Ecosystem Management Of Island With Fixed Link To The Mainland Based On Ecological Vulnerability Simulation And Prediction

Around the world,numerous sea-cross bridges have been constructed for economic reasons.The accessibility of islands can be largely improved with fixed link to the mainland by the construction of sea-cross bridges and tunnels,which results in a rapid increase of tourists and economic income.Meanwhile the accelerated increase of built-up land and tourists will change the island ecosystem deeply.It is urgent to estimate the impact of sea-cross bridges on island land use and the island ecological vulnerability,derive the threshold of anthropogenic influence on the island,and provide pertinent ecosystem management strategies.In this study,the Zhujiajian Island which has a fixed link to the mainland was selected for investigation.Remotely sensed images were used as data sources.Field work based spatial modelling was used to simulate the change of ecological vulnerability.The observed land use and the simulated land use without fixed link to the mainland were compared to derive the impacts of sea-cross bridges.Island Ecological Vulnerability Index(IEVI)was used to evaluate the ecological vulnerability of Zhujiajian Island.Land use and tourists change in the next 20 years was simulated to estimate the change of island ecological vulnerability.Ecosystem service value adjusted with ecological vulnerability(AESV)was formulated to assess island ecosystem services for Zhujiajian Island in the next 20 years.The threshold of anthropogenic influence and the sensitive area of ecological vulnerability were obtained based on the prediction of ecological vulnerability.The main results are:(1)The ecosystem of Zhujiajian Island is in good condition now,with limited area at moderately and severely vulnerable status.Natural factors are the congenital factors of island ecological vulnerability,and human disturbance are the coercive factors.The ecological vulnerability index of zhujiajian island is between 0.68 and 1.77,and the proportion of moderate and moderate vulnerability regions is less than 1/10.The severe vulnerability area is mainly distributed at places with steep slopes superimposed with intensive human disturbances caused by roads.The moderate vulnerability area is distributed at place with large topographic relief or intensive human disturbances.(2)The rapid increase of tourists and built-up area are the key factors of anthropogenic influence that contribute to the increase of ecological vulnerability.The land use of island is greatly affected by sea-cross bridges,with growth rate of built-up land 1.59 times higher than that before the bridge construction.Compared with the scenario of without fixed link to the mainland,the centroid of built-up area moved about 500 m to the southeast,while the centroid of farmland moved nearly 300 m to the northwest.After having fixed link to the mainland,the number of tourists in 2010 was 2.35 times that before connected in 2009.In 2015,the number of tourists reached 5.58 million,an increase of more than 8 times compared with that before the sea-cross bridge was finished.Future construction of sea-cross bridges forming fixed link between island and mainland should consider the economic development needs of the island,the carrying capacity of the island resources and the ecosystem responses together,before the feasibility analysis.(3)With the rapid increase of anthropogenic disturbance,the ecological vulnerability of the island tends to increase.The number of tourists and built up area should be controlled according to the ecological vulnerability threshold analysis.Space control countermeasures were proposed based on spatial sensitivity analysis of ecological vulnerability.In 2035 the area of severe vulnerability will increase by 78%,and the area of mild vulnerability will increase by 201 ha(33%).One third of the non-vulnerable area will become vulnerable.Around 2025,the non vulnerability and marginal vulnerability would decrease at the maximum rate,and the growth rate of other types of vulnerability area also reach the maximum.So the threshold of tourists in Zhujiajian Island is between 16-17 million per year.The upper limit of built up area is between 2400-2500 ha,which means 90% is already used.Therefore,it is necessary to formulate targeted measures to control the scale of tourism population and built-up area.According to the vulnerability assessment and sensitivity analysis,the Zhujiajian island can be divided into prohibited development zones,restricted development zones and conditional development zones with different ecosystem management strategies.(4)Forest is the most severely affected landscape by ecological vulnerability.The spatial heterogeneity of ecological vulnerability leads to a faster decrease in the ecosystem services value.Compared with traditional ecosystem services,the value of forest ecosystem services adjusted with ecological vulnerability is 17% lower,and the value of ecosystem services of the whole island is 14% lower.Forest,which accounts for 45% of the island’s area,provides two-thirds of the island’s ecosystem service value.The value of forest ecosystem services adjusted with by ecological vulnerability is 23% lower than the traditional assessment.Natural factors are the congenital factors that form the island ecological vulnerability.However,due to the construction of bridge between the island and the mainland,the island faces rapid growth of human disturbance,with increased ecological vulnerability.The assessment of island ecological vulnerability based on the prediction of human impact can provide scientific basis for island land connection project planning and island ecosystem management with fixed link to the mainland.