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7
The Urban Ecology of Metropolitan Phoenix: A Laboratory for Interdisciplinary Study

Charles L. Redman


Because an ever-increasing proportion of the global population resides in cities, it is essential to improve understanding of the recursive relationship between population and the environment. Toward that end, seven years ago we undertook a comprehensive study of the long-term urban ecology of central Arizona’s rapidly growing urban region. Called the Central Arizona–Phoenix Long-Term Ecological Research project (Grimm et al., 2000; Grimm and Redman, 2004), it is part of the Long Term Ecological Research Program, a program of 26 sites sponsored by the National Science Foundation (Hobbie et al., 2003). In addition to the challenges of investigating ecological patterns and processes over long temporal and broad spatial scales, an urban system involves the complexities of intense human participation. Associated with human participation in the system are economic and social drivers, radically altered land cover, flows of materials, and the impacts of a built environment. As in traditional long-term ecological research, interdisciplinary collaboration of ecologists, biogeochemists, earth scientists, and climatologists is fundamental, but added to the mix are sociologists, geographers, economists, political scientists, urban planners, anthropologists, civil and environmental engineers, mechanical and chemical engineers, and many community partners who share the zeal for understanding the urban ecosystem. Although we realize there is a significant difference among the perspectives needed to understand an urban system, in contrast to a system in which human participation is relatively modest, we think that lessons learned through wider collaboration will prove useful to all long-term ecological research programs and to



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Population, Land Use, and Environment: Research Directions 7 The Urban Ecology of Metropolitan Phoenix: A Laboratory for Interdisciplinary Study Charles L. Redman Because an ever-increasing proportion of the global population resides in cities, it is essential to improve understanding of the recursive relationship between population and the environment. Toward that end, seven years ago we undertook a comprehensive study of the long-term urban ecology of central Arizona’s rapidly growing urban region. Called the Central Arizona–Phoenix Long-Term Ecological Research project (Grimm et al., 2000; Grimm and Redman, 2004), it is part of the Long Term Ecological Research Program, a program of 26 sites sponsored by the National Science Foundation (Hobbie et al., 2003). In addition to the challenges of investigating ecological patterns and processes over long temporal and broad spatial scales, an urban system involves the complexities of intense human participation. Associated with human participation in the system are economic and social drivers, radically altered land cover, flows of materials, and the impacts of a built environment. As in traditional long-term ecological research, interdisciplinary collaboration of ecologists, biogeochemists, earth scientists, and climatologists is fundamental, but added to the mix are sociologists, geographers, economists, political scientists, urban planners, anthropologists, civil and environmental engineers, mechanical and chemical engineers, and many community partners who share the zeal for understanding the urban ecosystem. Although we realize there is a significant difference among the perspectives needed to understand an urban system, in contrast to a system in which human participation is relatively modest, we think that lessons learned through wider collaboration will prove useful to all long-term ecological research programs and to

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Population, Land Use, and Environment: Research Directions others interested in integrating social and environmental perspectives (Redman, Grove, and Kuby, 2004). The detailed examination of a human-dominated urban ecosystem has led us to question how and to what extent the patterns and processes in human-dominated systems require qualitative changes to traditional ecological theory (Collins et al., 2000). So far, most ecologists working in cities have relied on the view of humans as disturbing forces and equated urban environments with extreme conditions. Assigning the residual values from traditional analyses to the human component of the ecosystem appears to work, up to a point, just as the Ptolemaic explanation of the solar system could be elaborated to fit empirical observations. Rather than elaborate on what may be fundamentally insufficient, at some point it is more effective to reconceptualize the theory to better explain the patterns. This strategy calls for integrating new elements into ecological theory. Certainly not all ecological theory must be refined, nor will all changes be radical, but we think that the pervasive presence and impact of humans on all global environments, not just urban ecosystems, requires one to be open to change. This chapter reviews the interdisciplinary approaches of the Central Arizona–Phoenix Long-Term Ecological Research project toward the interaction of land use change, population, and environment. It continues with a review of two related projects: Agrarian Landscapes in Transition, which examines the relationship between urban growth and regional transformation, and Networking Urban Ecological Models, which integrates data from several public agencies to solve problems of mutual interest to academic and nonacademic researchers. This review is a stepping-off point for a brief discussion of our efforts to work with local land managers and public officials and a new project that is explicitly aimed at improving the application of science to decision making. The chapter concludes with a discussion of how these projects have led to a refinement in the conceptual approach being used and suggests how our observations direct us to areas in which ecological theory should be reexamined. CENTRAL ARIZONA–PHOENIX LONG-TERM ECOLOGICAL RESEARCH The overarching goal of the broader Long-Term Ecological Research program is to understand patterns and processes that underlie long-term changes in ecosystem structure and function. For an urban ecosystem, success in achieving this goal also hinges on understanding the complexities of intense human participation in the system—with attendant economic and social drivers, radically altered land cover, accelerated cycling of materials, and heretofore unresearched ecological impacts of a built environment (Redman, 1999a). The particular challenge for our project is to conduct a

