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Conceptualizing the built environment as asocial–ecological systemSebastian Moffatt a & Niklaus Kohler ba CONSENSUS Institute , 205 Stark's Road, Salt Spring Island, BC, V8K 1M3, Canada E-mail:b University of Karlsruhe , 59 Kurfuerstenstrasse 3, D-76137, Karlslruhe, Germany E-mail:Published online: 28 May 2008.

To cite this article: Sebastian Moffatt & Niklaus Kohler (2008) Conceptualizing the built environment as a social–ecologicalsystem, Building Research & Information, 36:3, 248-268

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Conceptualizing the built environment as asocial^ecological system

SebastianMoffatt1 andNiklaus Kohler2

1CONSENSUS Institute, 205Stark’s Road,Salt Spring Island,BCV8K1M3,CanadaE-mail: smoffatt@ConsensusInstitute.org

2University of Karlsruhe, 59 Kurfuerstenstrasse 3,D-76137 Karlslruhe,GermanyE-mail: nk@nkohler.eu

Formulating a unified theory of the built environment may require that the built environment be understood as a complex

social–ecological system, where multiple-related metabolisms interact at different scales. From this broad systems

perspective, the dividing line between what is considered as nature and what is considered as built environment

becomes a cultural attribute that changes with the historical context. Over the past four centuries, notions of

environmental accounting and material metabolism have expanded from year-to-year economic and biological

exchanges to energy, material, financial, and information flows extended through time and space. At present, the

necessary extension of system limits in time and space is best achieved by combining a number of methods, including

flow-based models and resource-conservation-based models, and top-down and bottom-up modelling approaches.

Artefacts, flows, and actors can be linked over time by means of a common framework for describing the built

environment, and by life cycle-oriented product modelling techniques. Despite such advances, existing theory seems

incapable of fully integrating spatial and physical relationships, and is especially challenged when dealing with

concepts of time. Ecological models provide a useful basis for new timing tools that integrate different time scales,

past and future, and that allow for an assessment of adaptive capacity and other aspects of system resiliency. These

models can be used to understand better the impact of different managerial and social policies at both the macro- and

the micro-level. The management of the long-term evolution of this social–ecological system can only be assured

through appropriating ecological concepts of time, and by integrating the history of nature with the history of human

culture.

Keywords: built environment, conceptual frameworks, ecosphere, ecosystem, metabolism, sustainability, temporal

perspectives, theory-building, time, urban systems

Formuler une theorie unifiee du milieu bati peut necessiter que ce milieu soit compris comme un systeme socio-ecologique

complexe ou des metabolismes multiples interagissent a differentes echelles. A partir de cette vaste perspective de

systemes, la ligne de partage entre ce qui est considere comme la nature et ce qui est considere comme le milieu bati

devient un attribut culturel qui change avec le contexte historique. Au cours des quatre derniers siecles, les notions

d’ecocomptabilite et de metabolisme materiel se sont elargies et sont passees d’echanges economiques et biologiques

d’une annee a l’autre a des flux d’energie, de materiels, de finances et d’information s’etendant dans le temps et

l’espace. Aujourd’hui, l’extension necessaire des limites du systeme dans le temps et dans l’espace est realisable

en combinant un certain nombre de methodes, y compris des modeles bases sur le flux et des modeles bases sur la

conservation des ressources et des approches de modelisation descendantes et ascendantes. Artefacts, flux et acteurs

peuvent etre relies dans le temps au moyen d’un cadre commun pour decrire le milieu bati et les techniques de

modelisation de produits orientees sur le cycle de vie. En depit de tels progres, la theorie actuelle semble incapable

d’integrer totalement les relations spatiales et physiques et est particulierement en danger lorsqu’il s’agit de traiter de

concepts de temps. Des modeles ecologiques fournissent une base utile pour de nouveaux outils de synchronisation

qui integrent differentes echelles de temps, passees et futures, ce qui permet une evaluation de la capacite

d’adaptation et d’autres aspects de la resilience du systeme. Ces modeles peuvent etre utilises pour mieux comprendre

BUILDING RESEARCH & INFORMATION (2008) 36(3), 248–268

Building Research & Information ISSN 0961-3218 print ⁄ISSN 1466-4321 online # 2008 Taylor & Francishttp: ⁄ ⁄www.tandf.co.uk ⁄journals

DOI: 10.1080/09613210801928131

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l’impact des differentes politiques de gestion et politiques sociales aux niveaux macro et micro economiques. La gestion

de l’evolution dans le long terme de ce systeme socio-ecologique ne peut etre assuree que par l’appropriation de concepts

ecologiques de temps et par l’integration de l’histoire de la nature dans celle de la culture humaine.

Mots cles: milieu bati, cadres conceptuels, ecosphere, ecosysteme, metabolisme, durabilite, perspectives temporelles,

elaboration de theorie, temps, systemes urbains

IntroductionThe notion of ‘built environment’ is relatively recent.1

In common parlance, the built environment generallyrefers to the:

manmade surroundings that provide the settingfor human activity, ranging from the large-scalecivic surroundings to the personal places.2

It responds to the need of a multitude of professionsand approaches that are concerned by this definitionto find a common framework for communication andelaboration. In an era when environmental costsand long-term impacts are of increasing interest, andwhere urbanization is transforming large areas of theEarth, the expansive notion of built environmentmore easily conveys a broader ‘systems’ perspective,where dynamic relationships exist between a greaternumber of built elements. The rigorous models orig-inally developed for individual buildings can bescaled to entire cities, and trade-offs can be exploredbetween, for example, building design and infrastruc-ture requirements, or urban form and resource effi-ciency. Whereas the formal and spatial aspects of thebuilt environment have been analysed in depth formany years (Lawrence and Low, 1990), and pro-fessional inquiries about the different parts of thebuilt environment have been especially rich in the last15 years (McClure et al., 2007; Schiller, 2007), thebroader system aspects of the built environment havenot been the object of research, and no comprehensivetheoretical framework seems to exist.

