Thursday, February 16, 2012

Urban Ecology HAS Changed

A Perspective on Points from Ramalho and Hobbs, As Reported by the BBC on 6 December 2011

A news report by the BBC on an article critical of urban ecology appears at  I find that the report, though true to the article by Ramalho and Hobbs, should not go without comment.  Urban ecology is not the backward pursuit that the report might lead some to believe.  The original article by Ramalho and Hobbs, entitled “Time for a change: dynamic urban ecology,” appears in TREE at

A published reply, to which I contributed, also exists.  Mark J. McDonnell, Amy K. Hahs, and I have offered a reply to the original article by Ramalho and Hobbs.  The reply has been accepted by TREE, and is published online at

Changed Already

From the BBC report: “The way researchers assess urban ecology needs to change in order to take into account the way modern cities are developing.” 

The discredited Burgess urban ring model.
Urban ecology has in fact already changed drastically over the last two decades, both because of committed long-term support for urban ecological research, and the closer integration of social and biophysical research efforts.  Since the early 1990’s, when urban ecology was reinvigorated both as a component of mainstream ecology and as an important “boundary discipline” capable of linking ecology with social sciences and with urban design, the field has gone well beyond the concepts and approaches that were available in the mid 1980s and early 1990s.  

Furthermore, urban ecology has productively employed spatially realistic and flexible models that recognize urban areas as shifting, patchy mosaics.  Complaining about ring models, such as the holdovers from the Chicago School, or about linear transects as research tools, misses much of the conceptual and empirical progress of two decades of contemporary urban ecology.

Diverse Urban Transformations
Shenzen, China. (c. Brian P. McGrath)
Interaction among bioecological researchers, social scientists, and urban designers, among others, has firmly embedded within ecological thinking the variety of modes by which cities now change.  There are shrinking, post-industrial cities, burgeoning refugee cities and districts, virtually instant cities in Asia and Africa, and even high density settlements far from traditional urban centers but which through dynamic diasporas that ebb and flow, rely on resources, capital, attitudes, and opportunities that originated in the more classically recognized cities.

Non-linear Models
The simplistic way that urban rural gradients have been interpreted by many is a disappointment.  However, there have been repeated efforts to clarify that a linear transect for studying a spatially complex mosaic is not necessarily the same thing as an urban-rural gradient (Cadenasso et al. 2006).  The vintage of the gradient concept in ecology and the sophisticated and well established strategies for studying complex environmental gradients in spatially patchy contexts (Austin 2005, Fox et al. 2011) would seem to make it unnecessary to emphasize the non-congruence of gradients and transects.  Yet, the conflation is a common one. It is no less correct for being common.  Again, the literature has more depth and richness than Ramalho and Hobbs or their BBC correspondent seem to recognize.

Contemporary Patterns
The BBC correspondent states Ramalho “explained that, historically, cities grew slowly in a relatively compact manner, through progressive rings of urban development.”  The ring model, developed in the 1920s, was almost immediately critiqued by social scientists, and improved as a sectoral model even in the 1930s.  So the insight that the concentric ring model of urban development is flawed is not a new discovery.

Contemporary patterns are said to be ‘markedly different’ from the allegedly slow, ring-like march.  The description that then appears is one of a complex, heterogeneous mosaic that includes green, blue, grey, and brown components intermingling spatially.  Ramalho is further quoted in the BBC report: “Cities are growing very rapidly, they are increasingly expansive and dispersed, sprawling in … spider-like configurations across large distances, and embedding fragments of other land uses in the rapidly changing landscape.”  (Note, ellipsis in original BBC quote.)

Is this a new insight?  Hardly.  Consider this quotation from pg 128 from Pickett et al. (2001):

Thimphu, Bhutan. Doubling in 6 yr
“Cities are no longer compact, isodiametric aggregations; rather, they sprawl in fractal or spider-like configurations (Makse et al. 1995). Consequently, urban areas increasingly abut and interdigitate with wild lands. Indeed, even for many rapidly growing metropolitan areas, the suburban zones are growing faster than other zones (Katz & Bradley 1999). The resulting new forms of urban development, including edge cities (Garreau 1991) and housing interspersed in forest, shrubland, and desert habitats, bring people possessing equity generated in urban systems, expressing urban habits, and drawing upon urban experiences, into daily contact with habitats formerly controlled by agriculturalists, foresters, and conservationists (Bradley 1995).”

