孑遗植物长苞铁杉(Tsuga longibracteata)分布格局对未来气候变化的响应

长苞铁杉(Tsuga longibracteata)是中国特有的珍贵树种,不仅对研究裸子植物的系统发育、古生态和古气候具有重要作用,而且该树种具有造林、用材和药用等方面的较高价值。研究长苞铁杉在气候变化下的分布格局变化是制定其保护和可持续利用的重要基础。采用最大熵模型(MaxEnt),结合不同时期(当前、2050年和2070年)和不同二氧化碳排放情境下(RCP2.6和RCP8.5)的气候因子变量,探讨气候变化与物种地理分布格局的关系,预测长苞铁杉的潜在分布区变迁。本研究考虑了空间约束对物种分布的限制作用,构建了气候因子预测模型(C)和气候+空间约束因子预测模型(C+S)分别进行潜在分布区预测,比较其结果差异。结果显示,最干月降水量和温度年较差是影响长苞铁杉地理分布的主导气候因子,空间约束因子对长苞铁杉未来的地理分布有重要影响。随时间年限增加,长苞铁杉总潜在适生区面积降低,特别是中高等级的适生区面积有不同程度地减少,分布范围总体向北移动,这些变化趋势在RCP8.5情境下更加突出。这一结果表明未来气候变化会导致长苞铁杉种群分布范围收缩和生境适宜度下降,加剧其受胁程度。加入空间约束因子后,C+S模型的预测精度更高,结果更符合长苞铁杉的迁移、扩散特性。长苞铁杉未来的核心分布区仍位于现存的湘、桂、黔结合部,表明其具有"原地避难"的特性,应进一步加强对现有野生资源的保护。渝、川、鄂结合部的大巴山等地区是未来气候变化下长苞铁杉的理论分布区域,可作为长苞铁杉应对未来气候变化的引种地区,应提早进行人工引种、栽培等前期研究。研究结果可为气候变化背景下长苞铁杉的保护、物种迁地保存和可持续管理提供科学依据,也可为准确预测濒危、珍稀植物的地理分布范围提供方法参考。

The suitable distribution area of Tsuga longibracteata revealed by a climate and spatial constraint model under future climate change scenarios

Tsuga longibracteata is a unique, precious, relic tree species in China, which has been used for afforestation, as well as timber and medicine. Further, the plant is worth studying because it is important in the study of phylogeny of gymnosperms, paleoecology, and the Paleoclimate. Predicting changes in suitable distribution areas of Tsuga longibracteata under climate change scenarios are an important basis for formulating its conservation and development strategy. In this study, the Maximum Entropy Model (MaxEnt) was used to explore the relationship between climate change and the geographical distribution of the species in different time periods (current, 2050, and 2070) and carbon dioxide emissions (RCP2.6 and RCP8.5), to predict the changes in the suitable distribution areas of Tsuga longibracteata. In addition, the spatial constraints on species distribution were considered, and the climate factor prediction model (C) and climate + spatial constraint factor prediction model (C+S) were respectively used to predict the changes in potential distribution areas of the tree. The results showed that the precipitation for the driest month and the annual temperature range were the dominant climatic factors affecting its geographical distribution with spatial constraints on having some important influences. With the increase in time, the total suitable distribution area of the tree was reduced, especially the most and more suitable distribution areas decreased greatly and shifted towards the north, which were more prominent trends in RCP 8.5 scenario. Our findings indicated that future climate change may lead to shrinkage of the Tsuga longibracteata population and decreased its suitable habitat area; thus, increasing threats to its population. On adding the space constraint factor in the model, the prediction accuracy of the C+S model was higher, and the results more strongly fit with the migration and diffusion characteristics of the tree. The core distribution area in the future was still located at the junction of the three provinces in Hunan, Guangxi, and Guizhou, where the tree is currently distributed, indicating the junction is a refuge place for the tree in the future climate changes. In addition, the Daba mountain area in combination with the Chongqing, Sichuan, and Hubei are the theoretical distribution area of Tsuga longibracteata in the future under climate change. They can be used as new introduction culture areas of the tree under the future climate change. The results provided a scientific basis for the conservation and sustainable management of the species in the context of the climate change, and a case integrating spatial constraint into a climate model for species distribution prediction, which will benefit accurate prediction of the geographical distribution of endangered and rare plants.