Paleodistribution of Cercidiphyllaceae and Future Habitat Prediction for Cercidiphyllum japonicum Under Climate Change.

The Earth's environment is an important factor driving the evolution and distribution of biodiversity, with particular regard to endangered species, whose special evolutionary history and ecological environment changes profoundly impact their distribution and even survival. This paper conducts a preliminary analysis of the coupling relationship between the geological history distribution pattern of plants in the Cercidiphyllaceae, a unique East Asian group, and paleoclimatic changes, exploring the evolution of Cercidiphyllaceae's geographic distribution pattern. The MaxEnt model was used to construct the potentially suitable habitats for Cercidiphyllum japonicum in different periods, such as the current and future (2050s and 2070s). Research shows that Cercidiphyllaceae once exhibited relatively high diversity, with 21 fossil species assigned to 5 fossil genera. From the Late Cretaceous to the Eocene, when the global paleotemperature was relatively high, they were widely distributed in the mid-high latitude regions of the Northern Hemisphere. Since the Oligocene, with the global temperature decline, the number of species of Cercidiphyllaceae has decreased sharply, and the distribution habitats have also migrated to lower latitudes. Especially after experiencing multiple glacial periods in the Quaternary period, most species became extinct. Currently, only two species of the genus Cercidiphyllum remain, namely, C. japonicum and Cercidiphyllum magnificum, which are only discontinuously distributed in China and Japan. Under the current climatic conditions, the suitable habitat area of C. japonicum in China is 1,316,200 km2, primarily concentrated in the Hengduan Mountains and Qinling-Daba Mountains. However, as temperatures rise because of global warming, the plant's viable habitat is projected to shrink significantly. In the 2050s and 2070s, the lightest contraction and the largest suitable habitat area are under the RCP6.0 climate scenario; in contrast, the most severe contraction and the smallest suitable habitat area are under the RCP4.5 climate scenario. These findings offer valuable insights for conservation efforts targeting this species, as well as other endangered plant species facing similar threats.