Saturday, October 13, 2018

What's Hidden in the New York Times Maps of All the Buildings in America?

Much well deserved amazement and attention has been heaped on the recent map of "every building in America," by Tim Wallace, Derek Watkins, and John Schwartz, published on 12 October 2018 in the New York Times.  The Times' interactive maps are a real treasure and a wonderful opportunity to explore the multiple geographies of the United States as one wishes.  Their building map appears at this link:

City of Poughkeepsie NY from the NYT map. Buildings are black and everything else is white.

As amazing and useful as this map is, as an urban ecologist, I am struck by some of its limits.

First, the map shows buildings in black, and everything else (read that again -- everything else) in white.  This is called "figure ground" by architects, and has been for hundreds of years the standard way to represent cities (e.g. Mayr and Mayr 2018).  Big differences between cities show up this way.  

The New York Times maps do us the huge favor of showing us figure-ground for an entire nation, based ultimately on some Microsoft computer wizardry.  (Read THAT again: figure-ground for an entire nation.)  This is pretty awesome.  So awesome, that I had to resist the temptation to use terminology my Mother would not have approved of.   

The maps show how urban form in its starkest form relates to big contrasts in how cities are laid out.  The maps show the various continental patterns of urbanization, the influence of land tenure in the different European colonial powers, the role of major contrasts in topography, and the culture of land parcelization throughout the nation.  These are -- again -- amazing patterns to see.  And that the Times has made this treasure available to all of us is pretty neat.

OK, so what is wrong with this wonderful map.  The "everything else" is a problem.  Garry Peterson of the Stockholm Resilience Centre has reminded us that the large among of infrastructure associated with all these buildings is invisible in these maps.  Somewhere in all that white space, there are paved streets, walks, and car parks; there are wires, cables, and pipes of multiple clean and waste-bearing sorts; and -- from my bioecological perspective -- there are at least trees, grass, shrubs, wildlife, pests, microbes, streams, wetlands, rock outcrops, and bare soil. 

In other words these wonderful maps entirely miss the fact that our urban places -- cities, suburbs, exurbs -- are ecosystems.  They have the buildings roughly represented by these wonderful maps, but they also have constructed and reshaped surfaces, biological organisms, the deep physical context of the places covered, filled or "reclaimed" for building on, and more social components than I can fairly even wave my hand at here.

These black-on-white maps have been bread and butter for urbanism for hundreds of years.  But they deceive us into thinking that cities are physical things.  Even worse, they seduce us into thinking that cities are only built.  At best the usual antidote to this seduction is the equally simple idea that cities are primarily social phenomena.

No.  These things are all wrong, even though useful on some levels.  Cities are hybrid ecosystems, meaning that biology, society, construction, and physical fundamentals (geology, soils, climate, and so on) interact in the spaces so glibly shown as figure ground.

Don't be taken in by this overly simplistic beauty.  Use it as an entry to the real complexity and "multicolored" beauty of urban places.

Steward T.A. Pickett


The NYT article on the interactive map:

Mayr and Mayr 2018 with some nice background on the utility of Figure/Ground diagrams:

Monday, October 8, 2018

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

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

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

Sustainability is Technically Complex

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

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

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

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

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

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

Constraints of the Sanitary City

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

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

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

  • The sanitary city may be seen as a tool to preserve the health and productivity of an industrial work force.  The sustainable city must adopt a stance of environmental and social equity, rather than be driven by the economic interests of a wealthy elite.
Other contrasts can be drawn between the sanitary city and the sustainable city models (Grove 2010; Pickett et al 2013).  However, this short list points out that there are key differences between the two.

New Recipes for Sustainable Urban Transformation

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

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

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

Bon appetit!

Steward T.A. Pickett

Background Publications.

Allen, T.F.H. and T.B. Starr. 1982. Hierarchy: Perspectives for Ecological Complexity. University of Chicago Press, Chicago.
Cadenasso, M. L., S. T. A. Pickett, and J. M. Grove. 2006. Dimensions of ecosystem complexity: Heterogeneity, connectivity, and history. Ecological Complexity 3:1–12.

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

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

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

Grove, J.M. 2010. Cities: Managing Densely Settled Social–Ecological Systems. Pp 281-294 In F. Stuart Chapin, III, Gary P. Kofinas and Carl Folke (eds.) Principles of Ecosystem Stewardship Resilience-Based Natural Resource Management in a Changing World. Springer, New York.
Melosi, M. V. 2000. The Sanitary City: Environmental Services in Urban America from Colonial Times to the Present. University of Pittsburgh Press, Pittsburgh.

