The Historical Distribution And Migration Trend Of The Relict Plant Ginkgo Are Studied Based On The Random Forest Model

It is an indisputable fact that climate change,especially global warming,will lead to glacier melting,sea level rising,ecological degradation,and so on.Species habitats will migrate with the change of climate conditions,which further affect ecological diversity.Therefore,the research on species response to climate change based on species distribution models(SDMs)is the mainstream trend.Relict plants,known as"living fossil" plants,have survived the drastic changes of geological and climatic environment until now.Because of their special status,they play an irreplaceable role in global biodiversity conservation.In this study,Ginkgo biloba L.was taken as the study object.Based on 122 sampling sites of G.biloba in China and 17 selected environmental variables including climate,topographic and human influence index,using Random Forest model to predict the suitable distribution of G.biloba in the past(Last Glacial Maximum(LGM),Mid-Holocene(MH)),current,and future(2050s,2070s)under four representative concentration pathways(RCP2.6,RCP4.5,RCP6.0,and RCP8.5).Three evaluation indexes(AUC,Kappa,and TSS)were used to evaluate model accuracy.According to the factor contribution,the main factors affecting the distribution of G.biloba were screened,the suitable threshold and environment condition for the growth of G.biloba was further obtained by factor response curve.By overlaying the suitable habitats of G.biloba in LGM and current,to identify the potential refugia during the glacial period and analyze the formation causes.In addition,we compared the suitable distribution of G.biloba under different RCPs in the future to judge the spatial distribution pattern,the transfer trajectory of the centroid,and the expansion or contraction trend under climate change.Finally,we analyzed the results of human influence index participating in the modeling,and discussed the influence of human activities on the distribution and transmission of G.biloba.The main conclusions of this study are as follows:(1)At present,the suitable habitats of G.biloba basically cover most areas from the south of Qinling-Huaihe Line to the east of Hengduan Mountains,which are mainly distributed in Chongqing,Hubei,Hunan,Jiangxi,Anhui,Zhejiang,Jiangsu,and Fujian Province.The topographic areas include the plains of the Middle-Lower Yangtze plains,Sichuan Basin,Yunnan-Kweichow Plateau,Southeast Hills,which are dominated by subtropical monsoon climate.(2)The evaluation index values constructed by the model in each period are all of the high accuracies,indicating that all models are successful in predicting accuracy.The order of evaluation results is AUC(0.92?0.96)>TSS(0.7?0.85)>Kappa(0.61?0.79).(3)There are six major environmental variables affecting the growth of G.biloba.Bio 11(mean temperature of coldest quarter)is 2??10 ?,Bio 12(annual precipitation)is 900 mm?1800 mm,Bio2(mean diurnal temperature range)is 7 ??9 ?,Bio 17(precipitation of wettest quarter)is 190 mm,Biol(annual mean air temperature)is 14 0C?20 0C,and Bio 14(precipitation of driest month)is more than 32 mm will promote the growth of G.biloba,indicating that the suitable environment is characterized by high temperature and abundant rainfall in summer,mild and less rain in winter.(4)Results show that the potential refuges of G.biloba during the glacial period are located in the southern section of Hengduan Mountains,central and Eastern China.The flat terrain together with the protection of the surrounding high mountains prevented the invasion of cold air so that G.biloba can be preserved and continued to this day.(5)The habitat expansion or contraction of G.biloba in the future is mainly manifested by the shrinkage of the middle and lower reaches of the Yangtze River,especially in the Plain of Hubei and Hunan,Poyang Plain and the Hanjiang Plain.From 2050s to 2070s,the spatial distribution of G.biloba will become more and more dispersed along the "east-west" direction,and the centroid gradually will shift to the northwest high latitudes with the passage of time.(6)The presence probability of G.biloba increases with the increase of human influence index,which indicates that human activities have played a promoting role in the growth of G.biloba,mainly reflected in the protection of ancient tree resources and the cultural communication.This study reasonably predicts the potential habitat distribution of G.biloba in long-term scale under climate change.It also predicts the possible refugia of G.biloba in the glacial period and the change of spatial distribution pattern under future climate change,which will provide a theoretical basis for the in-situ and ex-situ conservation of relic plants.