Basically, the built environment can only be defined incontrast to the ‘un-built’ environment, or the eco-sphere. In a system representation, both the builtenvironment and the ecosphere can be considered ascomplex, dynamic self-producing systems:

These systems exist in loose, nested hierarchies,each component system contained by the nextlevel up and itself comprising a chain of linked sub-systems at lower levels. The built environment as aself organising system functions as a ‘dissipativestructure’ requiring a continuous supply of avail-able energy, material, and information necessaryto produce and maintain its adaptive capacity andrejecting a continuous stream of degraded energyand waste back into the ecosystem (entropy).

(Rees, 2002, p. 253)

The relation between the built environment and theecosystem does not exist as such outside of history.On the contrary, it is constantly changing, reflectingthe evolution of social systems and influencing thisevolution in turn. It is therefore more appropriate todefine the built environment not as an object but associal–ecological system:

Prior work suggests that social–ecologicalsystems . . . are neither humans embedded in anecological system nor ecosystems embedded inhuman systems . . ., but rather a different thingaltogether. Although the social and ecologicalcomponents are identifiable, they cannot easilybe parsed for either analytic or practical pur-poses.

(Walker et al., 2006, p. 1)

Cultural perceptions of what is meant by society andnature are also changing historically. The modernworld view has emphasized the dichotomy betweensociety and nature as two equal entities, wheresociety influences or even dominates nature. A moreunified theory of socio-ecological systems is now thefocus of much discussion within both the naturalsciences (e.g. ecological economics) and the socialsciences (e.g. human ecology). A theoretical basis fordefining the built environment depends, in part, onhow this contextual discussion evolves. Fischer-Kowalski and Weisz (1999) have synthesized a newtransdisciplinary framework that facilitates a unifiedtheory. Their framework incorporates two key con-cepts: the socio-economic metabolism and the coloni-zation of natural processes. Metabolism refers to thebalanced flows of energy and materials between thehuman and natural subsystems of the material realm.Colonization describes the appropriation by cultureof elements of the material realm in order to reproduce(and possibly expand) society:

With this conception of society, the delimitationof societies becomes historically variable. Eachcultural system claims that it is made up ofcertain humans as well as of material elements,which are considered to belong to it.

(Fischer-Kowalski and Weisz, 1999, p. 242)

Typically what belongs to culture are those parts of thematerial realm that must be carefully regulated andcontrolled (with intent), including not only the bodies

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of humans, but also domesticated plants and animals,and artefacts such as the built environment.

The present paper will attempt to explore in moredetail the historical dynamics of this complex social–ecological framework. It is hoped that by buildingupon a broader systems perspective, it may be possibleto move towards an effective theoretical basis forunderstanding the built environment. Given themassive rates of growth and change now occurring inthe built environment worldwide, it is easy to see thepotential benefits of a stronger theoretical foundation.In general, new theories tend to introduce a few widelyapplicable problem-solving strategies that help to unifyperspectives among disparate groups. They can alsohelp to generate a more consistent and coherent setof methods and models, with shared assumptionsunderlying a common frame.

A short historical description is provided on how therelation between the built environment and the ecosys-tem has evolved from the 16th-century. The historicaldescription is not just background, but provides a keypart of the argument for defining the built environmentas a concept dependent upon historical context.A closer inspection is then undertaken of the currentapproaches to conceptualizing the built environmentand its relation to ecosphere. Four dominant themesare identified, and each is discussed in terms ofintended purpose, key methods, strengths and weak-nesses. Finally, some strategic directions are presentedthat address what appears to be the greatest weaknesswithin the existing methods.

Historical perspectives on the builtenvironmentHistorians and geographers have tended to see the builtand natural environment less as compartments within amaterial realm and more as a continuum, with varyingamounts of human influence upon nature. The conti-nuum becomes especially important when long-termviews are taken, either for ecological or for humansystems. For example, Braudel (1949) describes howhuman activity has transformed many parts of theMediterranean through thousands of years of clearing,terracing, ditching, planting, harvesting, fires, andthrough accumulated layers of roads, bridges, damsand buildings. He argues that only from a long viewis it possible to understand the physical and socialgeography of a region. Human-dominated landscapesnow include vast areas of the Earth’s surface, and itis hard to define areas that are not affected to somedegree. This may have been the case for a long time.Redman (1999) examines the impacts that humanactions have had on the environment in the past10,000 years, arriving at the conclusion that therehas not been a ‘pristine environment’ (i.e., unaffected

by humans) for at least 10,000 years and maybelonger (p. 199). From this long view, the questioncan be posed – what is ‘natural’ and what is ahuman ‘artefact’?

The Fischer–Kowalski framework suggests that thelevel of intent, regulation and control are determiningfactors for differentiating human from natural(Figure 1). On the surface, this makes sense. An aban-doned ruined building in decay becomes part of naturesince it receives no attention and no investment. Con-versely, a rural park that requires on-going planning,protection, trails, monitoring and perhaps substantialinvestments in visitor transport may qualify, for somepurposes, as a human or built environment. The ques-tion of where to draw the line always depends upon thecultural context – particularly the information needsof the decision-makers – and this changes with timeand place. Presumably wherever the line is drawnbetween built and non-built, it should intersect all ofthe culturally significant flows of resources and infor-mation, since it is these flows, and their influences,that constitute the relationship. However, theFischer–Kowalski framework leaves unansweredthe many contextual questions – including spatialand temporal dimensions – that may need to beconsidered.

What is especially interesting is just how much differ-ence can occur in the relationship as the culturalcontext changes. In an extreme case, it can be arguedthat all aspects of nature today receive care and atten-tion directly or indirectly. For example, the MontrealProtocol protects the ozone layer from excessivedepletion, and the Kyoto Protocol attempted toreduce greenhouse gases emissions in order to protectthe integrity of all ecosystems from climate change.

Figure 1 A model of the social^ecological system that placesthe built environment (an artefact) in an overlapping zonebetween culture and nature, with causation occurring in bothdirections.Source: Fischer-Kowalski andWeisz (1999, p. 242)

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Both these conventions required substantial ‘invest-ment’ by humans in protecting and regenerating whatmight traditionally be defined as ‘natural’ systems orecosystem services. In a global economy that supportsover 6 billion humans, the entire concept of nature or‘wilderness’ as a pristine exterior is a romantic andpotentially dangerous fiction that denies reality. Allhealthy ecologies are now fully engaged – directly orindirectly – in serving the needs of humanity and arethe focus of care and regulation. To varying degreesthey constitute a kind of remote critical ‘green’ infra-structure for cities, serving to clean air and water,recycle nutrients, replenish biodiversity, fertilize andprotect agriculture crops, and so on. All of whichemphasizes the difficulties today in defining that partof the material realm which should be ‘culturallyappropriated’ and defined as a built environment.