It is interesting that the early concentric ring model for Chicago was in fact developed to explain and intervene in the explosive development of that city in the early 20th century: Chicago had doubled in population in a decade due to immigration from novel sources: southern and eastern Europe, and African Americans from the southern U.S.  So speed of growth is not in fact a uniquely contemporary phenomenon.  

Simple Categories?
It is manifestly true that just calling something urban, or suburban, or rural, yields little insight into what drivers may actually be in play.  However, the call for using environmentally meaningful and measurable factors to understand the effects of urban structure and urban change is not new (Pickett 1993).  Indeed, we can point to developments that seek to unpack the metaphorical labels often used in urban ecology research (McIntyre et al. 2000).  The concept of the “ecology of prestige” (Grove et al. 2006b), and a novel, integrated conceptualization of urban land covers (Cadenasso et al. 2007) are examples. 

Furthermore, social complexity is recognized as a driver through such things as property regimes (Grove et al. 2005), and through institutional structures and indeed of networks of organizations (Ostrom 1990). 
Urban ecologists and social scientists have also recognized the impact of spatial context on the various patches within urban mosaics, whether they are natural, built, or the still more common hybrid patches (Grove et al. 2006a, Cadenasso and Pickett 2007, Shane 2007).  

A recent approach to factor analysis, based on updating a classical conceptual model originally developed in soil science, also illustrates how urban ecologists have been approaching this problem (Pickett and Cadenasso 2009).  Both social and biophysical factors are addressed in this framework.  Such a hierarchical framework can accommodate the sharper focus, that is, attention to detailed driving variables, as well as the aggregated variables which are sometimes useful for coarse scale analyses and comparisons.  Such a flexible, hierarchical approach has been called for by urban ecologists in the past (Wu and David 2002).

Urban Change
Change landscapes in shifting urban mosaics.
The long-term perspective illustrated by such studies as BES and the Central Arizona Phoenix LTERs has been a crucial addition to contemporary urban ecology (Grimm et al. 2000).  The role of social, political, and biophysical legacies, and the resultant path dependencies are well recognized features of urban systems (Bain and Brush 2004).  Such legacies must be considered when bringing ecological knowledge to bear in understanding and improving urban systems.  The growing data on temporal changes are already an important part of contemporary urban ecology (Boone et al. 2009, Grove 2009).  This information is not only important for conservation of native and managed biodiversity, but for designing and managing for greater urban sustainability in the future (McGrath et al. 2007).

The Bottom Line
While Ramalho and Hobbs identify many positive attributes of a contemporary urban ecology, I believe that these are already in place, and are exemplified by a lot of the work in BES as well as other urban ecology efforts around the world.  The sophistication and evolution of contemporary urban ecology as an integrated, socio-ecological pursuit (Cadenasso and Pickett 2008), but which brings the best of mainstream ecology together with cutting edge social science and urban design should be more widely recognized. 

