Are cities ecosystems—analogous to natural ones—of nature, infrastructure and people? Does thinking about cities in this way help us think about urban design?

Marina Alberti, Seattle.  Erik Andersson, Stockholm.  Sarah Dooling, Austin/Boston.  Paul Downton, Melbourne.  Thomas Elmqvist, Stockholm.  Nancy Grimm, Phoenix.  Dagmar Haase, Berlin.  Dominique Hes, Melbourne.  Kristina Hill, Berkeley.  Madhusudan Katti, Raleigh.  Francois Mancebo, Paris.  Clifford Ochs, Oxford.  Steward Pickett, Poughkeepsie.  Stephanie Pincetl, Los Angeles.  Rob Pirani, New York.  Richard Register, Berkeley.  Eric Sanderson, New York.  Alexis Schaffler, Berkeley/Johannesburg/Cape Town.  Vivek Shandas, Portland.  David Simon, London.  Jane Toner, Melbourne.  Yolanda van Heezik, Dunedin.  Ken Yeang, Kuala Lumpur.  David Maddox, New York. 
30 June 2017

Many voices. Greener cities. Better cities.
Every month we feature a Global Roundtable in which a group of people respond to a specific question in The Nature of Cities.
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Hover over a name to see an excerpt of their response…click on the name to see their full response.
Marina Alberti, Seattle Instead of aiming at control, we must embrace uncertainty and redefine principles of design to acknowledge the complexity of hybrid ecosystems—expanding the heterogeneity of forms and functions in cities to support both human and ecological functions.
Erik Andersson, Stocklolm More organic, constantly changing and evolving cities could help to shift worldviews back to being grounded in change and changeability rather than control and permanence.
Sarah Dooling, Austin/BostonThe danger of an object-oriented systems approach to urban ecosystems is that it is inattentive to consequential political conflicts arising from competing values and unshared goals.
Paul Downton, MelbourneThe complexity of extended organisms and cities in particular make it difficult to demarcate inviolable distinctions between when it’s an organism and when it’s an ecosystem.
Thomas Elmqvist, Stockholm What we really need is closer collaboration among a diverse set of knowledge holders in natural science, social science, humanities, and among practitioners. The term ecosystem, originating from natural sciences, may alienate groups we need to include in diverse city-building conversations.
Nancy Grimm, PhoenixAs ecologists we would be arrogant to assume that our models alone suffice to understand the multifaceted drivers of change. It’s imperative to continue to expand the concept of the urban ecosystem to incorporate a multidisciplinary view.
Dagmar Haase, BerlinCo-evolutionary planning and governance means the elimination of sectoral thinking and actions that favour more holistic concepts of urban, regional and local regeneration, resilience and adaptation.
Dominique Hes, MelbourneCities are ecosystems but they are not well adapted to place; indeed, we have displaced their ecological functions. For this reason, cities have not yet reached their full ecological maturity or potential.
Kristina Hill, BerkeleyCities meet the definition of ecosystems, with important limits—understanding urban ecosystems must start with an awareness of the ethical and conceptual pitfalls of studying human behavior without considering human values.
Madhu Katti, RaleighOf course cities are ecosystems. More interesting is to ask what kind of an ecosystem cities can be rather than worrying about how unnatural a blight they are on more “natural” landscapes.
François Mancebo, ParisCities are ecosystems and a lot more than that: they are social-ecological systems.
Clifford Ochs, OxfordYour habits are our habits, your throwaways are our takeaways, and while you’ve done all the work to make the city for yourselves, we could not resist moving in, migrating across the grid, and settling down.
Steward T.A. Pickett, PoughkeepsieThe deep definition of the word ecosystem is notable for what it leaves out—the minimal baggage carried by the idea makes it nimble and broadly applicable.
Stephanie Pincetl, Los AngelesThe danger of an object-oriented systems approach to urban ecosystems is that it is inattentive to consequential political conflicts arising from competing values and unshared goals.
Rob Pirani, New YorkConsideration of the social benefits of resilience technology, and the civic ecology that it can engender, may well determine whether our urban ecosystems and all of their inhabitants can successfully adapt to a changing future.
Richard Register, OaklandComparing our cities to complex living organisms seems much more fruitful—in other words, to our own bodies, our organ systems, our limits. I think of this as the “anatomy analogy”.
Eric Sanderson, New YorkA city is an ecological landscape—and a landscape, to scientists like me, is the particular pattern of ecosystems, their composition and arrangement, that forms a habitat for plants and animals. Even for people
Alexis Schaffler, Berkeley/Cape Town/JohannesburgPerhaps our insight is not really in viewing cities as ecosystems, but instead lies in how the cities-as-ecosystems idea causes our urban thinking and designs to evolve.
Vivek Shandas, PortlandWhat then can be done to address the historical inequities of applying urban ecological knowledge to exclusionary planning practices? First is the recognition that urban ecological research is not value-neutral.
David Simon, GothenburgPerhaps in the future, the ecosystem analogy might become more apt, but at present it is unhelpful and inaccurate, obscuring or concealing far more than it might superficially promise as heuristic device.
Jane Toner, MelbourneCities are ecosystems but they are not well adapted to place; indeed, we have displaced their ecological functions. For this reason, cities have not yet reached their full ecological maturity or potential.
Yolanda van Heezik, DunedinThinking about a city as a collection of ecosystems influenced by their surrounds could be a more helpful way to inform urban design, and make it easier to identify the elements that make up each particular ecosystem.
Ken Yeang, Kuala Lumpur/LondonWhereas ecosystems are living entities, our existing towns and cities are, in effect, inert structures unlike living things, and have operational and industrial systems that give nothing of biological value back to nature.
David Maddox

About the Writer:
David Maddox

David loves urban spaces and nature. He loves creativity and collaboration. He loves theatre and music. In his life and work he has practiced in all of these as, in various moments, a scientist, a climate change researcher, a land steward, an ecological practitioner, composer, a playwright, a musician, an actor, and a theatre director.


Are cities ecosystems in the senses in which we think of classic natural and ecological areas outside of cities? After all, urban spaces are connected mosaics of green space, biodiversity (including people), non-biological structure, biophysical processes, energy flows, and so on. That sounds a lot like a natural ecosystem.

For example, here is one definition of a natural ecosystem (from

An ecosystem is comprised of all the non-living elements and living species in a specific local environment. Components of most ecosystems include water, air, sunlight, soil, plants, microorganisms, insects and animals.

That could be a description of a city. Or not (perhaps depending on the city).

But perhaps more importantly, does thinking explicitly about cities as ecosystems help us? Does it offer us any insight into urban design? For example, are our goals for cities—sustainability, resilience, livability, and justice—advanced by an urban eocsystem concept?

Many of these contributors say, yes, certainly, cities are ecosystems. Not all, though. A few more are skeptical that an ecosystem concept is central to planning better cities. The more common belief among this group might be that a socioecological and landscape approach to cities is more important, and one that is imbued with values.

Marina Alberti

About the Writer:
Marina Alberti

Marina Alberti is Professor of Urban Design and Planning and Director of the Urban Ecology Research Lab at the University of Washington. Her research focuses on complexity, resilience, and eco-evolutionary dynamics in urban ecosystems.

Marina Alberti

Cities are in fact ecosystems. Tansley (1935) defined an ecosystem as a community of living organisms in conjunction with the nonliving components of their environment interacting as a system. Eugene Odum (1971) expanded the definition, calling it “a unit that includes all the organisms, i.e., the community in a given area interacting with the physical environment so that a flow of energy leads to clearly defined trophic structure, biotic diversity and material cycles, i.e., exchange of materials between living and non-living, within the system” (p.12).

But one key element—the dominance of humans—makes cities different from many other ecosystems. And that changes everything: composition, processes, dynamics, functions (Alberti 2016). By building structure and infrastructure in cities to support their needs, humans redistribute organisms and the fluxes of energy and materials leading to a distinct biogeochemistry (Picket et al. 2001, Grimm 2008), biotic diversity (Groffman et al 2014), and energy and material cycles (Bai 2016).

All organisms modify the environment to create their habitat and facilitate their survival, and humans are no exception. Darwin (1881) spent his final years observing and describing the effects earthworms had on soil formation. Earthworms feed on plant debris and soil. Because they concentrate the organic and mineral constituents of what they eat, their casts contain more available nutrients than surface soil. Beavers build dams that dramatically alter riparian landscapes across North America—and thus maintain and increase both species richness and habitat heterogeneity (Wright et al. 2002). Ecologists have documented how the changes of many organisms—the ecosystem engineers– can influence organismal distribution and abundance and ecosystem processes at the local and larger scales (Wright and Jones 2002).

So what makes cities different? Although we do not yet have conclusive evidence on whether species diversity and energy flows in cities are qualitatively different, or simply an end point of a continuum, urban ecosystems operate outside the envelope of values observed in natural systems (Grimm et al 2008). Compared to systems not dominated by humans, urban ecosystems are highly disturbed environments (Grimm et al. 2017), very heterogeneous in both space and time (Pickett et al. 2016): complex mosaics of biological and physical patches in a matrix of infrastructure, human organizations, and social institutions.

The ecology of urban ecosystems is only one of the elements that makes cities different. Humans and their communities add a new level of complexity. Humans design and build cities on the basis of their preferences and values. Urban ecology lacks a theory and science of human habitats comparable to those used to study other species’ habitats that fully acknowledges the complexity of the human species and societies. Often we study cities as ecological systems, disregarding the fundamental fact that they are built for humans. Developing a theory that fully includes humans as key agents of ecosystems will require an extraordinary new collaboration among a broad range of disciplines.

Instead of aiming at control, we must embrace uncertainty and redefine principles of design to acknowledge the complexity of hybrid ecosystems—expanding the heterogeneity of forms and functions in cities to support both human and ecological functions.
The ecosystem concept in ecology does not fully reflect our current understanding of dynamic human-dominated ecological systems that may operate far from equilibrium (O’Neill 2001). In his MacArthur Lecture in Ecology, Robert O’Neill (2001, 3276) argued that the assumptions behind the ecosystem paradigm limit our thinking and the questions we ask because they emphasize some properties of nature while ignoring others (Alberti 2016). Crucially, ecosystems can change state in response to a spectrum of variable conditions (Holling 1973); they have evolved over millions of years through changes in biotic-abiotic interactions. But since the Industrial Revolution, humans have increasingly dominated such interactions, creating novel ecosystem functions never observed before (O’Neill 2001; Tilman and Lehaman 2001). Yet in ecology, humans are the only species considered to be external to ecosystems. Furthermore, emphasis on the self-regulating nature of ecosystems has limited the view of disturbance that we now know is critical to understanding stability and ecosystem function.

During the past hundred years, advances in the scientific understanding of ecological systems have called for integrating humans into ecology (Alberti et al. 2003). In ecology, scholars no longer see ecosystems as closed, self-regulating entities that “mature” to reach equilibrium. Instead, they acknowledge that ecosystems have multiple equilibria and are open, dynamic, highly unpredictable, and subject to frequent disturbance (Pickett et al. 1992). But only in the past decade have scholars of urban ecology started to expand their conceptual frameworks and methods of analysis to better represent socioecological interactions (Pickett et al. 2013). To study urban ecosystems, we must integrate multiple agents and boundaries and analyze processes at multiple scales, ranging from local to metropolitan, regional, and global. We must also explicitly represent human agents and link urban structures, biophysical processes, and human behaviors to ecosystem functions.

Cities as hybrid ecosystems

In my recent book, Cities That Think like Planets, I advance the hypothesis that cities are hybrid ecosystems: the product of co-evolving human and natural systems. Urban ecosystems emerge from complex interactions and feedbacks between the human, natural and technological system components of urban ecosystems (Alberti, 2016 (figure below). From an ecological viewpoint, they differ markedly from historical ecological systems (Milton 2003). But urban ecosystems also differ significantly from historical human settlements: they are novel habitats and contain both natural and human historical features.

Credit: The Urban Ecosystem, Alberti 2017, in Press

I suggest that if we are to understand ecosystems in which humans are the key players, we need a paradigm shift in the way we study these ecosystems (Alberti 2016). As hybrid ecosystems, cities operate at the border of a phase transition between alternative behavioral states governed by either historical or novel feedback mechanisms. As ecosystems are increasingly dominated by human action, they move toward a new set of feedback mechanisms. Their state is unstable. We can drive them to collapse or we can consciously steer them toward outcomes we desire. But what is a desired outcome? Desired by whom? What is the role of human values in urban ecosystems? Framing a new science of hybrid ecosystems implies addressing the diversity of human values, their conflicts, and the ethical dimensions.

Designing urban ecosystems

We also need a paradigm shift in system design to accommodate the complexities in these highly interdependent and adaptive hybrid urban ecosystems. Myths and uncorroborated assumptions about how nature works, have led to failures in designing and managing urban environments (Holling et al. 2002). The assumptions that the elements of a system can be controlled and their boundaries can be defined have dominated system design and engineering for a long time influencing both the field and the practice. Urban designers and planners, for example, have assumed for a long time that ecosystems are stable and that their processes and dynamics are relatively well understood and predictable, thus one can find an optimal solution among a set of possible alternatives—but that is clearly not the reality in urban ecosystems.

How do we design complex hybrid systems in which the components are highly diverse, interconnected, and interdependent? (Alberti 2017, In Press) How can we design and build infrastructures that are resilient to unexpected and uncertain environmental change? How can we coordinate the interventions of diverse institutions operating at many scales under a diversity of constraints? How can we resolve conflicts among multiple stakeholders?

Instead of aiming at control, we must embrace uncertainty and redefine principles of design to acknowledge the complexity of hybrid ecosystems. This implies expanding the heterogeneity of forms and functions in urban structures to support both human and ecological functions and supporting modularity of infrastructures to create interdependent decentralized systems. We need to expand our capacity for experimenting and learning. And most of all we need to find new ways to creatively engage the communities in designing the cities of the future.


Alberti M. 2017, In Press. Simulation and Design of Hybrid Human-Natural-Technological Systems. Technology | Architecture + Design

Erik Andersson

About the Writer:
Erik Andersson

Erik Andersson works as associate professor in sustainability science at the Stockholm Resilience Centre.

Erik Andersson

Were cities ever anything other than ecosystems? With additional layers of complexity added to them, of course. I like to think in terms of principles, connections and functions, and they relate to systems, across systems. When we get down to basics, cities are made up by components reacting and acting on their surroundings. We navigate the physical structure and interact with the biological components, although the functional pathways and drivers behind dynamics may have a strong human flavour and a high degree of facilitation. Reframing urban studies in ecological terms may be more or less informative. There certainly are cases where I think ecology can help highlight implicit or neglected system characteristics that would merit more attention. Cities have been conceptualised as ecosystems before, but digging deeper into ecological theory exposes a number of insights and considerations that could be interesting for a broader discussion of what cities are and how they work. And, as the logical follow-on, how they could work differently.