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Population, Land Use, and Environment: Research Directions comprehensive study of central Arizona, one of the most rapidly urbanizing regions in the country, which includes Phoenix and four of the state’s five next-largest cities: Mesa, Glendale, Scottsdale, and Chandler. To address this challenge, our researchers have been committed to interdisciplinary collaboration from project inception, under the broad umbrella of earth, life, and social sciences; engineering; and planning and policy (Grimm and Redman, 2004). The Phoenix metropolis, comprising over 20 municipalities, is situated in a broad, alluvial basin where two major desert tributaries of the Colorado, the Salt, and Gila rivers, converge (see Figure 7-1). The basin, dotted with eroded volcanic outcrops and rimmed by mountains, once supported a vast expanse of lowland Sonoran desert and riparian vegetation. The plant association of the upper Sonoran life zone (on outwash slopes and pediments) is the saguaro-paloverde, with creosote bush dominating in low- FIGURE 7-1 Boundaries of the Central Arizona–Phoenix Long-Term Ecological Research site (outlined) encompassing an area of 6,400 km2.

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Population, Land Use, and Environment: Research Directions land, flatter areas. The study site (6,400 square kilometers, km2) includes the rapidly expanding Phoenix area, along with its agricultural and desert surroundings. The region’s population has increased by 47 percent since 1990 to over 3.2 million people (U.S. Census Bureau, 2000). Although the population growth rate was faster early in the twentieth century, numerically the growth of Phoenix has occurred mostly in the second half of the century (see Figure 7-2). Initially, that expansion consumed mostly farmland, but the newest housing has primarily replaced desert land, leading to spatial variation in the extant vegetation and the structure of residential landscapes. Reliance on irrigation to create and sustain agricultural production and urban landscapes hastened the sharp contrast between managed landscapes, with their exotic plants, and undeveloped desert, with its native vegetation (Hope et al., 2003). This process generated a frequently quoted newspaper series, which claimed that urban growth was consuming “an acre an hour” of desert lands. The costs of extending the water infrastructure and other social factors have resulted in a remarkable uniformity of residential lot size across the metropolitan region that defies national patterns (Knowles-Yánez et al., 1999; Gammage, 1999). Construction of local reservoirs and the Central Arizona Project canal (Kupel, 2003), the devel- FIGURE 7-2 Maricopa County population and population rates of change by decade for Maricopa County and the United States, 1910-2000. Maricopa County population figures roughly correspond to the CAP LTER figures.

