Science of the Total Environment 408 (2010) 2425–2434
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Science of the Total Environment j o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / s c i t o t e n v
Review
Urban ecosystem health assessment: A review Meirong Su a, Brian D. Fath b,c, Zhifeng Yang a,⁎ a b c
State Key Joint Laboratory of Environment Simulation and Pollution Control, School of Environment, Beijing Normal University, Beijing 100875, China Biology Department, Towson University, Towson, MD 21252, USA Dynamic Systems Program, International Institute for Applied Systems Analysis, A-2361 Laxenburg, Austria
a r t i c l e
i n f o
Article history: Received 24 December 2009 Received in revised form 1 March 2010 Accepted 2 March 2010 Available online 26 March 2010 Keywords: Urban ecosystem health Health assessment Ecosystem indicators Ecosystem model
a b s t r a c t Due to the important role of cities for regional, national, and international economic development and the concurrent degradation of the urban environmental quality under rapid urbanization, a systematic diagnosis of urban ecosystem health for sustainable ecological management is urgently needed. This paper reviews the related research on urban ecosystem health assessment, beginning from the inception of urban ecosystem health concerns propelled by the development needs of urban ecosystems and the advances in ecosystem health research. Concepts, standards, indicators, models, and case studies are introduced and discussed. Urban ecosystem health considers the integration of ecological, economic, social and human health factors, and as such it is a value-driven concept which is strongly influenced by human perceptions. There is not an absolute urban ecosystem standard because of the uncertainty caused by the changing human needs, targets, and expectation of urban ecosystem over time; thus, suitable approaches are still needed to establish health standards of urban ecosystems. Several conceptual models and suitable indicator frameworks have been proposed to organize the multiple factors to represent comprehensively the health characteristics of an urban ecosystem, while certain mathematical methods have been applied to deal with the indicator information to get a clear assessment of the urban ecosystem health status. Instead of perceiving the urban ecosystem assessment as an instantaneous measurement of the health state, it is suggested to conceptualize the urban ecosystem health as a process, which impels us to focus more studies on the dynamic trends of health status and projecting possible development scenarios. © 2010 Elsevier B.V. All rights reserved.
Contents 1. 2. 3. 4. 5.
Introduction . . . . . . . . . . . . . . . . . . Generation of urban ecosystem health concerns . Urban ecosystem health concept . . . . . . . . Urban ecosystem health assessment standards . . Urban ecosystem health assessment methods . . 5.1. Indicators . . . . . . . . . . . . . . . . 5.2. Mathematical models . . . . . . . . . . 6. Urban ecosystem health assessment case studies. 7. Discussion and conclusion . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . .
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1. Introduction
⁎ Corresponding author. Tel.: + 86 10 58807951; fax: + 86 10 58800397. E-mail address:
[email protected] (Z. Yang). 0048-9697/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.scitotenv.2010.03.009
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
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critical mass for growth and maturation (Jacobs, 1961, 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. 2. 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 research provided the theoretical foundations and technical ability of assessing urban ecosystem health status. The word “health”, usually is applied to a human or other discrete living organism. We diagnose the life around us as well, ill, or dead, and when ill hopefully curable by doctors or veterinarians. When human presence was lower and ecosystem services fully available, not much attention was given to the health of the ecosystem. It was the Scottish geologist (naturalist), Hutton (1788), who first linked the concept of health with ecosystems. In a paper presented to the Royal Society of Edinburgh, Hutton stated that the Earth is a super-organism with selfmaintainable ability regarding its health. He explained further that natural ecosystems possess the common characteristics of a complex system including a self-regulation mechanism of sustaining the integrity and
resilience, even though it is not the same as an organism (Rapport et al., 1995). Meanwhile, scientific research mainly focused on traditional disciplinary subjects, not much attention was paid to multidisciplinary topics such as ecosystem health. Thus, after Hutton, there was a long quiet before the ecosystem health topic resurfaced as an academic activity. In 1929, Clements and Weaver (1929), in conjunction with their concept of community succession and climax theory, envisaged the ecosystem as a living individual, with attributes of health. A little later, Leopold initiated the contemporary discussion about ecosystem health by first proposing the concept of land ethic in 1941, in which the “land” he defined is similar with the functioning ecosystem (Milsky, 2004). Leopold's ideas were seminal in their contribution to the development of concern for land health. In his eco-systemic view, the land ethic incorporates ecology with aesthetics, stability, and integrity. One measure to assess ecosystem integrity is based on how it adapts and responds to external stresses (Guidotti, 1995). Together these attributes comprise the land's health. Leopold used the term “land sickness” to describe land dysfunction (Leopold, 1941) and he also considered ecological renewability as its important feature of landscape health. In the following decades, advancements were made in related subjects including stress ecology, ecosystem ecology, natural resource management, environmental ethics, and ecosystem medicine attributing to the contribution of many respectable researchers and academic societies (e.g., Woodwell (1970), Barrett (1976), Odum (1979); Rapport et al. (1979, 1985); Costanza et al. (1992), Ecological Society of America - see Table 1). It was becoming evident that ecosystems were being seriously damaged by human activities; and, as a result, human life quality was being negatively impacted. The analogy between human and ecological health matured further contributing to the development of a diagnosis heuristic for ecological restoration. At the same time, a new consciousness of public concern arose regarding ecosystem health caused by environmental pollution and ecological degradation. Due to the efforts of Ulanowicz (1986, 1992), Schaeffer et al. (1988), Rapport (1989, 1992, 1993), Costanza et al. (1992), Mageau et al. (1995), and others, the ecosystem health concept has attracted wide attention and interest. Research and case studies on different scales including farmland (Waltner-Toews, 1996), lake (Smol and Cumming, 1998), river (Boulton, 1999), bay and watershed (Costanza and Greer, 1998), forest (Menéndez et al., 1998), and desert grassland (Whitford, 1998) have been launched. Several related academic organizations were established, with associated conferences (see Table 1). Many academic journals and books were published (see Table 1), all advancing the understanding of ecosystem health by researchers and the public. In summary, when human activities resulted in adverse environmental changes that jeopardize sustainability and impair ecological functions and societal services (Vitousek et al., 1997; The Heitz Center, 2002), the inevitable social, economic, and human health costs provided grounds for addressing the ecosystem health in a holistic way (Rapport et al., 1998a). The time for integrated approaches to environmental management had come. To fill this need for ecosystem assessment, the ecosystem health concept was a welcome way to assess the underlying stress or “health” of ecosystems. 3. 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 relationships, thus its health status should take various factors into account in an integrated way rather than
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Table 1 Important historical events during the development of ecosystem health. Time
Event
b 1900 1900–1939
— Hutton (1788) first introduced natural health concept; Earth as a self-regulating, super-organism. — Clements and Weaver (1929) regarded ecosystem as a living individual with healthy and unhealthy attributes; inspired by community succession and climax hypothesis. — Leopold (1941) first defined “Land health”; used “Land sickness” to describe land dysfunction. — Soil and Health Society in New Zealand published the journal Soil and Health in 1942 (Zeng et al., 1999). — Leopold proposed “Landscape health”; as “…the capacity of the land for self-renewal.”a (Rapport, 1998). — Woodwell (1970) highlighted the affects of pollution stress on ecosystem structure and function. — Barrett (1976) addressed the importance of stress ecology. — Odum (1979) promoted systems ecology; ecosystem with self-regulation and feedback which can recover under certain stress; various unhealthy symptoms under external stress do not need management intervention. — Rapport et al. (1979) further developed Leopold's “land health” theory; put forward the term “Ecosystem medicine” as way to evaluate the ecosystem in an integrated way. — Ecological Society of America held a symposium “Integrated method for presenting and managing the stressed ecosystem” at the annual conference in 1984 (Costanza et al., 1992). — Rapport et al. (1985) pointed out that the ecosystem cannot be regarded as an organism and does not respond independently under adversity. — Ecologists like Costanza and Rapport stated ecosystems are dysfunctional under stress, thus unable to provide basic services for humans; raising ecosystem health concept and call public attention to environmental degradation (Kristin, 1994). — WHO first set up the Healthy Cities Project in 1986, intending to improve factors that influence citizen's health such as housing, environmental protection, social benefit, education and urban planning, and finally prevent illness and promote health, by community participation and common efforts from various sections (Department of Health, Hong Kong Special Administrative Region, 2007). — Schaeffer et al. (1988) first discussed measuring ecosystem health; put forward assessment principles and methods. — Rapport (1989) explained ecosystem health as the system's stability and sustainability which can be denoted by vigor, organization and resilience. — Aquatic Ecosystem Health and Management Society was established in Canada, 1989 (Zeng et al., 1999). — Rapport (1992) further developed Schaeffer's idea of defining health as “absence of disease” into integrated distress syndrome at the ecosystem scale. By this time, ecosystem health was widely studied by scholars and researchers. — Journal of Aquatic Ecosystem Health was published in 1992, renamed Journal of Aquatic Ecosystem Stress and Recovery in 1997 (Zeng et al., 1999) — Ecosystem health: new goals for environmental management (Costanza et al.) was published in 1992 (Ren et al., 2000). — First international symposium on ecosystem health and medicine was organized in Ottawa, 1994; International Society for Ecosystem Health was established, with regular subsequent symposia (Zeng et al., 1999). — Journals Ecosystem Health and Journal for Ecosystem Health and Medicine were initiated in 1995 (Ren et al., 2000). — Shear (1996) developed an ecosystem health assessment for the Great Lakes. — Harpham (1996) compared urban ecosystem and public health between the urban and rural areas in Gambia. — Journal Aquatic Ecosystem Health and Management was started in 1998 (Zeng et al. 1999). — Several important books about ecosystem health were published, e.g., Evaluating and Monitoring the Health of Large-scale Ecosystem (Rapport et al., 1995), Ecosystem Health (Rapport et al., 1998a), Managing for Healthy Ecosystems (Rapport et al., 2002), Ecosystem Sustainability and Health-A Practical Approach (Waltner-Toews, 2004). — Guo et al. (2002) started study on urban ecosystem health in China, introducing urban ecosystem health concept more fully in China.