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

Wednesday, September 19, 2018

Evolution of the Baltimore Ecosystem Study

Since 1997, the Baltimore Ecosystem Study (BES) has enjoyed the support of the Long-Term Ecological Research Program of the Division of Environmental Biology of the US National Science Foundation. That support is coming to an end, but the Baltimore Ecosystem Study will live on, due to the desire of key partners who have been joined together for 20 years to increase the understanding of Baltimore as a social-ecological system, and to improve its livability, sustainability, and equitability.

The support of the LTER program has been instrumental in helping BES establish a mission devoted to four major goals: 1) Pursue excellence in social-ecological research in an urban system; 2) Maintain positive engagement with communities, environmental institutions, and government agencies; 3) Educate and inform the public, students, and organizations that have need of scientific knowledge; and 4) Assemble and nurture a diverse and inclusive community of researchers, educators, and participants.

Nothing speaks to the future better than BES education.
Although the NSF's LTER support has been crucial in bringing BES to its current maturity, the contributions of the Baltimore Ecosystem Study are too important to urban ecological science, to the jurisdictions of metropolitan Baltimore, to the state of Maryland, and to federal resource management agencies and compacts, to allow the effort to falter.  Consequently, the partners and constituents of BES are reorganizing as a consortium to maintain their shared research and practical efforts, to seek additional sources of support, and to build on the unique foundation of over two decades of interaction and problem solving.

Over the coming months, key partners, including Cary Institute of Ecosystem Studies, the University of Maryland, Baltimore County, and the USDA Forest Service, plan to work with leading non-governmental organizations, local and state  agencies to explore an inclusive governance structure and establish a complementary strategy for building an ongoing funding base for the project.

BES has established and maintained unique, long-term data on watershed function, the land cover of the urban region, the biological diversity and biological community structure of the metropolis, and the role of human decision making at household, community, and governmental levels as interacting controls on the development and change of the urban region.  

The integrated understanding generated by BES is crucial in moving the Baltimore region toward the more sustainable future that jurisdictions and communities so earnestly desire.  Resilience and equitability are important facets of the sustainability visions and plans that exist in the region.  The Baltimore Ecosystem Study is very well poised to help the Baltimore City, the five counties of the metropolitan area, and the larger Chesapeake region to design sustainability goals and to provide the scientific basis for evaluating progress toward meeting these goals.

BES -- sometimes characterized as the "Baltimore School of Urban Ecology" -- is a distinctive, integrative approach to contemporary urban ecology.  The approach provides a powerful platform to advance and apply scientific research, education, and community engagement. Indeed, BES is an acknowledged exemplar for such integration that has informed similar efforts around the world.
BES is adapting to a changing funding regime, but it is also working to remain at the forefront of social-ecological research and application.  The partners making up BES as a consortium are as committed as ever to making it an effective, ground-breaking exploration at the frontier of urban ecological science and application.

Steward Pickett and Emma Rosi

Saturday, April 21, 2018

Why Do Urban Ecology?

The ecological science of understanding the structure, workings, and change of urban places has three main reasons to be (raisons d'ĂȘtre, if you prefer the French).  One is the fact that urban systems are one of the world's most dynamic and increasingly predominant environments.  The second is that ecological understanding can contribute to improving cities and urban regions.  Finally, studying urban systems can improve the science of ecology itself.  These reasons are the universal ones for pursuing urban ecology.

Studying the Urbanizing World. 

Ecology was established as a science when the human population of the world mostly lived in rural places.  They were farmers, harvesters of trees or fish, denizens of villages and small towns closely related to the management of resources and the transport and economy of commodities.  Even during the dawn and consolidation of the industrial era, large, dense cities were unusual places for people as a whole to live.

This rural and natural-resource based residency is now rare for people.  Within the last decade, the addresses of the majority of people have shifted from the countryside and small settlements to cities, suburbs, and urban regions.  More than 50% of the Earth's human population now count as urban dwellers, as defined by the various governments of the world. 

This urbanization of the world's people and places is continuing at a rapid pace.  The United Nations estimates that more than 60% of humans will be urban by 2030.  Converting persons and places from rural and village life to urban involves ever more extensive connections. 

