ReviewUrban ecosystem health assessment: A review
Introduction
Cities play many roles in human civilization, acting as centers for economic activity and social change as well as a cultural crucible in which the concentration of people and activity allows the necessary critical mass for growth and maturation (Jacobs, 1961, Jacobs, 1984). Cultural concepts of ecosystem and human health have been linked through cities and human settlements since ancient times as evident in religious tenets, philosophical systems, codes of conduct, and more practical matters, such as wastewater treatment, sanitation, and municipal waste management (Guidotti, 1995). The goal of a city is to realize the benefits of dense population centers without compromising the ecological services or ecosystem health. Ecosystems satisfy human demands by acting as a source for resources and a sink for waste. Specifically, when the pressures are within the ecosystem's regenerative capacity, it is able to realize self-restoration through natural purification and other ecological processes. Early cities were probably safer than the surrounding hinterland because of increasing prosperity and better protection. The level of degradation was low. However, as cities grew, they developed increasing problems with resource shortages, waste disposal, itinerants, fresh food distribution, and epidemics—the healthfulness of urban residents probably declined relative to the peasantry (Guidotti, 1995). In spite of these issues, cities continued to grow and concentrate. Today, cities now hold more than half of the world's population, with many residents living in squalid conditions putting pressure on local and regional environmental resources. Therefore, there is a need for valid indicators and methods of “health” assessment of urban ecosystems. As a socioeconomic-ecological complex system (Ma and Wang, 1984), an urban ecosystem consists of residents and their environment in certain time and space scales, in which, ecological-speaking, consumers are the dominant component lacking producers and decomposers. To support the huge consumption in urban ecosystems, a large amount of materials and energy are extracted from the surrounding countryside and beyond, which makes the urban ecosystem dependent and fragile. The urban ecosystem status is indeed vital and thus a comprehensive health assessment is urgent. This paper reviews the related research to help us understand the rough contour of urban ecosystem health assessment.
In order to understand the current concepts in urban ecosystem health assessment, it is useful to review the history, from the early ideas to the state-of-the-art. Although the future is not determined by history, awareness of the development pathway is beneficial for finding related problems and anticipating future prospects. Therefore, this paper begins from the inception of urban ecosystem health concerns, followed by the concepts, assessment standards, indicators and models, and case studies.
Section snippets
Generation of urban ecosystem health concerns
Generally speaking, system dynamics are induced by both internal factors and external drivers, and the genesis of the urban ecosystem health concept was no different. Urban ecosystem health became a scientific topic and received public concern due to both internal and external reasons. For the former, various environmental problems, erupting from rapid urban development, required that the health status of the urban ecosystem be attended, while for the latter, progress in ecosystem health
Urban ecosystem health concept
Even though there is not any confirmed definition of urban ecosystem health, just like the concept of ecosystem health, there exist certain basic common characteristics: (1) ecosystem services maintain a productive capacity, (2) system integrity is key component of urban ecosystem health, and (3) assessing urban ecosystem health requires a systems perspective. As a complex system composed of natural, societal and economic components, the urban ecosystem is a network of multiple interactive
Urban ecosystem health assessment standards
The terminology “health” is usually associated with certain physiological standards, such that the system is considered healthy until certain parameters do not conform to the normal range. For example, human body temperature is between 36.2 °C and 37.5 °C while the heart rate is between 60 to 100 bpm. Similarly, ecosystem health can be measured with respect to standard reference conditions (Campbell et al., 2004). The difficulty is in identifying the appropriate state variables to measure and the
Urban ecosystem health assessment methods
To assess urban ecosystem health, the theoretical background from systems ecology as well as practical guidance from the decision-making for urban planning and management should be taken into account. Thus, certain methods that can link these two aspects are needed. Assessment indicators are selected as well-suited instruments to reflect the urban ecosystem health status according to their characteristics of abstracting information from a complicated system to reduce the complexity and to
Urban ecosystem health assessment case studies
Based on the established indicators and mathematical models, concrete case studies of urban ecosystem assessment have been conducted, ranging in scales from urban clusters to the city and to districts. Specifically, many studies of urban ecosystem health assessment were conducted on Chinese cities, including the administrative capitals of the state and provinces with available abundant statistics data, like Beijing (Zhou and Wang, 2005, Yu et al., 2008), Shanghai (Zeng et al., 2005), Guangzhou (
Discussion and conclusion
The very concept of “health” is a value-driven, mission-oriented notion. It means that the concept of health is formed, constructed and managed according to human goals and value preferences. Even though the ability to maintain the internal ecosystem structure and function is critical, the goal of the urban ecosystem health is determined mostly by human values, in that human beings are the main drivers of urban ecosystems. Thus, human need is emphasized in the concept and indicators of urban
Acknowledgements
This work is supported by the National Natural Science Foundation of China (grant nos. 40871056, 40901269), and National Basic Research Program of China (973 Program, grant no. 2005CB724204). Meirong Su conducted this research while on sabbatical at Towson University with support from the above mentioned grants.
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