Monday, December 21, 2015

A New School of Urban Ecology: Contributions from Baltimore

Modern American urban ecology can be said to have come to fruition to a large extent in Baltimore.  Of course there are other cities where parallel, reinforcing, or complementary research and engagement activities are taking place, and all contribute to the emerging edifice of contemporary urban ecology.  But the work in Baltimore has a distinct flavor that helps understand what is novel about today’s urban ecological science.  Much of this is summarized in the book by Grove et al. (Grove et al. 2015).

The Relationship of the Baltimore School to the Baltimore Ecosystem Study

The Baltimore School owes a great deal to the Baltimore Ecosystem Study.  The Baltimore Ecosystem Study, like its sibling the Central Arizona-Phoenix project, is a National Science Foundation-supported research and education project, first funded in 1998. Indeed, the long-term funding of integrated urban social-ecological research started by the NSF in these two projects is a major reason that contemporary urban ecological science now exists as a part of mainstream ecology and as an important cross-disciplinary effort.  Additionally, urban research in Seattle, Chicago, New York and Boston has also grown rapidly over the last 20 years.  Deeper roots of urban ecology in Europe and Asia have “hybridized” with the emerging American contributions to produce a broad, integrated, and rapidly evolving discipline (McPhearson et al. 2016).

A good way to describe the Baltimore Ecosystem Study is to examine its mission statement.  Briefly, the mission of the Baltimore Ecosystem Study is to:

  • Pursue excellence in social-ecological research in an urban system; 
  • Maintain positive engagement with communities, environmental institutions, and government agencies;
  •  Educate and inform the public, students, and organizations that have need of scientific knowledge; and
  • Assemble and nurture a diverse and inclusive community of researchers, educators, and  participants.

What is a School of Thought?

It turns out that this multifaceted mission can be said to suggest the existence of a school of thought and practice (Cadenasso and Pickett 2013).  A school comprises a set of related and reinforcing components (Morris 2015 p. 201).  Schools consist of 1) theories, concepts, and models; 2) linked research approaches, 3) a network of student and professional training; 4) modes of application to practical issues, and 5) a community that shares and advances goals unifying the other components. Schools are often invisible, and their basic assumptions and approaches are rarely stated and even less rarely evaluated.  And of course, schools may differ from one another.  We believe that as a mode of thought and practice, the Baltimore School represents a scientific culture that actually extends well beyond the confines of the Baltimore Ecosystem Study and its study region.

One reason that we articulate a Baltimore School is to contrast it with the classical Chicago School of Urban Ecology (Cadenasso and Pickett 2013).  This school was developed in the opening decades of the 20th century in the department of sociology at the University of Chicago.  This was the founding department of American sociology, and its members were anxious to codify a novel approach to studying the social structure and dynamics of cities.  Although such a study would be important in an of itself, because Chicago was the fastest growing city in the world -- ever -- at that time, there was the added urgency of developing a sociology adequate to the task of understanding a new kind of city.

The Chicago School was clearly a sociological invention.  Yet, it has been called a school of urban ecology.  This labeling has persisted or re-appeared ever since Park and Burgess's pioneering book on The City (Park and Burgess 1925).  Some sociology textbooks of the last few decades even explain the long-standing critiques that led to the demise of the Chicago School in the 1930s in terms of ecological flaws (Gottdiener and Hutchison 2000).  So several of us (Cadenasso and Pickett 2013, Grove et al. 2015) thought it wise to reinforce knowledge that 1) the Chicago School was not the contemporary representation of ecological understanding of urban systems, and 2) that there were new approaches, intellectual tools, and integrated networks that were worthy replacements.  Hence, we articulated the tenets of a school of social-ecological science that could be labeled a school.  We have been heartened that Sharon Kingsland, a leading historian of science at Johns Hopkins University specializing in ecology, agreed with the use of the term school for this effort.

The positive aspects of the Chicago School include 1) its focus on urban rather than rural settlements, 2) the use of the case history approach, 3) empirical techniques such as interviews and field surveys, 4) the use of a clear theoretical framework motivated by competition among different uses and community types within the city, and 5) a recognition of cities as dynamic and mutable.  Many of these features are conspicuous advances over the urbanism that preceded the Chicago approach, which employed a more physical or formal, and a more static view of cities.  

