Impact of Climate Change on the Narrow Endemic Herb <i>Psilopeganum sinense</i> (Rutaceae) in China

<i>Psilopeganum sinense</i> is a perennial herb endemic to the Three Gorges Reservoir Area (TGRA) of the Yangtze River and its surrounding regions. This species is crucial for ecological conservation and regional socioeconomic development. Recent extreme weather events in the TGRA have directly and indirectly caused local losses of numerous wild populations of <i>P. sinense</i>. Given the severe survival crisis induced by climate change, it is essential to explore the effects of climate change on the potential distribution of <i>P. sinense</i>. Although there is a general awareness of the adverse effects of climate change on various species, there is a lack of comprehensive studies focusing on the long-term effects and detailed climatic variables influencing the distribution of <i>P. sinense</i>. In this study, we aimed to use the random forest (RF) algorithm to analyze the redistribution of <i>P. sinense</i> across several critical climatic periods. The results indicated that the main variables limiting the present geographical distribution of <i>P. sinense</i> were precipitation seasonality and the mean diurnal range. Currently, <i>P. sinense</i> is mainly distributed in the riparian zone of the TGRA and its surrounding areas, exhibiting a relatively narrow climatic niche and habitat fragmentation pattern. Historically, distributions under past climatic conditions were relatively intact and more extensive than the current distribution area. During the last interglacial period, a broad distribution of highly suitable areas was observed in eastern Sichuan Province, northern Chongqing, and central Hubei Province, exhibiting a continuous distribution pattern. Future climate scenarios indicated a projected 32.84% decrease in suitable areas under RCP4.5-2050s. In northern Chongqing, the ecological corridors established in highly suitable habitats would fragment and gradually separate. Some previously unsuitable areas for <i>P. sinense</i> could transform into potentially suitable habitats because of climate change; however, these suitable areas might exhibit fragmented and discrete distribution patterns. In general, both the shrinkage of suitable habitats and habitat fragmentation would compress the already limited survival space of <i>P. sinense</i>, leading some populations to prematurely confront critical survival decisions under severe climate pressures. Our results not only provide a scientific basis for managing <i>P. sinense</i> resources in the context of climate change but also serve as an important reference for restoring wild <i>P. sinense</i> populations.