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Population, Land Use, and Environment: Research Directions opment of air conditioning, and the widespread use of motor vehicles have been triggering factors, each accelerating the region’s growth. We began the project with an overarching research question that continues to guide us today: How do the patterns and processes of urbanization alter the ecological conditions of the city and its surrounding environment, and how do ecological consequences of these developments feed back to the social system to generate future changes? This question focuses our thinking on the interaction within and between the ecological and human domains in the context of a changing, expanding urban metropolis. For us, the process of urbanization is at its heart one of land use change, reflecting the transformation of either the Sonoran Desert or irrigated farmland to municipal or industrial use. Increasing land surface coverage by buildings and roads as well as transformed landscapes, the redesigned hydrological system, the spread of impervious surfaces, and the transformation of habitats characterize this process. Although the study of change is a strong element of our approach, we are also concerned with relatively stable patterns and aspects of the system. Although dozens of researchers have investigated these issues, we are only a fraction of the way toward our goal. While identifying and monitoring the ecological consequences of urbanization, we have only begun to understand how these consequences influence the social system and generate future changes. Our research question must also address a range of scales, with the focal scale being the whole ecosystem, but with interesting questions asked at lower and higher levels of a time-space scale hierarchy. In some cases, feedbacks may occur at scales different from the primary scale the research addresses. In describing our findings, we refer to the following scales: Individual land use patch types: these can be land use or land cover patches or even smaller units (i.e., households, lots, parks). At this scale, our research has primarily characterized ecological and social patterns. Mosaics of patches: here the focus is on the relationships among individual patches. Whole ecosystem: several efforts have been made to describe ecological conditions without referring to the heterogeneity in the urban ecosystem, but by treating the system as a “black box.” The central Arizona–Phoenix ecosystem in a regional context: the ecosystem interacts with its surroundings in quantifiable ways. For example, the city can be seen as a source or sink for elements. Urbanizing central Arizona in a global context: Can lessons learned in central Arizona–Phoenix be transferred to other dryland regions internationally?

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Population, Land Use, and Environment: Research Directions The hierarchical, patch dynamics model developed for this project (Wu and David, 2002) provides a framework for integrating different kinds of models (e.g., population dynamics, ecosystem processes, land use, and land cover change) across these different spatial scales. Such a framework is necessary because both ecological and socioeconomic patterns and processes in any urban landscape occur on a variety of scales, and hierarchical linkages among scales often significantly affect the dynamics and stability of urban development. The patch dynamics approach focuses not only on the spatial pattern of heterogeneity at a given time, but also on the pattern’s change over time and its impact on ecological and social processes. Because cities are both expanding and changing within their boundaries, the dynamic aspect of this approach is crucial to a complete understanding of urban ecological systems. LAND USE AND LAND COVER CHANGE An improved understanding of past, current, and future land cover and land use transformations is essential to investigating the urban ecosystem and, in particular, its relationship to population and environment. Crucial to the patterns we witness is the region’s population growth. Having acknowledged the central role that the growing presence of humans plays in these changes, we turn our attention to what governs the perception of the current patterns and of the implications of each alternate perception. Land use change ensues from human decision making that occurs in the context of social institutions and is influenced by drivers that range from economics and cultural traditions to expected economic or ecological benefits. It is vital to recognize that broad-scale social and environmental conditions, as well as local ecological and human legacies, constrain and sometimes guide the range of possible trajectories for land cover and land use. At an earlier workshop on integrating social science into the Long-Term Ecological Research network (Redman et al., 2004), we developed a conceptual model to articulate these diverse approaches. At the center of the model and at the core of integrated inquiries is a set of interactions, the foremost being land use change (see Figure 7-3). We suggested that to implement this model requires three iterative stages of research: (1) collecting background information on “external” biogeophysical, political, economic, and demographic conditions; (2) describing and monitoring changes in both ecological and social patterns and processes that drive the system we define; and (3) investigating the nature of, and monitoring changes in, interactions resulting from the patterns and processes. Land use change is probably the most direct indicator of system change of those indicated. Land use change alters the hydrological system, air movement, settlement spread, trophic communities, primary productivity, land surface char-

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Population, Land Use, and Environment: Research Directions FIGURE 7-3 Conceptual framework for long-term investigations of social–ecological systems from Redman, Grove, and Kuby (2004). acteristics, and the overall ecological footprint of the city. Open-ended questions, such as determining the level at which excessive urban growth impacts water supply, air quality, or agricultural viability, are of paramount importance to the citizens of central Arizona. At what point in the urbanization process do cities contribute to, or become susceptible to, catastrophic vulnerability such as infrastructure inadequacy, transportation gridlock, air pollution extremes, geologic hazards, and health risks? Drawing on extant resources for the analysis of land use change has allowed us to proceed quickly and provide summary analyses that are of immediate interest to our local collaborators. Nowhere is that scenario more apparent than with our Historic Land-Use Project. We drew on available aerial photography, satellite imagery, and municipal and county records from 1912, 1934, 1955, 1975, 1995, and 2000, and, with modest additional analysis, developed maps of broad land use categories (agricultural, desert, recreational, and urban) that provided a context for many of our subsequent studies (see Figure 7-4). Local media and government agencies have also used these maps, giving our project early recognition. This historical analysis of land use has revealed that one aspect of spreading urbanization and the dominant land use transition has changed over the past century. Phoenix and neighboring municipalities began a decade after the Civil War as a series of scattered communities in a broad expanse of farmland. The amount of land in agrarian use continued to increase rapidly from 1912 to 1934, increased more slowly from 1934 to 1975 (expanding at the periphery as land was converted to urban at the core), and declined

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Population, Land Use, and Environment: Research Directions FIGURE 7-4 Land use maps of central Arizona–Phoenix.

