Identifying the ideal habitats for authentic herbs to cope with climate warming: a case study of Forsythia suspensa.

Forsythia suspensa (Thunb.) Vahl, a widely used medicinal plant, especially its fruits in the green fruit stage, is called "Qingqiao" (QQ). However, the effects of climate change on the quality of QQ have not been reported. Therefore, this study conducts an analysis from the perspective of quality distribution and further proposes future stable distribution areas. In this study, F. suspensa distribution data were collected through field surveys and online sources. Phillyrin and forsythoside A contents from selected QQ production areas were then combined and analyzed via the maximum entropy model alongside stepwise regression equations to assess the potential effects of future climate on QQ quality. The results suggest that under various representative concentration pathway (RCP2.6, RCP4.5, and RCP8.5), the QQ quality areas, which are based on the two key contents, decreased. The environmental factors influencing the phillyrin content were significantly negatively correlated with the soil texture classification and precipitation of the driest quarter, whereas the forsythoside A content was significantly negatively correlated with the mean diurnal range and precipitation of the driest quarter. The stable quality regionalization prediction of F. suspensa is expected to remain mainly in North China, with a northward shift of the centroid suggesting a potential response to global warming. These findings provide a foundation for F. suspensa conservation and sustainable development of these resources.