More organic, constantly changing and evolving cities could help to shift worldviews back to being grounded in change and changeability rather than control and permanence.
I will limit myself to two points here, one on time and one on space, and both concerned with function. Space first. Connectivity and the flows and exchange it facilitates is a central concern in cities, and one most obviously manifested in different infrastructural systems. With an emphasis on structure, physical structure. Ecology emphasises that connectivity has two aspects, structural and functional connectivity. I think we sometimes believe that structure is everything; instead, our perceptions, and how we act on them, may be quite as decisive. Connections exist where we understand them to exist, barring some clear misunderstandings. And connections are not just about getting from A to B; while we believe in our maps, sectoral divisions, and clear delineations ecological theory and research points to the importance of edges not as lines but as zones of mixed influences and different functionality.

Then there is the issue of time and our preference for clear and bounded functionality. There is a potential clash between the selective forces at work in and on cities. Considerable human effort and ingenuity have gone into trying to make cities into something other than ecosystems, yet perhaps now is the time to allow them to be ecosystems. Why? Ecosystems come with temporal dynamics, change, cyclicity and evolution. Cities have been prime examples of command and control approaches where built infrastructure is intended to last, and often to support the same function throughout its lifespan. Evolution has proven the utility of open-ended functionality by showing how tweaking the same design just a bit can provide a different, or added, functionality. Invention is more often a case of bricolage and making use of what is already there, with a clear parallel to evolution, than a result of intentional creation of something truly ‘new’. Making urban design a bit more open-ended would do loads of good for cities’ capacity to adapt.

The city, perhaps even more than most other social-ecological systems, suffers from a conceptualisation where we see ourselves as somewhat external observers and users of the system. Yet they are lived-in systems where our presence and long-term exposure and interaction with our surroundings actually is the system. A functional understanding of the city, one based on interactions, similar to that of ecosystems could provide a fresh perspective on design needs and ways we could think about our cities. It is no news that experiences and perceived qualities depend on multiple, interacting factors, where individual components may change. For example, we don’t really want the physical streets and roads when we build infrastructure, we want the function of mobility, which is generated by our understanding and use of structure. Which may shift much more rapidly the structure itself. More organic, constantly changing and evolving cities could help to shift worldviews back to being grounded in change and changeability rather than control and permanence.

Sarah Dooling

About the Writer:
Sarah Dooling

Sarah is an interdisciplinary urban ecologist, with 17 years of experience in urban ecology, social work, and wildlife management. She works on colaborative design projects and policy development efforts that integrate ecological design, environmental planning and social equity issues.

Sarah Dooling and Stephanie Pincetl

Beyond progress and ruin: an empowered urban ecology for the Anthropocene

To think of cities as ecosystems is an ecologically radical idea. Declaring places profoundly altered by human construction as ecological holds the potential for transcending the binary, and sometimes oppositional, categorization of people versus nature characteristic of most Western world’s knowledge domains. Yet, the idea of urban ecosystem contains the histories of Cartesian dualities. Recognizing the reciprocity between many different human communities and their non-human neighbors means rejecting nature as independent of urbanization. Social issues, like poverty, become environmental issues. But we’re not there yet.

The danger of an object-oriented systems approach to urban ecosystems is that it is inattentive to consequential political conflicts arising from competing values and unshared goals.

Ecology developed as a science of categories and classifications, committed to revealing patterns with wide applicability. Understanding urban ecosystems as places where people and nature co-evolve is difficult for ecologists because these particular co-evolutionary partnerships upset stable Linnaean categories that are used to organize the world’s life independent of humans. Communities and species were, and continue to be, considered objects of study, separate from and undisturbed by investigators.

The idea of urban ecosystems challenges the anti-urban bias among 19th and 20th century ecologists who considered urbanizing landscapes void of ecological value, degraded by pollution, and cut up by networks of infrastructure. With the eradication of nature the concept of ecosystem in the urban context had little purchase among ecologists. Today, many urban ecologists draw from systems theory to link social and ecological components through themes of connectivity, emergence and contingency. Cities are now considered hybrid systems, a designation undergirded by the pervasive binary categorization held so dear by natural scientists.

Yet, the urban ecosystem concept is insufficient because it leaves out urban realities, such as racism, poverty and criminal justice, because they fall outside conventional topics of ecological investigation.

Cities have developed out of unique urban histories. The legacies of urban renewal and racist policies reinforce pathways of urban development marked by exclusive beneficiaries. Modernity’s narrative of urban progress is undercut by the logic of disposability and excessive surplus that plays out in the dynamics of urban homelessness, multi-generational poverty and racism. Despite conceptual advancements, current ideas of urban ecosystems among urban ecologists remain analytically silent on the power of politics and economics to organize relations between people and nature. They remain silent about the need to understand how humans organize themselves and enroll nature in their power relations. In our era of deepening inequities, questions about the transformation of nature, by whom and for what purpose are increasingly salient as urban patterns of economic and racial segregation intensify while cities are simultaneously held up as the salvation of global sustainability and climate resilience. As many critical thinkers have reminded us, social changes always have ecological consequences, and environmental changes are never socially neutral.

Cities are places of growth and decay, chaos and patchiness. The objective stance of systems theory towards this unpredictable and untamed environment is insufficiently capable of questioning dominant urban scenarios. The danger of an object-oriented systems approach to urban ecosystems is that it is inattentive to consequential political conflicts arising from competing values and unshared goals. Where then do we find the theoretical justification that motivates eliminating practices of disposability and excessive surplus? As researchers, our challenge in these times of uncertainty and loss is to attend to significant moments of difference and variation in co-evolutionary relationships, which may point to a transformative re-imagining. We offer a way forward.

We consider cities as subjects, full of diverse living networks and marked by inequities harmful to communities of people and biota, rocks and soil. We intend to build a science of cities from the inside out, where the historical richness, contradictions and inequities of each city informs context-specific understandings of urban ecosystem. We urge justice and equity — for people, biota and rivers — as central starting points for research, policies and place making. Making equitable urban societies becomes the common goal underlying efforts to become resilient and sustainable. We call for developing a post-Cartesian science that recognizes contingency and mutual construction of the places we live: humans-in-nature, nature-in-humans.

An empowered urban ecological science recognizes the limitations of systems thinking, Linnaean classification, and ecological ideas of ecosystems. Boundaries between humans and environment are dissolving into multitudes of diverse communities interacting across patches of relational intensity. Empirical work, liberated from constraining scientific ideologies, can aid in nurturing collaborative survival by coordinating disturbance and conservation across patches.

The Anthropocene is an Epoch of Reconfiguration. We are being called to develop creative alliances that cut across politics and knowledge domains. Re-building analytic categories starts from the ground up, and involves exchanges across formal and vernacular ways of knowing, where arts, sciences and design converge on pressing issues. Most critically, we must start telling stories that carry us beyond progress and ruin, into the possibilities of ecologically vibrant and socially equitable communities that can sustain in a precarious world.

Stephanie Pincetl

About the Writer:
Stephanie Pincetl

Pincetl has written extensively about land use in California, environmental justice, habitat conservation efforts, urban ecology, water and energy policy.


Paul Downton

About the Writer:
Paul Downton

Writer, architect, urban evolutionary, founding convener of Urban Ecology Australia and a recognised ‘ecocity pioneer’. Paul has championed ecological cities for years but has become disenchanted with how such a beautiful concept can be perverted and misinterpreted – ‘Neom' anyone? Paul is nevertheless working on an artistic/publishing project with the working title ‘The Wild Cities’ coming soon to a crowd-funding site near you!

Paul Downton

Ecocities and the extended organism
or what the hell has the evolution of cells got to do with social justice?

Are cities ecosystems? Yes. And maybe.

If an ecosystem is “a biological community of interacting organisms and their physical environment” it is also a baseline description of any city. My understanding of ecology is that, for the purpose of studying interactions and interdependencies between organisms and their environment, any set of creatures and their habitat can be understood as an ecosystem once a logical boundary is set. So you can study the ecosystem in an unwashed five day old coffee cup, or someone’s mouth, or a savannah. Or a city.

Logically, the interacting organisms in a city ecosystem include all its humans and non-humans, and the interactions might be as prey and predator, or human-to-human relationships that can be expressed in ways ranging from kinship ties to law suits. All are interdependent. Social concerns, including goals of livability, justice and equity, have to be considered integral to the making and ongoing life of a city and why the ecosystem concept and its paradigm of interdependency advances our understanding of how those goals might be reached.

The complexity of extended organisms and cities in particular make it difficult to demarcate inviolable distinctions between when it’s an organism and when it’s an ecosystem.
Earth’s biosphere is the biggest ecosystem we are able to study but even its boundary is hard to determine exactly as it includes the moon, without which there would be no tides (and like the child working out their first address, you can go on to include other planetary motions, the sun, without which there’d be no life at all, and the rest of the galaxy). Regarding the Earth as an ecosystem hasn’t prevented theorists, including the redoubtable Margulis, from proposing that it also operates as a self-regulating organism (the Gaia Hypothesis).

Cities are organisms too. An organism isn’t conventionally thought of as an ecosystem, but it is. We human organisms carry within and upon us any number of thriving ecosystems, some healthy, some less so, but we are not mere hosts for ecosystems, we are things made up from all our intermingling ecosystems from the bacteria in our mouth and guts to the mites that crawl around our skin. Each of us is an individual and each of us is a legion of organisms. We are only healthy when they, and their relationships with each other, are functioning in an ecosystemically healthy way.

Calling a city an ecocity sets up expectations. It implies a relationship between ecology and the city that isn’t conveyed in terms like sustainable and green except by ponderous definition. That relationship is the key to understanding that even if a city is not, by itself, an ecosystem, it can exist only because of its relationship to living systems. Once you’ve got the message that an ecosystem is integral to the city’s existence you have to pay attention: if the city is to be healthy, then the larger ecosystem that contains it has to be healthy.

Are cities’ ecosystems like a natural ecological area? If there’s life, that’s nature at work, that’s “natural”. Humans manufacture cities, but they are still part of nature – as far as we know we haven’t been teleported from some abiotic planet of pure machine intelligence elsewhere in the galaxy and even if we had you’d have to start arguing about what constitutes life and where it comes from… as Barry Commoner said “Everything is connected to everything else”.

Defining the health of a city ecosystem means defining the health of its constituent organisms, and in the city the dominant organism is us. So a healthy urban ecosystem requires healthy people and healthy people require a healthy urban ecosystem.

An ecosystem contains a collection of interdependent organisms; an organism is a collection of interdependent ecosystems. Very fractal. It goes on down to the scale of individual cells, where the very existence of cells with nuclei (eukaryotes) is now understood (thanks to the work of Lynn Margulis) as dependent on a symbiotic relationship between organelles that are descended from bacterial species that were once independent.

Building on Richard Dawkins’ “Extended Phenotype”, J. Scott Turner observes that many species make artefacts that are essential to their capacity to survive, be it through creating places in which to birth and succour their young (bird nests) or air-condition their colonial habitat (termite mounds). He calls this species+artifice an “extended organism”. Our species has evolved to be dependent on making the complex artificial habitat we call a city. We need cities to survive, people+city is, arguably, an extended organism. In all cases, with all species, the extended organism has to be able to function without damaging its environment, it has to evolve in a way that sustains the operation of the larger ecosystem within which it resides. Beavers cut down trees to build their extension but, over time, the impact of their dams and lodges has resulted in the beaver+lodge organism evolving as a positive contribution to the overall functioning of its local environment—it has evolved to become a healthy part of a larger ecosystem. Which is exactly what the human+city organism needs to do. Although cities are massively complex compared with birds’ nests, they are just as essential. One could study the life of organisms that reside in and depend on the nest as an ecosystem. One could study the life of organisms that reside in and depend on the city as an ecosystem. The complexity of extended organisms and cities in particular make it difficult to demarcate inviolable distinctions between when it’s an organism and when it’s an ecosystem.

Relationships and symbiosis are key. If the interdependent parts of a city have a functionally symbiotic—as in mutually beneficial—relationship with other parts, that is a part of being healthy and will enhance social cohesion. Relationships are about the exchange of information. Both the quality of that information and how it is exchanged affects the consequent relationship. And those relationships are at the core of how city ecosystems work.

In a city, virtually all relationships are made and mediated by people. That includes relationships between individuals, between people and their institutional and physical artefacts, and between people and the rest of nature. (Shall we bulldoze that wetland because it’s worth more as a building site, or protect it because its role in our ecosystem is greater than anything that money can value?) The values, aspirations and attitudes of those people are paramount in determining the type and quality of those relationships. (Do we bulldoze that run-down part of town because it’s worth more as a building site, or redevelop it to provide a healthier environment for its residents even though they’re not individuals of high net worth?) That’s why purely mechanistic approaches to city making can’t work in the long term. It’s why cybernetic systems (including smart city algorithms) can work, but all such systems rest on assumptions embedded in value-based decisions. Information connects everything and in an urban ecosystem what constitutes good or bad depends on the exercise of a set of values. Bulldozers, hammers, trucks, cars, big data, zoning laws—anything can become a weapon. Tools will do what we want them to do. To deal with the information flows and interdependent nature of an urban ecosystem its planning and management must transcend disciplinary boundaries.

Cities are human constructs and for justice and equity to be part of the city, they have to be considered and included from the outset and consciously maintained as part of the life of the city regardless of whether we define it as an ecosystem or an extended organism.

Thomas Elmqvist

About the Writer:
Thomas Elmqvist

Thomas Elmqvist is a professor in Natural Resource Management at Stockholm University and Theme Leader at the Stockholm Resilience Center. His research is on ecosystem services, land use change, natural disturbances and components of resilience including the role of social institutions.

Thomas Elmqvist

What we really need is closer collaboration among a diverse set of knowledge holders in natural science, social science, humanities, and among practitioners. The term ecosystem, originating from natural sciences, may alienate groups we need to include in diverse city-building conversations.
Although I fully agree that the current framework of cities as social-technological systems is too narrow and should be complemented with the view of cities as complex social-ecological-technological systems, as recently advanced within urban ecology and based on social-ecological systems perspectives. This advance is critical given that the continuum of urbanity includes many characteristics and processes other than the particular density of people or land area covered by human-made structures. However, I remain skeptical that the use of the concept of ecosystem to depict cities and urban regions will be of help in this regard.

The ecosystem concept has a precise meaning in ecology and was originally defined by the British Ecologist Sir Arthur George Tansley. In 1935 Tansley published The use and abuse of vegetational terms and concepts, in which he introduced the ecosystem concept: “An ecosystem is a community of living organisms in conjunction with the nonliving components of their environment interacting as a system”.  This may look like an attractive way of viewing cities and urban regions as a system of interacting living components (humans, plants, animals, microbes) as well as non-living components (buildings, soil, water, etc.), and would imply a holistic view and a systems perspective. However, I am skeptical. The reason is that it may be counter-productive. What we really want to achieve is a closer collaboration among a diverse set of knowledge holders in natural science, social science, humanities and among practitioners. By using the concept of ecosystems of a city or urban region, originating as it does from natural sciences, we may alienate exactly the group of people we want to include: the social sciences, humanities, practitioners, etc. I fear that it may simply put some people off, when in fact we want to reach out and be inclusive.