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Population, Land Use, and Environment: Research Directions

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Population, Land Use, and Environment: Research Directions from 1975 to 2000. Until 1975, the urban fabric expanded to adjacent land, soon transforming the discrete communities into a continuous metropolitan zone. Although this spread into adjacent farmland continues today, most new developments since 1975 have occurred on former desert lands, often some distance out from the nearest residential area. This shift—from urban residential development on former farmland, in which water once used on the farm was diverted for municipal uses, to development in pristine desert areas farther from canal and surface water distribution systems—has profoundly impacted water policy and real estate opportunities (Knowles-Yánez et al., 1999; Gammage, 1999). Interestingly, the need to build expensive infrastructure to service these new residential developments has led to the construction of housing on small lots in a relatively compact fashion. In a Brookings Institution study of 13 large U.S. cities, Phoenix, surprisingly, was found to be one of two cities that became more compact between 1970 and 2000 (Fulton et al., 2001). New, and often very expensive, homes are being built on lots that are the same size or even smaller than the lots of modest homes near the center of the city. This pattern has resulted in a relatively uniform density across virtually all of the metropolitan area. 200-POINT SURVEY Given the broad expanse of the central Arizona–Phoenix ecosystem—6,400 km2 defines the study area, and the watershed is several times that size—and its spatial heterogeneity (Luck and Wu, 2002), characterization of the landscape at a finer scale than the Historic Land-Use Project would require a major field survey and a sampling strategy. To ensure widespread spatial distribution and allow more intense sampling of the urban core, we used a dual-density, tessellation-stratified random sampling design (see Figure 7-5). This design, which established 204 sampling points randomly selected in a grid cell of 5 by 5 km (with outlying points established in every third grid cell, hence the dual density), allows us to measure numerous environmental variables in a 900 m2 plot. Among the collected data at each plot is information on meteorology, soil chemistry, surface characteristics, pollen, arthropods, bird abundance and diversity, woody plant genera, and above-ground biomass. In addition, because the entire data set is georeferenced in a series of ArcInfo files, we can superimpose social data (from the census, the Historical Land-Use Project, and other available information) on this extensive snapshot of the central Arizona–Phoenix ecosystem, which we intend to repeat every five years. Although data analysis from our first (spring 2000) application of the 200-point survey design is ongoing, already we have discerned a difference in potential driving and controlling variables between urban plots and

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Population, Land Use, and Environment: Research Directions FIGURE 7-5 Central Arizona–Phoenix study area boundary with major freeways and 200-point survey locations (white triangles). desert plots, as well as within socioeconomic divisions of the urban plots. A basic finding from our survey of how human activities inadvertently alter the environment is that while soil nitrate concentration is spatially auto-correlated in the desert plots, as one would expect from traditional ecological experiments, no such spatial relationship exists for the urban plots (Hope et al. no date). We think this difference reflects the extent to which human management has introduced heterogeneity into the soil’s chemical properties at a scale much smaller than that found in deserts where non-anthropogenic processes dominate. One example of how explicit human choice can lead to an association between social and ecological variables is the positive correlation of the richness of woody vegetation (recorded to genus), a measure of plant diversity, with median family income (derived from the 2000 census) for the urban plots (see Figure 7-6; Hope et al., 2003). Although this intriguing pattern is a correlation and does not necessarily imply causation, the finding leads us to new research questions about the mechanisms by which humans control their environment. The data indicate that plant diversity (resulting from landowner choice) increases with family income, yet this relationship appears to level off when income

