Climate-induced range shifts support local plant diversity but don't reduce extinction risk.

INTRODUCTION: Anthropogenic climate change is reshaping where plants can live. As temperature and precipitation patterns shift, many species are moving to stay within suitable environmental conditions. Predicting how these range shifts will affect future biodiversity requires knowing both where suitable habitats will occur and whether species can reach them. The latter is challenging because dispersal abilities differ widely among species and depend on landscape structure, anthropogenic barriers, and climatic conditions. Large-scale biodiversity forecasts therefore often rely on overly simple assumptions—such as no dispersal, unlimited dispersal, or identical movement rates for all species—thus adding major uncertainty to projections and conservation planning. RATIONALE: We used the largest global database of observed plant range shifts (BioShifts; 14,488 records across 6579 plant species) to build models that predict species-specific range shift velocities. Combining 6.8 million plant occurrence records, an ensemble of two top-performing habitat models, and climate projections from 10 global circulation models, we mapped current and future suitable habitats—areas with favorable climate, soil, and land use—at 8 × 8 km resolution for each species. Our analysis covers 18% of known vascular plant species under four greenhouse-gas emissions scenarios for 2081 to 2100. We then overlaid the projected future suitable habitats with species-specific range shift velocities to determine where each species is likely to persist or expand by the end of this century. From these results, we estimated global extinction risks, changes in local species richness, and temporal species turnover in community composition. RESULTS: Overall, 7 to 16% of modeled plant species are projected to lose >90% of their range across emissions scenarios, placing them at high risk of extinction. Most of these losses (70 to 80%) stem from suitable habitats disappearing as a result of climate change, rather than from dispersal limitations, indicating that climate-induced habitat loss, rather than an inability to keep pace with changing climate, is the primary threat. Although range shifts are unlikely to prevent many global extinctions, they will strongly reshape local species composition. Plant movements into newly suitable habitats are expected to increase local species richness across 28% of Earth's land surface, maintain latitudinally averaged species richness in the tropics and subtropics (35°S to 35°N), and generate substantial species turnover in mid-latitudes (30° to 50° in both hemispheres). By contrast, in regions north of 50°N, warming is so rapid that most plants cannot keep pace, leading to widespread local extirpations and sharp declines in species richness. CONCLUSION: Range shifts can help sustain local species richness but are unlikely to provide much relief from global extinctions. To reduce extinction risks, identifying and protecting climate change refugia to safeguard biodiversity, and expanding ex situ conservation efforts, such as global seed bank and botanic garden networks, may be more effective than facilitating migrations. At the same time, conservation strategies should anticipate changing community compositions and ecosystem functioning as new species arrive and ecosystems reorganize. In high-latitude regions where dispersal lags considerably behind the rapid warming, improving habitat connectivity, reducing human-made barriers, and where appropriate, assisting species movement could help maintain local species richness, ecosystem productivity, carbon sequestration, and ecosystem stability. Future climate-driven plant range shifts and consequences for global species diversity redistribution. [Credits: icons in this figure are from https://www.flaticon.com/] Climate change is driving widespread plant range shifts, yet their consequences for extinction and biodiversity remain unclear as realistic range shift dynamics have rarely been incorporated into global-scale biodiversity models. We integrate species-specific range shift velocities into species distribution models to project distributions of 67,664 plant species (18% of all global flora) by 2081 to 2100. Across emissions scenarios, 7 to 16% of species are projected to lose >90% of their range, placing them at high risk of extinction. These losses are driven primarily by climate-induced habitat loss, rather than dispersal limitation. Although range shifts offer little relief from global extinctions, they are projected to increase local plant richness across 28% of Earth's land. Facilitating range shifts may thus sustain local richness but not reduce global extinctions. Editor's summary: Climate change and other massive global changes are increasing the risk of extinction for many species. Two papers in this issue address the extent of extinction risk to plants. Wang et al. used species distribution models to predict range shifts in response to climate change for more than 60,000 plant species. They found that 7 to 16% of these species will be at high extinction risk by 2100 across emissions scenarios. Forest et al. combined phylogenetic information with species extinction risk assessments to show that more than one-fifth of flowering plants' evolutionary history is currently threatened, a ratio similar to that seen in vertebrate groups. Considering the extent to which people depend on the productivity and diversity of plants, these studies show what is at stake from uncurbed anthropogenic global change (see the Perspective by Scherson and Luebert). —Bianca Lopez [ABSTRACT FROM AUTHOR]