What should we use instead? I think that we should define an Urban Sustainability Science and develop a new framework that explicitly addresses the question of multiple-scale interactions, feedbacks, tradeoffs, and synergies among components (human and non-human) in complex urban systems. The challenge is still, however, how do we integrate diverse scientific approaches and knowledge domains grounded in multiple epistemologies and how do we further integrate with other non-academic knowledge systems.

Nancy Grimm

About the Writer:
Nancy Grimm

Nancy B. Grimm is an ecologist studying interactions of climate change, human activities, resilience, and biogeochemical processes in urban and stream ecosystems. Grimm was founding director of the Central Arizona–Phoenix LTER, co-directed the Urban Resilience to Extremes Sustainability Research Network, and now co-directs the NATURA and ESSA networks, all focused on solving problems of the Anthropocene, especially in cities. Grimm was President of the Ecological Society of America (ESA) and is a Fellow of AAAS, AGU, ESA, SFS, and a member of the NAS. She has made >200 contributions to the scientific literature with colleagues and students.

Nancy Grimm

Are cities ecosystems? Of course they are. But does this concept satisfy the requirements for understanding these complex, heterogeneous, adaptive, self-organized systems? Over the past twenty years, urban systems have come to be seen as complex, adaptive, social-ecological-technological systems (SETS). Yet the core ecosystem concept remains fundamental to understanding them. It is a simple idea that can accommodate the complexities of diverse components arranged in space in a variety of ways, as well as dynamic change, that are hallmarks of urban systems.

As ecologists we would be arrogant to assume that our models alone suffice to understand the multifaceted drivers of change. It’s imperative to continue to expand the concept of the urban ecosystem to incorporate a multidisciplinary view.

The ecosystem concept is the foundation of my thinking, originally as a stream ecologist but then as an urban ecologist. An ecosystem is a piece of Earth (writ large) with biotic and abiotic elements (i.e., the structural components of the system) that interact within a boundary. The interactions involve energy, matter, and information; ecosystem ecologists often refer to these as function but a more general term is processes. The boundary idea sets some folks off: if we can’t see a clear, unvarying boundary, then the ecosystem can’t be a real thing. But in fact, the fluidity of the boundary (and our ability to define it to suit our purposes) is perfect for urban ecosystems—systems that have massive throughput (movements of materials into and out of the ecosystem) and large dependencies on external, connected ecosystems. If we identify a boundary for convenience sake (for example, a jurisdictional boundary or a transport boundary), we can quantify these movements across the boundary and that dependence becomes a definable characteristic of the system (i.e., internal stocks relative to import rate gives us residence time for a material).

Ecosystem structure in urban ecosystems is unique. Not only do we have the organisms within populations that are structured and located in space; we also have the artifacts of human enterprise: the built environment. And we have unseen structure, for example of culture, government, economic systems, and power hierarchies. These additional elements of structure don’t negate the idea of cities as ecosystems but they cause us to ponder the types of biotic and abiotic elements that make up these ecosystems. The SETS concept helps to incorporate the built environment and social institutions; I would argue that SETS is a sub-set of the more general term, ecosystem, even though in common usage ecosystem refers to named biome types like forest, desert, or lake (so why not city?). Cities are SETS, and so are parts of cities like neighborhoods, parks, and infrastructure of various kinds. Perhaps the most important thing about SETS is that they are systems. This means that we cannot consider the parts in isolation, since they interact to form the whole.

As with structure, some of the processes and material, energy, and information flows of cities are unique in character. For example, the exchanges of information in social networks via the internet are phenomena that change so rapidly today they defy understanding using traditional ways of knowing. Yet these information pathways may drive dynamic change in urban ecosystems. A key characteristic of ecological processes in urban ecosystems is the degree to which human decisions control them – usually, quite a lot! For example, we know that instead of traditional biophysical variables that determine rates of primary production in Phoenix, it is the amount of outdoor irrigation, which is subject to the whims, desires, financial capacity, and access to infrastructure of urban residents that sets the rate of production.

Traditionally, the ecosystem concept hasn’t handled spatial heterogeneity well (think of the classic ‘black box’ approach to ecosystem energy budgets). The rise of landscape ecology, with its recognition of multiple systems arrayed in configurations that could affect process, was therefore a boon to understanding our world. And so it was for urban ecology: urban ecosystems are very heterogeneous on some scales, more so than many ‘native’, non-urban systems, and urban ecologists have recognized that heterogeneity as key to understanding cities. Deciphering how the configuration of parks, rivers, transportation infrastructure, housing developments, and central business districts affects biodiversity, ecosystem function, or ecosystem services is an important frontier for building sustainable cities.

Change is ubiquitous in the Anthropocene. Urban ecosystems are subject to massive change driven by social, ecological, and technological processes. Ecological theory—for example, disturbance theory (Grimm, Pickett, Hale, and Cadenasso, 2017, Ecosystem Health and Sustainability 3(1):e01255. 10.1002/ehs2.1255)—can contribute to our understanding of change. Yet as ecologists we would be arrogant to assume that our models alone suffice to understand the multifaceted drivers of change. The imperative is to continue to expand the concept of the urban ecosystem, bringing in the extensive knowledge of cultural and social systems, values, and hierarchies that has developed through the work of our social-science colleagues, the knowledge of infrastructure needs from our engineering colleagues, the creativity and vision of our design colleagues, and the practical understanding from practitioners who work and make everyday decisions in cities. An inclusive concept, the ecosystem can accommodate these ideas and diverse perspectives toward a better understanding and ultimately a pathway to transformative action for our cities.

Dagmar Haase

About the Writer:
Dagmar Haase

Dagmar Haase is a professor in urban ecology and urban land use modelling. Her main interests are in the integration of land-use change modelling and the assessment of ecosystem services, disservices and socio-environmental justice issues in cities, including urban land teleconnections.

Dagmar Haase

Does thinking explicitly about cities as ecosystems offer us any insight into urban design? Are our goals for cities—sustainability, resilience, livability, and justice—advanced by an urban eocsystem concept? Some reflections based on my research on urban ecosystems in national and international contexts: Over the last two centuries, both scale and rate of change of cities have developed rapidly. Yet in terms of space, less than 5 percent of the Earth’s surface is urban. And not all urban areas are expanding or expected to grow in the future.

Co-evolutionary planning and governance means the elimination of sectoral thinking and actions that favour more holistic concepts of urban, regional and local regeneration, resilience and adaptation.
Cities are unique among all landscape types because they are where the human-inhabited, built, and ecosystem services provisioning spaces overlap and interact. Cities are rich in the niches for organisms they provide, such as almost invisible spaces between buildings and open soil or unused constructions and in the number of species that use them such as raccoons, the green woodpecker, Acer species (maple), or cactus species. What has become clear in recent decades, starting with the Millennium Ecosystem Assessment and strongly supported by the Economics of Ecosystems and Biodiversity-TEEB-process and protocol since 2009, is that ecosystems in and of urban areas—urban ecosystems—can provide a range of benefits that include recreation facilities, local food production and, most importantly for coastal cities, storm water control, to sustain and improve human life, health and well-being.

Understanding how such urban ecosystems function, how they change, and what limits their performance can add to an understanding of ecosystem change and governance in an ever more human-dominated world. Is there a novel concept or a new way to approach this? Recent ways of thinking combine both to promote dialogue between academics and practitioners in the field of urban ecosystems and ecosystem services and to build a novel framework of co-evolution in today’s cities. It is vital to recognize that urban systems are both highly complex and a product of ongoing emergence, suggesting the need for co-evolutionary approaches to managing the city as a social-ecological system and the integration of ecosystem approaches into spatial planning frameworks. For example, plans encouraging a compact city model could be used in combination with interim-use sites designated in the inner city as temporal refuges for nature, ecosystem services and nature experience by urban residents in the form of a participatory co-development process and multi-stakeholder usage. Thus, the rather static compact city model also includes temporal-spatial windows of green, spatial flexibility and land-use dynamics. Co-evolutionary planning and governance also mean the elimination of sectoral thinking and actions that favour more holistic concepts of urban, regional and local regeneration, resilience and adaptation; this approach includes the global context and network, which involves many and varied actors.

Not exclusively in shrinking cities, but most notably, the concepts of green and blue services provide the potential to move from a comparatively simple “land-use view” of green, brown, and blue areas in cities toward a valuation of ecosystem goods and processes and spatial potentials for each piece of land. A co-evolutionary approach also needs to explicitly address the technological, transport and built system/sphere of the city, as these include important aspects of and opportunities for co-design and co-development. In cities, the built and technical infrastructure is often viewed as the most important line of defence against natural hazards and disasters.

By contrast, more flexible ecosystem-based solutions include elements and processes of urban nature, such as green and blue infrastructure, permeable pavement, and nature imitations such as bioswales and wetland-like constructed retention basins, to name a few. They afford both city dwellers and planners a new way to think about risk and safety based on the dynamics of nature and ecosystems. For example, an ecosystem could be designed so that it does not completely prevent water from entering an urban environment but instead reduces the amount and velocity of the water and thus the risk to people; the same design keeps water in the city as buffer in times of drought and heat.

Thus, in the long run, nature-imitation, or biomimicry designs help cities live with nature and become more resilient and prepared for different types of hazards. Such nature-based solutions mediate the relationship between human activities and ecosystem processes in urban landscapes and, if developed appropriately, could mitigate human impact. In developing nature-based solutions for a city, including the co-existence of built, grey, brown, green and blue places, it is essential to include the full spectrum of urban land uses.

Despite the considerable progress in urban planning, governance and land management, a fundamental rethinking is urgently needed regarding what makes both the natural—urban ecosystems—and built “infrastructures” of the urban community adaptive and resilient to current and future social-ecological challenges, such as flood and storm hazards, other climate extremes, air pollution and large-scale economy-driven land-use interventions such as densification and gentrification.

The Clara Zetkin Park in the city of Leipzig, a wonderful expression of the human habitat in urban areas. Photo: Dagmar Haase
A green roof in the city of Leipzig—another wonderful expression of the human habitat but also flora and fauna habitat in urban areas. Photo: Dagmar Haase
Jane Toner

About the Writer:
Jane Toner

Jane Toner is a Biomimicry Professional seeking to create innovative design solutions that are ecologically regenerative, socially just and joyous.

Jane Toner and Dominique Hes

This short paper is based on the work of practitioners and academics in biomimicry, biophilia, positive development and regenerative development. We cover 4 points in response to the above challenge. We argue that cities are ecosystems but they are not well adapted to place; cities have not learnt from the nature of place and have displaced its ecological functions; cities have not yet reached their full ecological maturity or potential; and, how our cities can learn from nature strategies to benefit all life.

Imagine walking through a tropical rainforest. Light is dappled and muted, the air is warm and steamy. Trees reach for the sun, harnessing freely available energy that nourishes the whole system; they provide support and scaffolding for mosses, lianas and epiphytes that add complexity to the forest’s architecture and they in turn provide habitat and niches for other organisms. Water is a precious commodity that is harvested, filtered, stored and cycled through the system. Below your feet, the ground is moist and teeming with unseen life breaking down forest debris, silently cycling nutrients that promote the growth of the rainforest. Mycelial networks connect the trees below the soil, transferring information and resources between them. Everything is intertwined and interdependent; all elements of the rainforest inadvertently collaborate to nurture a thriving system greater than the sum of the parts.

Cities are ecosystems but they are not well adapted to place; indeed, we have displaced their ecological functions. For this reason, cities have not yet reached their full ecological maturity or potential.
Our cities are ecosystems too but they are currently not as well adapted or resilient as the ecosystems they’ve disrupted and are nested within. While life abounds in cities, diversity is limited and dominated by one species. Cities are the culmination of our species’ survival strategies, helping us mitigate the extremes of environment, shaping our culture, and extending our range on the planet.

There is no doubt that humans are clever ecosystem engineers. We have transported, accumulated and consolidated many resources to shape our cities and yet, for all our cleverness, we have forgotten that we are part of nature and subject to the same rules as the rest of life.

Rather than creating conditions conducive to all life we have been focused on our own species’ needs and spent excess energy and resources in maintaining stasis (even if we label that as growth). Cities could currently be viewed as being biophobic, or manifestations of our disconnection from nature.

What if our cities learnt from mature ecosystems like the rainforest?
Photo: Jane Toner

Cities have often replaced the ecosystem services freely supplied by nature with engineered systems that are more energy intensive, less effective and that create other problems solved in a similar fashion.

Ecosystem functions are biotic and abiotic processes involving the exchange of energy and nutrients that contribute to the health of an ecosystem, while ecosystem services are what our ecosystems “do” for us, the benefits they provide our species. These include: providing habitat, sequestering and cycling carbon, trapping nutrients, decomposing matter, recycling waste, filtering water, and pollination.

If we view cities as ecosystems yet to reach maturity, we can plan to enhance their capacity to support life, human and non-human by learning from organisms and systems adapted to the same place and have solved the same challenges. For urban design, this means that our cities need to evolve symbiotic relationships with organisms that provide ecosystem services. We can do this by creating a complex array of varied niches at different scales, different levels of contribution to increase the emergent evolutionary potential of cities.

Lichen is a mutually beneficial symbiotic relationship between algae and fungus. Fungus provides the structure while algae provides energy harvested from the sun.What if our cities had a mutually symbiotic relationship with nature? Photo: Jane Toner

For urban design, the implications are transitioning the city to be better adapted and more resilient. By integrating nature to restore ecosystem services we also meet our own biophilic needs, increasing the potential for human health and happiness. We are a young species still learning how to fit in and it is time we remembered that we are nature and that connection with it promotes our own well-being.

What needs to be valued is that, as Australian indigenous culture suggests, cities also have a potential role in benefiting nature. That is, the human capacity within the city can understand future change and therefore support nonhuman systems to better adapt. Designing this mutual reciprocity into our cities is the challenge of the future.

We have countless opportunities for our cities to become mature ecosystems embrace this relationship by relearning and applying the deep patterns that nature has evolved to survive and thrive on Earth.

Life builds from the bottom up. Layer by layer, ecosystems have evolved from bare rock, concentrating and transforming locally available, easily accessible, abundant resources into dynamic complex systems that promote and reward interconnection and interdependence. Cities have also evolved in a similar way, the layering here is historic and often based on ways of economic and industrial change. The challenge then is for the urban designer to think of a city as a constantly evolving co-managed rainforest, savannah or reef, intrinsically intertwined with the ecosystem in which it resides.

Dominique Hes

About the Writer:
Dominique Hes

Dominique is the Director of the Thrive research hub at the University of Melbourne. She works on projects aimed at co-creating a thriving future.