1940–1969
1970–1979
1980–1989
1990–
a The book “A Sand County Almanac” written by Aldo Leopold (1886–1948) was published posthumously. The final version was edited by a team of family and colleagues led by his son, Luna Leopold, and published a year after his death by Oxford University Press.
only focus on such partial elements as water, soil, air or vegetation. Regardless of the underlying environmental ethics (e.g., bio-centric ethics, anthropocentrism, and holism), all inseparable components and their relationships should be considered within the urban ecosystem, for one must affect and be affected by others in the ecosystem. The concept of ecosystem health has experienced roughly three development phases, i.e., first focusing on the characteristics of ecosystem itself (Karr et al., 1986; Ulanowicz, 1986, 1992; Schaeffer et al., 1988; Schaeffer and Cox, 1992; Woodley et al., 1993; Costanza et al., 1998), then turning to services for human (Rapport, 1989; National Research Council, 1994; Mageau et al., 1995; World Resources Institute, 1995), and finally combined characteristics of ecosystem and services for humans (O'Laughlin, 1996; Rapport et al., 1999). Building on the previous experience of ecosystem health, the concept of urban ecosystem health combines the ability to satisfy reasonable demand from human society and maintain its own renewal and self-generative capacity. Therefore, urban ecosystem health is an integrated subject that includes ecological, socioeconomic and human health perspectives. To a certain degree, this is inevitable because the most important characteristic of the urban ecosystem is its dominance by humans. Several concepts of urban ecosystem health have been developed through the ongoing scientific research and management projects, based on different frameworks, emphases and objectives, as cited and analyzed in Table 2. Different from many scientific concepts, urban ecosystem health is not defined as a standard quantitative measurement, but rather described as what healthy urban ecosystems should or should not contain. This statement reflects the vagueness of urban ecosystem
health. Based on the acknowledged need to sustainably integrate reasonable human demands and the ecosystem's ability for renewal, the inclusive factors of a healthy urban ecosystem can be drafted from both the human and ecological dimensions, as shown in Fig. 1. 4. 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 range of acceptable values for those states (Cabezas and Fath, 2002). In one approach, the features of the impacted ecosystem are compared with one considered undisturbed or pristine (Rapport, 1992, 1993; Calow, 1993), without any human disturbances (Waltner-Toews, 2004). The difficulty is in finding commensurate undisturbed systems. The problem is even more acute when dealing with urban ecosystems. On natural systems the human disturbance is subsequent to its natural condition, whereas urban ecosystems are artificially constructed. Therefore, it is much more difficult to assess the intact condition of urban ecosystems. In fact, there does not exist an absolute or fixed standard of the urban ecosystem because of the uncertainty caused by the complexity and openness of the urban ecosystem as well as changing human needs, targets, and expectation of urban
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Table 2 Typical applications of urban ecosystem health concept. Originator WHO
Conception of urban ecosystem health
Defined city health as a system “that is continually creating and improving those physical and social environments and expanding those community resources which enable people to mutually support each other in performing all the functions of life and in developing to their maximum potential” (Hancock and Duhl, 1988). Int. Dev. Stated that urban ecosystem Research Centre health includes not only the health and integrity of the natural and built environment, but also health of urban resident and whole society (Colin, 1997). Hancock Based on the relationship among economy, environment, and society, put forward the conceptual framework of healthy cities. And also summarized the six related elements of healthy urban ecosystem, including 1) population health and distribution, 2) societal wellbeing, 3) government management and social equity, 4) human habitat quality and convenience, 5) natural environment quality, and 6) impact of the urban ecosystem on the larger-scale natural ecosystem (Hancock, 2000). Guo Understood urban ecosystem health from both ecological and socioeconomic view, in which the former means the complex natural-economicsocial urban ecosystem is stable and sustainable and resists external adverse factors, while the latter means the urban ecosystem sustainably provides ecosystem services for urban resident (Guo, 2003).
