The Human Ecosystem: What's Missing?

The human ecosystem concept is one of the most common tools used in the Baltimore Ecosystem Study LTER.  Adopted from a team of social ecologists and sociologists who were involved in community forestry in the Himalayas, the application of such approaches to underserved areas in American cities, and the conservation and management of US National Parks, the concept is remarkably broad and adaptive.  The human ecosystem is not necessarily tuned to emphasizing the intellectual flavor of the week or most current headline issue for cities, urbanization, sustainability, or development.  However, its inclusiveness, nested hierarchical nature, and adaptability makes it well suited to dealing with shifting or even new emphases in social-ecological systems research and application (Figure 1). 

Figure 1.  The Human Ecosystem Framework
(Adapted from Machlis et al. 1997)

What are some of the hot topics that might seem to be missed in our discussions or presentations, but which in fact have a home in the human ecosystem framework?

Political ecology.  

This is at once a scholarly area and a subject of activist attention.  As a scholarly field, it examines the relationships of politics, economics, and environment.  As a social movement, it focuses on the inequitable distribution of benefits and costs of environmental decisions.  The social movement can be seen as a part of a larger social or environmental justice agenda. 

The multidimensional relationships with which political economy is concerned exercise several components of the human ecosystem framework.  Among the bioecological features, catalogued in the “ecosystems pattern and process foundations” component of the framework, many are relevant, including the distribution of energy, water, nutrient, and biomass resources, the kinds and levels of contaminants and pollution of air, water, and soil, and the heterogeneous or mosaic distribution of all of these factors.  Heterogeneity is important because control of access to resources, exposure to hazards, or distribution of benefits is subject to social – that is power and political – control.  Not all persons, groups, or institutions may be uniformly represented across a spatial mosaic.  The social control of access, exposure, and benefit engages many of the components of the human ecosystem framework.  The social ordering by factors of identity, rank hierarchies, and norms are key to the differential power relationships in human ecosystems.  Social rank hierarchy can further be broken down into ranks based on wealth, control of territory, social status, knowledge as a kind of capital, and, tellingly, power.  Among the social and cultural foundations, the distribution of populations, including by race, class, gender, or ethnicity, and the distribution of information by various institutions may reflect power relationships.  Of course the access to or participation in the institutions of sustenance, health, justice, education, etc. are also dependent on power relationships.  Other aspects of the human ecosystem framework (Figure 1) can also be used to investigate and explain, and therefore intervene in, power relationships in the urban social-ecological systems. 

Technology.  

Recently, our colleague N.B. Grimm has emphasized the fact that social-ecological systems have significant technological content.  Grimm at the 2013 Congress of Urban Ecology, the first such international meeting of the Society of Urban Ecology (SURE), introduced the term Social-Ecological Technical System, or SETS to emphasize the role of technology in how people think about urban ecosystems. 

This healthy reminder and highlight does no violence to the human ecosystem framework.  A classical representation of the significance of technology in human environment relationships is the POET model.  Under this general model, environmental change is said to be a function of human population, the way that humans are organized, and the technology available.  Explicit recognition of the role of technology in urban systems appears in the classical work of Borchert (1967), who notes that urban form in the United States shifted with the introduction of new technologies.  

Emphasizing transportation technology, Borchert proposed five epochs of American urban change: 1) sail and wagon (1790-1830), 2) steam powered ships and initial rail roads (1830-1870), 3) national steam rail network (1870-1920), 4) interstates and propeller air transport, and finally 5) satellites and jet propulsion.  American urban transformation continues, with other epochs hypothesized to represent the “slow growth” proposed in the 1970s of the oil embargo (Phillips and Brun 1978), or perhaps an epoch defined by the technology integrating global finance, manufacturing, and consumption.  In any event, the significance of technological innovation, change, and even retrenchment are clearly major components and drivers of urban change.  These latter technologies have a great deal to do with the current global teleconnections of urban systems with each other and with more rural and wild lands (Boone et al 2014).