Kristina Hill

About the Writer:
Kristina Hill

Hill works on adaption to climate change in biophysical and social systems at the University of California, Berkeley. Her focus is on design for sea level rise and flooding.

Kristina Hill

Cities are a type of ecosystem, because they contain all the components and connections we use to define such systems. But since they both include and are shaped by people, urban ecosystem research is more akin to medical research than to traditional ecological studies. Like medical research, urban studies require the articulation of an ethical framework before questions, methods, or conclusions can be developed. The scientific method should not be applied to cities without the use of an explicit ethical frame.

Cities meet the definition of ecosystems, with important limits—understanding urban ecosystems must start with an awareness of the ethical and conceptual pitfalls of studying human behavior without considering human values.

Urban ecosystems have been studied for more than a century. For more than 100 years, urban ecological theories have developed from the idea that natural processes, built environments and human communities are part of an interacting system of stocks and flows. As early as 1829, J. C. Loudon proposed a design for London using concentric greenbelts to improve air quality and human health. Large-scale urban design interventions were constructed in New York and Boston by Ellen Swallow Richards and Frederick Law Olmsted, with the explicit aim of influencing human health and urban ecology as early as the 1870’s. These projects launched the American professions of landscape architecture, environmental engineering and public health. Current urban design efforts based on Olmsted’s early examples often contribute to urban stratification by social class. In the 1960s, Donella Meadows and her colleagues at MIT applied the system concept to human populations, economies and natural resources, in order to model the possible consequences of the over-use of natural resources. Their results have often been used to argue for limits on population growth in developing countries, with negative consequences for women. Herbert Sukopp studied ecology in cities, focusing on the microclimates and species distributions of West Berlin’s confined spaces in the 1970s. Sukopp arguably introduced the field of urban ecology. He did it within the nexus of a tense geopolitical conflict, but tried to restrict his questions to non-human species.

In contemporary ecology and planning, a group of scientists and planners in the San Francisco Bay area are actively using the concept of “Operational Landscape Units” (OLU’s) to build a map of estuary shoreline reaches in which processes establish a pattern of connections, similar to a watershed but based on nearshore geomorphic and hydrologic processes as well as upland flows. These OLU maps will become the basis for planning urban adaptation strategies for sea level rise. They are based on the concept of an ecosystem, with stocks and flows, as well as theories about spatial connectivity that come from landscape ecology. Urban OLU’s are becoming an important vehicle in the SF Bay region for understanding linked systems driven by groundwater dynamics, sediment transport, wave energy regimes, sewer pipes forming “sewersheds,” and gradients in salinity and water quality, among other human and non-human drivers. This approach will help us come up with urban designs for coastal adaptation to flooding while supporting biodiversity and ecosystem services, which we would otherwise lose if we protect cities with new storm surge barriers, seawalls and levees alone. It will also identify surprising vulnerabilities in our existing underground infrastructure systems, and allow us to predict new contamination risks that will affect many lower-income communities.

I argue there are important limits to the successful application of ecosystem concepts to humans and the built environment. When E.O. Wilson sought to extend evolutionary genetic theories to human societies in the 1970s, critics were quick to point out that culture and social environments also shape human behavior to a very significant degree. Ethical questions immediately emerged about the scientific characterization of human behavior, and the extent to which it is determined by processes of natural selection or by individual choice and social communities.

Anyone who studies urban ecosystems today must start with an awareness of the ethical and conceptual pitfalls of studying human behavior without considering human values. Applying the concepts of dominance and competition to human social and biological diversity provides a case in point. Research shows that exposure to lead in soil reduces learning ability, and that exposure to air pollution causes genetic damage in human children. If those children are subsequently disadvantaged in social competition, implying that this is “natural” (i.e., the result of natural selection), would be both incorrect and reinforce the repressive dynamics of the economic concept of social class. If urban ecosystem studies are used to naturalize social dynamics, the science will be seen as justifying social hierarchies that restrict social movements in pursuit of greater equity. Particularly in an era of increasing economic and ethnic divisions, studies of urban ecosystems that include human health and behavior require a clear ethical foundation. The limits in this context reveal the limits of scientific method generally, which is that our selection of research topics, our approaches, and the uses of scientific findings are all influenced by power dynamics within human societies.

In summary, I would argue that while urban systems can be studied as ecosystems, an ethical framework is required a priori. Ethical perspectives will change over time, as culture changes. But the need to understand social influences on scientific research – both in development and in application – is acute. Without a clearly articulated ethical framework, scientists should recognize the philosophical limits of the scientific method by restricting themselves to the study of ecology “in” cities, not “of” cities.

Grunewald in Berlin was the kind of landscape studied by Herbert Sukopp in the early days of urban ecology, circa the mid 1970’s. It was a politically symbolic landscape as well as an ecosystem inside the city walls.
Madhusudan Katti

About the Writer:
Madhusudan Katti

Madhusudan is an evolutionary ecologist who discovered birds as an undergrad after growing up a nature-oblivious urban kid near Bombay, went chasing after vanishing wildernesses in the Himalaya and Western Ghats as a graduate student, and returned to study cities grown up as a reconciliation ecologist.

Madhu Katti

Coral reefs of the land

It is a hard nonliving complex three-dimensional structure built by living beings, often covering extensive areas of habitat, and unlike anything else naturally found in the vicinity. It is the product of the labor of an organism that has evolved to transform the materials in its surroundings into a protective home for itself and its progeny. It is built in layers, growing upon itself as its occupants continue to build it over generations. It does the job of protecting its inhabitants well enough to outlast them, standing firm over scores of generations, thousands of years. It helps concentrate the flow of energy and materials from its surroundings to make life more efficient for its denizens, thriving sometimes even in places that otherwise seem deserted.

Of course cities are ecosystems. More interesting is to ask what kind of an ecosystem cities can be rather than worrying about how unnatural a blight they are on more “natural” landscapes.
It not only provides shelter and resources and a supply of energy to the species that built it, but also supports a wider range of other species that may come seeking its riches and adapt to new ways of making a living in this strange new construction. It can vary in appearance and color and occupants from one part of the world to another. It is large enough in some places to be visible from space. It is resilient to a surprisingly wide range of environmental variation, yet vulnerable to catastrophic collapse under conditions such as rising sea levels and warming ocean temperatures. And even when it collapses, and is no longer able to support its creators and main occupants, it continues to loom in its place, casting shadows deep into history, until the patient forces of water and wind and temperature wear it down and its remains wash up on some shoreline in the sands of time.

It is a coral reef, built by ingenious soft-bodied, tough little creatures that can scarcely survive on their own in the vast ocean outside its protections. It is a city, also built by ingenious creatures with bodies softened by civilization, too clever by half, but creative and tough as hell, that may also struggle to survive outside the city walls.

Coral reefs are ecosystems rich in biodiversity, often concentrating biological productivity and wealth amid relatively poor waters. Coral reefs are described as rainforests of the ocean, harboring as much, if not more biodiversity underwater as tropical rainforests do on land. They stick out in the underwater landscape as distinctly as forests full of tall trees do in terrestrial landscapes, marvelously unlike anything around them, but teeming with a richness of diverse marine organisms that have evolved to be uniquely adapted to life in the coral reef, lured by its richness to tie their evolutionary fate to that of the reef itself.

Explaining to children how a coral reef functions like a city. Photo:

It may seem odd, but coral reefs are also often likened to cities. The City, that quintessential “artificial” construction by human beings alienated from nature, symbolic of how we pave over natural ecosystems, is often used as a metaphor to understand and explain the complexity of coral reefs. There are even children’s picture books full of wonderful artwork that explain how coral reefs function much like cities: where tall structures rise up from the ocean floor like skyscrapers; where schools of fish and mollusks and crustaceans scuttle about busily at work commuting among productive nooks and crannies where they can feed and nest and raise babies securely; where diverse species evolve to specialize in different tasks, much like guilds of craftsmen and workers in medieval cities divided up human labor to make it more efficient, enabling us to produce ever more wonders of craft and art and technology, diverse and creative, and also sometimes horrific.

We have never debated whether coral reefs are complex ecosystems in their own right, worthy of protection. We should also be long past debating whether cities are ecosystems. Of course they are, unique ones described in much of the recent literature as complex social-ecological systems, because we like to pull the human social elements apart from the “natural” in our cartesian ways of thinking. A much more interesting exercise is to ask what kind of an ecosystem cities can be rather than worrying about how unnatural a blight they are on more “natural” landscapes.

As they stand, and unlike coral reefs, cities are not founts of biological diversity amid less diverse landscapes. In the relatively short timespan of human history, cities have become known more for destroying biodiversity rather than enhancing it anywhere, although more recent work in urban ecology is finding a surprisingly high diversity of species in many cities. Do cities destroy other habitats and ecosystems? Of course. Do cities cause local extinctions of many species? Undoubtedly, because we never built them as habitats for any species other than ourselves. Indeed it would seem that we build cities as places where we seek refuge from “nature” in all its vagaries and its “red in tooth and claw” horrors. Yet, we also bring a lot of that nature, and many other species, with us into the city, planting some in our gardens, growing others on our walls and balconies, feeding and watering many with intent or benign neglect, and willingly or unwittingly sharing the bounty of resources we concentrate for ourselves in cities. We know now that we depend on many of these other species for food, water, and air, for our bodies and our minds, and for our culture and artistic inspiration—even though we never built cities for anyone but our own selves. Just like the mindless tiny organisms that build coral reefs.

But unlike the coral organisms, we have minds capable of reflecting on our own actions, and of imagining different futures. Imagine building cities more intentionally like coral reefs on land. The oldest cities are just a few thousand years old, an order of magnitude younger than the oldest coral reefs. That deeper span of time has allowed coral reefs to evolve into the diverse ecosystems we now celebrate and whose decline through our actions we dread and lament. Yet, to borrow that tortured phrase from urban land developers, the coral organisms simply built their little shelters, and they came: all the diverse algae and plankton and fish and mollusks and crustaceans in the ocean to evolve together into a diverse ecosystem thriving under the ocean. A growing body of research on urban wildlife is now showing us that many species on land are also coming into our cities once we build them, so long as we leave enough of our surplus of resources for them. Recognizing the value of nature and wildlife, the biological and cultural ecosystem services they provide us in the current jargon, we are also actively bringing other species into our cities. Why not go all the way and reimagine our cities as bustling diverse coral reefs on land?

Surely, if we build cities with intention, with niches full of unique resources, many other species will come on their own, and over time will adapt and evolve into unique urban creatures, tying their fates to ours just like the house sparrow or the chimney swift have done. Even underwater, our artifacts, like sunken ships, can act as surrogates for species fleeing damaged coral reefs, and are being used intentionally to restore reef ecosystems threatened by warming oceans and rising seas. It is not hard to imagine some of our major coastal cities also turning into such surrogate reefs as they submerge under the rising oceans. So let us also reimagine and reinvent our cities as terrestrial reefs, as rich and full of other species as we can learn to coexist with, becoming not just their competitors and killers, but also their gardeners and nurturers and symbionts. Let us think as deep into the future as the coral reefs teach us about the past, and turn the metaphor of the coral reef as a city into the real city as a coral reef, diverse and resilient and full of evolutionary ferment to match the tides of our changing world.

Francois Mancebo

About the Writer:
Francois Mancebo

François Mancebo, PhD, Director of the IRCS and IATEUR, is professor of urban planning and sustainability at Reims University. He lives in Paris.

François Mancebo

Almost everybody agrees on the fact that cities can be considered as complex systems. Are they ecosystems? Proving it is another kettle of fish altogether. The idea that cities are complex systems took shape in the sixties from two standpoints:

Cities are ecosystems and a lot more than that: they are social-ecological systems.
On the one hand, the very idea that cities are complex systems originated in the seventies with the article of Eugene Odum “The Strategy of Ecosystem Development”, which describes urban areas as ecosystems. Many authors continued in this vein later, one of the more famous being Wackernagel and Riess with their book Our Ecological Footprint. In this sense we can consider—as far as cities are concerned—complex system and ecosystem are used synonymously.

But on the other hand, at approximately the same time, many authors developed the notion of cities as complex systems from a completely different perspective. The general system theory from Ludwig Van Bertalanffy combined with Norbert Wiener’s cybernetics and Warren Weaver’s organized complexity to provide a conceptual framework to another vision of the city as a complex system. This vision described the city mainly through mobility and transport, energy and financial flows, logistics etc.

Thus, in the eighties, two distinct visions of cities as complex systems were encapsulated in two metaphors: The machine metaphor, usually associated with rigid urban projects, and hub and spoke transport models—which eventually generated dysfunctional social design, ineffective land use, pollution and congestion—and the organic one, built in analogy to organisms—the city as an ecosystem. Well, that would be too simple! Two more visions emerged then: The first one developed by Jane Jacobs considered cities as social-economic systems, while second one, supported by Manuel Castells, primarily saw cities as networks for information exchange.

Later, urban planners and scientists began to realize that cities could not be modeled as equilibrium systems changing smoothly and progressively. Discontinuous and chaotic change reigned everywhere in urban areas. New structures and behaviors emerged constantly, in an unpredictable way. A consequence of this new insight is that urban planners started focusing on how emergent patterns could be generated in the city, by examining how people make decisions—or even micro-decisions—and how local actions confront and aggregate into global patterns. To do so, it proved necessary to consider cities not only as complex systems, but also as complex adaptive systems as mentioned by Michael Batty.

Mitchell Waldrop explains in his key book Complexity—The Emerging Science at the Edge of Order and Chaos, that complex adaptive systems can learn from experience and change accordingly. Two characteristics of complex adaptive systems are of significant importance to the structure and functioning of the cities: simple decisions made by individuals aggregate to give rise to complex global patterns, and each agent is co-evolving with the structure resulting from the actions of all the others; change stays dormant up to a tipping point at which these systems flip dramatically and irreversibly into a different state, which is almost impossible to predict. Many irreversible futures are possible.

The agents that interact in the complex adaptive systems of the cities are social and biophysical by nature. From this point of view, cities may be considered as social-ecological systems. What differentiates social-ecological systems from non-human complex adaptive systems is that the former deals with humans who apprehend their world through abstract thought. This symbolic construction is based on the ability to use language and symbols, to communicate across space and time. It has to do with the capacity of human beings to learn from the past, imagine the future, and finally materialize these thoughts in new types of entities that only exist in the noosphere (institutions, political and economic structures, as well as values, norms and beliefs). Erik Swingedouw highlights the circulation and metabolism of nature in urban areas, the role of history in producing them, and how this production drives, and is driven, by unequal power relationships, economic inequities, and competing knowledge. Marina Alberti demonstrated in her article “Integrating Humans into Ecology: Opportunities and Challenges for Studying Urban Ecosystems” that it is impossible to explain how human societies can be integrated in the ecological systems of a city, except by considering the city as a social-ecological system.

So, finally cities are ecosystems and a lot more than that: they are social-ecological systems, as I show in a recent paper “Sustainability Science in the Light of Urban Planning.”

