Why is Urban Sustainability so Hard? The Trap of the Sanitary City

A few months ago, I was having a lively discussion with some serious and dedicated undergraduates at a university I was visiting.  The fact that they were disappointed with their training in sustainability came up -- They felt they weren't being told how to practice sustainability.  This provided an opportunity for interesting engaged discussion, and helped me clarify some of my own thoughts.  Here's what came up for me.  I'll frame these thoughts in the context of urban ecology, since that's where I usually think about sustainability.  In fact it is hard to think about sustainability in any kind of ecosystem without including urban connections.

There are two basic reasons for the difficulty.  Sustainability is technically complex, and sustainability, unlike traditional strategies of urban management, doesn't yet have a recipe.  Here I'm following a distinction between complicated and complex (Allen and Starr 1982).

Sustainability is Technically Complex

Sustainability was first introduced in the 1970s.  But its most famous articulation is that of the Bruntland Commission in 1987.   This canonical definition emphasizes not only the need to consider the effect of current decisions on future generations and on people and places distant from the seat of decision making, but it also emphasizes that three things must be considered jointly: environmental integrity, economic vitality, and social equity.

Right off the bat, it is clear that sustainability is a multifaceted pursuit.  So it is likely to be complex because there are many components of each facet, and the facets will most likely interact.  If one acknowledges that sustainability tacitly assumes the subject to be a "human ecosystem," the reason for the resulting complexity of sustainability becomes clear.  Human ecosystems contain, at the minimum, biological components, physical environmental components, constructed components, technology, social structures, political processes, and economic resources.  And this long list is only indicative.  The interactions between and among components guarantee that efforts to assess and guide sustainability must involve all the components.  Non-linearities, multiple and scale-crossing feedbacks, and temporal lags would all lend considerable complexity to sustainability.

The Classic Sanitary Approach to Cities Is, in Contrast, Complicated

Contrast the complexity of sustainability to the way that cities have mostly been considered.  Most cities in areas that have experienced a history of industrialization can now be called "sanitary cities" (Melosi 2000).  The rise of the industrial city, especially when powered by coal, was a polluted affair.  Acidic and particle-laden smoke from factories and home fires made the air a "foul and pestilent congregation of vapours," to quote Shakespeare (Hamlet Act II, Scene 2).  The concentration of so many people in new settlements hurriedly built to house the new industrial workers who flocked from the countryside, led to fecal pollution of streams and even in many cases well water.  The industrial cities on Europe and North America, although desirable to waves of new migrants due to economic opportunity and intellectual and other freedoms, were clearly bad for people's health.  Bouts of mortality from waterborne diseases characterized these cities, and as late as the 1950s, significant mortality resulted from the "killer smogs" in some cities.

From the waste and disease of these industrial behemoths a new model of the city emerged.  Called by Martin Melosi (2000) "the sanitary city," this city model involved new ways of laying out cities and the development of infrastructure to provide clean water and convey sewage away from the city, for example.  In addition, the sanitary city model required new forms of governance, new modes of financing infrastructure, and new zoning regulations aimed at reducing hazards and promoting health.  In some cities, these structures began to emerge in the mid to late 1800s, while in other cities of the Global North, the physical and institutional structures did not emerge until the early 20th century.  In the United States, the efforts to clean up both urban and non-urban environments continued through the passage of the Clean Water Act in 1972, and the Clean Air Act in 1970.

Sanitary cities are governed through various departments charged with generating and maintaining the key infrastructure, or managing the solid and water-borne waste flows so that people were usually separated from the most noxious threats.  "Late" Sanitary Era development changed the strategy from shunting wastes "away" from the city, or at least away from districts inhabited by the wealthy and empowered, to reducing and treating wastes.  The ethical attention to populations and locations downstream and downwind was an important development in the sanitary city strategy, one that recognized the integration of urban areas with larger regional, and in the case of air pollution, continental-scale areas.

Constraints of the Sanitary City

The sanitary city strategy can be considered a success.  Sanitary cities are not the killers that the smoke shrouded, sewage drenched killers that Charles Dickens novelized.  But when compared with the more comprehensive strategy of sustainability, the sanitary city has some real shortcomings.  Some of these are in fact problematic legacies that must be overcome.  In the language of resilience theory, a sanitary city can harbor "rigidity traps" that hamper the transition to sustainability.  Here are some examples:

• Sanitary cities are governed from the top down, with resources provided by public funds.  Shortfalls in city funding can impair the functioning and maintenance of the massive physical infrastructure required for sanitation.  The sustainable city may benefit from alternative funding structures.