Baltimore is a prime example of the role of shifting technologies.  For instance, the urban fabric of Baltimore, as described in Hayward and Belfoure (1999), shifted markedly with each transition -- from the walking city, through the city of horsedrawn trolleys, through the electric commuter rail, through the automobile era.  The industrial power of Baltimore similarly reflects major technological shifts, from the water power of the “fall line” through wood fueled steam, through coal powered manufacturing and steel production.  Other overlapping shifts, such as the opening up of the American South and Southwest with the availability of air conditioning technology there, and government policy for the location of defense industries away from the vulnerability of the east coast so feared during World War II, played a role in Baltimore’s post-industrial shift to a joint service, tourism, and knowledge footing.

In the Human Ecosystem Framework, technology appears foundationally in such things as the source of energy (e.g. water power, vs. wood, vs. coal), or the path of water flow (the location at the fall line between the Piedmont and the Coastal Plain).  Technology also is reflected in the amassing and deployment of labor, as in the contrast between slavery and voluntary immigration as sources, and the shift in capital investment in water-mill industry and canals versus the creation of America’s first long haul railroad – the Baltimore and Ohio.  

The technologies available and the pursuits different technologies make available have powerful influence on social identity, demographic structure, community and neighborhood cohesion and the like.  For example Baltimore still embraces a historical identity as a seafaring town.  This is shown by the fact that a waterfront neighborhood is still referred to as Canton, in honor of Baltimore’s fast clipper ships that cemented trade between China and the U.S. East Coast.  Or the fact that Fells Point, the location of Baltimore’s first deep water port, still retains the ameities and reputation as a freewheeling entertainment district reflecting its early tradition of hosting sailors on leave.  The coal-fired industrial era is honored in the Middle Class Mythology of Baltimore and its blue collar ethos.  These things are all features that find a home in the human ecosystem framework, for example in cultural myths, social identity, and temporal cycles of change in demography and institutional and organizational structures.

Infrastructure.  

Another hot topic these days is infrastructure.  Strictly speaking, infrastructure is what undergirds the various components of a system.  Infra means below.  It is the supporting structure, linkages, flows in any system.  The human ecosystem may seem to be blind to the built and engineered components of urban ecosystems.  This is because the human ecosystem framework assumes those physical foundations.  In 1997, we worked to refine understanding of the bioecological foundations of the human ecosystem.  The original discussions by Machlis and colleagues certainly included the bioecological and biophysical aspects of human ecosystems in the “resource system” component.  Perhaps because buildings, streets, supply pipes, electrical wires, railroads, sewers, storm drains, and so on are such conspicuous parts of urban ecosystems, we hardly felt the need to call attention to them.  Cities are so often defined based on density of built structures and of human inhabitants that pointing toward buildings and infrastructure could be tacitly assumed.

However, a later description of the human ecosystem as a model template showing major kinds of components and their connections attempted to make this assumption clear.  Cadenasso et al. (2006) is a good example of this integration of built – and hence infrastructural – components into general interactive and classificatory models of urban ecosystems (Figure 2).  There is nothing wrong with pointing to the various components of systems as infrastructure, but in a sense, that seems redundant with saying that an urban place is a human ecosystem comprising social, biotic, built, and physical (e.g. soil, topography, climate) components.  Infrastructure is just another word for components, really.  The big idea is that cities, suburbs, and exurbs are systems that contain many specific features and connections, and that those span and connect biology, physical environment, buildings, social processes and the myriad feedbacks among components.

Figure 2. A process model template of the human ecosystem.

A healthy outcome of the infrastructure label may be helping people to remember the often invisible biological components of cities, suburbs, and towns.  Infrastructure is now often spoken of as gray, blue, and green.  This division suggests that the complex system of the city or more broadly, the urban region, depends on services and structures provided by plants, animals, and microbes, and that these services emerge not only from partly or (almost) entirely engineered features, but also from parks, yards, street plantings, derelict field and lots, open streams, wetlands, and freeflowing atmosphere.  Planning, design, management, policy, and education will be better served, and will better serve the human population when the contributions of biological infrastructures and their components are understood and effectively employed.

