基于生态系统服务的城市化区域生态风险表征方法研究

快速城市化导致城市周边区域生态系统服务损失并引发生态风险。以多种类型的生态系统服务作为生态风险的评价终点，构建了基于服务价值量的城市化区域生态风险表征方法，以北京市为例对方法进行了应用，并进行了风险评价结果的不确定性分析和参数敏感性分析。案例研究显示2015年北京市生态风险总体处于低风险接近中等风险水平，低风险和极低风险区域面积占全市的50%以上，主要分布于北京市西部和北部，高风险和极高风险区域面积占20%左右，主要分布于中心城区。生态风险空间格局特征表明北京市城市区域的扩张造成周边区域生态系统服务的下降，导致生态风险水平的上升。研究提出的生态风险指数同生态系统服务当量因子间具有显著的线性关系，可用于估算生态系统服务价值。不确定性和参数敏感性分析表明生态风险指数计算结果变异较小，指数具有较高的可靠性。研究方法能够综合表征城市化区域的生态风险，定量表征结果便于决策者理解，具有应用于风险评价和管理实践的价值。

Research on ecological risk characterization methods for urbanized areas based on ecosystem services

Rapid urbanization processes result in the losses of ecosystem services in the surrounding areas of cities and cause ecological risks. Currently, there is a lack of ecological risk characterization methods for urbanized areas based on ecosystem services. This research developed an ecological risk characterization method based on ecosystem service values, which use multiple ecosystem service types as the ecological risk assessment endpoint. Moreover, we applied this risk characterization method to evaluate the ecological risks in Beijing and analyzed the uncertainties and the parameter sensitivities in the risk assessment. The results of the case study show that the ecological risks can be separated into five levels according to the frequency distribution of the ecological risk index values in Beijing in 2015. The mean values of the risk index was 0.64, meaning that the ecological risk was overall at the low level, but very close to the middle level in Beijing. The areas showing low and very low risk levels occupied about 50% of the total area of Beijing, distributing mainly in the west and north of the region; the areas presenting high and very high risk levels accounted for about 20% of the total area of Beijing, which were mainly distributed in the central areas of the region. Overall, the ecological risks exhibited an apparent spatial heterogeneity and urban-rural gradient characteristics in Beijing. Moreover, the ecological risks showed a generally similar declining trend to the artificial surface ratio from the urban areas to the rural areas in space. The spatial pattern of ecological risks implies that the expansion of the urban areas in Beijing caused the decline of the ecosystem services in the surrounding areas, which led to the increase in ecological risks. The proposed ecological risk index exhibits a highly significant linear relationship with ecosystem service equivalent weight factors and therefore, can be used to estimate the total value of ecosystem services. The calculation generates results with small variations using the risk index proposed in this study to estimate the ecological risk in a region with fixed land use composition, meaning that the proposed ecological risk index has a relative high reliability. The method proposed in this study can comprehensively characterize the ecological risks in urbanized areas and generate results that are easy to understand for decision makers, and therefore, has potentials to be applied in the practice of risk assessment and management. Future studies using the ecological risk index we propose need to choose more reliable methods to calculate ecosystem service values, so as to obtain more accurate risk assessment results.