12 July 2012

Urban-rural Gradient

Definition: An ordering of sites based on the predominance of buildings and infrastructure, coupled with dense human population, in contrast with sites having sparse infrastructure and low human population density.  Other criteria, such as some physical or biological environmental measurement, such as pollution, or social contrasts such as dependence on an economy based on consumption, finance, transportation, versus dependence on agriculture or management of natural resources, can be used to contrast urban and rural sites. 

Examples: Urban-rural gradients can sometimes be found as continuous lines from an old downtown, through suburbs, and ending in forested or agricultural areas (Figure 1).  

Figure 1. The transect from the Bronx in New York  City to forested stands on the same bedrock in rural western Connecticut.  The transect was used to expose a gradient of adjacent land covers, road densities, and traffic volumes affecting forest stands (from McDonnell and Pickett 1990).  The quantification of the gradient in terms of the human variables is found in Medley, K. E., M. J. McDonnell, and S. T. A. Pickett. 1995. Forest-landscape structure along an urban-to-rural gradient. Professional Geographer 47:159-168.

Figure 2. The patchy distribution of pigeons at random sampling locations in Baltimore city.  The distribution is heterogeneous, but does not follow linear transects from the core of the city to the suburban edges of Baltimore.  C.H. Nilon & P.S. Warren.

Why important: Urban-rural gradients, both direct transects in space, and abstract comparisons based on quantitative or qualitative differences found in metropolitan areas, have become a widespread tool for research in urban socio-ecological systems.

For more information:
·        McDonnell, M. J. and S. T. A. Pickett. 1990. Ecosystem structure and function along urban-rural gradients: an unexploited opportunity for ecology. Ecology 71:1232-1237.
·      Hahs, A. K. and M. J. McDonnell. 2006. Selecting independent measures to quantify Melbourne's urban-rural gradient. Landscape and Urban Planning 78:435-448.
·      Clergeau, P., J. Jokimäki, and R. Snep. 2006. Using hierarchical levels for urban ecology. Trends in Ecology and Evolution 21:660-661.
·       Dow, K. 2000. Social dimensions of gradients in urban ecosystems. Urban Ecosystems 

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