Clifford Ochs

About the Writer:
Clifford Ochs

Clifford Ochs, Ph.D. is Professor of Biology at the University of Mississippi. He is an aquatic ecologist and conducts research on the Mississippi River and other aquatic ecosystems. Additionally, he is Director of the Mississippi Water Security Institute.

Clifford Ochs

The city ecosystem—the street view of a common resident

Sometimes we move alone, other times we move en masse, after the sun has set, a migration from street to dump, and back to safety. If you stay in the light, you may not notice us. But pay attention when passing a dark alley, and you may see our glowing eyes, and hear our high chirps of communion.

Your habits are our habits, your throwaways are our takeaways, and while you’ve done all the work to make the city for yourselves, we could not resist moving in, migrating across the grid, and settling down.
Perhaps you think we are out of place in your city, that we don’t belong. Oh, please. As someone has said: “If you build it, they will come”, and so we came, and we’ll stay. How could we resist? It’s like you created this place to meet not only our needs, but our desire.

It’s dark. Mostly, it feels safe. And everything we could want is nearby. The pantry is always stocked, with crusty bagels, a piece of hot dog, sometimes with a little cheese sauce, pigeon tartare. Garbage, spillage, dusky stormwater, toasty sewer pipes, plenty of pack mates. Like you, we are yearning to be free, and here in the city you have built for us, we surely are.

Warmth is appreciated, and thanks be to you, the city is a heat generator. Pavement catching sunlight, taxies and furnaces burning oil, its organic flotsam and jetsam radiating heat into the atmosphere. Baby, even when it is cold outside, we stay warm and cozy in our rent-controlled little homes, we and our passenger fleas snoozing the day away.

Come darkness, when we do venture out, we must be cautious. Many rewards await us, but all is not safe, the city is also home to terrible predators. Cats are the worst, quiet, leaping, crazy, red in tooth and claw. When we see a cat, a cry goes out, run, find a crack in a wall, stay still until the danger slinks on. With patience and luck, we will survive another night, and tomorrow there will be even more of us!

It is our secret weapon. With all the nibbles you leave behind, a warm nook, and the right kind of company, make room for babies. Lots. A dozen at a time is not unusual, and it takes only a few weeks to make them, and shortly after birth, we are ready to make some more. Really, if it wasn’t for the cats, an occasional terrier, the diabolical contrivances of human pests, and an unfortunate tendency for internecine conflict, how much faster our family would grow.

People, thank you for the city. Your habits are our habits, your throwaways are our takeaways, and while you’ve done all the work to make the city for yourselves, we could not resist moving in, migrating across the grid, and settling down – waiting each day for the sun to set, and the streets to be our playground.

Steward Pickett

About the Writer:
Steward Pickett

Steward Pickett is a Distinguished Senior Scientist at the Cary Institute of Ecosystem Studies in Millbrook, New York. His research focuses on the ecological structure of urban areas and the temporal dynamics of vegetation.

Steward T. A. Pickett

A city must be an ecosystem

The fundamental idea of the ecosystem is one of the clearest in contemporary ecology. It has survived intact since it was introduced by Sir Arthur Tansley in 1935. Few scientific concepts have such longevity.

The deep definition of the word ecosystem is notable for what it leaves out—the minimal baggage carried by the idea makes it nimble and broadly applicable.
According to Tansley, and leaders in ecosystem ecology since his time, an ecosystem occupies an area and comprises the complex of biological organisms in that place along with the physical environment complex, and the interactions among these two complexes. The use of the word “complex” indicates that there are interactions within the biological and the physical parts of an ecosystem as well as between them.

So an ecosystem is a place that combines interacting biological organisms and physical features. The biological includes the conspicuous plants such as trees and herbaceous species, the microbes such as fungi, bacteria, and viruses, the animals ranging from large carnivores and scavengers, to the inconspicuous creatures like worms and insects. But the key word—interacting—is what makes it a system.

The deep definition of the word ecosystem is notable for what it leaves out. Indeed, the minimal baggage carried by the idea makes it nimble and broadly applicable. The definition of the ecosystem does not require things like closed boundaries, stability or equilibrium; nor a focus on any particular time or spatial scale. It doesn’t require or deny directional changes through time, or an inevitable terminal condition of diversity or productivity.

The sort of things the definition leaves out, however, become the fodder for research questions or applications. The features absent from the definition can be addressed in specific ecosystem models that apply to certain broadly distributed conditions, or to particular locations or time periods. A researcher or practitioner can always ask, what if the ecosystem I’m studying or designing were in equilibrium, or had closed boundaries for some material? The model that an investigator creates would take the basic idea and add the constraints she wanted to investigate. But notice that in this application something new becomes apparent: the fundamental definition is free from most assumptions, whereas the specification of the basic concept in a particular model states explicit assumptions, exposing them to test. The ecosystem concept and its specification describe a two tiered strategy: concept as clear but lightly burdened generalization, applied though many different specific models that state the precise assumptions they make. This is a common strategy in science.

As specific ecosystem models have proliferated and been tested, ecosystem thinking has broadened in practice. In some ways this evolution has confirmed the wisdom of avoiding assumptions in the definition, such as equilibrium or closed material boundaries, or strict spatial isolation among ecosystems. The breadth of models has demonstrated that actual ecosystems can have an amazing variety of forms, contents, and dynamics. For example, various specific models have documented that ecosystems are three dimensional bodies, extending deep within terrestrial soils or aquatic substrates, and high above the canopies of tall trees. Other modern insights include the widespread role of natural disturbance in shaping ecosystems, or the almost universal presence of humans, human effects, and human legacies in ecosystem structure and function. None of these conditions is required, but neither are they excluded by the fundamental definition—which brings us back to cities.

How could a city, or a suburb, or a town, or an agricultural village not be an ecosystem? Cities have biological components—including of course humans—but also wild organisms passing through or adapted to the new range of conditions that exist in cities. Organisms long-adapted to and dependent on human largess and waste are a part of urban ecosystems as well. Soil invertebrates, fungi, and bacteria inhabit urban soils and waters. Urban organisms are as involved in the transformation of energy and matter, and the transmission and receipt of information, as are their wild cousins.

Urban systems of course contain the particular physical environment within which and with which the organisms interact. Sunlight for photosynthesis, the cues of daylength and the seasonal swings of temperature, the exaggerated heat budgets, the stresses of low humidity, the soils, rubble, and fill as substrates, the rush of wind through the streets or the stagnation of air in deep street canyons, and the alteration of topography, with its importation of stone and the alkaline ingredients of concrete, are among the many aspects of urban physical environments.

All of these interacting components define an urban instance of the basic idea of the ecosystem. And all of these components reflect the desires, plans, mistakes, accidents, and unintentional effects of decisions made by individual people, households, and institutions. Clearly the physical environments of cities are constructed by or profoundly modified by people. Equally clearly, the biological complex of cities where humans are the predominant actor, has social features as well as compositional and spatial biodiversity.

All of this complexity and dynamism fits easily within the basic definition of the ecosystem, and invites the burgeoning of specific models that contribute to surprise, delight, and utility in the urban sciences and design professions. In an era of global urbanization, climate change, and deepening social inequity, urbanists must recognize the many jobs that even the inconspicuous biological elements of the urban ecosystem perform.

But beyond recognizing the role of the biological component of urban ecosystems, it is imperative to increase the ability of these systems to do ecological work. This means leaving or making space for organisms, which are the creators of ecological work, in new or retrofitted cities. It means allowing streams to interact with marshy banks. It means growing trees to form connected canopies for reasons of aesthetics and climate moderation. It means supporting food webs that generate local crops and control problematic species. Finally, it means sharing benefits equitably among empowered and marginalized people. These are important outcomes that can come from acting on the idea that any city must be an ecosystem.

Rob Pirani

About the Writer:
Rob Pirani

Robert Pirani is the program director for the New York­-New Jersey Harbor & Estuary Program at the Hudson River Foundation. HEP is a collaboration of government, scientists and the civic sector that helps protect and restore the harbor’s waters and habitat.

Rob Pirani

Cities are ecosystems! Let’s help them adapt and evolve

Cities are ecosystems! Affirming that people and our culture cannot be considered apart from nature offers both useful metaphors and new urban practices. But just as people are a particular and complicated part of the biota, cities are ecosystems with some particular and complicated characteristics. Improving our understanding of those details can certainly improve urban planning and design.

Consideration of the social benefits of resilience technology, and the civic ecology that it can engender, may well determine whether our urban ecosystems and all of their inhabitants can successfully adapt to a changing future.
What is less clear is whether human-dominated ecosystems, like cities, can successfully evolve in the rapidly changing world we have created. Rapid population increases, urbanization, introduction of novel contaminants and species, and now climate change all pose challenges to both people and other urban inhabitants.

Consider how understanding cities as ecosystem improves both the built and natural worlds.

By definition cities are a human adaption to help produce and distribute energy, transform materials, and shape their consumption. Healthy ecosystems have a balance of production, consumption, and decomposition. Cities can promote virtuous cycles that return these materials and energy to new uses. Whether building soils by composting organic waste or creating buildings that recycle and reuse the rain, urban planners and designers are fostering a host of more sustainable practices.

Understanding cities as ecosystems can also help us conserve and restore valued ecological characteristics and services. The ecological structure and functions of our urban greenspaces and waterways provide people with a wealth of services, from moderating air temperatures to producing fish. Defining these ecological characteristics is an important way of improving management and defining restoration goals. Identifying the value of these services is a critical piece of information that can help us locate and design buildings and infrastructure so that they positively contribute to nature. These ecological characteristics also define place, the genius loci that makes each city special and valuable.

But can understanding cities as ecosystems change the way cities adapt and evolve? The evolution of ecosystems is shaped by life histories, natural selection and the biological evolution of organisms over time. Cultural forces guide the evolution of cities. These individual and group decisions operate for the most part on the time scale of markets and politics, and do not always account for ecological considerations. In particular modern society tends toward silo management and investment by sector and by jurisdiction, making it difficult to advance integrated decisions at an ecosystem scale.

Consideration of how we can successfully employ natural and nature-based coastal features to increase the resiliency of our waterfront cities offers some specific lessons for what is needed to move forward.

The health of our coastal cities/urban ecosystems are increasingly vulnerable to the impacts of flooding, due to the combination of human population growth, real estate pressures, sea level rise, and coastal storms. Here in New York and New Jersey, Hurricane Sandy and its aftermath continues to pose challenging questions of how to mitigate mounting hazards to people and property along our urban shorelines. Such challenges will only increase with a rapidly changing climate.

One set of answers is the increased use of natural and nature-based features for coastal adaptation (NNBFs). Such strategies recognize that natural features along our urban shorelines, like beaches, coastal dunes and wetlands, have evolved over the years to survive and indeed thrive in face of changing sea levels and storms. Nature-based features are engineered infrastructure designed to employ the characteristics of these coastal landscapes, specifically offering services such as coastal risk reduction, restored habitat, and stormwater management. The US Army Corps of Engineers (, US Housing and Urban Development (, National Oceanic Administrative Agency (, state and local agencies (for example see the Coastal Green Infrastructure Plan for New York City at ), and academic partnerships such as Sustainable Adaptive Gradients in the Coastal Environment are actively promoting these concepts.

The promise of NNBFs, like other green infrastructure and green building technologies, offers a kind of symbiotic evolution. That adapting our cities can meet the linked challenges of more people and a changing climate in a way that improves or at least sustains the rest of the ecosystem.

To meet this promise will require new metrics for success and the means of adaptively managing these living shorelines. It will require the will to cooperate across boundaries. It will require the science needed to understand whether such infrastructure does indeed provide an ecological lift. It will require rethinking permit guidance to allow for this hybrid infrastructure. There are many efforts to better define these metrics and monitoring requirements, and consider needed policy and management changes.

But perhaps most critically, successfully deploying such technology will also require designers and engineers and decision makers to consider how to better integrate long term monitoring, community stewardship, and social resiliency into engineering decisions and practice. NNBFs, like most green infrastructure, require time for plants and animals to establish themselves. Monitoring and in many cases active stewardship is critical for their enduring success.

This need for stewardship offers an opportunity for engaging community and building the social resiliency critical to mitigating coastal and other hazards. Consideration of the social benefits of this technology, and the civic ecology that it can build, may well determine whether our urban ecosystems and all of their inhabitants can successfully adapt to a changing future.

Richard Register

About the Writer:
Richard Register

Richard Register is the Founder of the International Ecocity Conference Series and the NGO, Ecocity Builders.

Richard Register

Are cities ecosystems—analogous to natural ones—of nature, infrastructure and people? Not so much.

There is a better comparison: with complex living organisms in all their three-dimensional glory.

Ecosystems are certainly crucial to the health of their living inhabitants. And certainly lessons like “conserve energy and utilize renewables primarily” and “recycle assiduously” are good lessons for the functioning of cities as well as relevant models for our education about biological systems of rich biodiversity and high biomass. As individuals and groups of people, we are fed by the environment and by observing, say, trees that grow great and provide shelter from rain and wind in their hollow trunks, or under their big branches, we can learn something leading into architecture, for example. Maybe that’s where architecture started.

Comparing our cities to complex living organisms seems much more fruitful—in other words, to our own bodies, our organ systems, our limits. I think of this as the “anatomy analogy”.
But where cities have come to date is something far more complex: add to buildings systems of transportation, paved and rail, supply delivery, recycling and waste disposal back into the environment, public open spaces such as parks and plazas, designed treatment of elements of nature from river and water fronts to rooftop gardens and window box gardens attracting hummingbirds and bees. Then there are special function organs like restaurant, arts, education and medical districts and the various zones of built infrastructure for various other functions, neighborhoods of different cultural emphases. So though there is much to consider regarding designing healthy cities to be gained by looking at the way our all-embracing environments work, there is much more to be learned from complex living organisms.

Nature hints architecture

In fact, the more I think about it the more I think we are off on the wrong foot to make a big deal of the analogy between cities and ecosystems. In a sense, that’s what sprawling suburbs do. Comparing our cities to complex living organisms seems to me much more fruitful, comparing cities, in other words, to our own bodies, our organ systems, our limits. I think of this as the “anatomy analogy”.

There is a basic mathematical truth at the heart of the universe here, a geometric truth: complexity becomes well ordered in three dimensions, like the compact ultra efficient form of living beings like us. The “environment” models scattered two-dimensional layouts such as hyper inefficient car-dependent, land, resources and energy squandering sprawl development. That two-dimensional layout of ecosystems is not purely so–of course. Take a kelp forest 250 feet from anchorage to top, or a redwood forest towering almost 390 feet tall, more including roots, 3-D to that degree. But the general and overall form, covering vast areas of land and waters of these environments is basically 2-D.

At the core of the issue is that three dimensions works—overlapping lines of connection, either by simply “bumping up against one another, one function to another” and with overlapping veins, nerves, lymph ducts, digestive/excretory tubes, etc. But try to squeeze it all down to the flats like suburbia tries to do and you have a tangled mess of concrete and steel freeway over- and underpasses, miles and miles of pipes and wires that in the compact form of highly mixed uses well organized is much, much shorter, more materials and energy conserving.

