Risk Assessment Of Alien Plant Invasion In Wetlands In The Yangtze River Delta Ecological Green Integrated Development Demonstration Area

Wetland ecosystem is an important and special type of ecosystem widely distributed around the world.It is located in the transition zone between aquatic and terrestrial ecosystems.Its special environmental conditions provide a greater possibility for the colonization and spread of exotic plants.Once exotic plants become invasive speces and difficult to eliminated.It is of great significance to study the invasive level and damage degree of exotic plants in the invasive area.According to the management rule of alien species of exotic species in the Yangtze River Delta ecological green integrated development demonstration area.This study takes Qingpu District of Shanghai as an example,3S technology,field sampling inventory,Analytic Hierarchy Process(AHP),risk assessment index system,etc.were used.The main results are the following:(1)Based on the field inventory of different wetland types,a total of 64 species of exotic wetland plants were recorded,belonging to 32 families and 53 genera,of which the most families were Asteraceae,followed by Fabaceae and Poaceae.,Amaranthaceae etc.Referring to Wu Zhengyi's(2003)division of the distribution types of seed plants in the world,the flora composition of exotic plants in this region can be divided into 5 types and 2 variants.It includes five types: widely distributed(widely distributed in the world),pan tropical(widely distributed in the tropics),East Asia(tropical and subtropical)and tropical South American discontinuity,north temperate zone,East Asia and North America discontinuity.The pantropics(widely distributed in the tropics)and the north temperate zone contain one variant respectively,which are distributed intermittently in the pantropics,north temperate zone and South Temperate Zone dominated by the southern hemisphere.The analysis of invasion routes showed that there were 33 species of exotic plants introduced intentionally,accounting for 51.56%,and 31 species of exotic plants were introduced unintentionally,accounting for 48.44%.The most species of exotic plants originate from the Americas,followed by those from Asia,and there are fewer species of exotic plants originating in Africa,with only 2 species,accounting for 3%.The life forms of exotic plants are mainly perennial herbs and annual herbs,of which 23 species are perennial herbs,accounting for 35.94%.(2)According to the construction principles of the risk assessment index system,based on the complete biological invasion process,aiming at the key characteristics of alien plants in the introduction stage,colonization stage,diffusion stage,harm and control stage,and combined with the distribution and abundance of alien plants in the process of field investigation,an alien plant invasion risk assessment index system suitable for this region is constructed.The indicator system is divided into three levels,including 6 first-level indicators,13second-level indicators and 35 third-level indicators.The weights of indicators at all levels are calculated and determined using the Analytic Hierarchy Process(AHP).(3)According to the survey data of exotic plants,42 species of exotic invasive plants that have constituted a certain degree of invasive behavior in China were screened out,and risk assessment was carried out,and different invasion risk levels were divided,and corresponding management strategies were proposed.There are 21 species of invasive exotic plants with high risk(first-level warning level),of which Asteraceae is the most species,accounting for 28.57%,followed by Amaranthaceae,accounting for 19.05%.These high-risk exotic invasive plants is unacceptable,and strictly prohibited to be introduced.There are 14 species of invasive exotic plants with medium risk(secondary warning level),of which Asteraceae is the most species,accounting for 21.43%,followed by Scrophulariaceae,accounting for 14.29%.Invasive alien plants with a risk level of medium have certain invasion risks,and monitoring and prevention work should be strengthened.There are 7 species of low-risk(three-level warning level)invasive exotic plants,of which the most species are Asteraceae,accounting for57.14%.Most of the low-risk invasive alien plants are intentionally introduced as ornamental plants or artificially cultivated.The proportion of imported invasive plants through intentional introduction is as high as 71.43%.These low-risk exotic invasive plants are acceptable,the feasibility of introduction is high,but it still needs to be regularly monitored.(4)From the perspective of the spatial distribution characteristics of invasive exotic plant families,Compositae is the most widely distributed in the study area,followed by Amaranthaceae,Scrophulariaceae,Leguminosae sp.,etc.From the perspective of the overall spatial distribution range,the high-risk(first-level warning)invasive alien plants have the widest distribution range,and are widely distributed in lake wetlands,river wetlands and artificial wetlands,especially in Dianshan Lake(DSH)in lake wetlands and artificial breeding ponds(YZT)in artificial wetlands,the distribution is more significant.The invasive exotic plants of medium risk(secondary early warning)have a wide distribution range,and they are distributed in different wetland types,with the largest distribution in lake wetlands,followed by artificial wetlands The low-risk(three-level warning)exotic invasive plants have the smallest distribution in Qingpu District,only distributed in the Ximao River(XMH)of river wetlands and a small number of artificial wetlands.The spatial distribution range of invasive exotic plants with different risk levels is in descending order: high risk(first-level early warning)alien invasive plants > medium risk(second-level early warning)exotic invasive plants > low-risk(third-level early warning)exotic invasion plants.