Main feature Pursues economic development and urban ecosystem to improve human health. Urban ecosystem integrates healthy lifestyles, environment, and society.
Urban population under certain socioeconomic, cultural, and political conditions should be emphasized.
Urban ecosystem health is similar with urban sustainability, which can be represented by the common focus, only the former pay more attention to the human health.
Healthy urban ecosystems should possess multiple characteristics from various aspects, including vigor from aspect of external representation, diversity and harmony from structural aspect, and regulation and efficiency from function aspect.
ecosystem over time (Odum, 1989). Under this circumstance, suitable alternative approaches are needed to establish health standards of urban ecosystems. Based on extensive case studies, the International Development Research Centre and World Health Organization have put forward criteria for what constitutes a healthy urban ecosystem, such as ecological sustainability, social equity, public health, and effective community management (Hancock, 2000; WHO Regional Office for Western Pacific Region (WPRO), 2000). Their approach is similar to that of finding a pristine natural ecosystem for assessing ecosystem health in that the standard range of the urban ecosystem health indicators is based on conditions of a comparative eco-city, garden city, or those with excellent performance in environmental protection (Guo et al., 2002; Sang et al., 2006; Guan and Su, 2006; Peng et al., 2007). Taking Guo's research as an example (Guo et al., 2002), the standard of each indicator is divided into five grades, in which the reference of the first (best) grade
is defined based on the eco-city's planning or suggested value from related literature or national standards, while that of the last (worst) grade is based on the worst value observable in a Chinese city for each standard. And then, based on the two established anchor points, the remaining three middle grades are determined through interpolation. For example, the indicator “treatment rate of urban domestic waste water”, uses a five grade standard ranging from very healthy, relatively healthy, critically healthy, relatively unhealthy, and ill, defined as 100%, 95%, 70%, 50%, and 30%, respectively. As shown with the urban ecosystem health concept, the urban ecosystem health standard should integrate ecological, socioeconomic and human health perspectives. However, it means that the urban ecosystem health standard is determined by simultaneously considering the all three aspects, which are all influenced by human activities. Therefore, the urban ecosystem health standard is a kind of human interest or value preference (Ryder, 1990), for the urban ecosystem is established, constructed, impacted, managed and utilized by humans. Even though the researchers try to study the natural and ecological attributes of the urban ecosystem in view of the geographical, thermodynamic, or biophysical perspectives, it is still impossible to remove the human imprint and subjectivity when it comes to the health standard of urban ecosystems. Consequently, the standard of urban ecosystem health may alter with time and changing subjective human needs, which means the health evaluation results for the same ecosystem could be quite different in different time or under different human interests. One approach is to design standard values for urban ecosystem health indicators now and redesign them when human expected objectives change over time, e.g., setting the standard of indicator “treatment rate of urban domestic waste water” in critically healthy range as 70% in 2005, which might be raised to 80% in 2015 if new information about water borne illness is available. Another option is to consider a more progressive approach in which health standards automatically update over time. A dynamic standard could be established using an optimal reference set according to the indicator values of different assessed urban ecosystems through set pair analysis (Su et al., 2009b). The latter is theoretically more defensible, but practically more difficult to implement.
5. 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 connect the theoretical ecological background with related political practical requirements (Müller and Wiggering, 1999; Müller et al., 2000; Müller and Lenz, 2006). Since multiple indicators from aspects of social, economic, ecological, and human health are all considered where the ecological meaning of each individual indicator is ambiguous (unlike the indicators of vigor, organization and resilience for the natural ecosystems which have their own fixed measurement and sufficient ecological information), then certain mathematical approaches are required to deal with the indicator information to get a comprehensive and clear assessment of the urban ecosystem health status.