Conclusion

The message here is that the human ecosystem framework (Figure 1), a hierarchical enumeration of the kinds of biophysical and social structures, resources, processes, and outcomes that make up not only cities and towns, but also wilderness and production landscapes, is adequate to include contemporary and important concerns of power, justice, technology, and infrastructure.  The human ecosystem framework can be considered a causal hierarchy, in which general causes or factors are broken down into more specific mechanisms and interactions.  Specific models of human (in general) and urban (in particular) ecosystem structure, function, and dynamics will draw upon several to many of the ideas and features included in the human ecosystem framework. 

The framework is complemented by a process model template (Figure 2).  This process model template emphasizes that urban systems are composed of biological components and their interactions, physical environments and their links, social structures and interactions, and built components and the interactions among them.  This model template emphasizes the comprehensiveness of kinds of components of cities, suburbs, and exurbs, as well as the interactions among the various components.

Thus, rather than neglecting important contemporary topics in social, engineering, historical, and political realms, urban ecology has frameworks and model templates that in fact can easily accommodate these features.  Technology is a part of the built environment, Power is an aspect of the social structures, and infrastructure is a way to group various built components, networks, and interactions.

References

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

Borchert, J. R. 1967. American metropolitan evolution. Geographical Review 57:301-332.

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

Hayward, M. E. and C. Belfoure. 1999. The Baltimore rowhouse. Princeton Architectural Press, New York.

Machlis, G. E., J. E. Force, and W. R. Burch. 1997. The human ecosystem. 1. The human ecosystem as an organizing concept in ecosystem manageme

Phillips, P. D., and S. D. Brunn. 1978. Slow Growth: A New Epoch of American Metropolitan Evolution. Geographical Review 68:274–292.

The Kind of Solution A City Is

A while ago I wrote about Jane Jacobs’ insight that cities were complex systems[i].  The stone that she dropped in the urban pond in 1961 has rippled widely, and the ideas of cities as complex adaptive systems, with emergent properties, good and bad resilience, and non-linear dynamics now guide much cutting edge urban research.

Of course, when Jacobs used the word problem, she meant an intellectual problem to be solved, and her answer suggested complex systems theory as an approach to understanding cities.  But the word “problem” also calls to mind an antonym.  To every problem there might be considered to be a solution.  In this spirit, with apologies to Jane Jacobs, I ask what kind of a solution a city is.

To get to my answer, I do have to admit that some urbanists have interpreted cities as literal problems, in the negative sense.  For example, members of the Chicago School of Urban Sociology in the 1920s emphasized urban pathologies.  They contrasted the issues that existed in cities with the ideal of village and rural life as they experienced it in turn of the 20th century America.  They studied such things as competition among immigrant communities and the distribution and behavior of gangs.  Of course, there are real negatives associated with cities, including pollution, disease contagion, crowding and stress, for example.  Recent research by Bettencourt and West (2010) has pointed out several negative factors, such as crime, that increase at greater than linear rates with city size.

The Lure of the City

A design for urban farming in vacant lands in West Baltimore.
From an urban design studio supervised by Brian McGrath
and Victoria Marshall.

In spite of the negatives of urban living, cities continue to draw humanity to them.  Urban areas are seen as a solution by societies, governments, individuals, and households who vote with their feet or with their policies.  Edward Glaeser (2011) has discussed at length the draws that urban areas clearly hold for people and institutions.  For instance, cities in the broadest sense, are a prime locus of innovation.  The serendipitous interactions of knowledge workers in cafes, bars, restaurants, and informal gatherings are important sources of new ideas and approaches.  Interestingly, the well known power of social media, which can theoretically operate at a global scale in service of creativity, have not replaced the sparks of face-to-face interaction among diverse people.  Institutions such as businesses and universities clearly recognize the power of the city as a source of creative interaction. 

But individuals also yearn for the city for their own reasons.  People seek access to health care, education, jobs, consumer goods, and excitement.  In particular, some urban migrants seek release from the strictures of tradition, the anonymity to pursue a lifestyle not sanctioned in a less urban setting, or to replace a livelihood taken away by industrial agriculture or resource exhaustion in the countryside.  These lures, presented briefly in narrative form can be considered the services or opportunities provided by urban areas. 

Economies of scale are another way to address the lures of the city.  Again, Bettencourt and West (2010) provide statistical meat on the narrative bones.  They show over a range of city sizes a clear savings in terms of per capita infrastructure, resource use, creative products, and so on.  There is roughly a 15% savings in many areas of urban structure and process compared to urban population size.  In a sense, cities and larger urban areas exist to provide these solutions, these lures.

