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 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. |
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
Acknowledgement.
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.
http://www.annewhistonspirn.com/pdf/Spirn-EcoUrbanism-2012.pdf.
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.