This is the basic formula also expressed as “access by proximity.” My father, a sailor and a pilot, liked to say, imagining tacking toward the finish line, “the shortest distance between two points is a straight line”.

But the more fundamental truth is “the shortest distance between two points is moving the points close together”. You can’t get more basic than that and that’s exactly what’s at the basis of the preference for using the complex living organism as an urban model over the much more fundamentally two-dimensionally semi-organized environments of various ecosystems.

Eric Sanderson

About the Writer:
Eric Sanderson

Eric Sanderson is a Senior Conservation Ecologist at the Wildlife Conservation Society, and the author of Mannahatta: A Natural History of New York City.

Eric Sanderson

Cities are not so much ecosystems as they are ecological landscapes

In the biological sciences, we think of life as a set of Russian dolls, with different kinds of scientist to examine each type of matryoshka. Cells are made of molecules, and so there are molecular biologists (and biochemists) to study them, and cellular biologists to study the cells. Cells are organized into tissues studied by histologists; tissues are assembled into organs, which are studied by anatomists and physiologists. (For the human organism, you see a cardiologist for your heart and a nephrologist for your kidneys.) Organs in turn make up organisms, the province of classical biological types: mammologists for the mammals, ornithologists for the birds, herpetologists for the reptiles and amphibians, ichthyologists for the fish, entomologists for the insects, botanists for the plants. Each branch of science has its own division of the evolutionary tree to care for.

A city is an ecological landscape—and a landscape, to scientists like me, is the particular pattern of ecosystems, their composition and arrangement, that forms a habitat for plants and animals. Even for people.
Once we start to nest organisms into the environment, we enter into the realm of ecology. Community ecologists study the interactions between and among different kinds of organisms; ecosystem ecologists study the interactions of ecological communities with the non-living aspects of the environment: water, air, soil, nitrogen, energy, and so forth. And landscape ecologists, my particular tribe, study the assembly of ecosystems into mosaics that vary in space (i.e. what you see looking out of an airplane) and in time (i.e. what you see in a time lapse movie.) One could go on to speak of regional ecology (and ecologists) and planets and their devotees, and eventually, if we find life on another world, then exobiology and trans-planetary ecology will be latest academic fad, but we’re not there yet. For now, when it comes to cities, I think landscape is the doll on which we should focus our energy. Because cities are not singular ecosystems, they are ecological landscapes composed of many kinds of ecosystem.

As I wrote in another context some years ago:

To landscape ecologists, a landscape is not just a considered view of the outdoors (as seen in a landscape painting), nor is it a manicured garden (as created by a landscape architect); a landscape, to scientists like me, is the particular pattern of ecosystems, their composition and arrangement, that forms a habitat for plants and animals. Even for people.
—from Mannahatta

And what are these urban ecosystems? Buildings, streets, sidewalks, gardens, empty lots, baseball fields, parking garages, bridges, ponds, lakes, streams, forests, grasslands, beaches, marine waters, and so forth. Since an ecosystem is itself a composite of living and non-living elements, one can distinguish them by their different biotic and abiotic components. A forest is not only the trees, shrubs, herbs, squirrels, fungi, bacteria, etc. but also the soil, water, and energy. A building also qualifies as an ecosystem by this definition, inhabited by living people and our commensal pets and also composed of non-living walls, floors, ceilings, insulation, furnishing, electrical wires, and so on. Just because an ecosystem is designed by a human being doesn’t mean it’s not an ecosystem. Indeed if we began to think of buildings as the ecosystems they are, we might design them better.

More to the point, urban ecosystems are arranged in distinct and recognizable patterns as landscapes. Just take out your phone and look at a mapping application of your favorite city neighborhood. Rarely does nature compose such exquisitely structured and rigorously enforced patterns. Hardly does nature lay down such straight lines or place such elements of fundamental difference in such close proximity. And never does nature let a singular idea (the city grid, impervious pavement, the motorcar) run roughshod over all others as we have it in most 21st century cities.

To the extent that we want to find and restore nature in urban landscape, landscape ecology must be our essential framing discipline, embracing of many disciplines, and yet providing its own tools and thought processes. Remember within the landscape are all of nature’s other Russian dolls and their devotees: ecosystems, communities, plants and animals, and so on, down the biological hierarchy to the molecular level. Landscape ecologists integrate across these ways of imagining nature and then bring to bear our own expanding bag of tricks. On the theoretical side, landscape ecologists might wax eloquent about how disturbance processes (e.g. fires, floods, gentrification) change the urban form or habitat models can be deployed to predict where different species (or subsets of a species, drug dealers, philanthropists, potential sweethearts, etc.) hang out. Landscape ecology helps us see the urban mosaic in terms of its connectivity for not one or a few transportation modes, but for the many different types of organisms co-inhabiting the city, and for energy, biogeochemicals, sewage, and other materials, intentionally or inadvertently passing through. Landscape ecology opens us to explore the complex scaling rules that explain how the ever-changing interactions of the city work themselves out at different levels and for different reasons and into different spatial forms. Similarly, the tools of a wildlands landscape ecologist can provide insights for the technologically-minded urban planner, who deploys GPS, GIS, satellite imagery, aerial photography, computer modelling, visualization, and so forth to make a better landscape of ecosystems, that is, a city.

Alexis Schaffler

About the Writer:
Alexis Schaffler

Alexis is a doctoral student from UC Berkeley's Department of Landscape Architecture and Environmental Planning, at the College of Environmental Design. Her research interest is the shift towards multifunctional infrastructure, a framework that connect commonplace services such as transport, potable water, sanitation, housing with other functions, such as ecosystem services, climate action and sustainable resource use.

Alexis Schaffler

Cities as ecosystems—a cultural reflection

As an academic and occasional policy advisor from the Global South, “cities as ecosystems” has been an attractive metaphor. Intellectually, I was brought up by what I call academic activists or planners, taking on the challenge of urban sustainability in a context of familiar development struggles. Our context commonly appears in terms of ‘unprecedented’ urbanization, often without the necessary growth; inequality and unemployment; and perverse infrastructure legacies of unsustainable resource use and environmental degradation.

Perhaps our insight is not really in viewing cities as ecosystems, but instead lies in how the cities-as-ecosystems idea causes our urban thinking and designs to evolve.
Retrospectively, cities-as-ecosystems was a natural step on my journey investigating options for more sustainable urban futures. In 2013, I led a Green Infrastructure research project at the Gauteng City-Region Observatory (GCRO), a partnership between academic institutions and governments in South Africa’s smallest, but most densely populated urban region. Green infrastructure offered exciting analytical opportunities—we could develop impressive maps, visuals and economic values—to show how the region’s green assets form a network that provides ecosystem services in the same way as conventional grey infrastructure. In 2013, the GCRO published a State of Green Infrastructure, the first of its kind to visualize and assign economic, as well as cultural values to green infrastructure, the “interconnected set of natural and constructed ecological systems, green spaces and other landscape features.

The indigenous and planted trees in Gauteng, strikingly showing the extent of tree cover within the urban core, roughly covering Johannesburg. Although the majority are planted and non-indigenous, the trees in Gauteng provide important services, such as air purification and erosion control. The map also demonstrates the power of high resolution satellitle imagery in mapping individual ecological assets such as trees (Khanyile, 2017).

Like other similar endeavors, there have been necessary evolutions to the GCRO’s green infrastructure work. Much of this evolution rests on the ecosystem services metaphor, which helps us to understand the benefits provided by ecosystem to society. This metaphor is the basis of impressive work around the world that assigns green infrastructure a monetary value, with the ultimate goal of incorporating these values into municipal budgeting and accounting procedures.

The endurance of the GCRO’s green infrastructure work is inspiring. Compared to my preliminary, and admittedly naïve work, their current green infrastructure engages spatial, economic and social analyses that contain more of the necessary detail for understanding cities as ecosystems. While innovative at the time, our 2013 State of Green Infrastructure report encountered major data challenges as we learnt about the deficiencies of our local government datasets. This was illuminating, highlighting the critical role of data consistency and capacity, but it was also very costly, requiring the services of external data contractors with the requisite data and technical capacities.

Perhaps most importantly, the GCRO’s Green Infrastructure City-Lab facilitates the sharing and co-production of knowledge between government officials and other stakeholders to develop green infrastructure within municipal planning (Culwick & Bobbins, 2014). This is a welcome resolution to our early situation with local government databases. The connection and interest between scholars and government practitioners may well prove the most important anchor in future work. There are important movements to watch within some of Gauteng’s local governments expressing interest in green infrastructure as a more formal strategy for urban planning.

Yet, I am also cautious of the above in my current role as a PhD scholar at UC Berkeley’s College of Environmental Design. In part, there is a romanticism in thinking about cities as ecosystems, particularly whether green infrastructure can truly contribute to meet our ever-demanding human needs. We also have to be wary of the attractive, yet rather ambiguous, renditions that use ecology to model urban processes. This is most clear in the North American discourse, Landscape as Urbanism, with a following of ‘intellectual’ designers, eluding to ecology in their vocabulary but largely producing intriguing visual renditions and models of cities as complex ecosystems (Duany et al., 2013; Corner, 1999: Waldheim, 2008).

I do find conciliation in remembering the linage of ‘bringing nature back in’ to urban design and planning. Olmstead’s ‘parkways’ concept, Howard’s Garden Cities, proposals in Spirn’s The Granite Garden (1965), McHarg’s Design with Nature (1969), and Hough’s City Form and Natural Process (1984) are important examples in history showing both the intellectual and strategic power of viewing cities as ecosystems. The GCRO’s green infrastructure work is certainly part of this global lineage and experimentation with what it means to articulate, and invest in, cities as ecosystems. Yes, this casts a wide net of intellectual idealists and activists, but perhaps our insight is not really in viewing cities as ecosystems, but instead, lies in how the cities-as-ecosystems ideas causes our thinking and designs to evolve.

One of the best lessons we receive is, of course, from practice. Portland, Oregon, presents a unique case of two sustainable urban design experiments attempting to integrate social and ecological functions. The New Urbanist project, Jamison Square, includes an iconic fountain, a boardwalk, an outdoor gallery and often features in media as a socially vibrant, active and lively public space” (Senville 2015). In contrast, Tanner Springs Park, emerging later in the city’s history as a Landscape Urbanist project, primarily a stormwater project that transitions from a relaxing meadow with stone walkways, a cleansing biotope and wetland plantings (Senville 2015). Duany et al. argue that Tanner Park is largely devoid of humans, rather focusing on maintaining prairie grasses and preventing the adverse aesthetic effects of citizens’ and animals feet and posteriors (2014).

The social and ecological differences of Jamison Square and Tanner Park are not necessarily unhelpful trade-offs. There is immense value in foregrounding the vital functions performed by landscapes, such as mitigating climate or providing drainage. Highlighting landscape infrastructure as well as the more commonplace, albeit often invisible networks of transit or waste disposal systems also opens urban design to the crucial sustainability question of how to sustain urban functions given available resources. The conundrum in designing more sustainable urban forms is therefore how to provide for social and ecological urban functions in a way that resonates with humans, without comprising affordability nor the requirements for density, mix and scale (Kelbaugh in Duany et al., 2014, Hill & Larsen, 2014). As Thompson reflects, while working through the nature-cultural dichotomy is complex and challenging, urban design experiments are an essential part of responsive, creative and catalytic thinking about the major structuring elements of urban form (2012). While sustainable urban design experiments often reveal the discontents of paradigmatic thinking, they are also significant as empirical opportunities to critically reflect on the realities of ecological and social integration in urban form.


Corner, J. 2006. Terra Fluxus, in The Landscape Urbanism Reader, edited by Charles Waldheim, 21-33. New York: Princeton.

Culwick, C., Bobbins, K., Cartwright, A., Oelofse, G., Mander, M. and Dunsmore, S. (2016). A framework for a green infrastructure planning approach in the Gauteng City-Region, Johannesburg: Gauteng City-Region Observatory.

Duany, A. & Talen, E. 2013. Landscape Urbanism and its discontents, Dissimulating the
Sustainable City. Canada: New Society Publishers.

Gauteng City-Region Observatory (GCRO). 2015. Green Infrastructure City-Lab. Online]. Available:

Hough, M. 1984. Urban Ecology, a Basis for Design, in n City Form and Natural Process. New
York: Routledge.

Khanyile, S. (May 2017) ‘Mapping green infrastructure in the Gauteng City-Region‘ Conference poster, Resilience for development colloquium 2017

McHarg, I. 1969. The Plight, in Design with Nature, 31-41. New York: The Natural History

Schäffler, A., Christopher, N., Bobbins, K., Otto, E., Nhlozi, M.W., de Wit, M., van Zyl, H., Crookes, D., Gotz, G., Trangoš, G., Wray, C. & Phasha, P. (2013) State of Green Infrastructure in the GCR, Johannesburg: Gauteng City-Region Observatory.

Spirn, A.W. 1965. The Granite Garden: Urban Nature and Human Design, Basic Books, Inc.,
New York

Waldheim, Charles. 2006. Landscape as Urbanism, in The Landscape Urbanism Reader. NewYork: Princeton Architectural Press.


David Simon

About the Writer:
David Simon

David Simon is Professor of Development Geography at Royal Holloway, University of London and until December 2019 was also Director of Mistra Urban Futures, an international research centre on sustainable cities based at Chalmers University of Technology, Gothenburg, Sweden.

David Simon

I have always been wary of organismic analogies seeking to compare human artefacts such as urban systems or individual cities with the human body or natural systems because they never stand up to inspection. Even possibly the most famous analogy of natural systems across very different scales, namely James Lovelock’s Gaia hypothesis, which likens Planet Earth to the human body, is analytically problematic despite its innate appeal as a rhetorical device.

Perhaps in the future, the ecosystem analogy might become more apt, but at present it is unhelpful and inaccurate, obscuring or concealing far more than it might superficially promise as heuristic device.
Fundamental to natural systems, including ecosystems as variously defined (including the version cited in the curatorial note) is the holistic integration of all their components within a system which makes the whole more than the sum of its parts and is normally sustainable. That said, ecosystems are not closed systems since they exchange nutrients with adjacent systems through different mechanisms, in part through being open to the atmosphere, soil and groundwater.

Individual cities are also open, indeed, far more so than ecosystems: there are constant inward and outward flows of resources and wastes of various sorts, commodities, people and finance. Despite our current and very necessary preoccupation with urban sustainability, no individual city or even system (network) of cities is sustainable in the sense of being autochtonous. No matter the extent of nutrient and water recycling and waste reduction, progress towards carbon reduction and renewable energy, or shift towards integrated and efficient public transport, cities are necessarily open and reliant on such fluxes and flows. Indeed, it is important to acknowledge that this is not a failing but both by necessity and design. No city anywhere has ever been able to survive for an extended period when cut off from its hinterland and isolated, as in a siege.

