Ecological homogenization of urban USA

www.frontiersinecology.org © The Ecological Society of America U land-use change has been identified as one of the major components of environmental change because of its effects on climate, water, biodiversity, carbon (C), 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 US increased by almost 50%, extending over 1.4 million km and encompassing more than 80% of the US population (Brown et al. 2005). Most of this growth was suburban and exurban. According to results from the US Census Bureau’s national census in 2000 (www.census.gov/ main/www/cen2000.html), suburban growth surpassed growth in cities, regardless of city-specific population dynamics and economic trajectories (Katz et al. 2003). A visually apparent but scientifically untested outcome of contemporary US land-use change is ecological homogenization across urban areas, wherein human dominance and land-management practices render suburban systems more similar to other, geographically distinct cities than to adjacent native ecosystems (McKinney 2006; Pouyat et al. 2007; Pickett et al. 2011). Such homogenization would be exhibited in biophysical structure, where neighborhoods across biophysically different regions come to have similar patterns of human infrastructure (including roads, residential lots, commercial areas), vegetation structure, and aquatic features. This homogenization may also result in ecological transformation, with replacement of natural vegetation assemblages by turfgrass, popular or weedy plant species, and impervious surfaces. Residential land management is fundamentally a local process, an expression of the decisions of individual land managers and households. However, decisions on yardscaping and other kinds of management may be tied not only to variables at the scale of individuals or households, but also to broader social structures (eg family dynamics), socioeconomic status (eg wealth), neighborhood-level norms, and national-scale marketing and retail activity (Grove et al. 2006; Zhou et al. 2009; Larson et al. 2010; Roy Chowdhury et al. 2011; Cook et al. 2012). Most fundamentally, cities are socioecological systems that are built by and for humans. There is a strong need to develop a theory and science of human habitats comparable to the study of the habitats of other species. We hypothesize that the multi-scalar drivers and dynamics of residential land management lead to two important continental-scale patterns in urban ecosystem structure and function. First, similarity in people’s decision-making processes across broad areas promotes convergence and homogenization in urban ecosystem structure and function across biophysically dissimilar settings. Thus, residential ecosystems in different places are more MACROSYSTEMS ECOLOGY