The Impact Of Climate Change On The Potential Distribution Of The Invasive Plant Spartina Alterniflora

While causing irreversible ecological catastrophes,the biological invasion also brings great economic loss to many countries.With the rapid progress of global economic integration and the increasingly frequent international trades,exotic species have more opportunities to invade and spread.In the context of climate change,biological invasion may enter a new round of expansion.Predicting potential distribution of exotic species and preventing them from entering the suitable habitats are important measures to prevent and control the expansion of invasive species.With the invasive species of Spartina alterniflora in coastal regions as the research objects,this study utilized MAXENT model and geographic information system(ArcGIS)and respectively constructed climatic niche model and environmental niche model through influencing the major climate and environment factors,so as to predict the current and potential distribution patterns of Spartina alterniflora at different climatic situations.Based on this,the area under the curve(AUC)value of Receiver Operator Characteristic(ROC)curve was evaluated.The model with the highest accuracy was selected to analyze the importance degree of environmental factors and climate factors on model building.After obtaining the prediction results of the current and potential distribution patterns of Spartina alterniflora at different climatic situations,this study defined the potential regions of Spartina alterniflora according to the suitable regions and unsuitable regions divided by the corresponding thresholds of 10%training data set and the three suitable grades divided by the evaluating "possibility" presentation of IPCC.The main results are as follows:(1)With the support of ArcGIS platform,further analysis was conducted on the dominant temperature and rainfall variables that influenced the distribution of Spartina alterniflora under different climate scenarios in the future.According to the results,under different climate scenarios in the future,the main temperature variables(the lowest temperature in August and the highest temperature in June)showed obvious trend of increase,but the growing rates were different.It was found that the amplification in the north was higher than that in the south.And the amplification in the inland was higher than that in coast.The amplification under RCP8.5 was higher than that under RCP4.5 scenario.The variable changes of main precipitation(in March,April and September)were relatively complex.To be specific,the rainfall increased in the Shandong Peninsula and its Northern regions,with the amplification of 0-25mm,while the rainfall in the southern regions of Shandong Peninsula didn't showed consistent variation trends.Relative to the RCP8.5 climate scenarios,precipitation of most areas increased under RCP4.5 climate scenarios.(2)The results of environmental niche model displayed that altitude,soil type,precipitation in March and April,the highest temperature in June,the lowest temperature in August,as well as precipitation in September,soil organic carbon content and soil electrical conductivity were the dominant environmental factors that influenced the major environmental factors on the potential distribution of Spartina alternifora.The comprehensive analysis demonstrated that Spartina alterniflora was suitable to grow in coastal areas with rich precipitation,high soil salinity and low altitude.The most favorable ecological niche parameters of Spartina alterniflora were the precipitation of 50-150mm in March,the precipitation of 100?200mm in April,the soil electrical conductivity around 1.5?12.5ds/m and the altitude around-2?6m.(3)According to results of environmental niche model and climate niche model,the suitable regions of Spartina alterniflora were distributed extensively on the coastal zones from the Liaodong Bay in Liaoning to Fangcheng Port in Guangxi,where the coastal regions of Jiangsu,Shanghai,Zhejiang and Fujian provinces were the most suitable areas for Spartina alterniflora due to the high connectivity of the large patch.Besides,there is patchy distribution of suitable areas in Liaodong Bay,Bohai Bay and Shandong Yellow River Delta.Moreover,the suitable distribution areas in Guangdong and Guangxi were relatively fragmented,showing irregular distribution along the coastline and low altitude regions.In addition,it is necessary to take these regions with few existing distribution areas but large vacant areas of high and moderate suitable distribution areas as the potential invasion areas of Spartina alterniflora,including coastal areas in Liaoning;Fuqing Bay,Futou Bay and Zhaoan Bay in Fujian;Chaozhou,Shantou,Jieyang,Shanwei,Zhuhai and Zhanjiang in Guangdong;Beihai Port in Guangxi and northwestern coastal areas of Taiwan.(4)In the future,the suitable distribution of Spartina alterniflora increase under RCP4.5 climate scenario and decrese most under RCP8.5 scenario.The result indicate that the distribution of S.alterniflora can adapt to wide-range climate changes under RCP4.5 scenario than RCP8.5 scenario.As climate change,the potential distribution of Spartina alterniflora will transfer to higher latitude and lower altitude.The suitable distribution of Spartina alterniflora will extend to the north and south,and the area of it will increase to 120300 km2 in 2050,and decrease to 107300 km2 in 2070 under RCP4.5 climate scenario.By contrast,under RCP8.5 scenario,the suitability level of Spartina alterniflora will reduce and the areas sharply fell,showing the trend of extending lower altitude regions.The coastal bays in the south of Hangzhou bay will be more fragment.The area of projected suitable distribution of Spartina alterniflora will decrease by 67%(from 110700 km2 to 70500 km2)in 2050,and decrease to 73300 km2 in 2070.(5)Under the current and future climate scenarios,Jiangsu,Shanghai,Zhejiang Zhoushan Islands,Taizhou Bay,Fujian Minjiang River Estuary,Zhangjiang River Estuary,as well as Shanwei,Jieyang and other coastal areas in Guangdong reserved large areas of suitable distributions.Thus,it is vital to set them as key monitoring areas to govern.