The Chicago School - first wave of US urban ecology.

But the Chicago School ultimately declined for many reasons.  The social shortcomings of the Chicago School have been well known for a long time (Hawley 1986).  It took rural and small settlement life as a desirable norm, and cast many urban phenomena in terms of pathologies.  It explained changes in neighborhoods and districts as interactions of unitary human communities.  It idealized spatial interactions and assumed sequential replacement of different residential and commercial zones.  It neglected individual or household behaviors.  It adopted explanatory models from plant ecology via analogy, but without recognizing that some of these, such as succession, were being challenged and refined in their home discipline even at the time (Light 2009).  Furthermore, because they adopted competition among communities as the predominant mechanism of urban change, they neglected positive social interactions.  It is also notable that they based many of their social assumptions on what are now seen as fixed, social-Darwinist view of races and immigrant groups.  Their distress at the massive arrivals of new immigrant groups -- African Americans from the South, and Europeans from southern and eastern countries -- is palpable in the 1925 book (Park and Burgess 1925).  Notable in this regard is their apparently willful ignorance of the more dynamic and empirically open approach to social science pioneered by W.E.B Dubois 20 years prior to the height of the the Chicago ascendancy (Morris 2015).

Contemporary Urban Ecology as a School of Thought and Practice

The Baltimore School is much more than a point-by-point refutation of the Chicago School.  Indeed, some of the practices of the Chicagoans, such as case study and empirical studies on the ground in communities, are mainstays of contemporary social-ecological understanding.  However, there are features that have emerged in contemporary urban ecology that are worth highlighting (Cadenasso et al. 2006a).

First, the Baltimore Ecosystem Study focused on an extensive metropolitan area as a social-ecological system.  Urban ecology must now extend well beyond “the city” (Boone et al. 2014).  Furthermore, the social and the biological are given equal intellectual weight, and the ultimate goal is to understand the urban system -- city, suburbs, and exurbs -- as an integrated social-ecological system.  This has required consistant interaction across a long list of disciplines.  Sociology, demography, geography, anthropology, economics, and history have melded their voices with plant ecology, wildlife ecology, remote sensing, hydrology, soil science, atmospheric science, geomorphology, metacommunity ecology, and stream ecology.  Within the social features of the system a vast array of power, technological, cultural, and political processes must be explicitly recognized.  We have found the human ecosystem framework to be a useful tool to enhance integration (Machlis et al. 1997, Pickett et al. 1997).

Second, the Baltimore School does not assume that cities and urban systems are pathological.  This is not to say that urban areas do not have environmental or social problems.  However, the goal of urban ecology is fundamentally to understand the structure and function of integrated social-ecological systems in all their spatial, temporal, and organizational complexity (Cadenasso et al. 2006b).  Urban ecology can and does often turn its attention to research questions that address important concerns of communities, managers, and policy makers.  But drivers and interactions that have positive, negative, and unintentional effects are all investigated without prejudice in contemporary urban ecology.

The phrase “spatial, temporal, and organizational complexity” used above is key to the Baltimore School.  Urban ecology must investigate complex spatial mosaics of regional extent.  Investigations focus on local to regional scales, and even extend to understanding the global influences on local and regional urban processes. Thus, spatial scale is a key concern of contemporary urban ecology.  

Temporal complexity sets urban ecology in a deep historical perspective, acknowledging that past decisions and the social and structural legacies they engender are important determinants of current system processes.  Furthermore, temporal change is ongoing in cities, and the dynamic models of particular times and places may not apply to other locations or trajectories of change.  Shrinking, post-industrial, sprawl, ghost, and shanty cities or districts are examples of the variety of dynamics urban areas are now experiencing (McHale et al. 2015).  

Organizational complexity introduces another important dimension of scale.  It indicates that decisions and behaviors can originate at individual, household, community, governance, and jurisdictional levels, for example.  Given that the institutions that exist on different organizational levels have different spatial extents and different longevities, the opportunity for complex, non-linear effects is great.