Over history, the cultural context for boundary settinghas changed, and so too has the relative value of adopt-ing a social–ecological framework. The 16th-centurysets the scenery for explicitly defining relations(drawing the line) between the built environment andthe ecosystem. Rising international commerce, theEnlightenment, the constitution of national states,and the coming Industrial Revolution were all factorsthat promised to transform both the material realmand society. Within this context Jean-BaptisteColbert, Minister for France’s Louis XIV, authoredthe Grande Ordonance (Paris, 1669), possibly thefirst significant attempt to apply a socio-ecologicalmodel. The Grande Ordonance scaled down thepublic debt by repudiating some obligations and redu-cing the value of others and set up a system of accountsin order to ensure a fiscal balance (Colbert, 1669).Colbert’s aim was to make France economically self-sufficient and he encouraged the growth of industrythrough subsidies and tariff protection. He rigidlyregulated the qualities and prices of manufacturedand agricultural products, and initiated a vigorousroad-building programme. Most significantly for thepresent historical account, his ordinance restrictedthe use of natural resources. It included the first formu-lation of the idea of sustainable management of forests(cutting in one year not more than the forest canproduce in one year). One of his disciples, theGerman nobleman Hans Carl von Carlowitz, was incharge of mining and forestry (wood was necessaryfor mining) in the German free state of Saxony.In 1713 he published a seminal book on sustainablemanagement of forests (Von Carlowitz, 1713). It isinteresting to see how the birth of a ‘resourceeconomy’, and the idea of enforcing sustainable ratesof harvest, occur before the industrial revolution, andarise out of the intellectual framework of theenlightenment.

It is, however, the 18th-century Industrial Revolution,and the consequent massive exploitation of nature

through chemistry and mechanics, that focusesattention on resource constraints and the need forlong-term balance of energy and material flows. Inthe 19th century the scientific disciplines of thermo-dynamics (Maier) and ecology (Haeckel) appear in par-allel and constitute until today the essential basis forunderstanding relations between the built environmentand the ecosystem. Most visibly, this focus is alsoreflected in the 19th-century Romantic Movement,with its new perspective on the relation betweensociety and nature. Less well known is the long anddeep discussions among leading economists, chemistsand political scientists on the relation betweeneconomy and nature. The notion of material metab-olism was expanded from a biological concept toinclude energy flows and material flows across natureand society. The entropic or one-way flow of energydefined by the second law of thermodynamics provedhighly controversial, but was eventually applied tosociety as a whole with a view to establishing solar-driven communities and sustainable lifestyles:

The link between the use of energy and the devel-opment of human culture, in the form of ‘socialenergetics’ . . . became well established anddebated in Europe around 1900.

(Martinez-Alier, 2005, p. 11)

By the close of the 19th-century, the stage was set foroperationalizing a model of the built environment asa complex social–ecological system. Patrick Geddes(1854–1932), a biologist and one of the first theoristsof the emerging town planning movement, arguedthat one should immerse him/herself in the geographyof the region before commencing urban planning(hence his famous dictum: ‘Survey before plan’).He noted how areas are unified by problems of theirdevelopment and by their resource base, and that ‘Ittakes the whole region to make the city’. He arguedthat ‘a city is more than a place in space, it is adrama in time’ (Geddes, 1915/68, p. 107). Historicalfacts and trends are as important as geographicalelements. Geddes attacked neoclassical economistssuch as Walras because they did not count flows ofenergy, materials and waste, and he built a sort ofinput–output table inspired by the Tableau Economi-que of the Physiocrat Francois Quesnay, which is rel-evant to the attempt today to develop a theory ofecologically unequal exchange between the metropoli-tan centres and the world peripheries (Geddes, 1884;Martinez-Alier, 2005, p. 28).

In 1898 Ebenezer Howard proposed building ‘gardencities’ to alleviate the social ills of industrial citiesand the declining population of the countryside(Howard, 1902). The new cities were to be carefullyintegrated into the surrounding landscape, ensuringworkers and their families access to rural amenitiesand green space, and allowing wastes to be sustainably

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recycled. Howard’s approach emphasized directcommunity action; the importance of practical civicinfrastructure; the need for regional-scale growth man-agement and the combination of environmental ame-nities with social justice (Freestone, 2002, pp.76–96). Although more prescriptive than theoretical(Howard never integrated Geddes’s theories), gardencities represent a first modern attempt to integrateeconomic, social and ecological design, and constituteone of the most enduring and influential urbanplanning concepts.

It appears that the 19th century created the chemical,physical, ecological and economic basis to formulatea theory where urban regions and their built environ-ments function as complex social–ecological systems.But at the turn of the 20th-century, the trail growscold. Instead, as the world is propelled through thewars and a massive industrialization and urbanizationcycle, the discussion on built environments is almostexclusively focused on urban reconstruction andmeeting the urgent need for housing and associatedinfrastructure. The wellspring of available energyreleased by the second Industrial Revolution createda modern world view, where problems of resourcescarcity and pollution could always be resolvedthrough additional energy and new technologies. Thecolonization of nature is extended through a globaltrading system, sprawling cities and industrial agricul-ture. The 19th-century perspective of a balanced, inte-grated system is no longer culturally significant.Instead, as Fischer–Kowalski points out, a kind ofdualism emerges that separates natural and socialsciences and obscures the system perspective:

mainstream social sciences leave us conceiving ofsociety or the economy as highly complex unitsto be explained solely by their internal mechan-isms . . . surrounded by an undifferentiated‘environment’ largely irrelevant for the system’sdynamics. The natural sciences exhibit the comp-lementary view. There, natural systems areviewed as highly complex units with many inter-dependences and, at the same time, humanagency is described by a single-actor-model ofvery low complexity (humans causingdisturbances).