• Sanitary cities are managed by licensed specialists who are responsible to specific, issue oriented departments.  For example, drinking water, sewage, planning, justice, finance, housing, may each be managed by different departments or bureaus.  The sustainable city requires that all structures and functions in an urban place be thought of and managed as a system, not a series of loosely connected administrative units.

• The sanitary city may be seen as a tool to preserve the health and productivity of an industrial work force.  The sustainable city must adopt a stance of environmental and social equity, rather than be driven by the economic interests of a wealthy elite.

Other contrasts can be drawn between the sanitary city and the sustainable city models (Grove 2010; Pickett et al 2013).  However, this short list points out that there are key differences between the two.

New Recipes for Sustainable Urban Transformation

To return to the question of why it is hard to learn the sustainable city, much less actually promote sustainable trajectories in real cities, another point must be made.  Urbanists, politicians, planners, designers, management professions, and even residents of cities, have had something on the order of 150 years to visualize, develop, and improve the sanitary city model.  Authors such as Graham and Marvin (2001) and Gandy (2003) have explained in depth the complicated nature of the sanitary city, and the long time it took to develop and deploy the physical, political, and social structures needed to build and operate it.  Yet, for many of us "urban/suburban fish" in the Global North, the sanitary city is the "water we swim in."  It hardly elicits a second thought.  We don't have to be taught what it means to run it.  We may be troubled by environmental injustices within it, or its growing susceptibility to climate change, or the buffeting by shifting global economic investment.  But we fundamentally understand what kind of thing and experience a sanitary city is.

Not so the sustainable city.  Those who are committed to the future of cities are in the process of creating a new model -- a new recipe -- for cities.   The recipe for sustainability must facilitate the internal environmental integrity, the regional effects, the social livabilities and equitability, and of course the hoped for economic productivity of urban places.  And this recipe hasn't had long to mature.  The fact that sustainability requires input from a diversity of residents, citizens, and officials makes the initial visioning process difficult, yet crucial.  The fact that sustainability governance in many cases has to be built on top of existing legal structures, and indeed, to compensate for the fragmented management of what should be dealt with as an integrated system, adds its own kind of complexity.  But, from an ecological perspective, perhaps the biggest hurdle facing urban sustainability is beginning to see cities as hybrid systems -- having inextricably linked biological and social-economic features.  The recipe can't just deal with ingredients as independent parts.

It is no wonder that learning and practicing sustainability is so difficult.  But the students who today are struggling mightily with what sustainability is, how to apply that thinking to the hobbled sanitary urban systems they may have inherited, and how to make trajectories toward sustainability in and outside of cities the norm, are the folks who will ultimately be able to say: "This is the new post-sanitary model of urban systems, this is how the sustainable city works, this is how you apply the model to cities that are brand new or the large number of cities in the Global South and East that haven't even had an industrial and sanitary phase, and this is how you structure governance networks to operate it."  One day, the sooner the better, the Sustainable City models will be off the shelf recipes with high altitude and tropical variants, and suggestions for culturally different flavors.

Bon appetit!

Steward T.A. Pickett

Background Publications.

Allen, T.F.H. and T.B. Starr. 1982. Hierarchy: Perspectives for Ecological Complexity. University of Chicago Press, Chicago.

Cadenasso, M. L., S. T. A. Pickett, and J. M. Grove. 2006. Dimensions of ecosystem complexity: Heterogeneity, connectivity, and history. Ecological Complexity 3:1–12.

Childers, D. L., M. L. Cadenasso, J. M. Grove, V. Marshall, B. McGrath, and S. T. A. Pickett. 2015. An Ecology for Cities: A Transformational Nexus of Design and Ecology to Advance Climate Change Resilience and Urban Sustainability. Sustainability 7:3774–3791.

Gandy, M. 2003. Concrete and clay: reworking nature in New York City. MIT Press, Cambridge.

Graham, S., and S. Marvin. 2001. Splintering urbanism: networked infrastructures, technological mobilities and the urban condition. Routledge, New York.