Go Where the Data Lead You

One facet of the Baltimore School is to not be bound either by vernacular "urban legends" or by preconceptions.  Urban areas are already the home of more than 80% of residents in wealthy nations, and globally, the urban population stands at greater than 50%.  This means that some manner of urban settlement -- whether dense city, compact suburb, suburban sprawl or exurban retreat -- is a matter of deep personal experience of most of humanity.  In other words, we all "know what a city is" and have personal opinions about the benefits, frustrations, or vulnerabilities of our urban (sensu latu) homes and workplaces.  But personal experience can be misleading and must be questioned when we enter the realm of urban ecological science.  We have debunked urban legends elsewhere (Pickett et al. 2008), and myths about trees and crime, misunderstanding the relationship of mosquitoes breeding and trees, the low biodiversity of vacant lots, are among "legends" currently being clarified.  The key is to follow the scientific approach of going where the data lead us, and to examine assumptions about social-ecological pathologies, ecosystem services, and structure-function relationships (Pataki 2013).  While these assumptions may reflect legitimate human values, and thus are quite legitimate motivators for research. The conclusions must arise from the data and not from the assumptions. 

The relationship of data to decision making brings with it an obligation for contemporary urban science to engage in the civic dialogs shaping and managing urban systems.  Science cannot ethically impose its wishes on urban systems, but it must legitimately share and explain its conclusions in the civic dialog, and engage with urban designers, planners, managers, and policy makers in their quest to improve the sustainability of urban systems and city life (Childers et al. 2014).

Where is the Baltimore School?

Baltimore PS 103, Attended by Thurgood Marshall  
This essay has sought to explain what a school is, and how the Baltimore School differs from and supersedes the long-discredited Chicago School.  The essay has not touched on other schools of urbanism, each of which has value.  The Los Angeles School (Dear and Dahmann 2008) for example, is helpful in advancing a regional understanding of urban systems.  Many of the other schools are predominantly motivated by urban design or planning concerns, or remain thoroughly rooted in social science traditions.  One of our goals in the Baltimore School is to suggest the importance of including ecological science perspectives and approaches in the study of urbanization, city/suburban/exurban mosaics, and in designing and managing for sustainability (McGrath 2013, Pickett et al. 2013).  The functional connections required to work with both ecological and social connectivities is the Continuum of Urbanity (Boone et al. 2014).  This emerging theory highlights the kinds of exchanges, influences, and effects that spread throughout and between urban megaregions even at the global scale. 

I close with a plea to see the Baltimore School as an expression of a broader and inclusive approach to incorporating ecological knowledge into understanding, envisioning, and managing the changing urban realm wherever it exists (McHale et al. 2015).  The Baltimore School isn't a little red schoolhouse at any particular crossroads, and it isn't just in or about Baltimore.  It is an invisible college and framework for an inclusive ecological-social approach to the emerging and ongoing complexities of urban systems worldwide.


Boone, C. G., C. L. Redman, H. Blanco, D. Haase, J. Koch, S. Lwasa, H. Nagendra, S. Pauleit, S. T. A. Pickett, K. C. Seto, and M. Yokohari. 2014. Reconceptualizing land for sustainable urbanity. Pages 313–330 in K. C. Seto and A. Reenberg, editors. Rethinking urban land use in a global era. MIT Press, Cambridge.

Cadenasso, M. L., and S. T. A. Pickett. 2013. Three tides: the development and state of the art of urban ecological science. Pages 29–46 in S. T. A. Pickett, M. L. Cadenasso, and B. McGrath, editors. Resilience in ecology and urban design: linking theory and practice for sustainable cities. Springer, New York.

Cadenasso, M. L., S. T. A. Pickett, and J. M. Grove. 2006a. Integrative approaches to investigating human-natural systems: the Baltimore ecosystem study. Natures Sciences Societes 14:4–14.

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

Childers, D. L., S. T. A. Pickett, J. M. Grove, L. Ogden, and A. Whitmer. 2014. Advancing urban sustainability theory and action: Challenges and opportunities. Landscape and Urban Planning 125:320–328.

Dear, M., and N. Dahmann. 2008. Urban politics and the Los Angeles School of urbanism. Urban Affairs Review.