Before the advent of the environmental movement:

one searches in vain for concepts referring to thematerial dimensions of the society–nature inter-action.(Fischer-Kowalski and Weisz, 1999, p. 2)

An exception to the trend, and an astonishing figure inthe first half of the 20th-century, is the German land-scape architect Leberecht Migge who formulated andimplemented the principles of urban metabolism in

development projects of social housing for workers.The Siedlungen (settlements) which he developed in1930 were based on detailed calculations of the necess-ary surface areas to cultivate food for the inhabitants.Each house had a garden just the right size, and wasdesigned to achieve complete recycling of materialsthrough composting of organic waste and the pro-duction of biosolid fertilizer from sewage – a balancedsocio-ecological metabolism for organics (Haney,2005)! Despite notable exceptions like Migge, it isnot until the late 1960s and early 1970s, with theenvironmental movement and the first oil crisis, thatsystem ecology, and the resulting general systemtheory, become the basis for more complex models ofthe interface between nature and economy (Odum,1983). Industrial ecology and its application to urbanmetabolism (Wolman, 1965; Duvigneaud andDenaeyer-De Smet, 1977; Baccini and Brunner, 1991)are followed by the establishment of a new field ofresearch into urban ecology.

The main discussion concerning the built environmentin the second part of the 20th-century is not the man-agement of scarce resources, and even less so itsrelation to the ecosystem. With oil hovering aboveUS$10 a barrel from 1947 to 1973, the urban exten-sion that is occurring within developed and undeve-loped nations is still dominated by the idea thatenergy and materials are indefinitely available andthat nature can be substituted in practically all its func-tions by new technologies. The future problems werenot seen as linked to the colonization of the ecosphere,but rather a possible colonization of outer space. Themanagement response to the second and third Indus-trial Revolution becomes the central problem forbuilt environments. Physical models for urban andregional planning are narrowly confined to transportengineering and construction management problems.In the 1970s the shock of the oil crises produced adebate on limits to growth and raised awarenessabout limited resources. This in turn gave birth to thenew field of environmental economics, which empha-sized questions like the value of nature, the importanceof long-term constraints, and issues of generationalequity. However, such questions were not reallypresent in the debates on urban and regional planning.

Economic mainstream theory presented relationsbetween the economy (and therefore also theeconomy of the built environment) and the ecosphereas exchanges between two equivalent systems(production-consumption). This leads to whatBromley (2005) calls ‘commoditization of nature’:

Nature became a constellation of waste disposalservices, with the nature of those services beingdefined in terms of what we need from nature.Oxygen demanding material uses different ser-vices from nature than the services demanded

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for suspended solids. The atmosphere can absorbcertain industrial pollutants, and vegetation cansequester others.

(p. 5)

The conceptual starting point for such economic analy-sis is the ‘circular flow of exchange value’ (Daly, 1991,p. 183). Most standard economics textbooks feature astandard circular diagram of economic process as ‘apendulum movement between production and con-sumption within a completely closed system’(Georgescu-Roegen, 1971, p. 177). Significantly, thismodel is totally abstracted from the ‘environment’within which the financial economy is actuallyembedded – there are no connections between themoney flows and biophysical reality. It is, therefore:

impossible to study the relation of the economyto the ecosystem in terms of the circular flowmodel because the circle flow is an isolated,self-renewing system with no inlets or outlets,no possible points of contact with anythingoutside itself.

(Daly, 1991, p. 196)

This economic view of an isolated social system thatencompasses the built environment is still a commonmind set within the building professions: nature doesnot exist (outside of gardens and urban green spaces)and thus its services carry no price (the impacts areexternalized).

During the era of globalized capitalism in the 20thcentury the application of economic discounting toalmost all types of environmental assets is also beingwitnessed. Discounting is used as a rational solutionto the social problem of making inter-temporal com-parisons of welfare, either in the marketplace or aspart of other investment and assessment procedures.Referred to by David Pearce as the ‘tyranny of dis-counting’, the net effect has been to diminish the per-ceived relevance of human–nature relations as theyextend through time (Pearce and Warford, 1993).This is especially alarming when applied to ecologicalresources that must be sustained over the long-term,but is also of particular relevance to how the long-lived elements of the built environment, includingbuildings, infrastructure and systems of land use andopen space, are perceived and valued. Despite itsalmost universal application, discounting is a crudetiming tool with many unfair and unreasonableresults. As Pearce argues, it is philosophically wrongfor society to discount wants based upon a time vari-able. All wants are in the future and what matters isthe satisfaction of wants as they arise, period. Particu-larly in the case of long-term community investments,the use of money market discount rates has beenseverely criticized both from environmental econom-ists and social scientists. Nevertheless discounting is

still standard practice and continues to be part offormal training for real estate and constructionmanagement.

In conclusion, it has taken several centuries toappreciate the complex nature of relations betweenthe built environment and the ecosystem. The basisfor environmental accounting has existed since themid-17th-century, and a scientific description hasexisted since the mid-19th-century. System ecology,as well as general system theory, have been understoodfor more than 50 years. All these methods representpowerful instruments for modelling the relationship.What seems to have been lacking is an appropriate cul-tural context. Neoclassical economic theory has helpedto generate a world view where nature can be ignored,or commoditized. Discounting has generated high timepreferences in decision-making, creating a world viewwhere the long-term performance of built environ-ments, including relationships to ecosphere, becomeirrelevant. Even the dramatic depletion of resources(peak oil), and the enormous impacts of megacitieson today’s ecosphere, have not been sufficient eitherto foster a social–ecological theory of the builtenvironment, or to overcome the short-term bias indecision-making.

But times are changing and perhaps a new cycle isimmanent. The dramatic scenario of climate changeand its irreversible effect on both ecosphere and builtenvironments has reframed the issue in terms of ‘sus-tainability or collapse’ (Constanza et al., 2007). Theresult is likely to be a rapid advance in the understand-ing of social–ecological systems, in concert with amore rigorous exploration of short- and long-termstrategies to manage the risks.