Grove, J.M. 2010. Cities: Managing Densely Settled Social–Ecological Systems. Pp 281-294 In F. Stuart Chapin, III, Gary P. Kofinas and Carl Folke (eds.) Principles of Ecosystem Stewardship Resilience-Based Natural Resource Management in a Changing World. Springer, New York.

 

Melosi, M. V. 2000. The Sanitary City: Environmental Services in Urban America from Colonial Times to the Present. University of Pittsburgh Press, Pittsburgh.

Pickett, S. T. A., C. G. Boone, B. P. McGrath, M. L. Cadenasso, D. L. Childers, L. A. Ogden, M. McHale, and J. M. Grove. 2013. Ecological science and transformation to the sustainable city. Cities 32, Supplement 1:S10–S20.

How Many Principles of Urban Ecology Are There?

By Steward T.A. Pickett (Cary Institute) & Mary L. Cadenasso (University of California Davis)

In 2008, we published a short paper on the principles of urban ecology (Cadenasso and Pickett 2008).  It was aimed at landscape architects and landscaping practitioners as a part of an "Ecological Landscaping" conference attended mainly by these professionals.  Consequently, we wanted to distill key insights of urban ecological science in digestible form, that could be linked to landscape design and management. 

We generated five general principles to satisfy these intellectual and practical requirements (Table 1).

Table 1: The Five General Principles from Cadenasso and Pickett (2008)

1. Cities are ecosystems.
2. Cities are spatially heterogeneous.
3. Cities are dynamic.
4. Human and natural processes interact in cities.
5. Ecological processes are still at work in cities.

We discussed some design, planning, and management implications for each of these principles, to make them useful for the audience.  We believe that such abstractions of the essence of urban ecology have value to researchers and students within this evolving discipline as well.

What's a Principle, Anyway?

The term, principle, is actually rather vague.  A principle can refer to any of the several conceptually oriented components of theory (Pickett et al. 2007; Table 1 in Cadenasso and Pickett, 2008).  For example, a principle can be a concept, a definition used to translate concepts to specific cases, a definition of a quantitative convention within a model, a confirmed empirical generalization, or a law.  Although principles interact with facts and observations, are not the same as individual facts or even collections of facts.  The construction of principles involves some degree of abstraction, idealization, summarization, and the use of relationships among observations or other parts of theory.

To be fair, we didn't specify exactly what kind of conceptual "thing" our five principles were in 2008.  In part, this is because there was no mature, complete, theory with a clear framework that could be used to identify what role the principles played in a larger urban ecology theory.  We believe that's still the case today.

Later, we expanded the roster of principles by digging deeper into mechanisms, the cross-disciplinary nature of urban ecology, and some widespread concerns that would support the linkage of the science to practices well beyond landscaping.  That analysis appeared in a massive encyclopedia (Pickett and Cadenasso 2012), but is being refined as part of a chapter we are writing for a book synthesizing the insights of the Baltimore Ecosystem Study.  In that expanded version, we enumerate 13 principles, providing more detail in several of the statements (Table 2).

Research and management in vacant lots (photo: C. Swan)

Table 2: A more complete and detailed enumeration of principles.  Modified slightly from Pickett and Cadenasso (2012).

1. Cities and urban areas are human ecosystems in which social-economic and ecological processes feed back to one another.
2. Urban areas contain remnant or newly emerging vegetated and stream patches that exhibit ecological functions.
3. Urban flora and fauna are diverse, and this diversity has multiple dimensions (e.g. taxonomy, cladistics, function, geographic origin).
4. Human values and perceptions are a key link mediating the feedbacks between social and ecological components of human ecosystems.
5. Ecological processes are differentially distributed across the metropolis and the limitation of services and excess of hazards is often associated with the location of human communities that are poor, discriminated against, or otherwise disempowered.
6. Urban form is heterogeneous on many scales, and fine-scale heterogeneity is especially notable in cities and older suburbs.
7. Urban form reflects planning, incidental, and indirect effects of social and environmental decisions.
8. Urban form is a dynamic phenomenon and exhibits contrasts through time and across regions that express different cultural and economic contexts of urbanization.
9. Urban designs and development projects at various scales can be treated as experiments, and used to expose the ecological effects of different design and management strategies.
10. Definition of the boundaries and content of an urban system model is set by the researchers based on their research questions or the spatial scope of its intended application.
11. Urban comparisons can be framed as linear transects or as abstract gradients, and the abstract comparisons acknowledge the spatial complexity of urban heterogeneity.
12. Urban land covers and land uses extend into and interdigitate with rural or wild land covers and uses.
13. The flux of water, including both clean water supply and stormwater management, is of concern to urban and urbanizing areas worldwide, and connects them explicitly to larger regions.

