fragmented understanding of their distribution patterns and ABS relationships, particularly concerning shrublands, has seriously impaired our capacity to predict catastrophic regime shifts. Based on 1 km resolution data and conditional potential analysis method, we investigated global distribution patterns of grasslands, shrublands, and forests, identified areas with ABS, and further evaluated vegetation susceptibilities to regime shifts. The results revealed a shrubland-grassland-forest transition pattern of dominant vegetation from arid to humid regions. Under certain precipitation conditions, ABSs were formed, with Asia accounting for the widest spatial extent and Africa covering the widest precipitation range. The susceptibility to regime shifts was mapped in areas with ABSs, which suggested that many forests across the globe were vulnerable to be replaced by grasslands. Future climate change was projected to increase the risk of forest loss in Africa and Europe as well as shrubland degradation globally. It is worth noting that 77 % and 80 % of resilience at ABS points was projected to decline under SSP245 and SSP585 scenarios, respectively, warning of an overall increase in the risk of regime shifts in the future. These findings contribute to understanding the potential vulnerability of vegetation to changing environment, and can provide significant information for adaptive ecosystem management strategies to mitigate or avoid the enormous costs of catastrophic shifts.