城市生态系统承载力理论与评价方法

Theory and evaluation of urban ecosystem carrying capacity

城市作为一个复杂的人工生态系统,其承载力的意义与生态学中的种群承载力意义有了很大差别。定义了城市生态系统承载力,强调其对维系城市生态系统健康的能动性特征,并在比较生物免疫力与城市生态系统承载力的相似性的基础上,构建了“城市生态系统承载力免疫学模型”作为其理论模型。在理论模型基础上设计其计量模型,分为天然承载力和获得性承载力两部分。并通过承载力与压力的相对变化趋势表达城市生态系统维系其健康水平的能力。以广州市为例,计算了广州市城市生态系统承载力与压力,获得二者的动态关系。结果表明,自1992年以来,广州市基本上处于一种经济发展与城市生态系统支持力同步发展的良性状态。

The urban ecosystem is a Social-Economic-Natural Complex consisting of human beings and their surrounding. The urban population and their activities jointly form the core component of the urban system, interlinked with the urban eco-environment. Because resources and environmental quality are crucial to the existence and development of an urban ecosystem, the development of an urban ecosystem is necessarily built on the basis of interactions among environmental carrying capacity (ECC), resource carrying capacity (RCC) and social-economic development capacity (SEDC). A single component's capacity should not be studied without considering the integrity of the whole system. In this paper, the concept of 'Compound carrying capacity' (CCC) is introduced and studied as an index of the interactions among ECC, RCC and SEDC, as a basis for meeting the challenges of urban sustainable development and eco-city building. Using this index, it is discussed in both theory fundamentals and quantitative models how these three kinds of capacity function to sustain the urban ecosystem. Significance and functioning of the urban ecosystem carrying capacity were interpreted in view of city development perspectives and characteristics of the compound urban ecosystem. The concept of CCC is introduced to improve the comprehensive understanding of this system's structure and functions. Compared with traditional concepts, the CCC of the urban ecosystem includes the ability to develop and thus is characterized by being more dynamic. This dynamism shows in the ability of cities to respond when put under pressure. Clearly, this dynamic is not endless, both environmental, resource and social-economic development capacities have limits. A comparative study of urban ecosystems and the human immune systems shows that both systems have similar features. Thus, the CCC model is discussed in this paper in light of the biology immunity theory. In this it is assumed that the urban ecosystem is the material input and its main function is to offer eco-services. The extent of these services is dependent on both the natural carrying capacity and the acquired carrying capacity of the urban ecosystem, and human beings are the receptor of the services. This theoretic model shows the carrier, the carried target and the carrying mechanism of the urban ecosystem's CCC. The methodology for both calculation and adjustment mechanism of the CCC is outlined, with reference to the urban ecosystem health index and evaluation models of sustainable development. This quantitative model of CCC includes five parts: the natural carrying capacity, the acquired carrying capacity, the integration of both basic and acquired carrying capacity, the absolute carrying capacity and the comparative carrying capacity of the urban ecosystem. In addition, a case study in Guangzhou city is described. Employing the CCC model, the complex carrying capacity of Guangzhou City was evaluated. This study showed that the CCC and pressure in Guangzhou were relatively balanced. The urban ecosystem was basically healthy, but in some parts, adjustments should be made in terms of economic activities and ecological restorations.