What do Principles Do?

These 13 more detailed principles (Table 2) explain or nest within the five general principles laid out in 2008 (Table 1).  This suggests that there can be levels of generality of principles, with some being very "high level" or general.  In the forthcoming book chapter, we identify a list similar to that in Table 1 as "metaprinciples."  The difference between the highest level metaprinciples, the nested general principles, and then the principles that operate through specific models suggests that the emerging theory of urban ecology has -- like so many theories in science -- a nested hierarchical structure.  Examples of hierarchical theory structures relevant to ecology include that of succession or vegetation dynamics, and of evolution (Pickett et al. 2007, Meiners et al. 2015). 

Indeed, the theory of ecology in general has been presented as a hierarchy of eight very general principles, with nested constituent theories that address more specific ecological topics and processes (Scheiner and Willig 2011).  Within each of these constituent theories there are one or more models that spell out detailed mechanisms, temporal and spatial contingencies, rules and exceptions to the rules.  Some of these model components may legitimately be referred to as principles, though the difference between those and the most general principles of an area may not always be evident in the use of the term. 

The discussion so far shows that principles can

• Identify the main concerns of a theory.
• Serve to link general and specific components of theory.
• Lay out expectations of mechanism or interaction.
• Summarize patterns of interest to the theory.

How are Principles Arrived At?

Our approach to principles has been from the top down.  That is, we have been motivated by identifying the most general principles of urban theory, and then sorting out how the mechanistic or pattern details fit within those areas.

A bottom-up approach is also possible.  Richard Forman (2016) identifies urban principles using a primarily bottom-up approach.  We interpret his strategy as bottom-up because his list of the descriptors of science appears in this order: concepts, principles, laws, models, hypotheses, and theories.  Principles appear early in what is tacitly an inductive series.  In addition, his list of principles that have developed in urban ecology since its 1970s origin amounts to 90 entries. 

The inductive nature of this list is also strongly suggested by Forman's demonstration that the principles reflect the nature of cities in which the research supporting them was conducted.  Forman lists 16 details of late 19th century cities, and 15 for late 20th century/early 21st century cities, to illustrate the contexts in which the 90 urban principles emerged.

One of Forman's main points is that urban ecology, as a collection of empirical generalizations embodied in his 90 principles, is different than the principles that have emerged from the study of natural areas.  Thus, urban ecology as a body of knowledge summarized in inductive principles is (necessarily) different from other kinds of ecology as bodies of knowledge served by their own inductive principles.  The search for urban ecology principles, on his analysis, appears to be an inductive, place-based pursuit.  This is a perfectly legitimate scientific approach, but the differences between it and the approach of Pickett and Cadenasso (2008; 2012) need to be acknowledged.

The place-based nature of Forman's principles points to an important opportunity for urban ecology as a global science (McHale et al. 2015).  An important point about Forman's inductive approach is that it appears to be biased toward cities of the Global North.  Thus, the trajectories of the industrial revolution, the subsequent development of the sanitary city (Grove 2009), and the nodal role of metropolises in colonial and corporate globalization (Seto et al. 2012) are the boundary conditions for his principles.  The rapidly emerging urban realm of the Global South has a different mixture of contexts (McHale et al. 2015).  The areas undergoing the most rapid urban conversion today may well generate some of the same conditions as have emerged in the cradle of urban ecological science.  However, it is very likely that today's urbanization in Asia and Africa will establish some boundary conditions that are quite different.  An important task of urban ecology will be to identify these differences, and to articulate -- from the top down -- or to discover -- from the bottom up -- empirical generalizations that fit these new situation.

Thirteen ways of looking at urban ecology (apologies to Wallace Stevens), arranged as a nested conceptual hierarchy.

Ecology/Ecologies: One Science, Many Models

The idea of principle is a flexible one, embodying much power in structuring a science, summarizing its insights, and motivating application.  However, the fact that principles point to a hierarchy of generality suggests something about what it means for a subdiscipline or a kind of system to have a "different ecology." 