Gottdiener, M., and R. Hutchison. 2000. The New Urban Sociology. McGraw Hill, New York.

Grove, M., M. L. Cadenasso, S. T. A. Pickett, G. Machlis, and W. R. Burch Jr. 2015. The Baltimore School of Urban Ecology. Yale University Press, New Haven.

Hawley, A. 1986. Human Ecology. University of Chicago Press, Chicago.

Light, J. S. 2009. The nature of cities: ecological visions and the American urban professions 1920-1960. Johns Hopkins University Press, Baltimore.

Machlis, G. E., J. E. Force, and W. R. Burch. 1997. The human ecosystem .1. The human ecosystem as an organizing concept in ecosystem management. Society & Natural Resources 10:347–367.

McGrath, B. P., editor. 2013. Urban design ecologies. John Wiley and Sons, Ltd, Hoboken.

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.

McPhearson, T., S. T. A. Pickett, N. B. Grimm, J. Niemelä, M. Alberti, T. Elmqvist, C. Weber, J. Breuste, D. Haase, and S. Qureshi. 2016. Advancing Urban Ecology Towards a Science of Cities. BioScience Accepted for publication.

Morris, A. 2015. The Scholar Denied. University of California Press, Berkeley.

Park, R. E., and E. W. Burgess. 1925. The City. University of Chicago Press, Chicago.

Pataki, D. E. 2013. Urban greening needs better data. Nature 502:624–624.

Pickett, S. T. A., M. L. Cadenasso, J. M. Grove, P. Groffman, L. E. Band, C. Boone, W. R. Burch, S. Grimmond, J. Hom, J. C. Jenkins, N. L. Law, C. H. Nilon, R. V. Pouyat, K. Szlavecz, P. S. Warren, and M. A. Wilson. 2008. Beyond urban legends: an emerging framework of urban ecology as illustrated by the Baltimore Ecosystem Study. Bioscience 58:139–150.

Pickett, S. T. A., M. L. Cadenasso, and B. McGrath, editors. 2013. Resilience in ecology and urban design: linking thoery and practice for sustainable cities. Springer, New York.

Pickett, S. T. A., W. R. B. Jr, S. E. Dalton, T. W. Foresman, J. M. Grove, and R. Rowntree. 1997. A conceptual framework for the study of human ecosystems in urban areas. Urban Ecosystems 1:185–199.

Image Credits: 
Kanagawa Oki Nami Ura (神奈川沖浪裏), literally, Under a wave off Kanagawa, woodcut print after Katsushika Hokusai (葛飾北斎) from the series 36 Views of Mount Fuji, created in the late 1820's, and first published 1832. This version is an undated modern reprint.  From Library of Congress
"PS 103 Old W Balt HD T Marshall" by Smallbones - Own work. Licensed under CC0 via Commons -

Monday, November 16, 2015

Shifting Urban Realities and Nature Beyond Parks

Traditionally, cities have been thought of as distinct from nature.  In fact, they have often been considered to be the antithesis of nature.  Ecological science in the past seemed to agree with these assumptions, and ignored cities in favor of wilderness or at least sparsely inhabited places.  During this traditional phase, nature was though of a an unchanging or perhaps a deterministically changing "other." 
Cherokee Park, Louisville KY. Nature in the city.
Into this world of a separate, lasting nature was   If urban and nature were distinct, then the burgeoning populations of cities would need a window onto this separate realm.  Parks would serve as a civilizing influence, a platform for socialization of rural and foreign migrants, a venue for healthful exercise, and a glimpse of the American sublime.  Parks would be an escape hatch from the pressures and pathologies attributed to cities by the scholars and activists of the maturing 19th century.
inserted the American philosophy of urban parks.

Ecology In the City and Ecology In Parks

Ecology, when it finally arrived downtown, would use parks as places to apply its biological toolkit in cities.  Parks, in cities, suburbs and exurbs, would provide the research sites in which to understand the effects of urban environments on organisms, soils, and ultimately on ecosystem processes.  But this understanding would still be framed in terms of the ecology of isolated green spaces in the urban fabric.  Perhaps the human population density or the proportion of impervious surfaces outside parks would serve as explanatory variables, but the emphasis was still on nature versus the urban.  As a participant in that initially cautious exploration of the ecology IN the city, I have to say that many unexpected things were learned -- things like the enhanced nitrogen dynamics of urban forests, the role of exotic earthworms in carbon and nutrient cycling, and the constraints on the regeneration potential of urban forests.

