Climate-driven "nowhere to go" for alpine plants: Impact of climate change on the geographic distribution of Dipsacoideae species in China

Many plant species are shifting poleward and upward in response to global warming, with alpine plants considered particularly vulnerable. As temperatures rise, these plants are forced to move to higher altitudes. However, as they ascend, the available land area diminishes, eventually leaving no higher ground for them to occupy, a scenario referred to as the “nowhere to go” hypothesis. Despite its significance, this hypothesis remains poorly tested across different elevations in mountain plant lineages using environmental niche modeling. In this study, we modeled the near-current (1970–2000) and future (2041–2060 and 2081–2100; SSP2–4.5 and SSP5–8.5) habitat suitability for Dipsacoideae species in China using MaxEnt. Projections for the middle (2041–2060) and end (2081–2100) of the twenty-first century indicate that the earlier-diverged genera, Pterocephalus and Triplostegia, are likely to experience significant range contractions, while most species of the more recently-diverged sister genera, Dipsacus and Scabiosa, are projected to expand, suggesting niche conservatism in Dipsacoideae. Most high-altitude species in southwestern China are projected to shift westward and upward, while the low-altitude species in northeastern China (D. japonicus and S. comosa) are projected to shift northward and downward. Percent changes in suitable habitat area showed no significant correlation with near-current suitable habitat area but were inversely correlated with the mean elevation of near-current suitable areas. These findings suggest that alpine species of Dipsacoideae in western China are much more vulnerable to climate change than low-altitude species in eastern China, thus supporting the "nowhere to go" hypothesis. Our findings highlight the roles of evolutionary history and spatial distribution pattern in shaping plant responses to climate change. There is an urgent need to expand protected areas and connectivity corridors in the high-altitude regions of the Hengduan Mountains, particularly in northwestern Yunnan.