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Population, Land Use, and Environment: Research Directions models, regulatory institutions, and economic dynamics at the time, people responded to these events by transforming one or more domains of the local coupled system. Box 7-1 presents a series of triggering events as they drove changes during the three periods. We apply the term “events” broadly, encompassing both challenges to the system and opportunities for advance, as well as those that emanated from within or derived from outside the region. At this point in our analysis, we have focused on events and opportunities that are easily recognizable to us and probably also to many of the residents living during those times. We expect that there also were more BOX 7-1 Triggering Events in the Interaction of Population, Agriculture, and Environment in Central Arizona The Emergent Years (1867-1940) Recognition of a vacant productive environmental niche (irrigable lower Salt River Valley) for producing crops to supply local soldiers and miners led to reexcavation of prehistoric canals and establishment of successful agriculture. Catastrophic floods followed by severe drought (1890-1903) led to cooperative action and use of federal funds to build the first major reservoir. World War I sparked greater demand for copper and cotton, leading to a boom in population, agriculture (see Figure 7-11), and commercial activity. The Boom Years (1941-1970) World War II generated military industry, air bases, and attendant infrastructure, familiarizing people with the region. In 1948, Motorola established an electronics facility in the valley, the first step in what was to reshape Phoenix’s economic base, attracting an influx of people looking for good jobs, and transforming the region’s rural character. Successful builders of large housing developments (e.g., John F. Long, Del E. Webb) provided abundant, low-cost housing that created the region’s characteristic suburban sprawl. Southwest Metropolis (1971-2003) National migration to the Sunbelt; people, industry, and commercial activity relocated to Phoenix. Groundwater Management Code, enacted in response to the threat of funding cut from the federal government, limited the expansion of farming, resulting in decreased agricultural acreage and the redirection of water from the agricultural to urban sector (Figure 7-11). Increased migration from Mexico and Central America altered the city’s demographic character. The drought from 1999 to the present combined with concern over quality-of-life issues may be leading to a shift in attitude concerning population growth as the necessary engine for the region’s economic viability.

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Population, Land Use, and Environment: Research Directions subtle triggering events that reflected the slow buildup of ecological factors, such as soil salinization and groundwater depletion, or that reflected sociodemographic forces, such as shift in ethnic composition or the source of migrants to the region. Figure 7-11 summarizes the above conceptual approach in a simplified model. The model clearly represents an iterative process, one that begins with the current state of knowledge and the impact of one or more triggering events that may emanate locally or be the result of external forces. Given the condition of the socioecosystem and current mental models, the perception and impact of the triggering event may change the mental models about appropriate decision making, leading to a change in management strategies, which may lead to a change in some aspect of the coupled human-natural system, which, in turn, may create new vulnerabilities to the system’s sustainability. This transformation may, in turn, lead to a change in the initial condition of knowledge and mental models. This cycle plays out at multiple scales from the individual to international, and the system is often driven by impacts of events across scales (e.g., national policy impacting local decisions or local lobbying leading to national policy change). The import of formulating this type of model is to determine the processes FIGURE 7-11 Acres irrigated. Note the peak in irrigated acres in 1955 and rapid drop after passage of the Groundwater Management Act in 1980, which prohibited new irrigation pumping.

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Population, Land Use, and Environment: Research Directions underlying past cycles and thus improve our ability to propose future scenarios and understand their implications. NETWORKING URBAN ECOLOGICAL MODELS AND ENGAGING PUBLIC AGENCIES Although we academics have conducted our own data collection and model building, working in an urban environmental context makes it clear that scientists working for federal, state, and local agencies have developed sophisticated models of subsystems of the urban phenomenon and collected data at a scale unobtainable with academic resources alone. We embarked on an ambitious project to bring together these two different domains of activity without sacrificing the autonomy of any party. Our early belief that the research of the Central Arizona–Phoenix Long-Term Ecological Research project scientists could and should be relevant to local public officials infuses this integrative effort. Although there have been instances of clear utility, there was an obvious gulf between our academically defined research agendas and the perceived needs of local public managers. Although recognizing this mismatch, we realized early on that we could not expect public officials to ignore legal restraints or public opinion, just as we hesitated to apply our academic research to immediate local needs. Instead, we embarked on a multiyear journey, initially called Greater Phoenix 2100, in which many of us have collaborated with public officials to find common approaches. In addition to learning more about the perspectives and needs of each party, we had to construct a bridging mechanism that was outside either entity and would function to inform and transform the mission-oriented work each of us did to something more useful to the other. The first tangible product of this collaboration was the Greater Phoenix 2100 Atlas, which defined 10 major challenges facing the metropolitan area.1 We then sought extant data that could be expressed in maps and tables, which would illuminate these issues and their possible trajectories 50 years into the future. We found that most of the maps did not derive from our own academic research but were drawn from the work of eight public agencies. Yet we at the university were uniquely well suited to bring together this disparate information. Moreover, our role in assembling this resource allowed us to convey what we think are the three operating assumptions that would make data like these valuable. To effectively address the socio-environmental challenges that confront modern society, information gath- 1   The 10 challenges are regional transportation; water: supply, use, and quality; air quality; pollen and allergies; changing demographics; Hispanic education; housing affordability; the high-tech new economy; open-space preservation; and the urban heat island.