From the perspective of the definition of ecology as a scientific pursuit, there is only one thing.  There is only one ecology: The scientific study of the processes influencing the distribution and abundance of organisms, the interactions among organisms, and the interactions between organisms and the transformation and flux of energy and matter.  Urban ecology merely adds an emphasis on human ecosystems in general, which include organisms, the physical environment and conditions, the human population and its social structures and processes, and the built and technological components (Cadenasso et al. 2006, Pickett and Grove 2009).  So there is only one ecology -- as a way to pursue science -- although there are many kinds of system it can apply to.

From the perspective of ecology as a body of knowledge, however, there can be several kinds.  These "ecologies" are different specific models or families of model, or sets of generalizations about kinds of systems or historical periods.  This is the analytic home for Forman's (2016) conclusion that urban ecology is different from the ecology of wild places.  What this means is that the bodies of facts, empirical generalizations -- or principles in his parlance -- are different when they emerge from urban systems than when they emerge from wilder systems.

We hope that this discussion clarifies two things.  Urban ecology, which focuses on inhabited and densely built systems, and other kinds of ecology, which focus on uninhabited but in some cases managed or otherwise anthropogenically impacted, are the same as scientific process, and from the perspective of generalizable drivers (e.g. Scheiner and Willig 2011).  They are different in terms of the facts and generalizations that apply within their domains.  Knowing how to array research and conclusions across conceptual gradients connecting built and uninhabited landscapes, is as Forman (2016) suggests, a crucial frontier for ecological science in a changing, connected world.

 

And the Envelope, Please!

To answer the question posed in our title, there are roughly a half dozen principles of urban ecology when one takes a combined top-down and empirical approach; but there are 90 when one takes a bottom-up approach to empirical summarization.  These approaches have complementary roles to play in advancing urban ecology, and reconciling them points to a nested hierarchy as a way to promote integrated urban ecological theory.

Literature Cited

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.  http://digitalcommons.lmu.edu/cate/vol1/iss2/4

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 Societes 14:4–14.

Forman, R. T. T. 2016. Urban ecology principles: are urban ecology and natural area ecology really different? Landscape Ecology:1–10. DOI:10.1007/s10980-016-0424-4

Grove, J. M. 2009. Cities: Managing Densely Settled Social–Ecological Systems. Pages 281–294in F. S. Chapin, G. P. Kofinas, and C. Folke, editors. Principles of Ecosystem Stewardship: Resilience-Based Natural Resource Management in a Changing World.

McHale, M. R., S. T. A. Pickett, O. Barbosa, D. N. Bunn, M. L. Cadenasso, D. L. Childers, M. Gartin, G. R. Hess, D. M. Iwaniec, T. McPhearson, M. N. Peterson, A. K. Poole, L. Rivers, S. T. Shutters, and W. Zhou. 2015. The new global urban realm: complex, connected, diffuse, and diverse social-ecological systems. Sustainability 7:5211–5240.

Meiners, S. J., M. L. Cadenasso, and S. T. A. Pickett. 2015. An integrative approach to successional dynamics: Tempo and mode in vegetation change. Cambridge University Press, New York.

Pickett, S. T. A., and M. L. Cadenasso. 2012. Urban ecology. Pages 273–301 in R. Leemans, editor. Ecological systems: selected entries from the encyclopedia of sustainability science and technology. Springer, New York.

Pickett, S. T. A., and J. M. Grove. 2009. Urban ecosystems: what would Tansley do? Urban Ecosystems 12:1–8.

Pickett, S. T. A., J. Kolasa, and C. G. Jones. 2007. Ecological Understanding. Academic Press, San Diego.

Scheiner, S. M., and M. R. Willig, editors. 2011. The theory of ecology. University of Chicago Press, Chicago.

Seto, K. C., A. Reenberg, C. G. Boone, M. Fragkias, D. Haase, T. Langanke, P. Marcotullio, D. K. Munroe, B. Olah, and D. Simon. 2012. Urban land teleconnections and sustainability. Proceedings of the National Academy of Sciences of the United States of America 109:7687–7692.

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 http://www.bbc.co.uk/news/science-environment-16032471  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 http://www.sciencedirect.com/science/article/pii/S0169534711003028

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 http://www.sciencedirect.com/science/article/pii/S0169534712000286

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.

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