Current perspectives, promisingmethods,missing piecesRising concern over environmental impacts andresource scarcities has generated significant progressover the last ten to 15 years in methods for exploringthe physical and economic relationships between thebuilt environment, society and the ecosphere.Methods such as life-cycle analysis (LCA) (Inter-national Standards Organization, 1997) and materialflow analysis (MFA) have been refined and standar-dized and a common framework of sorts has beeninitiated through building information models (BIM)and stock aggregation methods. Such advances arestill largely related to research – none is regularlyapplied by professionals in their standard practice.However, each contributes in its own way to an emer-ging, transdisciplinary approach. In combination, theseadvanced methods constitute the foundation for aformal systems perspective that quantifies the flowsand effects at every scale, and that alters how the

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built environment is perceived. Any new theory of builtenvironments is likely to emerge from this new systemsperspective.

In particular, it is worth examining four general themesthat appear to capture much of what is currently under-way: the extension of system limits in time and space; abalanced systems perspective; a common frameworkfor representing the built environment; and the needfor scalable perspectives, all the way up to thecomplex socio-ecological system.

The extension of system limits in time and spaceThe concept of built environment implies by definitionthe necessity to partition the material realm, definingsystem limits for mass and energy flows both in spaceand in time. In conventional practice, the built environ-ment is most commonly surveyed or analysed either asa piece of private property (the parcel), or as a collec-tion of properties with their associated buildings, infra-structure and constructed open spaces. Spatially, theanalysis of energy or mass flows is limited to whatcrosses the property limits. Temporally, the analysisis limited to the time period beginning with projectinitiation and ending with commissioning, or to atypical day or year of occupation and management.

Adopting a broader systems perspective means thatspatial limits must be extended and abstracted so thatthey reinforce an agreed division between what ishuman (part of society and its culture), and what isnature (part of the ecosphere). Resource flows(energy, materials, water, organic matter) for anyperiod of time can then be characterized and quantifiedat whatever point in space they come in from ecosys-tems (to be transformed or stored) and at whateverpoint in space they are finally returned to ecosystems(as waste, emissions and heat). In economic andsocial terms, these measured flows match the physicalunits used for calculating both internal costs andexternalities. The temporal limits must be extendedto match the spatial limits, as the chain of resourceflows is followed backward in time through theeconomy and into the ecosystem, or forward for thefull life span of a building or system, until its manyparts have been reintroduced into the circuits of theecosphere or economy.

It is this extended physical relationship that is imaginedwhen Patrick Geddes refers to urban regions as a‘drama in time’. Buildings and other elements of thebuilt environment become transitory events that trans-form the material world into complex chains of pro-ducts and processes spread out over time and space.The drama alters the scope and significance of designpractice, procurement and management for virtuallyevery element of the built environment. In a typicalbuilding, for example, up to half the construction

energy may occur off-site, in material processing andtransport. The operating phase of the building mayaccount for an even greater flow of materials thangoes into the initial construction. Over time, the clean-ing supplies and surface coverings come to represent asurprising large share of resource flows. The effects anddamages of some minor material flows (especiallytoxics) can outlast by many years the life span of thebuilding, the occupants and the owners.

At present, the only significant method available forextending time scales and developing a broader per-spective on built environment relationships isproduct-related LCA (Life Cycle Initiative, 2003;Gloria and Bare, 2003) Over the last 20 years LCAhas become a well-documented and internationallystandardized method. LCA differs from most otherenvironmental costing and assessment by extendingtime scales both forward and backwards. A product’slife cycle starts when raw materials are extractedfrom the Earth, and ends with waste managementincluding recycling and final disposal. At every stageof the life cycle, resources are consumed (or trans-formed) and emissions pollute the air, land or water.These environmental loadings (or stressors) impactthe environment functions upon which humanity andthe ecosphere depend. Because significant environ-mental impacts can arise at each stage, a fair and accu-rate environmental assessment of any product orservice must take into consideration the whole lifespan. What makes LCA different from other environ-mental assessment tools is a capability to integratetime-dependent inputs and outputs as part of environ-mental accounting. To date the widespread applicationof LCA to built environments has been frustrated bythe intensive data requirements and the risk of beingincomplete. However, database services are continu-ally improving, computer models are now adaptinginput requirements to the user’s capability and needs,and it is only a matter of time before such weaknessesare resolved.

A number of much more fundamental problems existwith LCA, and these speak to the question of whatnew theory may offer. LCA is a method that hasemerged out of resource economics and industrialengineering. Not surprisingly, it has not been well inte-grated into spatial design or construction management.For many industrial products, LCA can work withgross assumptions about where and how the productwill be used, or ‘released’. The location of use is anabstraction – the ‘economy’ or the ‘average market-place’. But for a building, the location of use is thesite – a key variable for consideration in design andmanagement decisions. At the most local scale, a build-ing site creates, by definition, an indoor environment –where the potential impacts of concern include workerproductivity and occupant security, comfort, safetyand health. When the scale expands beyond the

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isolated building, effects can be assessed on the parceland the surrounding neighbourhood. Localized effectsmay include the urban microclimate, solar and windaccess for adjacent buildings and gardens, neighbour-hood security, noise, public amenities, biodiversityand bio-productivity. At the regional scale, the build-ing and its systems will place demands on the commu-nity, affecting air quality and public health, economicdevelopment, the use of transportation systems, emer-gency preparedness, the loading of urban infrastructuresystems and the allocation of local ecological carryingcapacity. Each scale will be affected by the building’suse of resources, and associated emissions. However,once again LCA does not normally address theseimpacts and an expanded set of analytical andevaluation models may be required.

Spatial representations of natural systems were intro-duced to the design and planning process with greatexpectation in the early 1970s following the publi-cation of Ian McHarg’s Design with Nature (1969).Although such prescribed, mechanical approaches arenot appropriate for design teams today, tools are stillneeded to reveal how spatial dimensions affectrelationships between built environments and ecosys-tems, especially so in light of the current scale of urban-ization and the potential for local scarcities of energy,water and land. Analytical models and mappingmethods need to include hazardous sites and the costof risks across the landscape; the key ecological func-tions and their sensitivity to built environments; andthe local environmental resources that may be suitablefor supporting built environments including (especiallythe local energy resources, their quality and their avail-ability by season). Without integrating such spatiallyspecific information at the beginning of the designprocess, how is it possible for any team of professionalsto understand the long-term effects of their design andmanagement decisions?