5.1. Indicators Considering the different views of urban ecosystem health as well as various priorities and objectives, scientists have developed several indicators (Table 3), which directly focus on the topic of urban ecosystem health, and others address related research, e.g., Harpham (1996), Takano and Nakamura (1998), and WPRO (2000).
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Fig. 1. Basic inclusive factors of urban ecosystem health.
Except for the main urban ecosystem health indicators mentioned in Table 3, certain explanations should be provided for clarity, such as: (1) In addition to the WHO (Takano and Nakamura, 1998; WPRO, 2000), other organizations, like United Nations Centre for Human Settlements, International Institute for Sustainable Development, and the International Joint Commission, have made efforts to set up indicators of urban sustainable development, which are correlated with urban ecosystem health indicators (Guo, 2003). (2) Besides the conceptual model of PSR (pressure–state–response) (Zeng et al., 2005), others have also been applied to organize urban ecosystem health indicators, e.g., DPSEEA (driving force– pressure–state–exposure–effect–action) model, based on Spiegel et al. (2001), which defined the health indicators at the individual, household, and neighborhood levels in the urban ecosystem. (3) Some set up the indicator framework from the features of the urban ecosystem health, like vigor, function, and structure (Guo et al., 2002; Su et al., 2009b; Liu et al., 2009), while others organize the urban ecosystem health indicators in view of inclusive urban subsystems, e.g., natural, economic and social subsystems (Zhong and Peng, 2003; Wen and Xiong, 2008; Rong, 2009), and ecological, agricultural, production and living land-use subsystems (Zeng et al., 2005). (4) In addition to focusing on the spatial difference within urban ecosystems (Hu et al., 2005; Tian et al., 2009), related indicators emphasizing the temporal dimensional characteristics are also established to denote the urban ecosystem health development over time (Zhang et al., 2006). Even though different frameworks, including subsystem models (e.g., Guo et al., 2002), PSR (e.g., Zeng et al., 2005), DPSEEA (e.g., Spiegel et al., 2001), distance index and coordination index (Hu et al., 2005), and emergy (embodied energy) synthesis (e.g., Liu et al., 2009; Su et al., 2009b), are used to establish the urban ecosystem health indicators, certain common characteristics among these various approaches still can be found. First, all the frameworks pursue the same objective, i.e., choosing and organizing multiple indicators in a systematic integrated way to make sure the indicators can represent the character of the urban ecosystem as comprehensively as possible in a systems perspective. Second, factors from aspects of ecological state, economic development, social progress, and population health are included within the system perspective, which determines that much data are required from multiple subjects and fields, e.g., geographical and physical measure, ecological simulation, social assessment, trade information, economic and epidemiological statis-
tics. Third, amongst all the factors, human requirements are always emphasized. Fourth, considering the states and physical driving mechanisms, the indicators tend to be easy to understand and regulate, which is convenient and beneficial for the practical urban ecological management. 5.2. Mathematical models Besides the conceptual framework to establish a reasonable indicator system, additional mathematical models are usually needed to treat and process the indicator data to represent the internal characteristics of urban ecosystem health and further satisfy a health assessment. When considering the current mathematical models of urban ecosystem health assessment, they can be summarized into two categories: 1) understanding the urban ecosystem health's character and 2) dealing with problems emerge during the urban ecosystem health assessment. Concretely speaking, modeling urban ecosystem health is difficult due to certain features such as fuzziness, hierarchy, and multiple-attributes, and then such corresponding methods as fuzzy synthetic assessment model (e.g., Guo et al., 2002; Zhou and Wang, 2005; Fan, 2006; Tao, 2008), fuzzy optimal assessment model (Zeng et al., 2005; Lu et al., 2008), fuzzy assessment model combined with analytic hierarchy process (Luo, 2006), set pair analysis (Su et al., 2009a), relative vector comprehensive assessment model (Sang et al., 2006), attribute theory model (Yan, 2007; Wen and Xiong, 2008; Rong, 2009), and catastrophe progression method (Wei et al., 2008) are applied. Taking Guo's paper (2002) as an example, the urban ecosystem health problem was designed as a fuzzy synthetic assessment model: H = W × R, where H is the final urban ecosystem health status matrix; W is the weights matrix for the five assessment factors (vigor, organizational structure, resilience, ecosystem services maintenance, and population health), i.e., W = (w1, w2, w3, w4, w5); and, R is the relative membership degree matrix to assign each factor a standard grade (very healthy, relatively healthy, critically healthy, relatively unhealthy, and ill), represented as follows: 0
R11 B R21 B R=B B R31 @ R41 R51
R12 R22 R32 R42 R52
R13 R23 R33 R43 R53
R14 R24 R34 R44 R54
1 R15 R25 C C R35 C C R45 A R55
ð1Þ 0
1 r1j B r2j C C in which Rij = W1′ W2′ … Wk′ × B @ … A, and rij means the rkj membership degree of the ith (i = 1, 2, 3, 4, 5) assessing index to
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Table 3 Main urban ecosystem health (UEH) indicators. Person and reference
Indicators
Harpham (1996) compared urban and rural health in Gambia.
