Predicting The Suitable Distribution Area Of Abies Beshanzuensis:To Explor The Potential Dispersion Of The Plant Species With Extremely Small Populations

As an important feature of species,the species distribution is the foundation of macroecological research.The relationship between species and environment is of great significance for understanding biodiversity patterns and their maintenance mechanisms and for biodiversity conservation.Along with intensified human activities and climate change,more and more species are threatened,especially those with smaller distribution areas,special habitats,and narrow ecological boundaries.In order to protect world's biodiversity,it is necessary to give priority and emphasis to protect such Plant Species with Extremely Small Populations(PSESP).This activity helps to delay species loss,maintain ecological balance,and promote ecological sustainable development,which is of great significance to China's biodiversity conservation.As such a wild plant populations with small populations,narrow habitats,severe external disturbances and risky extinction at any time,Abies beshanzuensis is a typical representative of PSESP.At present,there are only three natural mature trees in the field,and it is one of the 12 most endangered species in the world.Since it had been discovered in 1963,although remarkable progresses have been made in seedling breedings through seed,cuttage and grafting,its survival and conservation still faces greater threat due to the extremely small actual distribution area.Once affected by extreme events(such as extreme weather,plant diseases and insect pests),it will cause serious irreversible consequences.Therefore,the ex-situ conservation is particularly important.The study of potential distribution areas of such very small populations helps to provide a scientific basis for the site selection of ex-situ conservation.In this study,A.beshanzuensis was taken as an example,and its potential distribution area was simulated by the maximum entropy model(MaxEnt).The model used the species distribution data in 12 sites found through field surveys,combined with climate data from the Worldclim Database and terrain data extracted from the Digitised Elevation Model(DEM)data.The limiting factor of large-scale distribution of A.beshanzuensis was further discussed.The MaxEnt simulation has an AUC(Area Under Curve)value of 0.998,indicating that the model has a good performance.The simulation of MaxEnt showed that the potential distribution of A.beshanzuensis is constrained in southeastern China with very small area.It is mainly distrabuted in Ji'an(southeastern Jiangxi Province),Lishui(southern Zhejiang Province),Nanping and Longyan(northwestern Fujian Province),Shaoyang,Yongzhou and Chenzhou(southwestern Hunan Province)and the central mountainous areas of Taiwan.The most suitable area is only 963.41km~2,along with the suitable area of2890.22 km~2 and low suitable area of 11560.87 km~2.The simulation further indicated that A.beshanzuensis tends to be grown in higher mountainous areas,with an average elevation of 1000-2000 m.The judgement through the jackknife method indicated that the environmental factors affecting the distribution of A.beshanzuensis mainly include precipitation of the driest quarter,temperature seasonality,and minimum temperature of the coldest month.Compared to the topography,temperature and precipitation are the key driving factors of the distribution of A.beshanzuensis.In recent decades,many works have been done on the rescue protection of the extremely small population of A.beshanzuensis,but its endangered status has not been cancelled.At present,more than 2,000 seedlings have been survived,and the expansion of A.beshanzuensis is the focus of next conservation work.Therefore,the ex-situ conservation in an appropriate way will be of great significance to the better understanding of the endangered mechanism of this species,the determinants of its distribution area and the conservation of PSESP.We therefore suggest,based on the model simulation,that the prioritized ex-situ conservation sites are in six national nature reserves in southeastern mainland of China and two national park from Taiwan Island,where the optimal growth condition have.They include the Wuyanling Mt.,Wuyi Mt.,Bamian Mt.,Nanfeng Mt.,Shunhuang Mt.and Jintong Mt.National Nature Reserves,and the Shei-pa and Taroko National Parks.After some relevant circumstances are ready,the species could be gradually expanded into its suitable growth distribution area.Hopefully,all of these efforts could effectively enlarge the actual distribution area of A.beshanzuensis.