So cities are no longer isolated enclaves, but are connected to rural and wild lands at great distances.  Those connections bring resources from other continents, spread wastes and pollution to other countries, and even affect the lifestyles of those people who are still identified as rural dwellers.  Although cities and their adjacent suburbs only cover about 3% of the land area in even the most densely urban nations, the effects of those areas are almost boundless.  Global climate change, for example, or toxification of global nutrient cycles are widespread outcomes of the intensity and metabolism of human settlements.  Urban is not just the city anymore.

Ecological science has ignored the urban for most of its history.  The oldest professional organization of ecologists dates to 1913.  Exploratory attempts by mainstream ecologists to extend their scope to cities can be dated to the 1970s.  

But substantial attention to the city and the urban didn't really take root in the United States until the late 1990s.  The neglect of urban areas has left ecologists as latecomers to one of the most massive planetary changes in recent history.  Focusing on urban ecology is required because urban systems -- cities, suburbs, and exurbs -- are an important global habitat type.  It is, of course, the habitat type that is now most familiar to people.

Urban Ecology to Improve Cities.

Cities and other urban systems have most often been approached as strictly designed, built, or engineered places.  While they are manifestly intended and constructed to support human habitation, protection, productivity, and delight, they do have ecological components.  Plants, animals, and microbes reside in cities, and contribute to the benefits and hazards that people experience in the urban realm.  Consequently, urban ecological knowledge has as much place as economics, social science, design, political science in assessing and understanding the functioning of cities. 
In particular, urban ecological science is relevant to several key attributes of cities:
  •        Livability, including psychological benefits and human comfort,
  •        Ecological functions as sources of ecosystem services,
  •        The intimate feedbacks among natural and human aspects of cities,
  •        Equity in the free ecological work available to social groups and classes,
  •        Contribution to sustainability and resilience, and
  •        Knowledge to support urban design and planning.

This essay can't detail all the support for these attributes, but the richness of these is widely investigated and ever more firmly supported.

Urban Ecology Improves Ecological Science

The flow of benefits is not just from science to urban systems.  Rather, science itself can reap benefits from investigating the formerly neglected urban systems.  The benefits include at least these:
  • Discover new combinations or levels of environmental factors in cities,
  • Bring insights and methods of other disciplines into ecology,
  • Promote interdisciplinarity and study of social-ecological systems,
  • Improve ecological theory by extending it to a new kind of system,
  • Test existing theories in a new environments, and
  • Link ecology better with design, planning, and engineering professions

Personal Reasons.

The three motivations or outcomes listed above are the public and professional ones.  But the list leaves out an important motivation -- the personal.  There is no way to generalize the personal reasons for pursuing urban ecological research because the mix of reasons is likely to be unique to each researcher.  Similarly, the particular order of events and experiences that draw a person into urban ecological science is likely to be idiosyncratic and specific to where and how they grew up, how they were educated, and who influenced them.  But the existence of those personal reasons is no less important for being individual and unique.

In my own case, my predilection for urban ecology only became apparent long after I had become an ecologist and had studied such places as post-agricultural oldfields, natural disturbance in primeval forest, and spatial heterogeneity in deserts, savannas, and unmanaged forest landscapes.  But thinking back on how I grew up, my personal roots supporting urban ecology reach deep.  I was educated by my Father about the history and complexity of the city he and I grew up in and where our family had lived for 4 generations.  But he also introduced me to the mystery and subtlety of forests at Boy Scout camp.  I must have thought that the woods and the city were both wonderful and interesting places. 
Downtown Louisville, KY viewed across the Ohio River from Southern Indiana.

The first bold steps into urban ecology were guided by colleagues Mark McDonnell and Rich Pouyat.  These steps were reinforced by former student and continuing colleague, Mary Cadenasso, a native of Oakland California and now a professor at UC Davis.  Her long family history in the Bay Area combined deep roots in viticulture and ranching, with the experience of vacationing in the Sierra Nevada.  She echoed my early experience that cities were as cool in their own way as were forests and mountains.

Now perhaps my personal motivation is continuing to change.  A new personal frontier has opened up for me with the desire to find the parallels between Aldo Leopold's "thinking like a mountain," and the need to apply ecology in new habits of thinking like a city.  That is, what are the ethical dimensions of urban ecology?  What are the moral implications of conceiving of linked cities, suburbs, and exurbs as ecosystems -- like Leopold's "mountain?"  In other words, is there an urban land ethic? 

