Ecological homogenization of urban America

a research project funded by the U.S. National Science Foundation program on “MacroSystems Biology: Research on Biological Systems at Regional to Continental Scales.”

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Non-technical abstract

Urban, suburban and exurban ecosystems are important and increasing in the U.S.  An apparent, but functionally untested result of urban land use change is homogenization across cities, where neighborhoods in very different parts of the country have similar patterns of roads, residential lots, commercial areas and aquatic features.  We hypothesize that this homogenization also involves ecological structure and functions relevant to ecosystem carbon and nitrogen dynamics, with continental scale implications.  Further, we suggest that understanding urban homogenization will provide the basis for understanding the impacts of urban land use change from local to continental scales.  We will use datasets ranging from household surveys to regional-scale remote sensing across six metropolitan statistical areas (MSA) that cover the major climatic regions of the US (Phoenix, AZ, Miami, FL, Baltimore, MD, Boston, MA, St. Paul, MN and Los Angeles, CA) to determine how household characteristics correlate with landscaping decisions, land management practices and ecological structure and functions at local, regional and continental scales. 

This research has the potential to transform both understanding of an important and increasingly common ecosystem type (“suburbia”) and the capacity to scale the effects of local land use change to regional and continental extents.  We will determine how urban land use change has affected carbon storage and nitrogen pollution at multiple scales, and further understanding of how humans perceive, value and manage their surroundings.

Introduction – urbanization and homogenization

Urban land use change has been identified as one of the major components of environmental change because of its effects on fluxes of water, carbon and nutrients across large areas of the globe (Foley et al. 2005, Grimm et al. 2008).  Between 1982 and 1997 the amount of urbanized land in the United States increased by almost 50% (Fulton et al. 2001), extending over 1.4 million sq. km. and housing over 80% of the U.S. population (Brown et al. 2005). Most of this growth is suburban and exurban.  In the 2000 census, suburban growth surpassed growth in cities regardless of city-specific population dynamics and economic trajectories (Duany et al. 2000, Katz et al. 2003). 

Urban, suburban and exurban ecosystems present a unique and difficult challenge to environmental scientists and managers.  These highly managed systems have large impacts on air and water quality and human well being, but the diversity of natural and human drivers, and high heterogeneity at small scales (10 – 100 m) complicate their analysis and management (Grimm et al. 2008, Pickett et al. 2010).  As interest in understanding the continental-scale impacts of environmental change increases (Keller et al. 2008), there is a critical need to develop conceptual and practical tools to address the complex controls and heterogeneity of increasingly important urban, suburban and exurban ecosystems. 

An apparent, but functionally untested result of contemporary U.S. urban land use change is ecological homogenization across cities, wherein human dominance and leading land-management practices render urban/suburban systems more similar to each other than to adjacent  native ecosystems (Pouyat et al. 2007, Pickett et al. 2010).  Such homogenization would be manifest in biophysical structure, where neighborhoods across biophysically different regions have similar patterns of roads, residential lots, commercial areas and aquatic features.  This homogenization would result in ecological transformation, with replacement of natural vegetation assemblages by turfgrass yards, popular plant species, and impervious surfaces (Turner et al. 1990, Byrne 2007, Cadenasso et al. 2007, Walker et al. 2009).