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Population, Land Use, and Environment: Research Directions ering, analysis, and decision making must take into account these principles. (1) Regions are often greater than their current political boundaries. (2) Time depth (both into the past and future) is longer than officials normally consider. (3) Virtually any issue of real concern is so complex that it requires information from a wide variety of sources. An on-line demonstration of this atlas connects users to a host of dynamic data resources at http://www.gp2100.org/eatlas. Assembling information for the atlas, providing electronic links to agency and university data sources, and focusing academics and the community on shared issues and data needs are important first steps, but we also wanted to develop tools for more effective collaborations. With funding from the National Science Foundation, we are building and deploying a distributed-information infrastructure so that the diverse demographic and ecological researchers as well as the management and policy communities in central Arizona can benefit from integrated urban models. This innovative approach can be used to overcome the barriers to access and use of regional models, while retaining their complexity. The project draws from recent developments in the Internet industry that seek to integrate distributed services through peer-to-peer networks based on standard communication protocols. A modeling exercise that couples climate, water, and land use change models from the Arizona State University’s Office of Climatology, the National Oceanic and Atmospheric Administration, the Arizona Department of Water Resources, and the Maricopa Association of Governments is evaluating the system’s effectiveness (see Figure 7-12). Each agency maintains responsibility for operating and updating their model and databases, while an external platform draws on the current version and data of each model and feed results from one as input to the next. The net result is an integrated analysis that was not possible heretofore. Researchers, informatics specialists, and community members are enthusiastic about expanding this line of research and collaboration. Close connections with agency personnel on this project as well as the Long-Term Ecological Research project laid the foundation for a new project that aims to develop decision-making tools. The Decision Center for a Desert City, begun September 2004, will focus on how to integrate science into policy and management decisions that have to confront the uncertainty created by climate variability as it relates to water supply in the central Arizona region. Officials from the top water providers, regulatory agencies, and municipalities have been engaged from the very beginning of this project, helping to craft the original proposal. Although related to all the other projects described in this chapter, this is the first instance in which the primary measure of success will be whether we have improved the way public policy decisions are being made.

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Population, Land Use, and Environment: Research Directions FIGURE 7-12 Chart illustrating networking to share models and data among three public agencies. GOING FORWARD WITH ACADEMIC AND APPLIED OBJECTIVES With insights gained from six years of urban ecological research and the foundation built with several interrelated projects, we are now ready to embark on a new phase of the endeavor. Until now we have (1) focused our investigations on an arid, urban ecosystem; (2) experimented with strategies that will be effective in this new study domain; and (3) found ways to work together across disciplines, especially in bridging the life and social sciences. In the initial years, we have had to emphasize background studies, baseline monitoring of a suite of variables, and experimentation that have led us to better define the processes that engage us. With these definitions in hand, we now can refine the substantive models and the patterns we observe and contribute to a more general understanding of urban ecosystems. At the same time, we hope to improve paradigms for the collaboration of ecology and social sciences. We have proposed three conceptual themes that we think will cast our empirical research into an integrative context. It is our goal that these interpretive themes will link field projects to the overarching research ques-