My scepticism about the analogy rests on three main factors. First, no existing city is fully internally integrated and harmoniously or efficiently functional. The extent of dysfunctionality, or harmony versus conflict, varies greatly but the diversity of urban residents in terms of both visible and invisible markers, and their divergent or overtly conflictual interests, militates against this. Second, with very few exceptions like mining company towns, urban areas are not designed and built at one time to a comprehensive plan with the explicit intent of becoming a “complete” entity in any way comparable to an organism or ecosystem. Instead, they grow in phases, usually incrementally or with distinct new neighbourhoods being added, at different rates at different times. Over time there is also periodic decline, dereliction and eventual redevelopment of areas or neighbourhoods that become obsolete as a result of technological change or shifting trade and political relations, or become depopulated or economically or socially undesirable through changing income or social profiles and preferences. Third, governance is often deficient or dysfunctional, with urban politics revealing differing degrees of contestation among different stakeholders and tensions between social welfare and private or corporate profit.

That said, current urban greening initiatives, often including wetland and river rehabilitation; rewilding of derelict or biologically degraded areas; networking of open space systems; water reuse and recycling; and small-scale renewable energy generation are increasing urban biodiversity, enhancing climate change mitigation and adaptive capacity, and providing more “green” jobs and livelihood opportunities. To some extent, then, these may be integrating urban areas in novel ways, also softening or blurring some of the sharp discontinuities referred to above, and enhancing urban liveability and wellbeing.

Furthermore, some critiques of technocentric visions of smart cities and urbanism are beginning to gain traction and might shift the focus towards more locally appropriate and sustainable interventions. Perhaps in the distant future, the ecosystem analogy might become more apt but at present it is unhelpful and inaccurate, obscuring or concealing far more than it might superficially promise as heuristic device.

Yolanda van Heezik

About the Writer:
Yolanda van Heezik

Yolanda van Heezik is currently exploring children’s connection with nature, and how ageing affects nature engagement. She is part of a multi-institutional team investigating restoration in urban areas, and cultural influences on attitudes to native biodiversity.

Yolanda van Heezik

The notion of the city as an ecosystem is not new—“the ecology of cities” as a paradigm was introduced in the late 1990s and the holistic nature of this paradigm implies that the city itself is an ecosystem. But how is a city ecosystem defined? It is difficult to define the spatial contours of any ecosystem, and this is certainly the case in cities, where the ecological footprint can be many times larger than the geographical boundary of the city itself. The quantities of food, energy and other natural resources and products that flow between the city and its surroundings are very large relative to that which is cycled within the city. Environmental philosopher Mark Sagoff (2003) argues that we need to be able to define an ecosystem before we are able to understand it, to manage it, and to develop general theories of ecosystem functioning, but that in fact we lack the “criteria that determine what kinds of things count as ecosystems”. The challenge for urban areas is how we can define a single ecosystem that encompasses all the variability that characterises any given city. If we are unable to identify a single ecosystem we can’t then re-identify it over time and in the face of change.

Thinking about a city as a collection of ecosystems influenced by their surrounds could be a more helpful way to inform urban design, and make it easier to identify the elements that make up each particular ecosystem.

An analysis by Cadenasso and Pickett (2008) of urban principles for ecological design and management, applies a widely-used definition to assert that cities are ecosystems; i.e. that they have “interacting biological and physical complexes”. The additional complexity added through acknowledging the role humans play in urban ecosystems, and the patterns and processes that result from interactions between social, built, and ecological components of the system, are seen as extensions of the basic ecosystem concept. It is possible though, that such an over-inclusive definition, which implies that the ecosystem can be of any size, with boundaries defined only by the research questions, might hinder the development of theories of ecosystem functioning that could be generalised across many cities.

Cities vary hugely in size, spatial form, and history. I live in a city in New Zealand that is so small that people from more populated countries might consider it not to even be a city. In contrast to the high-density megalopolises, New Zealand’s cities do not contain many millions of people, high-rise living, dense housing blocks, or extensive industrial and commercial area—rather they are cities of sprawling suburbs. A lack of clarity around what is considered ‘urban’ was identified by Pickett et al. (2009) as a challenge to developing an urban ecosystem theory.

Can ecosystem theory developed for huge cities, or very old cities, be generalised to newer small cities such as those in New Zealand? Perhaps it would be more useful to think of cities as collections of ecosystems. After all, if no settlers had arrived to occupy the space where I live, ecologists would not treat the area covered by my city as one ecosystem, but as coastal, sub-alpine, swamp, mixed-podocarp forest, and freshwater ecosystems, to name a few. Cities often occupy large areas and show very high cultural and socio-economic heterogeneity, as well as heterogeneity of land covers imposed on a variety of natural landforms. Treating the city as one ecosystem overlooks this variety.

Cities are usually characterised by significant dynamic change. Rapid changes in human population size and composition are followed by major changes in land cover characteristics and built infrastructure, which affect processes such as primary production and nutrient assimilation, as well as biodiversity characteristics, connectivity, and the production of goods and services. Interactions and feedback loops between social and ecological factors continually evolve in response to different cultural and socio-economic influences. In the face of constant and massive change, that can occur at different rates and in different ways across a city, is it appropriate to consider the city as one and the same ecosystem over time?

Does thinking explicitly about cities as ecosystems offer us any insight into urban design?

The holistic approach that is implicit in our understanding of ecosystem function, which recognises interactions and connections between constituent living and non-living parts, should provide pathways for better, more liveable urban design. The paradigm “ecology for the city” (Pickett et al. 2016) recognizes the applied role of ecological research and a responsibility to create a sustainable, liveable and resilient urban environment, and the term ‘ecological urbanism’ has been adopted to describe a more holistic approach to the design and management of cities. Resilience goals might be met using a socio-ecological approach, which acknowledges the unpredictability and complexity of city systems. This kind of holistic approach has been used at least in the short term in New Zealand, after the 2010-2011 Christchurch earthquakes, to not only restore the city to its previous state, but also to introduce regulations to ensure that the city would be better able to endure future disturbances.

Conceptualising cities as a series of ecosystems, rather than just one, could make urban design more tractable, since it wouldn’t be necessary to try to manage everything all at once. Much of my research has focused on private green spaces in suburbs or neighbourhoods. A focus on a coherent sub-area, such as a collection of suburbs or a neighbourhood as an ecosystem, would be useful, as ecological concepts could then be applied to urban design within and immediately around that space. For example, urban design could accommodate connectivity across suburbs and between other parts of the city in the spatial configuration of public and private green spaces and the location of highways and other transport corridors. Urban design could mitigate the impacts of hard edges, where suburbs abut onto other, less biodiverse, land covers. A holistic approach would accommodate the significant and dynamic human influence on management of private green spaces, and recognise important interactions, such as those potentially existing between human well-being benefits and biodiversity benefits. Thinking about a city as a collection of ecosystems influenced by their surrounds could be a more helpful way to inform urban design, and make it easier for us to identify the elements that make up each particular ecosystem.

Cadenasso, M & Pickett, STA. 2008. Urban principles for ecological landscape design and management: scientific fundamentals. Cities and the Environment 1(2): article 4, 16pp.

Pickett, STA, Cadenasso, ML, Childers, DL, McDonnell, MJ, Zhou, W. 2016. Evolution and future of urban ecological science: ecology in, of, and for the city. Ecosystem health and Sustainability 2(7) e01229. Doi 10.1002/ehs2.1229

Sagoff, M. 2003. The plaza and pendulum: two concepts of ecological science. Biology and Philosophy 18: 529-552.
Sanchez, AX, Osmond, P, van der Heijden, J. 2017. Are some forms of resilience more sustainable than others? Procedia Engineering 180: 881-889.

Ken Yeang

About the Writer:
Ken Yeang

Dr. Ken Yeang is an architect, planner, and ecologist. The Guardian newspaper named him as one of 50 individuals who could save the planet.

Ken Yeang

Whereas ecosystems are living entities, our existing towns and cities are, in effect, inert structures unlike living things, and have operational and industrial systems that give nothing of biological value back to nature.
Are our existing towns and cities ecosystems? Cities are referred to by many as ecosystems, but in reality and systemically they are not. Cities are far from ecosystem-like, being almost entirely inorganic and abiotic, mostly bereft of nature and biotic constituents (except for the occasional park, green squares, hedges, roadside trees and verges). Simply stated, cities do not have the complete biological structure of abiotic and biotic constituents acting together to form a whole that is the fundamental characteristic of an ecosystem.

Whereas ecosystems are living entities, our existing towns and cities are, in effect, inert structures unlike living things, and have operational and industrial systems that give nothing of biological value back to nature. Humanity’s existing towns and cities are mostly inorganic, synthetic, biologically inanimate and are parasitic and dissociated from nature yet dependent on its bioregion and its hinterland for providing the vitally crucial ecosystem services, for its food (mostly transported from distant sources), for its source of energy (which in most instances is not from renewable sources as in naturally-occurring ecosystems), for its water, for the raw materials that it needs for its incessant production of artefacts for humanity’s benefit for its everyday domestic and commercial existence.

Vivek Shandas

About the Writer:
Vivek Shandas

Professor Vivek Shandas specializes in integrating the science of sustainability to citizen engagement and decision making efforts. He evaluates the many critical functions provided by the biophysical ecosystems upon which we depend, including purifying water, producing food, cleaning toxins, offering recreation, and imbuing society with cultural values.

Vivek Shandas

Nature-Based Segregation: The inequitable ecological turn in planning practice

Walking down the residential streets in Seattle, Washington or Portland, Oregon, one cannot help to notice several small and vegetated areas that occupy portions of the street right of way. These minor changes to the urban landscape represent a physical manifestations of what I call an ecological turn in urban planning practice. This ecological turn refers to a change from two centuries of urban development that emphasized the importance of engineering systems for roads, buildings, and the myriad layers of infrastructure that make up our cities, to a recognition that patches of nature can provide services previously taken for granted or dismissed. Arguably, these attempts to change the gray infrastructure of roads and pipes to green receptacles to collect and infiltrate strormwater were the earliest modern examples of planning practice taking seriously the contributions in the field of urban ecology. As a result, cities around the world are attempting to reintegrate nature into human habitation, and increasingly looking to urban ecology for principles to inform planning practice.

What then can be done to address the historical inequities of applying urban ecological knowledge to exclusionary planning practices? First is the recognition that urban ecological research is not value-neutral.
While others on this blog are describing specific examples of nature-based solutions for cities, I argue here that the emerging ecological turn in planning practice remains conceptually and spatially a movement that benefits communities with privilege. Those who are white, higher-income, and educated have greater access to and benefits from urban nature, while those communities of color and lower income face a disproportionate burden from environmental pressures. These communities often live in “nature deserts” or places that are replete with the biggest disasters of planning practice, such as strip malls, big box stores, and/or mega transportation projects that least benefit communities most need. To take for example, evidence from around the U.S. that suggests an inequitable distribution tree canopy among cities, which as a simple yet poignant indicator offers a window into planning system that has not taken seriously the centuries of exclusionary practices that privilege the few.

While the history of U.S. planning practice is replete with stories of segregation, whether of schools, housing, or services, yet today, we face an ongoing ecological segregation that is amplifying environmental pressures to those most vulnerable in our cities. As many communities grapple with the foreboding challenge of managing the increases in frequency, duration, and magnitude of extreme climate events, we need now more than ever to integrate our knowledge about urban ecosystems into planning practice. As way of example, our research team at Portland State University is engaging with an international network of practicing planners — as part of a National Science Foundation Sustainability Research Network (SRN) — to understand the implications of extreme climate events on vulnerable populations. The project begins with the idea that all urban communities differ in terms of their knowledge of, access to, and control over resources, and that to create transformational change in cities we need to co-produce knowledge by engaging practitioners with researcher. Although the SRN is a first step and relatively limited in terms of the communities we can transform, a lot more needs to be done.

So what then can be done to address the historical inequities of applying urban ecological knowledge to exclusionary planning practices? First, is the recognition that urban ecological research is not value-neutral, and we have a responsibility as scholars, practitioners, teachers, and citizens to highlight those inequities. In our own work, we are attempting to understand how heat waves impact those most vulnerable and supporting climate action planning through identifying urban development projects that can reduce temperatures in low-income multifamily developments, while reducing expenditures on energy. Second, we must participate in the political process to ensure that science is part of any decision making process. Albeit a generally progressive Mayor and city council, Portland’s decision makers have been highly receptive to a scientific argument during public testimonies.

Finally, urban ecologists must engage in social movements that support the rights of communities that have been (and will continue to be) disproportionately impacted by the climate crisis. While ecologists applying their tools to urban systems may help to advance the ecological turn occurring in cities, without explicit and concomitant aims to restructure exclusionary planning systems, our work will not be transformational. Increasingly community groups with interests outside traditional environmental concerns recognize that climate change will amplify inequities (e.g. housing, transportation and employment access, education, etc.). By engaging with “non-environmental” organizations, urban ecologists can help to empower organizations that are reducing nature-based segregation, and improve the public goods upon which we depend. Indeed, thinking about cities as ecosystems can be transformational for building more resilient, livable, and just communities.

Marina Alberti

Marina Alberti

Professor of Urban and Environmental Planning University of Washington Seattle, WA USA Marina Alberti is professor of Urban and Environmental Planning in the Department of Urban Design and Planning in the University of Washington’s College of Built Environments. She directs the Urban Ecology Research Laboratory and the UW Interdisciplinary Ph.D. Program in Urban Design and Planning Her research focuses on Coupled Natural and Human Systems and Urban Resilience. She has led as a Principal Investigator a number large interdisciplinary research projects, the most recent studying the emergent properties of coupled human nature systems in two metro regions: Seattle, WA and Phoenix, AZ. Alberti’s work is grounded in complex system theory, system modeling and scenario planning. Dr. Alberti has authored or co-authored seven books and more than 50 peer-reviewed publications. Her most recent book Advances in Urban Ecology (Springer 2008) synthesizes the state of knowledge on the complex interactions between of urbanization and ecological function and articulates the challenges and opportunities for scholars of urban ecosystems.

16 thoughts on “Are cities ecosystems—analogous to natural ones—of nature, infrastructure and people? Does thinking about cities in this way help us think about urban design?

  1. Dagmar Haase, I appreciate your article on Co-evolutionary planning and governance. I wonder about including storm water control as an unqualified benefit. The pollution and nutrient transport to marine waters of the coastal city is an external cost that should weigh heavily in the assessment. It could be accounted for by including the receiving waters as part of the urban ecosystems analysis for a particular city. So managing the scale of the analysis (or model) will be important. Also, storm control, if including treatment or on-site treatment, could support an entire stack of benefits, so what we do with the ecosystems becomes paramount (also as you mentioned with the “grey, brown, green and blue places” and “green and blue” services). Thanks for so much food for thought and conversation. This will go far.