Literature Cited
Austin, M. P. 2005. Vegetation and environment: discontinuities and continuities. Pages 52-84 in E. van der Maarel, editor. Vegetation ecology. Blackwell Science, Malden, MA.
Bain, D. J. and G. S. Brush. 2004. Placing the pieces: reconstructing the original property mosaic in a warrant and patent watershed. Landscape Ecology 19:843-856.
Boone, C. G., M. L. Cadenasso, J. M. Grove, K. Schwarz, and G. L. Buckley. 2009. Landscape, vegetation characteristics, and group identity in an urban and suburban watershed: why the 60s matter. Urban Ecosystems 13:255-271.
Cadenasso, M. L. and S. T. A. Pickett. 2007. Boundaries as structural and functional entities in landscapes: understanding flows in ecology and urban design. Pages 116-131 in B. McGrath, V. Marshall, M. L. Cadenasso, J. M. Grove, S. T. A. Pickett, R. Plunz, and J. Towers, editors. Designing patch dynamics. Columbia, Graduate School of Architecture, Planning and Preservation, New York, NY.
Cadenasso, M. L. and S. T. A. Pickett. 2008. Urban principles for ecological landscape design and management: scientific fundamentals. Cities and the Environment 1:Article 4.
Cadenasso, M. L., S. T. A. Pickett, and J. M. Grove. 2006. Integrative approaches to investigating human-natural systems: the Baltimore Ecosystem Study. Natures, Sciences, Soci‚t‚s 14:1-14.
Cadenasso, M. L., S. T. A. Pickett, and K. Schwarz. 2007. Spatial heterogeneity in urban ecosystems: reconceptualizing land cover and a framework for classification. Frontiers in Ecology and Environment 5:80-88.
Fox, G. A., S. M. Scheiner, and M. R. Willig. 2011. Ecological gradient theory: a framework for aligning data and models. Pages 283-307 in S. M. Scheiner and M. R. Willig, editors. The theory of ecology. University of Chicago Press, Chicago.
Grimm, N. B., J. M. Grove, S. T. A. Pickett, and C. L. Redman. 2000. Integrated approaches to long-term studies of urban ecological systems. BioScience 50:571-584.
Grove, J. M. 2009. Cities: managing densely settled social-ecological systems. Pages 281-294 in F. S. Chapin, III, G. P. Kofinas, and C. Folke, editors. Principles of ecosystem stewardship: resilience-based natural resource management in a changing world. Springer, New York.
Grove, J. M., W. R. Burch, Jr., and S. T. A. Pickett. 2005. Social mosaics and urban community forestry in Baltimore, Maryland. Pages 249-273 in R. G. Lee and D. R. Field, editors. Communities and forests: where people meet the land. Oregon State University Press, Crovallis.
Grove, J. M., M. L. Cadenasso, W. R. Burch, Jr., S. T. A. Pickett, K. Schwarz, J. P. M. O'Neill-Dunne, M. A. Wilson, A. Troy, and C. G. Boone. 2006a. Data and methods comparing social structure and vegetation structure of urban neighborhoods in Baltimore, Maryland. Society & Natural Resources 19:117-136.
Grove, J. M., A. R. Troy, J. P. M. O'Neill-Dunne, W. R. Burch, Jr., M. L. Cadenasso, and S. T. A. Pickett. 2006b. Characterization of households and its implications for the vegetation of urban ecosystems. Ecosystems 9:578-597.
McGrath, B. P., V. Marshall, M. L. Cadenasso, J. M. Grove, S. T. A. Pickett, R. Plunz, and J. Towers, editors. 2007. Designing patch dynamics. Columbia University Graduate School of Architecture, Preservation and Planning, New York.
McIntyre, N. E., K. Knowles-Yanez, and D. Hope. 2000. Urban ecology as an interdisciplinary field: differences in the use of "urban" between the social and natural sciences. Urban Ecosystems 4:5-24.
Ostrom, E. 1990. Governing the commons: the evolution of institutions for collective action. Cambridge University Press, New York.
Pickett, S. T. A. 1993. An ecological perspective on population change and land use. Pages 37-41 in C. L. Jolly and B. B. Torrey, editors. Population and land use in developing countries: report of a workshop. National Academy Press, Washington, DC.
Pickett, S. T. A. and M. L. Cadenasso. 2009. Altered resources, disturbance, and heterogeneity: a framework for comparing urban and non-urban soils. Urban Ecosystems 12:23-44.
Pickett, S. T. A., M. L. Cadenasso, J. M. Grove, C. H. Nilon, R. V. Pouyat, W. C. Zipperer, and R. Costanza. 2001. Urban ecological systems: linking terrestrial ecological, physical, and socioeconomic components of metropolitan areas. Annual Review of Ecology and Systematics 32:127-157.
Shane, D. G. 2007. Urban patches: granulation, patterns and patchworks. Pages 94-103 in B. McGrath, V. Marshall, M. L. Cadenasso, J. M. Grove, S. T. A. Pickett, R. Plunz, and J. Towers, editors. Designing patch dynamics. Columbia, Graduate School of Architecture, Planning, and Preservation, New York, NY.
Wu, J. G. and J. L. David. 2002. A spatially explicit hierarchical approach to modeling complex ecological systems: theory and applications. Ecological Modelling 153:7-26.


mlnation said...

Steward: Thanks for this piece. When I read the article in TREE, I was similarly struck that the authors had not really kept up with urban ecology and were relying on some old models and ideas
that we have moved away from. I wondered if we weren't doing a good enough job of getting new thinking into print -- I get tired of seeing CAP's old conceptual model cited! At any rate, thanks for writing this response.

Bose said...

The fact that one man can help change so much just by standing up and speaking out tells you how much can be accomplished when we devote ourselves heart and soul to something we believe in.!@bose
Ecologist Career