Still more problematic is the current approach to timehorizons. Basically, LCA assumes a frozen future, withno changes in technology, no surprises, no new environ-mental constraints, no new demands on the building orland use. While this is a default condition that facilitatessome measure of ‘life cycle’ assessment, it is also mislead-ing and extremely limiting. In application it has lead to anumber of difficult methodological choices. Is it prefer-able to standardize on a mid-point or end-point evalu-ation (Life Cycle Initiative, 2003)? How should effectsbe partitioned if building products are eventuallyrecycled into new products? How can value be recog-nized for materials and systems that are inherentlymore adaptable? Despite much attention given to suchquestions, no agreement yet exists on how to constructplausible scenarios to allocate the many life cycleeffects to the various products and users, how to dealwith uncertainty, or how to translate past and futureimpacts into present costs (Hinterberger et al., 2002).

Although LCA is a powerful approach to accountingprecisely because it stretches time horizons, it isclearly inadequate on its own, and needs to becombined with foresight tools and a much broadertheoretical perspective on what is meant by ‘extendingtime’.

A balanced system perspectiveOne reason for defining built environments as systemsis to explore what might constitute a balanced, sustain-able relationship between natural and built. Theconcept of balance can vary depending upon how thesystem is defined, especially in regard to time horizons.At present, the focus is on understanding and control-ling the large mass and energy flows that cycle betweenbuilt environments and the construction sector, the restof the economy, and the ecosphere. Such flows aretracked as part of company and public accountingusing data derived from dollar exchanges. Non-commodified flows and stocks tend to be ignored.

A broader systems perspective assumes that within aclosed material realm, all flows between nature andbuilt environments must be balanced over the long-term. The key questions are how to live within fixedlimits or rates of flow, either by reducing demands orby achieving greater service value from any resourceinputs. Environmental accounting is the method foranswering such questions. Flows are tracked as theycycle from nature into built environments and ulti-mately back to nature. Environmental accounting issimilar to financial accounting and produces the samekind of balanced ledger.

At present, the only method for calculating and dis-playing a balanced set of flows through the builtenvironment is mass flow accounting (MFA) (Bringezuand Schutz, 2001). MFA uses a simple model of theinterrelation between the economy and the environ-ment, in which the economy is an embedded subsystemof the environment and – similar to organisms – isdependent on a constant throughput of materials andenergy (Organization for Economic Co-operation andDevelopment (OECD), 2004). The environmentalaccount (or mass balance) for modern economies ischaracterized by the accumulation of large physicalstocks of man-made assets: infrastructure and build-ings. They constitute the dominant part of producedman-made capital in industrialized systems. Similarto ecological resources (natural capital), this builtenvironment capital is becoming difficult or impossibleto replace and thus may need to be monitored, valuedand protected over the long-term.

Because MFA begins with inputs from nature, it ismuch easier for everyone involved to recognize whatis included, or excluded, from the analysis. Specifictools have been defined to assess material inputs

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along the whole life cycle of a product, including thehidden flows:

the total sum of all materials which are not phys-ically included in the economic output underconsideration, but which were necessary forproduction, use, recycling and disposal.

(Bartelmus et al., 2001, p. 22)

The main purpose of economy-wide MFA is to provideaggregate background information on compositionand changes of the physical structure of socio-economicsystems. However, MFA also provides an exceptionalmethod for revealing system dynamics for the builtenvironment at any scale, from parcel to urban region.Sankey (directional flow) diagrams are often used tosummarize the MFA visually as an entire connectedand balanced system. In a Sankey diagram the material

flows begin with inputs from nature, then flow intointermediary processes (any infrastructure used for pro-cessing, converting, storing, or regulating), and then intothe various end use(s). After use, flows may be recon-verted by infrastructure systems for reuse or recycling.Ultimately, all flows are directed to a category ofoutput (waste products emitted into air, into waterbodies or into landfills; long-term storage; export). Thebalanced accounting thus tracks every flow fromsource to sink (Figure 2). Sankey diagrams can be ani-mated to reveal the daily or seasonal peaks. Theconnections between each partition can be conditional,so that when limits are reached, the flows can be re-routed. In such ways the Sankey can help systemdesigners or property managers visualize MFA results,and develop scenarios that successfully match thequality and quantity of the resources to the requirementsof each end use.

Figure 2 An example of a ¢ve-partition metabolic pro¢le for a new resource-ef¢cient residence/parcel in Delhi, India, displaying thequantities and pathways for all water £ows during a typical day in the dry season. The data matrix that generated this Sankey can bestacked onto other parcels and aggregated to generate a balanced account for any £ow for the entire stock.Source: authors

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A combination of MFA and LCA can create a hybridapproach that has proven to be particularly adequatewhen analysing national building stocks and theirlong-term behaviour (Kohler et al., 1999). MFA pro-vides composite, upper limit values for each resourceor waste product as it crosses the line from nature tobuilt, and from built to nature. LCA gives muchmore detailed information on how the resources arepartitioned in between (assuming the data is availableand convenient), and thus allows for a more preciseand detailed exploration of system dynamics.

MFA ‘metabolic profiles’ can be developed for acountry, a region, a town, and for flows of energy,aggregates, water, people, organic matter, infor-mation, or money. The structure of a metabolicprofile tends to vary with the local resource base andthe level of technological development. Pre-industrialeconomies (or systems) are characterized by a diversityof inputs, and low levels of flow. Industrial economiestend to have much fewer inputs and larger flow quan-tities, with greater use of import/export and storage tobalance the flows. Resource-efficient economies tend tohave a diversity of inputs, and flow pathways that useextensive looping and cascading as a means to deriveadded value or service from any given input. All elsebeing equal, the more value squeezed out of any flow,then the smaller the input will be. In this way the meta-bolic profile reveals the ‘ecological efficiency’ for thebuilt environment as a whole system. Moreover, byrevealing the source, end use and sink for all flows,the MFA metabolism helps to focus attention on themost significant flows and interfaces, and on the mostobvious opportunities for ecological design (loopingand cascading).