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Population, Land Use, and Environment: Research Directions tion on the feedbacks among patterns of urbanization, population dynamics, ecological consequences, and human responses. 1. Scales and periodicities of ecological and human phenomena. Biological and physical processes occur at multiple scales intrinsic to the organism or to the geophysical context. Humans operate at varying scales as well, due to their physiology, social organization, economy, politics, and culture. The scales and periodicities of ecological and human phenomena sometimes match well and integrate easily, and sometimes they do not. These mismatches may introduce the risk of breakdown into the system or may, in fact, offer opportunities for growth or change. 2. Human actions that control variability at various scales and periodicities at which ecological systems operate. Humans act either to keep this variability within acceptable limits or to gain economic or political advantage from managing the variability. In what ways and to what extent does human control transform the socioecological system? For example, replacing dead plants, adding fertilizer, and irrigating all serve to buffer the plant community against climatic pressure, creating a socioecological system that would not survive without human intervention. 3. Resilience of socioecological systems. Cities (i.e., urban ecosystems) are complex, nonequilibrium, and adaptive systems. To what extent are human-dominated systems resilient? What are the threats to these systems, and what are their vulnerabilities? What qualities should we maintain, what aspects are we willing or anxious to eliminate? Can we build institutions that will protect urban socioecological systems from dramatic, undesirable changes and also promote qualities and functions deemed positive? Even with the addition of the new conceptual themes, the Central Arizona–Phoenix Long-Term Ecological Research and other projects described here continue to use traditional ecological and spatial theories to interpret the data patterns we observe. It is possible to explain data patterns by traditional ecological theory, but some patterns do not fit well and require special consideration. Researchers have often accounted for these deviations from normal pattern expectations by attributing them to human influence. However, these situations—and those in which the deviations are greater—may be domains in which devising a new integrated human ecological theory would be fruitful. Reviewing the results of our early environmental monitoring, three domains stand out as candidates for theoretical refinements: Uniquely human elements of perception, valuation, and goal orientation are major elements of decision making that influence virtually all

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Population, Land Use, and Environment: Research Directions aspects of ecosystem stability and change. We are specifically exploring this subject in our Ag Trans investigations (see Figure 7-13). Flows of nutrients, materials, and energy are often an order of magnitude greater in urban environments when compared with nonurban locales. In addition, there are new materials and new mechanisms for conveying flows in urban environments, both of which may act differently from their natural counterparts. Fragmentation of the environment into patches seems to follow some ecological guidelines but also seems to run contrary to basic ecological principles, with unexpectedly high levels of fragmentation often marking human-dominated environments. In our own fieldwork, we have found that the city of Phoenix, and we expect most others, have many more and smaller patches than the surrounding environment (Luck and Wu, 2002: Figure 3c). In the analysis of 200 plots across our study area, spatial autocorrelation explained plant genera diversity outside the city, but not within the built-up areas (Hope et. al., 2003). Applying linear gradient analysis to explain these differences, as is often done in ecological studies based on elevation differences or distance from the point of origin of a species, has limited utility in human-dominated cases. Rural-to-urban gradient analysis developed by urban ecologist Steward Pickett (Pickett et al., 1997) came closer to explaining the extant variability, but I would argue that a more complex, multicentered network model would be even more useful. An interesting additional observation is that, in the urbanized area we have studied, the expected species- FIGURE 7-13 Conceptual model of Agrarian Landscapes in Transition project, whose ultimate goal is to understand past cycles of land use and human response in order to propose future scenarios.