The Contexts for Solutions: Four Dimensions

“The” city is not just one kind of solution, however.  McHale and colleagues (submitted) identify four dimensions of contemporary urbanization: Diversity, Complexity, Diffuseness, and Connectivity.  These four characteristics are intertwined and interacting.  Together they describe what is new and exciting about cities for an urban ecologist.  The conceptual space identifies the realms in which new solutions for sustainability and resilience can be sought in urban social-ecological systems.

Diversity.  Looking at urbanization and urban change around the world reveals a vast diversity of forms.  The wealthy urban cores of Europe surrounded by less well off or segregated suburbs; the Post-World War II sprawl of the United States with thinning and sometimes even shrinking cores; the megacities or Asia; the metropolises of India and Latin America dotted with favelas and shantytowns; the urbanizing former rural “homelands” of South Africa are a part of the great global diversity of urban settlements.  No single simple model describes all the urban systems around the world, or even in a single country any more.

Complexity.  The early history of cities was marked by compactness and often clear differentiation of districts of cosmological significance, trade, residence, and so on.  Cities have always been characterized by heterogeneity of social groups and social standing.  Today, urban areas are marked by great heterogeneity within their perceptual or legal boundaries.  Neighborhoods occupied by different ethnic groups are cheek by jowl, formal and informal institutions divide up the space of service or influence, networks of transportation span walking, public modalities, private vehicles, and opportunistic sharing.  Such networks are layered and changing, and intersect with the patchiness of economic, social, biological, political, and governance features.  Urbanists continue to remark on the stark heterogeneity of urban areas – cities, suburbs, and exurbs – even as the grain size and patch configuration shift with time and use.

Diffuseness.  Hand in hand with complexity is diffuseness.  The boundaries within urban areas are often porous and functionally indistinct in contemporary urban mosaics.  Commuters move great distances, and the direction of travel is often not in a peripheral to central direction.  Many places that had been considered peripheral under older conceptions of single metropolitan cores are now destinations for travel that avoids such cores.  Diffuseness also extends to governance and institutional arrangements.  The issues and solutions for environmental and social problems are managed by collections of governments, non-governmental organizations that operate at various scales, and linked civil society activities.  Likewise investments and disinvestment span neighborhoods, districts, municipalities, and different kinds of lands in extensive urban-rural agglomerations. 

Connectivity.  Closely linked to diffuseness is connectivity.  The porosity of official and vernacular boundaries within urban regions means that connections between the different areas and included ecosystem types can be extensive.  But this connectivity now goes well and commonly beyond any particular urban node or region.  Global connections of finance, resources, wastes, cultural influences, talent, and livelihood are rife.  Consequently, teleconnections or connections at a distance are now contribute much to the form and functioning of urban regional landscapes.  These connections affect farms, rangelands, forest lands, marine and coastal fisheries, for example, as well as more obviously urban places.

Implications for City as Solutions

A typology of water management designs based on how
they use vegetated and non-vegetated components.
Figure by Brian McGrath, Urban Interface.

The global and regional “facts on the ground” of diversity of type, spatial complexity of mosaics, diffuseness of various boundaries in urban territories, and the connectivity at local, regional, and global scales, must be accounted for in solving urban problems.  Indeed, how to exploit these facts is an open question for improving urban sustainability. 

The diversity of urban forms means that there is the opportunity for trying different solutions in different kinds and contexts of urban systems.  It also means that solutions must be locally tuned and evaluated. 

Complexity means that solutions are likely to be heterogeneous even in a single urban region.  Adaptive approaches to governance, including that by formal and by informal institutions, are likely to be required across complex urban regions. 

Diffuseness means that solutions – and problems – will sometimes not respect formal boundaries.  Highly localized control and decision making cannot succeed without at least accounting for the positive and negative effects on adjoining patches or ecosystem types, neighborhoods and districts.  In fact, governance in both its formal and informal manifestations can take advantage of positive outcomes of diffuseness of solutions.

