The past, present, and future distribution of Calanthe graciliflora: implications for conservation and phylogeography

Abstract

Calanthe graciliflora, an orchid species endemic to China, is one of the most widely distributed members of the genus Calanthe, occupying the highest latitudinal range and exhibiting strong cold tolerance. These traits suggest key adaptations to diverse and extreme environments, making it an ideal model for studying plant responses to climate variability. Ecological niche models (ENMs) are powerful tools for simulating species' potential distributions across different time periods, thereby aiding biodiversity conservation. In this study, 75 filtered occurrence records of C. graciliflora and 19 climatic variables, derived from field surveys and herbarium records in China, were used to model the species' potential distribution across 6 periods (Last Interglacial, Last Glacial Maximum, Middle Holocene, Current, Future 2050s, and Future 2070s). Research findings indicate that key environmental factors influencing its distribution include mean diurnal temperature range (bio2), mean temperature of the warmest quarter (bio10), annual precipitation (bio12), and precipitation of the driest month (bio14). Historically, suitable habitats for C. graciliflora were primarily concentrated south of the Qinling-Huaihe River region, closely associated with the Qinling, Luoxiao, Nanling, and Mount Wuyi ranges. During the Last Glacial Maximum, extensive suitable habitats existed in southwestern China, subsequently contracting to refugia in the Qinling and Mount Wuyi areas, underscoring these regions as refugia for C. graciliflora. Future projections indicate an overall decline in suitable habitat, highlighting the significant impacts of global warming on its long-term survival. Notably, this study represents the first application of the MaxEnt model to infer historical refugia of C. graciliflora while simultaneously integrating analyses of its future distribution shifts. This work fills the gap in long-term climate response research for this species and evaluates the impacts of climate change on its distribution, providing valuable insights for its phylogeography and conservation practice. By further identifying core habitats and clarifying their climate sensitivity, the findings provide a basis for developing targeted conservation strategies that prioritize key ecological areas and mitigate the risk of habitat loss.