Metabolic profiles can reveal the extent of interdepen-dencies within a system. For example, a system may beespecially vulnerable if many critical demands dependupon a single source. Metabolic profiles can alsoreveal potential for ecological conflicts at differentscales. For example, future conflict may be inevitableif a large percentage of the available water, or anyother scarce local resource, is exported. Metabolic pro-files can help to identify trends in resource use by creat-ing a time-series MFA. For example, there may be atendency in advanced economies for dematerializationof certain processes over time, and the replacement ofmass flows by information flows (Kohler, 1998,p. 155).

MFA results are not yet standardized, which makes themethod difficult to use within design team or for pro-fessional development. Nevertheless, it is possible forresearchers to normalize and compare flows, and gaininsights into differences between built environmentsystems in different locations (Decker et al., 2000).MFA has also been used by researchers for long-termscenario development, and for exploring and

comparing the flow requirements of entirely different,hypothetical urban systems (Baccini et al., 1993).

One of the difficulties with using both MFA and LCAto model the socio-ecological system is the dependenceupon economic input output data for tracking resourceexchanges. Economic accounts often lump togethermaterials differently, depending upon whether theyare inputs to the economy (e.g. all types of new packa-ging) or as outputs (e.g. old corrugated cardboard),which makes it virtually impossible to balance theaccounts. Economic accounting also ignores theincreasingly important exchanges that occur outsidethe economy, for example by buildings that use distrib-uted micro technologies in combination with on-siteenergy, water and information.

A more significant problem with MFA is that, similarto LCA, physical flows are aggregated and viewed asa process divorced from the spatial aspects of design.Although some of the earliest Sankey diagrams, devel-oped in the mid-19th-century, were presented on maps,such as the famous march by Napoleon’s army toMoscow (Tufte, 1983), there is no longer any spatialinformation referenced on flow diagrams. It becomesdifficult to see how different spatial characteristics –the distribution or density of buildings on landscape,for example – might influence MFA results. Andwithout making such relationships more transparent,it is impossible for design teams to seek optimum sol-utions. Baccini and Oswald (2003) have proposed atransdisciplinary model that attempts to overcomethis critical divide by creating a common platform forcombining physiological and morphological perspec-tives. Such a transdisciplinary platform may be essen-tial if design teams and property managers are tobenefit from the insights of LCA and MFA. Yet, thisspatial dimension is lacking in the simplified socialecological framework.

A shared framework for representing the builtenvironmentA central challenge for any theory of built environ-ments is simply to cope with the complexity and mut-ability of elements and actors over time. A singleresidential building might be composed of 200 differ-ent materials, many of which are associated withspecialized producers, installers, and repair and man-agement technicians. If new theory is to help with pre-dicting impacts of decision-making on the performanceof the built environment, then one must perceive it tobe a system with a multitude of design, construction,operation, maintenance, and disposal processes relat-ing flows of materials to decisions by different actorsat different moments and places. This system is theinterface between culture and built environment. Inthe context of the Fischer–Kowalski framework, itdefines which parts of the material world that are

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deemed to be artefacts, and part of the builtenvironment.

Due to the high complexity factor, any model of thebuilt environment needs a way to describe which ofthe many subsystems are addressed, and a frameworkfor decomposing the many physical elements. If a con-sistent framework is adopted, it might help to unifymodelling activity. It should be possible to relate themass and energy flows to the financial and informationflows at each stage of design, planning, and manage-ment. A framework provides the context for develop-ment of tools for understanding simplifying suchrelationships.

The generalized application of life cycle costing (LCC)and LCA has been retarded by the lack of a robust andshared building representation (Kohler and Moffatt,2003, p. 21). The usual geometrical representation ofbuildings through plans, sections, elevations anddetails is in this context of limited interest. It is moreconvenient to base assessments on the textual,process-oriented building descriptions used for costcalculation and for tendering, i.e. to describe buildings‘as they are built’ (Kohler and Lutzkendorf, 2002,p. 382). For this purpose, a building can be decom-posed into functional units (or cost elements) such as1 m2 of exterior wall, a unit which is the sum ofmany specific building processes, prorated amongstmultiple components, and then normalized. Continu-ing the example, 1 m2 of exterior wall can then belinked to the basic inventory data and to whateverevaluation sets are of interest (e.g. mass flow,primary energy consumption, effect-oriented impactcategories, aggregate indicators). The functional unitof wall can further be described as layers of materials,each linked to information on life expectancy, main-tenance and cleaning cycles, energy consumptionduring use, recycling behaviour and possible down-stream paths. In this way it becomes possible tocalculate a multitude of performance indicators forthe particular wall section or element, including lifecycle costs, life cycle impacts, heat flow, vapour diffu-sion, off-gassing, toxicity, acoustic protection, fireresistance, construction time, and deconstructionpotential – all from the same physical representation.Ultimately such functional units can be cross-refer-enced and converted to the geometric representationsused by designers (e.g. the entire exterior wall asdrawn, excluding windows and doors). The resultwould then be a single, multi-purpose buildingproduct model based upon LCA and suitable formachine reading.

The search for such a multi-purpose information modelbegan with the STEP standard 20 years ago (Kohler,1995; Eastman, 1999). A first general solution is atpresent the development of a common BuildingInformation Model (BIM). A BIM represents in an

object-oriented three-dimensional model of the actualparts and pieces being used to build a building. Atpresent BIM are implemented for the main computer-aided design (CAD) software on the basis of the Indus-try Foundation Classes (IFC) industry standards (IFC,2007). Even if the present IFC release concentrates ongeometrical and functional properties of buildingsand elements, the process components are beginningto be implemented. It is possible to imagine mappinga scalable object and process description (from urbansettings comprised of building types and linear infra-structure, down to very basic construction and oper-ation processes) and eventually compile a completemetabolism representation. This metabolism can haveecological, economic as well as social dimensions thatevolve over time, as issues change. For example, itcan include for each functional unit the latest riskassessment information,3 with indictors on mid-pointand end-point effects and damages to human healthand to ecosystems. Despite the potential for such inte-grated information and decision-making, actual use ofsuch frameworks is still extremely limited and maydepend upon the emergence of most sophisticatedrating systems and market incentives, and on the evol-ution of flexible, scalable tools that can respond to thespecific needs and abilities of users.