Pros/cons
Economics Environment Public health statistics Health-seeking behavior Health expenditure Nutrition The World Health Organization: Internal character (1) Building from Healthy Cities Project, proposed 79 healthy External performance urban ecosystem indicators in 1996 Progress (WHO Regional Office for Western Pacific Region, 2000). Management and monitoring Proving service Budget and finance Community service (2) Further developed 459 indicators of a healthy urban ecosystem in 1998 Human health (Takano and Nakamura, 1998). Urban infrastructure Environmental quality Human housing and living environment Community's role and action Living pattern and prevention performance Health care and environmental sanitation service Education Employment and industry Income and domestic consumption Local economic and demography statistics Vigor: GDP per capita Guo et al. (2002) taking the classic framework from Organizational structure: the third industry ratio (Mageau et al., 1995; Rapport et al., 1998b) established UEH Resilience: treatment rate of urban domestic sewage indicators using 24 factors. Ecosystem services maintenance: comprehensive environmental quality index Population health: mean human life time
Zhong and Peng (2003) organized 30 UEH indicators using natural, economic and social subsystems framework.
Zeng et al. (2005) established an indicator system within the PSR (pressure– state–response) framework under ecological, agricultural, production and living subsystems.
Hu et al. (2005) put forward indices to measure the gap between urban developmental status quo of each factor and certain development objectives.
Su et al. (2009b) established a biophysical UEH indicator system using 17 related emergy-based indices.
Liu et al. (2009) developed an emergy-based UEH indicator integrating vigor, organizational structure, resilience and function maintenance.
Based on public health statistics, indicators are available and easily understood; under-emphasizes economic and cultural factors.
Human demand and community role are emphasized, through which the urban ecosystem are expected to be more suitable for human development. The indicator system is complicated hindering data availability and reliability.
Framework of vigor, organizational structure, resilience, ecosystem services, and population health has successful tradition and has been widely used in UEH assessment. Whether the indicators are sufficient and typical enough is an open research question. Natural: atmospheric and water quality The traditional method of dividing Economic: GDP per capita, energy consumption per unit urban ecosystem into natural, economic and social subsystems is GDP easily acceptable, but the ad hoc Societal: house area per capita, employment rate nature of the concrete indicators questions the overall scientific basis. Ecological: forest coverage rate and afforestation area per Using different land-use capita subsystems in urban ecosystem is Agricultural: farmland area per capita and grain meaningful for practical urban production per area planning and construction, but the Production and living: population density and house area PSR model's ability of reasonably per capita reflecting ecosystem health state is questioned to some degree. Distance index The indices are useful to describe the spatial difference with urban Coordination index ecosystem, but confirming the factors in urban ecosystems and collecting enough data is difficult. Vigor: emergy density Based on emergy synthesis, UEH is Structure: emergy diversity assessed on a biophysical index foundation. However, it is difficult Resilience: carrying capacity density based on renewable to put the assessment result into emergy practical management and Ecosystem service: regulation in an easily environmental loading ratio understanding way. Population health: emergy investment ratio net emergy yield ratio By establishing an integrated environmental loading ratio emergy-based indicator, it is clear emergy exchange ratio and simple to assess UEH status. emergy density However, whether the single
the jth standard (j = 1, 2, 3, 4, 5); W′k means the weights of the kth indicator under corresponding assessment factors. Based on these values, the relative membership degree matrix, in view of each factor and the comprehensive health state, marked as Rij and H respectively, can be calculated to reflect the urban ecosystem health levels. These levels are classified as very healthy, relatively healthy, critically healthy, relatively unhealthy, or ill, according to the largest membership degree value.