Humans as Components of Ecosystems

At the same time that ecological science was colonizing   By the last third of the 20th century, ecology as a discipline was beginning to adopt some new perspectives.  Primary among these was that humans were involved in almost all ecosystems.  Humans were components -- whether distant or local -- of virtually all ecosystems.  In my own case, the watershed event didn't take place in a city.  Ecological anthropologist Pete Vayda, his student Tim Jessup, and I designed a comparison of natural versus human-created gaps in Bornean rainforest at various distances from a village in East Kalimantan, Indonesia.  Their field work revealed that all canopy gaps combined natural processes and human actions.  If the middle of Borneo failed to provide natural treefall gaps, perhaps there were few places that might boast purely natural environments. 
Long Sungai Barang, Indonesia (by Akubra)
the novel frontier of the city, changing concepts of nature were beginning to crystallize.

The science of ecology began to discover ever more cases of humans as components of ecosystems.  That has become the expected norm.  The ideal of untouched nature is now seen as a very special and rare case.  Indeed, with climate change, perhaps it is fair to say that the nutrient loadings, precipitation amounts and distribution, seasonal shifts, and frequencies of storms, for example, are imposed by human action on even the most remote ecosystems.

Nature Beyond Parks: Ecology OF the City

As ecology in general began to recognize humans as components of ecosystems, so too was urban ecology beginning to explore beyond the comfortable locations of green spaces in cities.  Ecologists were beginning to interact with social scientists and urban designers to conduct research that encompassed entire cities, and indeed entire metropolitan areas.  Over the last 20 years or so, this approach of ecology OF the city, has produced many novel and in some cases quite unexpected findings.  The Baltimore Ecosystem Study, one of the two Long-Term Ecological Research projects located in a city, provides some examples.  One key insight is that the distributed biology of a city contributes to the absorption of nitrogen pollution.  Similarly, the combined vegetation of cities and suburbs contributes to reduced carbon loading into the atmosphere.  A third example is that tree canopy is unambiguously associated with reduced crime in Baltimore neighborhoods, despite variations in social and economic factors.  The exception proves the rule about trees and crime, since only in the three residential neighborhoods that abut abandoned industrial sites was increased crime associated with tree canopy.  This is hypothesized to be due to a low number of "eyes on the street" in such places.

Combining the insights from Borneo and other   Cities, and urban systems more generally, are human ecosystems, containing biological, social, built, and physical components.  The interactions in these ecosystems, which include material and energy transfers, and the movement of influence, information, and power, involve all four components.  Cities are now seen as being suffused with nature.
The Baltimore Human Ecosystem and spatial complexity.
lightly inhabited places, with the discovery of biological activity dispersed throughout urban systems, led to a revision of the traditional idea that cities and nature are antithetical.

Cities and nature can no longer be dichotomized.  However, this insight leaves the second half of the traditional assumptions about nature and cities still to be examined.  What of the view of nature as fixed, deterministic, or equilibrial?  Ecology has come to emphasize process and change rather than stasis.  Dynamics of plant succession, natural and human disturbances, and even changing climate leave natural systems or natural components of urban systems in periodic or constant flux.  Nature is not a fixed thing.  A watershed event in my own understanding of this idea emerged from my work at the Hutcheson Memorial Forest in central New Jersey.  This old-growth mixed-oak forest was set aside for conservation in 1956, using the philosophy of untouched, undisturbed nature.  But over the next five decades unexpected changes took place.  The arrival of exotic species such as Norway maple, wine raspberry, and stilt grass, the explosion of white-tailed deer, and the absence, since 1711, of Native American-set ground fires, have all contributed to the decline of oak dominance in what was once considered a stable forest.  Many of these changes result from the cultural and physical connections of the forest to the adjoining landscape -- the shift from farms to suburbs, the demise of deer hunting, the planting of exotic species in yards, and so on.  Although there are many management tools that could have helped maintain the desired 1950s forest structure and composition, the philosophy that nature is stable, prevented their application.  Nature itself, is dynamic, and when entwined with human actions, unpredictably so.

