How did climate drive the historical distribution of relict plants: a case study on Metasequoia using deep-time ecological niche modelling

Relict plants are those that once had a wide distribution but are now restricted to small areas. It is important to study the process of their distribution in the geological past to better understand the climatic factors that shape their current distribution. Metasequoia is one of the best-known genera of relict plants in Asia, with rich fossil records dating back to the Late Cretaceous. In this study, we used Deep-time Ecological Niche Modelling (DENM) and 755 Cenozoic megafossil records of Metasequoia to understand the pattern of its historical distribution and driving factors. The results showed that Metasequoia was widely distributed across mid-high-latitude regions during the Paleogene. Its distribution range contracted toward lower latitudes during the Neogene due to global aridification and cooling. Our results indicate that mean annual precipitation was the key factor shaping the distribution of Metasequoia during the Paleogene and Neogene. Later during the Pleistocene, a dramatic contraction of its distribution occurred due to glaciations, which also shaped the modern distributions of many relict plants in China. Our study supports that climate change is the main factor driving the distribution of relict plants and therefore provides crucial evidence for understanding their biogeographic histories and future conservation under climate change.