On the other hand, to address emergent problems within the urban ecosystem health assessment, related models are developed to reduce the influence of the existing problems on the final results. For example, urban ecosystem complexity and its impact on decisionmaking uncertainty were the main features of an urban ecosystem health assessment model by Shi and Yan (2007). And according to the problem of information loss when using the traditional assessment methods, a matter element model was developed (Dai et al., 2007; Liu
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et al., 2007). Choosing Dai's study as an example, the urban ecosystem health was defined by a matter element model as R = (M, C, X), usually defined as: 2 6 R=4
M
C1 C2 ∧ Cn
3 X1 X2 7 ∧ 5 Xn
ð2Þ
where M is the assessed object (urban ecosystem health state of a certain city, which can be divided into five levels, e.g., very healthy, relatively healthy, critically healthy, relatively unhealthy, and ill), C is the characteristic of M according to the specific research question (such as ecosystem health indicator), and X is the value of C. According to the original values of each health indicator and their designed standard values for each health grade, the relative relatedness between the actual urban ecosystem health status and each health standard can be obtained, from which the final health levels of the urban ecosystem can be confirmed, according to the largest relatedness principle. Retaining all original information in the model, the assessed values and the standards in different grades were confirmed to understand the urban ecosystem health level. The weights of various indicators, which represent their relative importance for integrated urban ecosystem health status, will have great impact on the final assessment results. The problem of assigning the indicator weights is still an open research question. There are mainly two kinds of methods to define the indicator weight, i.e., subjective or objective methods. The widely used subjective method usually defines indicator weights according to human judgment like experts' or professional experiences, e.g., the Delphi method and the analytic hierarchy process method (Yan et al., 2007; Bi and Guo, 2007). The objective approach is based on the statistical data analysis such as entropy (Zhou and Wang, 2005; Shi and Yan, 2007), factor analysis (Guan and Su, 2006), main component analysis (Lu et al., 2008), standard deviation analysis methods (Sang et al., 2006). Although the objective method seems and tries to be more scientific, sometimes it does not work well in practice, for it ignores the experts' and professional experiences which sometimes are applicable and useful for the actual management of urban ecosystems. Regardless of the conceptual approach for organizing indicators or the accompanying mathematical model, the data requirements are quite high and diverse, including characteristics of the environment, ecology, economy, society, and health. When it comes to the data requirements for assessing a specific urban ecosystem one has to integrate simultaneously multiple factors. Even for models that employ different methods or objectives, the data requirements are similar including information at scales from city to regional, such as statistical yearbooks, annals of local history, socioeconomic development reports, environmental quality reports, industrial activity information, natural geographical conditions, etc. And with so much macroscopic socioeconomic data included in the models, there is a tradeoff which limits precision often at the expense of generality and predictability (Levins, 1966). 6. 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 (Guo et al., 2002), Nanjing (Luo, 2006), Wuhan (Su et al., 2009a) and Chongqing (Yan, 2007), as well as coastal cities like Ningbo (Hu et al., 2005), and cities with good
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environmental quality like Xiamen (Su et al., 2009a) and Dalian (Dai et al., 2007), etc. Attention has also been paid to entire metropolitan regions (Bi and Guo, 2007) in that future development trends will influence the whole surrounding ecosystem (Fan, 2006; Yan et al., 2007). It can be concluded that the main aspects of urban ecosystem health assessment such as the economic, ecological and social performance have all been considered as influential factors for choosing the cases, taking into account the sufficiency and availability of data. In addition to various spatial scales, the emphasis of temporal scale can also differ within the case studies, including urban static form, comparison of this static form among different cities, or the temporal change analysis for a chosen urban ecosystem. The latter primarily focuses on the cities' developmental direction after reviewing trends in the urban ecosystem health status. For example, Yan et al. (2007) assessed the urban ecosystem health status in the New District of Northern Chongqing City based on established attribute theory model; the results showed that evaluated district in 2003 was rated as moderately healthy. Bi and Guo (2007) compared the urban ecosystem health states of eight cities in the Yangtze River Delta in 2004 by using analytical hierarchy process. The result indicated that the urban ecosystem health ranging from well to weak is Shanghai, Suzhou, Hangzhou, Nanjing, Wuxi, Ningbo, Changzhou, and Yangzhou. And choosing Beijing in 1996–2003 as a case, Zhou and Wang (2005) conducted the urban ecosystem health assessment on temporal dimension through fuzzy comprehensive evaluation method. The results showed that the relative urban ecosystem health status of Beijing city roughly increased from 1996 to 2003. Although with different emphases, all the case studies attempt to give the integrated health status of the urban ecosystem and develop more detailed analysis, concretely on the multiple factors of urban ecosystem health, such as the vigor, structure, resilience, ecosystem service maintenance and population health. The results provide insight on how to improve the important economic, social and ecological indicators. Regardless of the conceptual framework or mathematical models, the final recommendations to improve the urban ecosystem health condition are related to the macroscopic perspective of socioeconomic development, environmental management and ecological construction so that it is possible to link with practical urban planning and management.
