Spatiotemporal Expansion Dynamic And Potential Spreading Prediction Of Invasive Alien Plant Flaveria Bidentis (Asteraceae) In China

With the fast development of economic reforms and international trade,the invasions of alien species are increasing in frequency and their impacts are becoming more and more serious.It has not only caused the loss of biodiversity,but also destroyed the natural ecological balance and caused serious threats to the local ecosystem.Biological invasions could be viewed as a dynamic and orderly ecological process,and it has local spatiotemporally heterogeneous in geography and ecology.The range expansion of alien species is the critical reason for them to cause ecological problems in the invaded regions.It is essential to understand the expansion patterns of invasive species over space and time and their potential for further spread.It will help establish early monitoring and warning management measures.Flaveria bidentis(L.)Kuntze is a malignant alien weed that invaded China in the 1990 s.Until now,it has invaded more than 200 counties in Hebei and other four provinces in northern China.Because of the extremely strong reproduction ability of the F.bidentis,it is easy to form mono-dominant community after it invaded one region.It posed a great threat to the biological diversity and agricultural production of the invaded regions.The previous research mainly focused on its biological and ecological characteristics,competitive alternative mechanisms,chemical control,etc.However,it is unclear how F.bidentis has been introduced into China,what is its expansion route,and its speed.Comprehensive analysis of the invasion and expansion processes and its climate niche of F.bidentis are the key issues and main research contents to be addressed in this study.Based on this,our study firstly reconstructed the invasion and expansion processes of F.bidentis in China through field investigations,elucidate the spatiotemporal dispersal mechanisms.Then,we used the latest research methods to compare the niche signatures of F.bidentis population in China and its native and worldwide invasion.Finally,based on the niche signatures of F.bidentis in the global invasion process,the ecological niche model was used to predict the potential invasion areas in China under current climate and climate change.The historical invasion process reconstruction of F.bidentis in China showed that it first invaded Handan and Hengshui City in the southern part of Hebei Province in the 1990 s.Thenit began to spread toward neighboring regions along roads.The earliest occurrences of F.bidentis in one area mainly located at verges of the roads,especially the national roads.Among them,85% of the earliest occurrence points are within 2 km of major roads such as G107 and G106.It has now spread 350 kilometres to the north and arrived in Tangshan city in Hebei province,350 kilometres to the east and arrived in Guangrao county in Shandong province,100 kilometres to the west and arrived in Shanxi province,250 kilometres to the south and arrived in Kaifeng city in Henan province,respectively.The heterogeneity of the speed of spread of F.bidentis in different directions in China should be related to natural barriers and expansion route.The Taihang Mountains should be geographical barriers to prevent its spread to the west.But F.bidentis is breaking through this barrier gradually along the road with the human activities.We used F.bidentis and its closely related species,Flaveria trinervia(Spreng.)C.Mohr,as a composite species to analyze the signatures of climate niche changes.To gain insight into the dynamics of different components of F.bidentis' s niche,we performed these analyses on two climate datasets: one with variables selected by Maxent(Model M)and one with variables chosen a priori based on their putative ecological importance(Model E).The comparative analysis of climatic niches between the native and invaded areas in different regions of the world showed that its climatic niche in China was significantly different from its native.And its native climatic niche resembled that in Africa and Europe.The climatic niche differences between native and China indicated that the climate niche of F.bidentis in China may have shifted.Finally,based on the characteristics of climatic niche of F.bidentis in China and its global environment,the ecological niche model using F.bidentis and F.trinervia in the world,especially in China,was used to predict the potential distribution for F.bidentis in our country.The predicted results showed that in addition to the currently invaded areas,a large part of Shanxi,Ningxia,Gansu,Guangxi,Guangdong,Yunnan,Guizhou,Hunan,Jiangxi,Fujian,Jiangsu,Sichuan,Zhejiang,Chongqing,Shaanxi,and Hainan are its potential survival areas.At the same time,we also projected the current climate of F.bidentis to the future climaticscenarios(2050,2070)in order to predict the potential habitat under changing climate conditions in China.The results indicated that its potential areas in China will expand to the northeast and west,such as Gansu,Qinghai,Xinjiang,Tibet,Inner Mongolia,etc.Future climate changes may help them to break through the natural geographical barrier Taihang Mountains and promoted its toward west to Shanxi.In summary,F.bidentis has been brought into China by unintentional carrying of human activities,and then spread rapidly toward the neighboring of its earliest invaded foci along the roads.Until now,It is still in a stage of rapid expansion.It should continue to spread southwards and westwards from the invaded areas in the future.It is imperative to establish early monitoring at the forefront of expansion and to curb its further spread.