The Urban as Process

Auch et al. 2004. USGS Circular 1252.
What of the related idea that urbanization proceeds   This model sees urbanization as a universal, one-way journey.  Maps of urban spread as a red blob bleeding out over a green countryside, are common.  Such "red-blob" urbanization maps, obscure important things about cities.  First, they hide even the obvious biologically dominated land and water systems in cities.  This is especially the case with the slivers and fragments that do not excite the attention of planners or managers.  Yet, these small places have contributions to make to biodiversity, water absorption, nutrient retention, microclimate amelioration, and psychological well being.  Second, red-blob urbanization hides the fact that within cities and urban areas, different patches behave differently.  Even as cities grow outward, some core neighborhoods, old commercial districts, and industrial zones may thin and exhibit abandonment and demolition.  Urban change can be via growth, shrinkage, or shift.  Urban ecology has improved as a science so that it now addresses not only the coarse-scale regional expansion of cities and suburbs, but also the ecologically relevant dynamic heterogeneity within them.  Such spatial complexity has great potential to determine ecological functioning of both individual patches and the entire city-suburban-exurban mosaic.
via a set trajectory through mercantile, industrial, and sanitary phases as seen in the Northeastern U.S. or Europe?

Not only do combined city, suburban, and exurban systems change physically, they also change socially and institutionally.  The location of financial investment and disinvestment, the nature and intensity of economies ranging from industrial to service and from formal to informal, the change in household size and composition, the ethnic and demographic shifts in neighborhoods, are all examples of such drivers.   Especially relevant to parks are the changes that may occur in community perceptions, values, and expressed needs.  The desire for passive versus active recreation, for motorized versus muscle-powered activities, for play and sports equipment, for quiet seating, for rustic versus paved paths, and many other contrasting criteria exemplify the diverse judgments that different age cohorts, household types, and social groups may bring to parks. 

The complexity of the ecological role of parks begins to emerge here.  There are parallels in how urban ecology has come to be a more multi-disciplinary and process based discipline.  Starting from its origins as an ecology in the city, an inclusive study of urban systems as social-ecological systems with broad extent and internal variety has evolved.  Early in this scientific history, parks were a window on the effects of cities on ecosystem processes.  Looking at study plots in parks over the long term has confirmed that the parks themselves are dynamic due to succession, natural disturbance, human use, shifting management strategies or financial and human resources available.  Parks are clearly a dynamic element of the urban social and spatial fabric.  They are, to be sure, an element that hosts and amplifies the ecological work that cities and suburbs can do.  It is perhaps no fluke that one of the seeds that led to the establishment of the Baltimore Ecosystem Study was the interaction of Hixon Professor Emeritus Bill Burch with Dr. Ralph Jones, the late director of the Baltimore City Department of Recreation and Parks.  Stimulated by Burch's community-enhancing forestry work in Nepal, Jones invited Burch to explore similar work -- research and action -- in Baltimore.  The parks were key to this work, but like BES, the expanded ecology OF the city project the Jones/Burch interaction helped prepare for, the community forestry approach supported understanding of the entire city -- parks and all.

Some Principles about the Parallel Views of Parks and Urban Ecology

Can this entwined history of ecology and of parks be tamed with some principles?  The first few principles are the antidotes to the urban legends that introduced this essay.

1. Cities are not distinct from nature.  In fact urban systems are hybrids of social, biological, built, and physical components. 

2. Nature is not always stable or even stabilizing.  Nor is it unchanging.  In fact, natural systems and the natural components of cities are highly dynamic, exhibiting probabilistic and non-linear trajectories of change.  The capacity to adapt is a key part of natural change, but in urban areas management is an ingredient of adaptation, and is required to maintain a natural system or key biological component in some desired range.