7. 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 ecosystem health, and the health standard is also imprinted by human value preference. For example, the indicator “standard-reaching rate of water quality of potable water source”, is only important as meeting a human service not as a natural ecosystem function. When we review the development of urban areas (Fig. 2), the role for human value-orientation is always the dominant force for health assessment. Cities originated according to human needs such as commercial trade or military defense, and then as the city expanded, human activity reformed the urban ecosystem mainly based on comparing its status quo (in fact, the urban ecological process existed all the time and influenced the urban ecosystem status quo). Meeting human needs was the first priority. Eventually, when the damaged urban ecosystem also threatened human life, this compelled concern over ecosystem health.
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Fig. 2. Influencing factors of urban ecosystem health's generation.
By assessing ecosystem health, which combines analysis with societal values, a diagnosis of probable consequences of current behavior and options for changing course becomes available (Rapport et al., 1998a). In other words, the human desire for the urban ecosystem's mission must be admitted and emphasized by the concept of urban ecosystem health. This makes it vital to be able to understand and integrate human values into an ecological framework, which depends on the scientific progress of many areas. Coupling with the value-driven and goal-oriented character of urban ecosystem health and the site-specific ecological features, a standard, independent, reference state for urban ecosystem health does not exist. While the search for such a standard continues, other more flexible approaches have been pursued that allow for a comparison between different existing urban ecosystems or the changing trends over time for the same area (Hong and Fath, 2009). Both approaches are helpful for finding the limiting factors of urban ecosystems and improving their health levels. As a goal, “health” begs for indicators and models to measure the success of that goal. As for the urban ecosystem health indicators, methodological issues still need to be resolved to confidently integrate social, economic, ecological, resource, environmental, human health,
and other factors together (Dai et al., 2007; Guan and Su, 2006). Certainly more suitable indicator frameworks or conceptual models are needed to organize the multiple indicators in a more ordered and regulated pattern. Conceptual models focusing on the macroscopic system performance have easier access obtaining data and the results are more conveniently understood and linked with management. In some mathematical models (e.g., emergy synthesis, network analysis) used to analyze the inner features (e.g., the biophysical foundation) of the urban ecosystem, the indicator systems stem from systematic foundations but the data are more difficult to obtain and the results are harder to communicate to practical urban ecological regulation. An effective bridge between holism and communication is yet to be established. Instead of perceiving the urban ecosystem assessment as an instantaneous measurement of the health state according to the indicators and models, it is suggested to conceptualize the urban ecosystem health as a process (Boothroyd and Eberle, 1990) and regard the various measures of economic development level, social progress, environmental quality, and population health as outcomes reflecting the previous effort. It is believed to give us much more hope and prospect. That is exactly the role of urban ecosystem health assessment:
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1) discover the comprehensive health status by integrating multiple factors, 2) diagnose the limiting factors and confirm the developmental orientation of certain urban ecosystem through spatial and temporal analyses; and, 3) test the effect of management measures by investigating urban dynamics. Based on this perspective, perhaps the dynamic measure of how forcefully, effectively, and consistently the urban complex responds to changes in human and societal health and well-being and the integrity of natural ecosystems is most valuable (McMullan, 1997). And beginning from this idea, the cultural factor should be considered more in urban ecosystem health assessment, since culture influences urban development over the long-term, and these important drivers are more perceptually invisible and statistically undetectable than other factors. Research in urban ecosystem health assessment is driven by the rapid pace of urbanization and the increasingly deteriorated urban environment it entails. This is particularly true for regions experiencing large migration from rural to urban areas such as in China. This is one reason there has been so much focus recently on developing and applying these ideas in China, in spite of the fact that the first urban health study was only started in 1994 (Peng et al., 2007). Over the past few decades there has been much progress in the conceptual frameworks, the methodologies, the models, and applications to specific case studies. As a result, we have a much better understanding of urban ecosystem health particularly as a spatial comparison between different urban ecosystems. Future research will focus more studies on the temporal scale to analyze the dynamic trends and projecting possible development scenarios. Also, studies on smaller scales like the community and the sub-region can be developed with detailed geographical information and complemented with stakeholder questionnaires to get more specific ecological and socioeconomic data and also make the research more practical and beneficial for urban well-being. 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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