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Population, Land Use, and Environment: Research Directions area relationship of larger patches of the same type containing greater species diversity often did not hold. In many cases, small residential lots had high plant diversity and, although larger lots often had more diverse assemblages, sometimes they did not, and in many cases there seemed to be an artificial point at which diversity did not increase with size or wealth (see Figure 7-6). Thinking about this subject more generally, human-dominated systems, land use changes and, in particular, habitat fragmentation, are conditioned by all of the traditionally cited biogeophysical forces that are thoroughly discussed in the ecological literature—plus a complex, and sometimes intense, set of human factors. Throughout their history, humans have modified their environment to suit their perceived needs (Redman, 1999b). It is often suggested that humans have acted to homogenize habitats, reducing the diversity of landscapes and even entire regions. This consequence is particularly true of contemporary agrarian landscapes in which extensive monocropped fields have replaced naturally occurring plant diversity. However, I would argue that, at least as often, humans have acted to create additional boundaries in their environments, resulting in smaller patches than would exist without their presence. Having partitioned their world, humans then create mechanisms to bridge or permeate these boundaries. I think the tendency to further fragment the natural landscape relates to a combination of four powerful drivers. Through habitat fragmentation, humans act to better understand their surroundings, reaffirm their identity, create economic value, and construct asymmetric power relations. How these human drivers lead to boundary formation is discussed in anthropological and other social scientific literature, but not usually in reference to habitat fragmentation. One benefit of interdisciplinary research teams is that they bring together researchers who look at the same phenomena from different perspectives. Moreover, urban ecosystems, because of the clearly dominant influence of people, institutions, and the built environment, offer an exciting laboratory for examining alternative perspectives and formulating possible refinements for both social and ecology theory. ACKNOWLEDGMENTS This paper results from the work and cooperation of many researchers who have defined and carried out the projects I have described. Realizing that the number is large, I will point out the leadership of each project, and one can see from the reference list the names of others to whom I am indebted. The Central Arizona–Phoenix Long-Term Ecological Research project (NSF/DEB-9714833) is codirected by Nancy Grimm, who has left her talented imprint on much of what we do and what I think. I codirect the Arizona State University component of the Biocomplexity in the Environ-

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Population, Land Use, and Environment: Research Directions ment project, Agrarian Landscapes in Transition (NSF/DEB-0216560), with Ann Kinzig; communication with other partners, as well as help with this and other manuscripts, is overseen by Lauren Kuby, each of whom are key to making this complex program advance. The Networking Urban Ecological Models Through Distributed Services (NSF/EIA-0219310) is directed by Peter McCartney, who is able to perceptively understand barriers to collaboration and devise informatics approaches to bridge these barriers. The Decision Center for a Desert City (NSF/SES-0345945) is codirected by Patricia Gober, who has also been a key researcher in the Central Arizona–Phoenix Long-Term Ecological Research project, as seen in two of her creative projects described here. REFERENCES Anderson, J.R., E.E. Hardy, J.T. Roach, and R.E. Witmer 1976 A Land Use and Land Cover Classification System with Remote Sensor Data. (USGS Professional Paper 964.) Washington, DC: U.S. Geological Survey. Berling-Wolff, S., and J. Wu 2004 Modeling urban landscape dynamics: A case study in Phoenix, USA. [Special Issue.] Urban Ecosystems 7:215-240. Bolin, R., S. Smith, E. Hackett, A. Nelson, T. Collins, and K.D. Pijawka 2002 Toxic Tracts: The Development of Environmental Inequality in Phoenix Arizona. Presentation at the 2002 meeting of the American Geographical Association in Los Angeles, CA. Collins, J.P., A.P. Kinzig, N.B. Grimm, W.F. Fagan, D. Hope, J. Wu, and E.T. Borer 2000 A new urban ecology. American Scientist 88:416-425. Fagan, W.F., E. Meir, S.S. Carroll, and J. Wu 2001 The ecology of urban landscapes: Modeling housing starts as a density-dependent colonization process. Landscape Ecology 16:33-39. Fulton, W.R. Pendall, M. Nguyen, and A. Harrison 2001 Who Sprawls Most? How Growth Patterns Differ Across the U.S. A Report to the Brookings Institution. Available: http://www.brook.edu/es/urban/fultonpendall.htm [accessed February 10, 2005]. Gammage, G., Jr. 1999 Phoenix in Perspective: Reflections on Developing the Desert. (Herberger Center for Design Excellence.) Tempe: College of Agriculture and Environmental Design, Arizona State University. Gober, P. in press Greater Phoenix: Dynamics of Change in a Postmodern Metropolis. Philadelphia, PA: University of Pennsylvania Press. Gober, P., and E.K. Burns 2002 The size and shape of Phoenix’s urban fringe. Journal of Planning Education and Research 21:379-390. Grimm, N.B., and C.L. Redman 2004 Approaches to the study of urban ecosystems: The case of central Arizona–Phoenix. Urban Ecosystems 7:199-213. Grimm, N.B., J.M. Grove, S.T.A. Pickett, and C.L. Redman 2000 Integrated approaches to long-term studies of urban ecological systems. BioScience 50:571-584.

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