3. Parks are a just one entryway to nature in cities.  A lot of the nature in cities remains hidden -- even in parks.   Buried streams, nature in slivers on parcel boundaries, abandoned lots and brownfields, biodiversity represented by shy or small organisms -- all are a part of the nature of cities.  Of course, large parks are an important source of ecological wealth in urban systems.  But they are part of a larger network of nature in urban spaces.  The hybrid nature in cities goes well beyond parks.  Urban ecology has evolved -- from ecology IN to ecology OF -- along with this realization.

Next are principles that emerge from improved understanding of both cities and natural processes.  These help link ecological understanding and processes with the role of parks in cities.

4. Parks change.  Parks may have been designed to suit the needs and philosophy of a particular time period.  For example, their design might reflect decisions by elites in the Progressive Era, rather than a more recently articulated bottom up and inclusive process.  Sometimes the changes that parks exhibit were anticipated by their designers and builders, but the need for management may be forgotten by new generations of park users and managers.  Nor may the financial or personnel resources required for management be available over the long term.  Park change requires action.

5. Cities change too, and the demography and culture of park users -- whether across the street or across town -- is not fixed through time.  Park design and program reflect the values and needs of communities, and as communities change so too do the criteria for judging parks.

6. Parks are a process.  This phrase, coined during discussions among Karen Seto, Lisa Schroeder, Rebecca Salminen-Witt, and Colleen Murphy-Dunning of the recent 21st Century Parks conference at Yale, is perfect for weaving the threads in this essay together.  Parks are a complex process linking biology, society, function, and benefit together.  But contemporary urban ecology also focuses on the processes of social-ecological interaction that structure and transform city-suburban-exurban systems.  Our understanding of parks coevolves with the scientific understanding of urban systems, and with the needs, values, and resources of human communities and institutions.  This leaves us at the doorstep of the most inclusive ecology of them all - the ecology for the city.

Steward T.A. Pickett
Cary Institute of Ecosystem Studies
Millbrook NY


A presentation to the Conference entitled "Science and Management of 21st Century Parks," Hixon Center for Urban Ecology, Yale University School of Environmental Studies and Forestry, New Haven, 13 November 2015.

Background Publications

Cadenasso, M. L., and S.T.A. Pickett. 2008. Urban Principles for Ecological Landscape Design and Management: Scientific Fundamentals. Cities and the Environment 1(2): Article 4.

Cadenasso, M. L., and S.T.A. Pickett. 2013.  Three Tides: The Development and State of the Art of Urban Ecological Science. In Resilience in Ecology and Urban Design: Linking Theory and Practice for Sustainable Cities. S.T.A. Pickett, M. L. Cadenasso, and B. McGrath, eds. Pp. 29–46. New York: Springer.

Childers, Daniel L., Mary L. Cadenasso, J. Morgan Grove, et al. 2015. An Ecology for Cities: A Transformational Nexus of Design and Ecology to Advance Climate Change Resilience and Urban Sustainability. Sustainability 7(4): 3774–3791.

Childers, Daniel L., Steward T. A. Pickett, J. Morgan Grove, Laura Ogden, and Alison Whitmer. 2014.  Advancing Urban Sustainability Theory and Action: Challenges and Opportunities. Landscape and Urban Planning 125: 320–328.

Grove, Morgan, Mary L Cadenasso, S. T. A. Pickett, Gary Machlis, and W. R. Burch Jr. 2015. The Baltimore School of Urban Ecology. New Haven: Yale University Press.

McDonnell, M. J., A. K. Hahs, and J. H. Breuste, eds. 2009. Ecology of Cities and Towns: A Comparative Approach. New york: Cambridge University Press.

McHale, Melissa R., Steward T. A. Pickett, Olga Barbosa, et al. 2015. The New Global Urban Realm: Complex, Connected, Diffuse, and Diverse Social-Ecological Systems. Sustainability 7(5): 5211–5240.

Spirn, A. W.  2012. Ecological Urbanism: A Framework for the Design of Resilient Cities.

Troy, A., J. M. Grove, and J. O’Neil-Dunne. 2012.  The Relationship between Tree Canopy and Crime Rates across an Urban-Rural Gradient in the Greater Baltimore Region. Landscape and Urban Planning 106(3): 262–270.