Distribution of Tropical Vegetation From the Pliocene to the Anthropocene

Abstract

Aim: The tropics harbour most of Earth's terrestrial biodiversity. This biodiversity has been influenced by cycles of climatic stability and instability over millions of years and may be affected by abrupt changes in the near future. We reconstructed the geographic distribution of the major tropical vegetation types (deserts, semi-arid, shrublands, savannas, wetlands and forests) and their physiognomies from the near end of the Pliocene (3.3 Ma) to the late Holocene and projected changes for 2041–2060 under SSP2-4.5 and SSP5-8.5 scenarios. Location: Tropical regions worldwide. Time Period: From the near end of the Pliocene (3.3 Ma) to the late Holocene, with projections for 2041–2060. Major Systems Studied: Tropical vegetation types and physiognomies. Methods: We modelled vegetation types and physiognomies with deep learning algorithms using paleoclimatic variables and future climate estimates as predictors. In addition, we quantified the temporal stability and instability of climate, vegetation types and physiognomies. Results: Evidence from models and data shows reorganizations of tropical biomes, including changes in biome extent, spatial arrangement and connectivity, as well as forest retraction and the expansion of savannas and other open vegetation types. We identified historically stable nuclei, totalling about one-fifth of the tropics, contrasting with recurrently unstable ecotone zones. Future projections indicate potential widespread physiognomic opening and forest contractions by mid-century, with intensification under the SSP5-8.5 scenario, especially in the Amazon. Long-term stability in the Malay Archipelago, combined with projected instability, suggests greater sensitivity of endemic lineages to rapid disturbances. Conclusion: The results show that the magnitude of near-future changes resembles the final phase of the Pliocene, but compressed into a few decades, reinforcing the urgency of effective global policies for mitigating anthropogenic climate change so as to avert shifts towards novel, less forested or otherwise degraded equilibria of the exuberant tropical ecosystems.