Risk Assessment For The Reinvasion Of Spartina Alterniflora After Ecological Management

Spartina alterniflora is a world-wide invasive plant,and its invasion has many negative impacts on the stability of the coastal wetland ecosystem.In order to control S.alterniflora and restore birds habitats,the“Ecological Control of Spartina alterniflora and Improvement of Birds Habitats Project”was launched by Shanghai Chongming Dongtan National Nature Reserve in 2013,and comprehensive physical control of S.alterniflora was implemented.However,due to the existing S.alterniflora outside the management area and incomplete treatment of S.alterniflora,the propagules of S.alterniflora entered thoroughly managed area once again through tides,and the reinvasion of S.alterniflora appeared,which affected the outcomes of S.alterniflora ecological management and the implementation of the subsequent ecological restoration.Therefore,the risk of reinvasion should be evaluated urgently to grasp the potential risk areas areas of reinvasion of S.alterniflora.It will provide early warnings and decision reference for the further prevention of reinvasion of S.alterniflora and offer scientific reference to ensure the outcomes of ecological restoration in Chongming Dongtan.According to the research objectives above,this study established an indicator system and assessment method for the reinvasion risk assessment of S.alterniflora,which was based on the identification of the main environmental factors that affect the establishment and growth of S.alterniflora.Taking the natural tidal flat that has eradicated S.alterniflora in Chongming Dongtan as a typical study area,the risk assessment of reinvasion of S.alterniflora after ecological management was carried out,based on which the management strategies against reinvasion of S.alterniflora were proposed.The main studies were as follows:1.The main tidal environmental factors that affect the establishment and growth of S.alterniflora were identified.Through field experiments,we transplanted S.alterniflora rhizomes along elevation gradients on two types of tidal flats and monitored survival states of S.alterniflora and environmental factors such as elevation,hydrodynamics and sediment characteristics to identify the main environmental factors that affect the establishment and growth of S.alterniflora.The results of the experiment showed that the critical shear stress,median diameter,maximum flow velocity and elevation had a dominant effect on the colonization of S.alterniflora rhizomes(P<0.05).2.The indicator system and risk assessment method for the reinvasion of S.alterniflora was eatablished.We established an indicator database of risk assessment of biological invasion from two aspects of invasion pressure and invasibility.Based on the literature and results of the field experiment,an indicator system for the risk assessment of reinvasion of S.alterniflora was constructed.Through the determination of indicator weights,the standardized assignment of indicator data,and the calculation method of intergrated risk index,the evaluation method of risk assessment of reinvasion of S.alterniflora was established.3.The risk assessment for the reinvasion of S.alterniflora in Chongming Dongtan after ecological management was carried out and the management strategies was proposed.Taking the natural tidal flat that has eradicated S.alterniflora in Chongming Dongtan,Shanghai as a typical area,based on the indicator system and risk assessment method of reinvasion of S.alterniflora,the geospatialization and standardized assignment of each indicator was realized.The integrated risk index of reinvasion of S.alterniflora in Chongming Dongtan was calculated and classified.The risk assessment of reinvasion of S.alterniflora in Chongming Dongtan was realized.According to the results of the study,the areas of high-risk area,relatively-high-risk area,medium-risk area and low-risk area were 334.58 hm~2,785.25 hm~2,587.63 hm~2 and 231.09 hm~2,respectively.The high-risk areas were mainly distributed in the area of Bei Baxiao sluice,Dong Wangsha sluice and Bu Yugang,which were also the distribution areas close to the risk source of S.alterniflora.The relatively-high-risk areas were mainly distributed in the areas from Bei Baxiao sluice to Dong Wangsha sluice.Although the habitat here is suitable for the invasion of S.alterniflora,the distance from the risk source of S.alterniflora is not as close as that in the high-risk area,so the risk level has decreased.The medium-risk and low-risk areas were mainly distributed in the center of assessment area.These areas are far from the risk source of S.alterniflora,and the suitability of environmental conditions has also declined,so the risk level is lower.Based on the risk assessment results above,the management strategies for controlling the reinvasion of S.alterniflora were proposed,including strengthening the management of S.alterniflora,restoring indigenous plants in coastal wetlands,and strengthening the monitoring and management of reinvasion of S.alterniflora.