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.
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 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 exceeds a certain level (above $70,000). This leveling implies that aesthetic or other drivers of choice are satisfied even though there is available wealth to expand the diversity.
Perspectives in Urban Ecology Ecosystems and Interactions between Humans and Nature in the Metropoli
Researchers from six Long-Term Ecological Research projects have collaborated to study the intersection of humans, climate, and water in the context of agrarian transformations, both current and historical, because of their ubiquity and the tight coupling of human and environmental dynamics inherent in agrarian landscapes (Redman et al., 2002). Our central objective is to understand what happens when humans impose their spatial and temporal signatures on ecological regimes and then respond to the systems they helped create, further altering the dynamics of the coupled system and the potential for ecological and social resilience. The transitions of agrarian landscapes and life ways continue to take many forms, ranging from abandonment, to urban development, to more intensified agriculture. In the United States alone, 105 acres of agricultural land go out of production every hour; urban or suburban growth consumes about half that amount, and the remainder is used less intensely or actively conserved for its habitat values (U.S. Department of Agriculture Policy Advisory Committee, 2001). We conceptualize an integrated cycle of land use change affecting landscapes, altered landscapes affecting ecological processes, both influencing the ways in which humans monitor and respond to their surroundings, and those responses engendering further cycles of change.
Our findings provide insights into better understanding the dynamics of human-environment interactions. On the one hand, our individual decisions that are shaped, in part, by our mental models18 may trigger changes to the ecological characteristics of our natural environment. On the other hand, these behaviors may cascade to others through our social connections, which further transform natural ecosystems16,17,49 and/or feedback to our ecological knowledge, mental models, and decisions through our environmental connections50,51. Therefore, the condition of ecological health and the degree to which nature is allowed to function in urban areas can largely be associated with human perceptions, decisions, and practices at the individual or community level through complex feedback dynamics.
Projections suggest that by 2050, nearly 70% of the human population will become urban dwellers57; therefore, beyond identifying and diagnosing UKS, future work needs to focus more on better treating it. Here, we identify three overarching, but not mutually exclusive, treatments: (1) designing local institutions with heterogeneous land-management policies in a decentralized setting where local level decisions and governance systems nested into higher level governance settings; (2) fostering environmental connectedness through building cultural, architectural and cognitive links between humans and the natural environment; and (3) promoting adaptive learning and ecological knowledge that accommodates biodiversity and enhances the resilience of social-ecological coastal ecosystems42. These potential treatments are further explained below.
Finally, using programs like citizen science to enhance the ability of individuals in urban settings to engage with nature may contribute effectively to treating UKS67. These programs help residents identify and respond to local environmental issues by way of fostering adaptive learning about human-environment interactions through evidence-based practices. In addition, Kransy and Tidball (2012)13 presented a call to all institutions active in cities, including governments, non-profits, the private sector and universities to promote enhanced urban stewardship through Civic Ecology; a process by which local environmental stewardship actions can be initiated to enhance both the green infrastructure and community wellbeing of urban and other human-dominated systems.
Moreover, the human selection of traits associated with socio-cultural, economic, and governance drivers, often has consequences on the socio-ecological outcomes. For example, the selection of palm trees as street trees is known to enhance the service of esthetic experiences, since many of their traits are often considered visually pleasing (for example, their arboreal bearing and leaf arrangement)61. This service is very important in urban areas since it promotes the connection between people and nature, contributing to human well-being62,63,64.
We distinguish between perspectives on urban transformations in, of and by cities. The perspectives provide entry points for formulating and structuring research questions on urban transformations, integrating research approaches and knowledge, and deriving implications for practice.
The traditional concept of infrastructure likely began to expand to include nature in cities with the designs of Frederick Olmstead, then later with the work of Ian McHarg (1969) and, more recently, Frederick Steiner (2006). Awareness of nature in cities began to mature and become more widespread during the environmental movement of the 1960s and 70s. Since then, the importance and value of nature in cities has strengthened with the growth of urban ecology as both a discipline and an approach to understanding urban systems dynamics. With this strengthening has come the prevalence of several terms by European and U.S. urban scientists and practitioners to refer to nature in cities. Green Infrastructure (GI) is one (Tzoulas et al. 2006; Keeley 2011; Andersson et al. 2014; Larsen 2015; Koc et al. 2017); it is typically defined as the interconnected network of natural and semi-natural elements capable of providing multiple functions and ecosystem services encompassing positive ecological, economic, and social benefits for humans and other species (Benedict and McMahon, 2006; Koc et al. 2017). The GI concept has recently been expanded to Green-Blue Infrastructure (GBI), in order to include urban aquatic features (sensu Barbosa et al. 2019). Another more recently used term is Urban Green Space (UGS), defined as the natural, semi-natural, and artificial ecological systems within and around a city that comprise a range of habitats (Niemela et al. 2010; Cilliers et al. 2013; Aronson et al. 2017). Additionally, the term Nature-Based Solutions (NBS) has gained considerable traction, particularly in Europe (Eggermont et al. 2015; Cohen-Shacham et al. 2016; Maes and Jacob 2017; Kabisch et al. 2017; Frantzeskaki et al. 2019; Keeler et al. 2019), although this concept seems to be more focused on goal-oriented engineering rather than on the natural infrastructure itself (Nesshover et al. 2017, WWAP/UN-Water 2018). The definitions of GI, GBI, UGS, and NBS overlap considerably, and all are routinely coupled with the ecosystem services concept (e.g., Gomez-Baggethun et al. 2013; Andersson et al. 2015; Locke and McPhearson 2018; Keeler et al. 2019). GI and UGS are more strongly focused on terrestrial ecological features in cities; notably, a recent review and typology of GI by Koc et al. (2017) included no aquatic features, while a review of the GI literature by Haase et al. (2014), that was focused on ecosystem services, did not include urban wetlands. Similarly, applications of the GBI and NBS terms and concepts rarely discuss or include urban wetlands.
Our simplified and more concise definition of UEI encompasses all parts of a city that include ecological structures and functions. Ecological structure is the physical components that make up ecosystems (e.g. species, soils, waterways) while ecological function is the processes that result from interactions among the structural components (e.g. primary production, nutrient cycling, decomposition). UEI forms a critical bridge between nature in cities and the people that live in cities via its purveyance of urban ecosystem services (Figure 1). These ecosystem services are, by definition, the benefits that people gain from UEI and the resulting effects on human outcomes. Many of these ecosystem services result from the ecological function of UEI (the arrows in Figure 1 that connect function to ecosystem services to outcomes), but some are purely structural (the arrow in Figure 1 that connects UEI with outcomes). For example, urban trees are known for providing a number of function-derived ecosystem services, such as transpirational cooling and soil retention and development. But urban trees also provide services that are strictly tied to their ecological structure, including shade and habitat for wildlife. 2ff7e9595c
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