The pleasure I personally derive from understanding ecological complexity, heterogeneity, and dynamism in cities, is married with the desire to advance the human need for safe, delightful, healthful, diverse, and equitable urban places.


Urban ecological science is a required body of knowledge in an unprecedented and increasingly urban world.  It can help guide the way toward desired outcomes such as more livable, sustainable, and equitable cities.  But it can also improve ecological science in general by stretching and testing ecology's theoretical and empirical content.  Finally, urban ecology opens a frontier for exploring and exercising a personal -- and community -- ethical and moral sense. 

Steward Pickett

Wednesday, April 4, 2018

How Does a Long-Term Study Adjust Its Framework while Preserving Data Integrity?

Long-term ecological research is faced with seemingly contradictory constraints: It must maintain a consistent stream of rigorously comparable data over time while at the same time responding to conceptual and theoretical changes in the disciplines underlying those data.  How can such opposing  constraints be reconciled? 

BES has faced this challenge in developing its most recent proposal.  It was required to shift from a framework that -- although it highlighted a frontier topic in the understanding of social-ecological systems -- proved to be problematical for many readers.  In response, members of the project management team took a step back and sought ways to improve the conceptual framework.  First, they wanted to simplify the conceptual framework.  Second, they wanted to increase its parallelism with frameworks of other LTER sites.  Finally, they wanted to emphasize the interactions on multiple scales that caused the changes in urban social-ecological systems over time.

This stepping back took us to the foundations of BES.  The project was founded to examine the basic biophysical structures and functions in an urban system, and how they interacted with social processes, all in a context of change. 

The Founding Ideas of BES

So the founding question of BES asked: How do biological and social patch dynamics combine to shape and change a metropolitan area?  This question was operationalized by applying the watershed concept in a city-suburban-exurban matrix, and by examining nested hierarchies of social, biological, soil, and hydrological processes as potential causes of urban change. 

In revisiting the framework, we looked at what the first three phases of BES had accomplished, and what they suggested about refinements in the concepts.  Furthermore, we looked at the improved understanding of climate change and globalization that had developed over the nearly 20 year history of BES, to see what those insights suggested about revision of our framework. 

New Pressures in the System

It was clear that effects of climate change through sea level rise, increases in storm intensity and frequency, risk of drought, increase in heat waves, and shifts in species ranges were likely to alter the structure and functioning of our urban ecosystem.  Furthermore, globalization was likely to alter human migrations, increase the pressure from introduced and/or invasive plants, animals, pests, and diseases, as well as work continuing social-demographic changes within our region.  These ideas had not played significant roles in the initial conceptualization of BES, which was concerned primarily with testing how well ecological approaches worked in an environment where they had not been tried previously.

Conceptual Refinement about Urban Ecosystems

An additional refinement emerging from BES and other urban social-ecological research also played a role in the evolving framework.  Early on, leaders of BES and its sibling LTER, the Central Arizona Phoenix project, had pointed out the difference in studying ecology in the city versus studying ecology of the city.  The latter approach required an integrative, interdisciplinary stance and investigated all habitats in an urban-suburban-exurban matrix, not just the conspicuously green patches. 

Taking ecology of the city seriously generated a new land cover conceptualization and classification, and required examining the intimate feedbacks between social and biophysical processes over various temporal scales.  Indeed, the urban ecosystem is now seen as "coproduced" by natural and social processes, and consequently, to possess a hybrid social-ecological-technological structure (Rademacher et al. 2018).

Key Features of a New Framework

These insights, empirical advances, and conceptual refinements have led us to propose a new framework to support our continued collection and analysis of long-term data in the urban ecosystem.  The framework divides the research concerns into 1) exogenous drivers of change, 2) the structure of the urban ecosystem, consisting of biological, physical, constructed, and social components, and 3) the functional responses of the urban ecosystem.  All of these aspects -- drivers, structure, and responses -- interact with each other through time.  In addition, the functional responses of the urban ecosystem feed back onto its structure.  In a system that includes humans as individuals, groups, and institutions, the feedbacks may involve learning and adaptation or adjustment.

