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106 5 Resilience in Hybrid Ecosystems Variability and change are vital to the persistence and evolution of ecosystems. Studies of complex systems have uncovered direct relationships between variability in systems’ structures and their resilience. Change—both slow and fast—is integral to the workings of any natural system. This chapter articulates the hypothesis that variable patterns of urbanization and modular urban infrastructure may be key to cities’ resilience. I use three examples—carbon, nitrogen, and bird diversity—to illustrate the complex relationships between patterns of development and key slow and fast variables that regulate resilience in urban ecosystems. I argue that policies and management that aim to achieve stable conditions by optimizing only one system function at one scale may make systems more vulnerable and could eventually lead to their collapse. Resilience in hybrid ecosystems is an emergent property of co-evolving human and natural processes. We cannot understand the diverse expressions of present urban landscapes unless we consider the complex history of interactions between humans and nature over millennia. The collapse of the Mayan cities during the eighth or ninth century—still quite an enigma—has only recently been investigated from the perspective of coupled human-natural systems by integrating empirical evidence from different fields. A plausible hypothesis is that a severe drought, exacerbated by rapid deforestation and desertification in a time of unprecedented population density, led the Mayans to abandon urban sites in the Yucatán region (E. Cook, Hall, and Larson 2012). Complex interactions between human and natural processes are also key to under- Resilience in Hybrid Ecosystems 107 standing the resilience of old cities, including Rome and many others in the Mediterranean region, that have survived the test of evolving nature and civilizations. The landscape stratification that we can see in Rome today reveals how humans and nature co-evolved over nearly 2,800 years of change: ecological, economic, social, cultural, and political. To explain the structure, dynamics, and evolution of emerging ecologies in urban ecosystems—whether we are interested in the biodiversity of New York’s Central Park or Moscow’s Bitsevsky Park, or in the biogeochemistry of Seattle or Phoenix—we must acknowledge their hybrid nature. Although scholars of urban ecology have recognized the evolutionary nature of urban ecosystems and acknowledged their unique hybrid dynamics for some time, most empirical research is still grounded in divided paradigms. The knowledge that emerges from these paradigms is incomplete in a fundamental way. Emerging studies of coupled humannatural systems reveal new and complex patterns and processes that are not evident when social or natural scientists study them separately (Liu et al. 2007a). For the past few decades, teams of biologists, earth scientists , economists, geographers, and planners have expanded our understanding of urban ecosystems by uncovering key mechanisms that characterize coupled human-natural dynamics in urban regions (Alberti et al. 2003; Grimm et al. 2000; Pickett et al. 2001). Several important findings have emerged from this work (Alberti 2010; Grimm et al. 2008a; Pickett et al. 2011). Cities have a distinctive biogeochemistry because infrastructure that is engineered to move water and remove wastes alters hydrological processes and nutrient cycles (Kaye et al. 2006). Densely urbanized areas also have unique micro­ climates, such as heat islands, which influence atmospheric chemistry and air pollution (Grimm et al. 2008b). Evidence also suggests that the distinctive compositions of plant and animal species found in cities are strongly influenced by human perceptions and behaviors (Faeth et al. 2005). But these specific findings do not add up to an understanding of how such systems work and evolve; we must uncover the rules governing community assembly. One critical aspect of such an understanding is learning how the structures of urban ecosystems (i.e., diversity of components and degree of connectivity) relate to their dynamics. That is, which qualities best express and regulate function and change in hybrid systems? Recent 108 Chapter 5 evolution in complex science has begun to uncover direct relationships between complex network structures and their resilience. Scheffer et al. (2012) noted that two key qualities of system architecture—heterogeneity and modularity—might determine the likelihood of critical transitions and the emergence of thresholds and system shifts (i.e., a catastrophic bifurcation). Variability and change are two essential characteristics of ecosystems . It is the great variability found in nature that explains persistence and evolution. Change, whether gradual or abrupt, is integral to the way nature works. Emerging evidence shows that complex networks in which components vary and connectivity is incomplete tend to have...


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