Finally, connectedness means that problems and processes at great distances may have profound effects on any given urban ecosystem.  The accessibility of global markets to global factories and the length of global supply chains means that cities are at the whim of corporate decisions and lifestyle changes in countries and continents distant from their local control.  Solutions must be sensitive to such global connectivity.  Chasing investment that may itself be ephemeral in its geographic focus is a significant challenge.  Environmentally sensitive attempts to buffer a system from capricious decisions elsewhere are certainly called for, but planning for adaptive resilience rather than relying only on the rigidity of hard buffers is a major opportunity.

The Inclusive Sustainability of the Urban

A final opportunity for solution exists.  As the world population becomes increasingly urban, there may be a tendency to forget about the needs, wellbeing, and influences of those who still live in areas designated as rural.  Some nation’s policies are intensely urban focused, such as in China.  Other countries, such as those in Africa, face projected increases in populations such that the urban tide cannot help but rise.  Rural invisibility is a danger in such situations.  Not only must new and existing urban residents be protected from the vulnerabilities of rapid or ill-placed urban development, and exclusion from decision making processes about social and environmental services, but rural residents are at risk as well in this transition.  The connectivity of the urban and the rural in rapidly urbanizing countries is extraordinary.  In Asia and in Africa, for example, “circular migration” for work and in cities and the resultant disruptions of social capital in both city and countryside are existing or emerging issues.  In China, for example, the problem is recognized in policies of “urban-rural integration” which aim to narrow the gap in wealth and services between village and city residents. 

The diversity, complexity, diffuseness, and connectivity of urban settlements and rural and wild lands around the world, in specific municipalities, and in urban megaregions means that sustainability itself becomes a spatially and conceptually complicated set of goals and trajectories.  The kind of solution a city is likewise becomes a multi-dimensional, spatially extensive approach to sustainability.

Bibliography

Bettencourt, L. and G. West. 2010. A unified theory of urban living. Nature 467:912-913. 

Glaeser, E. 2011. Triumph of the city: how our greatest invention makes us richer, smarter, greener, healthier, and happier. Penguin Press, New York.

McHale, Melissa R., STA Pickett, Olga Barbosa, David N Bunn, Mary L Cadenasso, Dan L Childers, Meredith Gartin, George Hess, David M  Iwaniec, Timon McPhearson, M Nils Peterson, Alexandria K Poole, Louie  Rivers III, Shade T Shutters, and Weiqi Zhou.  A New Global Urban Realm:  Complex, Connected, Diffuse, and Diverse Socio-Ecological Systems. Sustainability, submitted.

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[i] http://besdirector.blogspot.com/2011/06/complexity-hidden-nugget-in-jane-jacobs.html

Why Come to Africa to Fully Understand Urbanization?

The transformation of the Earth’s human population to a predominantly urban home is one of the major milestones of the 21st century.  While urbanization in industrialized regions such as the United States and northern Europe has been intense for more than a century, understanding global urbanization requires that we look beyond the cities of those regions. 

Baltimore tells an ecological story that is shaped by the shift from an industrial economy to a service and knowledge economy, and now hopefully toward a sustainable trajectory.  Thinning in the core, shifts in density toward the suburban and exurban fringe are some of the physical features of that story, which are shared by many U.S. cities.  There are many social and ecological effects of these changes, and the Baltimore Ecosystem Study has discovered new features of urban biogeochemistry, physical environment, biodiversity, economic, and policy interactions among them.  However, there is still a need to put our intense focus on the Baltimore region into a broader context.  Where do the urban transformations that Baltimore is experiencing fit within the diverse trajectories and patterns that urbanization represents around the world?  How do we contribute to and fit within a broader theory of urban ecosystems and urban change?

To help answer this question, I have been interacting with colleagues in various countries.  A while ago, I wrote about my experiences in learning about urbanization in China (http://besdirector.blogspot.com/2014/10/baltimore-and-beijing-learning.html).  This year’s urban intellectual adventure has taken me to South Africa.