Exogenous Drivers

Exogenous drivers are those that originate or are controlled from outside of the local or regional urban mosaic.  Climate change is clearly exogenous, as are regional patterns of atmospheric deposition of gasses and particulate pollution.  Much of the economy of urban regions is driven by national and international investments, policy, allocation of jobs, and movement of resources and commodities.  Governance anchored beyond the city, such as requirements of regional compacts, state law and regulation, federal regulations, and private-public interactions, can affect a metropolis or its parts.  Technology emerging elsewhere may also alter the fluxes of matter and energy available to a city, and human population can be altered by regional, national, or international migration numbers and directions. 

Some of the factors enumerated as "exogenous" may, if they are managed or shaped within the city or metropolis, act as local or endogenous factors.  It is the origin and distance which determines exogeneity, not the specific type of flux or influence.  For example, the movement of people within a metropolis could reflect local environmental perceptions, behaviors, and organizational networks.

Ecosystem Structure. 

Exogenous and internal influences come together in the structure of the urban ecosystem.  Like all human ecosystems, urban areas consist of the biological organisms and the physical environment, but also of the various human and social structures, and the constructed environment.  The interactions among these four components drive the functional responses of the urban ecosystem.  All four urban ecosystem components are reflected in the ecosystem function.

Functional Responses. 

The functional responses are divided into three linked process realms, long used to organize BES data collection. Watershed biogeochemistry addresses the amount and content of water flowing through constructed infrastructure and biophysical features of catchments.  Local ecosystem production and nutrient transformations are driven by the biota, represented by plant, animal, and microbial communities. These are indexed by key sentinel species.  Human environmental perceptions, behaviors, and the actions of organizations constitute the social functions of the urban ecosystem.  Clearly, all three functional realms interact with each other.  Equally clearly, the functional interactions feed back on the structural filter by which external drivers impact the system.

Similarity with Other LTER Site Frameworks

This new framework is intended to be readily interpretable by ecologists working outside of urban areas as well as those who focus on urban places.  In fact, the general schema for the framework is very similar to that of the Hubbard Brook Ecosystem Study LTER, located in the forests of the White Mountains of New Hampshire.  Hubbard Brook is one of the oldest LTER projects, and focuses on understanding the dynamics of forested watersheds under the influence of exogenous factors and local management choices and ecological succession.  Exogenous factors are well illustrated by the Hubbard Brook study, where acid rain from distant sources was first identified in North America.  Current examples of climate changes include the role of reduced snow cover, and intensification of winter storms.  Of the existing LTER sites, the vast majority include some sort of exogenous factors in their roster of drivers.  Climate change, sea level rise, and human generated land use change are commonly identified as exogenous drivers.

Accommodating Long-Term Data 

For nearly 20 years, BES has collected continuous or repeated data sets on climate and weather, watershed hydrology, nutrient export,  water quality, biodiversity and key biotic populations, soil processes, land cover and land use, social structures, and social dynamics.  These data sets are arrayed across the seven core areas required of urban LTER sites, as stated in NSF's original request for proposals in 1997 (Table 1).

Table 1. Major BES research areas and their distribution across the LTER core research areas.

BES has revised its conceptual framework by identifying the fundamental ecosystem structures and processes represented by its ongoing, long-term data collection, while at the same time organizing the structures and processes differently than in its original conception.  In this way, we hope to have clarified the big ideas that motivate and tie together the data streams emerging from a still under-studied ecosystem type.  The framework combines some of the most fundamental ideas from ecosystem science with the novel structure and large changes represented by urban systems.

Steward Pickett and Emma Rosi

Background Literature

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

Pickett, S. T. A., M. L. Cadenasso, E. J. Rosi-Marshall, K. T. Belt, P. M. Groffman, J. M. Grove, E. G. Irwin, S. S. Kaushal, S. L. LaDeau, C. H. Nilon, C. M. Swan, and P. S. Warren. 2017. Dynamic heterogeneity: a framework to promote ecological integration and hypothesis generation in urban systems. Urban Ecosystems 20:1–14. DOI: 10.1007/s11252-016-0574-9

Rademacher, A., M. L. Cadenasso, and S. T. A. Pickett. 2018. From feedbacks to coproduction: Toward an integrated conceptual framework for urban ecosystems. Urban Ecosystems. DOI: 10.1007/s11252-018-0751-0

Zhou, W., S. T. A. Pickett, and M. L. Cadenasso. 2017. Shifting concepts of urban spatial heterogeneity and their implications for sustainability. Landscape Ecology 32:15–30. DOI: 10.1007/s10980-016-0432-4