  2. Vivek Shandas, I really appreciated your article on racism and its role in city ecosystems. When we consider modern ecosystem disasters such as Detroit from about the late 1960s and later, it becomes clear that the rich acquire their wealth with no concern for the destruction in their wake.
    I have always suspected that the United States is not a democracy, despite assertions by some of our most prominent party leaders to the contrary. We are Capitalist, with many of our ideals of expansion and wealth woven into the very fabric of our government. The Commerce Clause in our Constitution confers onto the wealthiest broad powers by which the rich can maximize their profits without the need to answer to anybody. Of course the modern era includes the EPA, the Paris Climate Accords and increased funding and implementation of green energy, but I will always think that the powerful private-sectors of our largest industries institute beneficial change only when such change will increase profit margins. More to the point, industries would still pollute unabated if it were not for public watchdogs, social media and government intervention in the form of sanctions and fines. However, I contend that it is these very points that actually increase environmental racism.
    Fines are expensive, and bad publicity can be devastating to a polluters. Additionally, unionized American workers are more expensive to employ and keep happy/healthy. So rather than pay to upgrade pollution control technology and pay high union-mandated employee wages, many industries either automate or move their operations. I will ignore the former and address the latter. Many industry titans would much rather build their products outside of American soil; the fewer workers’ rights and environmental protection laws, the better. Once built, they employ unskilled and barely educated locals en masse while reaping the benefits of not having to care about their workers or their effects on the environment. The rich win, and everybody and everything, lose.
    So my question is, what can we do to stop this? How can we plan an urban ecosystem that does not have a built-in disregard for the 99% of the human population? I often ask this, but my question is usually answered with a resigned shrug of the shoulders. What solutions, if any, are there? I welcome any questions, comments and/or insights into this troubling aspect of our Capitalist society.

  3. To Eric Sanderson’s last comment:

    After a fews days on vacation I’m just back a find your comment. So I’d like to carry on our stimulating conversation.

    I don’t think anybody in this roundtable considers that cities can be modelled strictly as ecosystems —in a kind of mimicry— nor that it would be possible to address the justice issue by reducing cities to ecosystems — at least not me. That being said the agents that interact in the cities are social and biophysical by nature. From this point of view, with many other authors I consider cities as social-ecological systems, or still coupled human-environment systems (let me suggest you a few readings: 1. Rees WE. Urban Ecosystems: The Human Dimension. Urban Ecosystem. 1997; 1:63-75, 2. McIntyre NE, Knowles-Yanez K, Hope D. Urban Ecology as an Interdisciplinary Field: Differences in the Use of “Urban” between the Social and Natural Sciences. Urban Ecosystems. 2000; 4:5-24; 3. Alberti M, Marzluff JM, Shulenberger E, Bradley G, Ryan C, Zumbrunnen C. Integrating Humans into Ecology: Opportunities and Challenges for Studying Urban Ecosystems. Bioscience. 2003; 53(12):1169-1179).

    You say that ecosystems “don’t exist outside of the time and place that binds them”. You’re absolutely right, and guess what: It is the same for cities. To quote the poet Charles Beaudelaire ” the form of a city changes more quickly, alas! than the human heart.” Erik Swingedouw highlights the circulation and metabolism of nature in urban areas, the role of history in producing them, and how this production drives, and is driven, by unequal power relationships, economic inequities, and competing knowledge (Swyngedouw E, Kaika M, Heynen, NC. In the Nature of Cities: Urban Political Ecology and the Politics of Urban Metabolism. London: Routledge; 2006). It means first that there exist ecosystems as components of the urban social-ecological system, and second that the interactions between these ecosystems and the societies have a lot to do with justice.

    I’d like to get back to our little argument about Darwin. It is quite easy to pick a key word, like dominance and competition, and count its occurrence in a book of more than 500 pages: you will find what you seek whatever you seek. I tried with “economy” (24 instances) and “social” (8 assertions) oh and 14 “vegetable”… does it mean that Darwin was a vegan?
    To go deeper in our debate, a few remarks:
    -Dominance (the predominance of one or more species in a ecosystem) is very different from domination (the exercise of control or influence over someone or something, or the state of being so controlled). In the domination there is something intentional, political: you decide to control somebody. It is about power. There are no such intentions in Darwin’s dominance. Oh by the way… in the whole book of Darwin there is not a single “domination” word anywhere, not one assertion, nothing… nada 😉
    -In Darwin’s work competition is mainly between different species. And you know what: there is only one human specie, whatever the skin, the wealthiness, etc. So yes, we have a problem with justice within our own specie but it has nothing to do with this poor Darwin.
    The transposition —I should say the misrepresentation— of Darwin’s notions in the field of social science by some economists, biologists and conservatives is just a sham. As I write in my last comment “struggle for life” means living long ago to reproduce yourself and transmit your genes to the following generation. This struggle, can consist in adaptation, hiding, symbiosis, cooperation etc. and not only in killing or being killed.
    And well, once again, I can’t see the point in mixing everything, ecosystem thinking and Darwin. Do you know (to use your favorite method) that the word ecosystem doesn’t appear one single time in Darwin’s book the Origin of Species? 0 assertions! In my opinion, it is not good science to compare apples with oranges.

  4. Dear François: Thanks for coming back to this. A fascinating discussion!

    We are speaking about the same Charles Darwin, right? At least in my copy of “The Origin of Species” Darwin often writes about competition and dominance. A quick search of for the word “competition” in the digitized version of the book available at finds at least 39 instances of the word. For example, on page 70, Darwin writes

    “… for, as varieties, in order to become in any degree permanent, necessarily have to struggle with the other inhabitants of the country, the species which are already dominant will be the most likely to yield offspring, which, though in some slight degree modified, still inherit those advantages that enabled their parents to become dominant over their compatriots. In these remarks on predominance, it should be understood that reference is made only to the forms which come into competition with each other, and more especially to the members of the same genus or class having nearly similar habits of life.”

    For 21st century extensions of Darwin’s argument about the importance of competition in evolution, I might point you to Pfennig and Pfennig’s wonderful 2012 book on the subject: “Evolution’s Wedge: Competition and the Origins of Diversity.”

    All of that is slightly beside the point though, with respect to the question we have been debating, which is, “are ecosystems a good model for justice in cities?”

    You are right of course to bring up the evolution of competition, as discussed in Axelrod and Hamilton’s seminal paper from 1981, and many since. Cities and ecosystems have instances of both cooperation and competition; that is part of what makes them such dynamic, productive places. Cooperation, as Axelrod and Hamilton point out is mostly likely to be a stable when it follows a strategy of “Tit for Tat.” That is, in the prisoner’s dilemma type game, to cooperate on the first step, and then reciprocate in all following steps. “Tit for Tat” means you return cooperation with cooperation and defection with defection. In other words, cooperation works best when it’s based on shared reciprocity.

    Putting aside the competitive characteristics of ecosystems for a moment, is cooperation in ecosystems a good model for justice in cities? The problem with I have with “Tit for Tat” cooperation is it can easily descend into “eye for an eye” type retaliation. Although the vast majority of interactions people have with each other in cities are positive and mutualistic, we all have had experiences of selfishness, callousness, and even active disregard. For cooperation to succeed in cities requires a willingness not only to cooperate first, but to cooperate second and third times; to have some notion and ability to forgive and forget, so that the larger existence of the city can continue.

    Ecosystems, as such, don’t have larger conceptions of themselves. As many have argued, they don’t exist outside of the time and place that binds them. Communitarian ideas of what a city or community is, and our obligations to it, seem to be derive from our human capacity to conceive of ourselves in intangible relationships with each other, with natural entities, and with the past and future. I think, for me, anyway, those notions of cooperation in the service of justice arise from outside a purely ecosystem way of thinking.

  5. At Eric Sanderson:

    I guess we should not mistake Darwin theory for Darwinism. Charles Darwin never spoke about competition, struggle for life or I don’t know what else. He considered that to reproduce oneself one has to be alive, which means that if you’re dead before reproducing you cannot transmit your genes to the following generation. It is not about being strong or weak, rich or poor, killing or being killed, which is a ideologically biased lecture of Darwin’s work on evolution.
    Moreover, ecosystem does not derive directly from Darwin (even if there are some indirect links as far as the ecological niche and stand dynamics are concerned) but from Eugene and Howard Odum. Howard was a sociologist and both brothers, and the vision of this brother Eugene (a biologist) concerning the ecosystems was that “interdependence leads necessarily to cooperation.” Quite different from your perspective of “domination” and “competition.”
    Indeed using ecosystem thinking to address social and environmental justice in the city is precisely working on cooperation, ownership and interdependence between all the components of the urban fabric and of the social fabric (be them humans or non-humans).

  6. So we went wrong when we tried to make cities socio-technical systems rather than ecosystems and re-entering ecology into the equation could hopefully help us move towards more sustainable cities (yes, the term is problematic). That doesn’t mean that ecosystems (here used to refer to ecological systems or landscapes without prominent social dimensions) should be the role model for our cities. Ecosystems are not just or fair, but this is something we can try to engage with. Perhaps we should here rather use the ecosystem metaphor to identify areas and dynamics we need to pay special attention to and even actively adjust?

  7. Thanks François Mancebo for your comment. (And apologies for not responding sooner.) I agree with you that justice and equality are not necessarily the same thing – that’s a good point. But does that mean we should look to the unequal distribution of resources in natural ecosystems as a model for human justice? This was a line of argument that social Darwinists made at the end of the 19th century to support all kinds of injustice. As we know ecosystems are structured by networks of interaction that include competition and domination of some species over others, largely as humans compete and dominate over other species in urban landscapes. Do we want to allow the organic process of natural selection to be our model for human interactions? I don’t think so. My larger point, which maybe I failed to express adequately, is that justice is a value separate from ecosystem thinking. We need to call for just AND functioning ecosystems in cities.

  8. I have one comment on the comment of Eric Sanderson. I think you make a confusion between justice and equality, which are two different notions. Justice is about fairness and sound functioning, not about everything and everybody being equal (like you say “Not all trees are the same size; not all birds lay the same number of eggs; not all streams receive the same amount of water”). And yes, some ecosystems are functional and others are not (ie a dystrophic lake, or a city with poisoned groundwater, or a segregated city where poor people live in very bad areas which may have a huge social and economic cost (health and security issues, destruction of the urban fabric etc.). Thus, considering cities as ecosystems can be a good standpoint to address social justice, which one again doesn’t mean equality for everyone and every thin, everywhere. By the way considering equality and justice are synonyms is something of a caricature, often used by people that don”t really wand to address seriously the issue of social justice.
    One last thing, I’m not defending my contribution to the roundtable here: As you may easily see, it is not about justice.

  9. Thanks everyone for your interesting thoughts. It appears there is broad consensus that we can think of cities as ecosystems (or ecological landscapes) in a useful way. Many of the pieces however link the concept of ecosystems to the concept of social justice. And that relationship is something I think I need more help thinking about.

    Let me say that I agree that cities, particular urban economies, should be more just. I also think we should promote and manage the ecosystem benefits of cities in a just way. But the value and utility of justice, as such, lies outside the idea of an ecosystem, near as I can tell.

    Ecosystems are patently not just. As systems they do not distribute resources (energy, materials, etc.) evenly between species or among individuals of a species. Not all trees are the same size; not all birds lay the same number of eggs; not all streams receive the same amount of water. One could argue that the injustice of cities is another hallmark of urban places as ecosystems, they are unjust in ways analogous to the ways that forests and marshes are.

    Maybe what is meant in the various essays is that social justice must include the ecosystem concept, not vice versa. That there can be no justice in human communities unless we also provide some justice to other species. And that neither species nor people can find justice unless we also address the least empowered community of them all: the future.

  10. David– I agree with Nancy. I think that a system approach helps understand connections, interactions, feedback and dynamics. An ecosystem approach applied to a socio-ecological system does imply understanding social conflicts, equality, and justice. I think that seeing cities as ecosystems implies acknowledging that humans are key players in our rapid evolving planet and to understand ecosystems we need to include the human species and their sociality, including its formal and informal institutions. We also need to recognize that human dominated ecosystems as other ecosystems are living systems that operate according to natural rules. Social justice will not be achieved if not informed by our best understanding of the functioning of living systems.

  11. I meant, to be clear, that ‘biophilia’ is already up for grabs and whenever I see the word I approach with caution… the artificial sky people love it!

  12. Sadly, I think the appropriators are already at work. And look what happened to ‘sustainable’! Our best hope is to carry on using the correct terms, with our language as accurate and meaningful as possible, and to keep on insisting on words meaning what they’re supposed to mean!

  13. David, I don’t think calling cities ecosystems changes the approach to justice, no. But having the ecosystem mind set perhaps does. Why? Because thinking in a systems way helps one (me, anyway) to recognize connections among parts that may seem disconnected on the face of things; I am struck by the prevalence of political strife in places experiencing water shortages, for example. A person’s view of their environment and the amenities (or detriments) it affords is strongly influenced by legacy – and modern – inequality in access (or exposure) to nature. Just as our own stances on whether ‘ecosystem’ or ‘political ecology’ are more appropriate conceptual frameworks for understanding cities are influenced by training and level of comfort with these difference concepts….

  14. Dear all – a wonderful collection. Though you may have to stick with ‘biophilia’ instead of ‘ecosystem’.. You’ve no doubt seen how ‘ecosystem’ has been appropriated into the business and especially tech development discussions.
    I don’t think the ‘appropriators!’ will take biophilia, but then of course, you never know.

  15. This is a question for Yolanda (or really anyone). You wrote: “For example, urban design could accommodate connectivity across suburbs and between other parts of the city in the spatial configuration of public and private green spaces and the location of highways and other transport corridors.”

    By accommodate connectivity you mean, for example, create ecologically functional corridors along linear routes? It has often occurred to me that street trees, if they were dense enough, could form corridors. Is there research of what is “dense enough”?

    In Barcelona a few years ago I was discussing city city officials their corridor idea, which was effectively lots of street trees. But they didn’t have a working definition of what density of canopy constituted a corridor, or when a corridor had a gap. It could be: “in leafy season at noon, a person can walk from the shore to the mountains entirely until the shade of a tree”. That doesn’t work for all species, of course, but at least it is a working definition.

    So, how could we move to functional (working) definitions of “connectivity among ecosystem elements”? Definitions that could serve planners and designers?

  16. I have a question about the relationship between the “cities as ecosystems” idea and justice. Several of the writers point out the core relation between ecology and environmental justice in cities. I agree. The justice issues are in two forms: inequity in who suffers from environmental deficits (e.g., pollution) and inequity in who has access to environmental benefits (e.g., street trees, resilience).

    Does thinking of cities as “ecosystems” change how we approach these issues of justice? I would think it does not. We need to reduce inequity in exposure to environmental deficits and increase equity in enjoyment of benefits. These seems like the province of ecologically-aware *planning* — it doesn’t seem like calling cities ecosystems, even though it is technically correct, advances the approach to justice.

    Now, acknowledging that ecology has consequences … there is a potential justice frame.

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