                               

What do I expect to learn about urbanization at the southern tip of Africa?  This visit follows on intense interactions with Melissa McHale of North Carolina State University and David Bunn, Director of the Knowledge Hub (http://www.knowledgehub.wits.ac.za/) at the University of the Witwatersrand Rural Facility near Bushbuck Ridge, South Africa.  These interactions have resulted in discussions and field trips that have identified features of urbanization that are not part of the standard American patterns of urban change (cf. McHale et al. 2013).

One reason that Africa is an important venue for understanding urbanization is that it is the next and last great frontier for urban intensification on the globe.  Everybody knows that the shifts from traditional, rural residence and lifestyle, agrarian livelihoods and consumption patterns to those that are shaped by urban attitudes, equity, economies, and information flows, are proceeding apace in China and India.  China has a purposeful policy of converting its vast population to the urban realm.  New city building, engulfing of villages in urban megaregions, and replacement of farming livelihoods with industrial employment are hallmarks of this transformation.  The diverse nations of sub-Saharan Africa exhibit an array of urbanization patterns and transformations from which the world might learn.

Africa is still predominantly a rural continent, in spite of hosting some truly huge cities like Lagos.  United Nations has estimated that the population of Africa may quadruple from its 1.1 billion by 2100 (http://worldpopulationreview.com/continents/africa-population/).  Population projections over the course of a century are admittedly subject to some uncertainty, but even if it is off some, the changes promised for Africa are immense.  The growth rate in sub-Saharan Africa is estimated to be especially large. 

This remarkable population growth has profound implications for urbanization in Africa.  Some urban population growth will be the result of people moving to established cities and towns.  Informal settlements and shanty towns are already a part of this trend, and will very likely continue to be.  In other cases, urbanization will involve the conversion of already dense rural areas into new form of settlement in which aspects of rural life ways and urban patterns of culture and consumption mix.  Already a great deal of African urbanization is occurring without the industrial-to-sanitary city conversion that is familiar in North America and Europe.  It is also proceeding with broad connectivity, but with little hard-wired infrastructure.  For example, cell phones link people and provide banking without bricks and mortar, along with new opportunities for scamming the unwary.  African urbanization also exhibits much more spatial and temporal flexibility than we are used to in the Global North.  Commercial and social uses of particular places shift over the course of a day in ways that are virtually unheard of in the highly zoned sanitary city. 

As I begin a month in northeastern South Africa to explore and discuss with colleagues the striking features of urbanization, here are some initial thoughts.  Some are captured in the literature already, and some are points of discussion and curiosity. 

• Africa will be the final frontier of global transformation from rural to urban, but the nature of the resulting patchworks will be different from those in the Global North.
• Urban areas and rural areas are parts of interconnected, patchy regions.
• The linkages between cities and rural areas in Africa flow both ways.  People move back and forth depending on jobs, informal employment, and government grants to the aged and for children.
• Rural and urban lifestyles mix and match with families and “households” spread across regional extents.
• Infrastructure for communication and electrical power may not always follow the gridded model with centralized supply and distribution.
• Consumption may be a more compelling model for urban migrants than the benefits of the industrial or sanitary city.
• Perhaps the biggest general idea, very relevant to Baltimore, is that what looks distinctly urban or distinctly rural may in fact be hybrid systems. 

These points, many of which are the topics of new or needed research, suggest a very different set of models for urbanization and indeed the continued change of urban regions than exist in North America.  In essence they bound a conceptual space in which the structure, function, and change in Baltimore are a subset.  Urban is no longer just about the city.

Acknowledgements.  In addition to host Prof David Bunn, Director of the University of the Witwatersrand Knowledge Hub for Rural Development at the Wits Rural Facility, I have been fortunate to share this visit with Prof Dan Childers from Arizona State University.  Financial support provided by a Fullbright Specialist Program grant, and the Urban Sustainability Research Coordination Network.

Bibliography

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

Knox, P., editor. 2014. Atlas of cities. Princeton University Press, Princeton.

McHale, M. R., D. N. Bunn, S. T. A. Pickett, and W. Twine. 2013. Urban ecology in a developing world: how advanced socio-ecological theory needs Africa. Frontiers in Ecology and Environment 11:556-564.

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

Simone, A. 2010. City life from Jakarta to Dakar: movements at the crossroads. Routledge, New York.

UN Habitat. 2014. The state of African cities 2014. United Nations, New York.