A more fundamental problem with current methods forrepresenting the built environment is that a preciseproduct-based data structure, based upon LCA andspecification standards, does not provide the perform-ance information needed to generate MFA profiles.The problem is exacerbated with the adoption of dis-tributed on-site systems that may create many two-way flows for resources. Although a large number ofmicro-models exist for estimating the flows ofresources for parcels, almost never are the flowsdescribed in terms that can be used to generate thespecific pathways upstream and down. If energy isused for lighting, how much then contributes to spaceheating? If rain water is captured on roofs and walk-ways, where does it go? Even where connections areknown, the data structure is completely lacking forrecording such information. How then does one assem-ble parcels into a larger system (buildings, blocks,neighbourhoods, towns and regions) that accountsfor flows?

What may be required is a new, complementary infor-mation structure based upon parcels and flows.A parcel may consist of a residential building and itsgarden, or a park, a road, a shopping mall, or asewage treatment plant. Regardless of use, everyparcel needs the same data structure because everyparcel has the potential for resource demand andsupply. A water factory still needs water for its ownkitchen and toilets. A typical apartment building inthe future may have a rain water cistern and septictank incorporated into the foundations, or infiltration

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trenches next to the street for treating surface run-off.Ultimately every parcel functions like a ‘transformer’toy, that at different times in the year, or at stages in itlifetime, may become a source of surplus water,energy, peak power, organic material, transportation,and more. Such ‘transformer parcels’ may require thatany new theoretical framework avoid common assump-tions that limit functionality of sites based upon primaryland use or standard building classifications.

Ascalable perspective that includes thenet effects forstocks and urban systemsThe impacts caused by the construction, operation,maintenance and disposal of the man-made environ-ment on the ecosystem have initially been consideredonly for the effects of final operating energy in newconstruction. This focus reflected a market-based inter-est in developing new technologies for new construc-tions, and the inherent bias towards simpleregulatory solutions, in particular enhanced buildingcodes and standards for new construction. Researchinterest began to shift ten years ago with the recog-nition that even when time horizons are extended to2035, over 75% of the building stock worldwide hadalready been built. Thus, sustainable performance ofbuilt environments can only be achieved throughbetter management of the existing stocks. In the indus-trialized European Countries, with their shrinkingpopulations and long-lived buildings and infrastruc-ture, the situation was even more pronounced.Methods were developed to understand the compo-sition and the dynamic behaviour of the stocks, andin particular to the operation, maintenance anddisposal problems (Kohler and Hassler, 2002, p. 227).

The flow-oriented approaches (LCA, MFA), based onsystem–ecological and thermodynamic modelling,proved to be very efficient, above all through the super-position of mass flows, energy flows, financial flows,and information flows. The bottom-up LCA creates ascaleable approach that can aggregate products intoassemblies, and assemblies into buildings, and build-ings into stocks at the urban, regional and nationalscale, without any loss in the life cycle inventory data(Kohler, 2006). Aggregation is also possible forMFA, since metabolic profiles for different parcelscan simply be stacked and added together to create asystem-wide profile, with flows still balanced for allclasses of inputs and outputs.

More recently, the flow-based approaches for stockshave been combined with the existing capital-basedapproach used in environmental economics (Bromley,1991; Pearce and Warford, 1993; Pearce, 2003, 2006).The capital approach is based on the long-term evolutionof different capitals, their interrelation and the possibilityfor substitution of one capital by another. Differentsystems (from a local community to an industrial sector

or to a national economy) can be considered as capitalstocks of different types: natural, man-made, humanand social, sometimes also cultural. (Kohler and Yang,2007, p. 4). By relating these different notions ofhuman, social and cultural capital, even if the definitionsdo not always coincide, an unusual opportunity iscreated for transdisciplinary research (Kohler andHassler, 2002; Hassler and Kohler, 2001). The builtenvironment is both a dominating part of the man-made physical capital, and a principle ingredient in thesocial capital in the sense that it constitutes the placefor social relations (Lawrence and Low, 1990, p. 484).If, for example, the physical condition of housingestates is deteriorating, tenants will begin to leave, creat-ing crowding or other disruptions in surrounding estates.Conversely, the built environment, through its complexhistorical composition, can only be maintained throughwell-trained professionals, and thus the preservation ofthe housing estate is dependent upon the existence ofhuman capital. At the same time the building and infra-structure stock constitute a cultural capital that allowsthe society to develop a shared world view and sense oftime, place and identity, which are key ingredients ofsocial capital. Durable and adaptable design practices,and preservation and restoration activity, thereforeaffect all forms of capital. The same arguments can bedeveloped through the concept of resiliency, wherenatural diversity, social diversity and cultural diversityare all factors that help systems adapt to change andsurvive shocks.

A sustainable development therefore requires that thedifferent forms of capital be considered together, andthat a loss in one be mitigated by an increase inanother (i.e. substitution). The amount and speed ofany substitution in capital can in itself become a cri-teria for sustainable development (Gunderson andHolling, 2001; Walker et al., 2006). In such ways thesocial–ecological model of built environments pro-vides an essential transdisciplinary method for definingand assessing sustainability.

‘Strong sustainability’ has priorized the conservation ofnatural capital with no substitution (Daly, 1991); weaksustainability (resource economics) tries to achieve nonet loss, but allows for possible substitutions betweendifferent types of capital (Pearce and Warford, 1993;Turner, 2006; Atkinson, 2008). Although suchdefinitions may allow for an integrated perspective, incomplex situations like building and urban design,there is no simple optimum, because it is not possibleto establish a single general target or optimizationfunction. Constraint satisfaction approaches aretherefore more promising. Limit values can beestablished for a variety of both quantitative and quali-tative constraints, over time, and together theycreate an n-dimensional solution space. This is particu-larly important when dealing with institutional pro-blems where fragmented budgets and single-purpose

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mandates often undermine the emergence ofsystem-wide solutions (Kohler and Yang, 2007,p. 10). Carefully constructed constraints for differentinstitutions can help to create a system that – as awhole – achieves positive synergies and satisfies thecarrying capacity of both local ecologies (e.g. water-shed) and local built environments (e.g. pipelines).

One difficulty with imposing constraints on complexsocio-ecological systems is communicating performancein a standardized and coherent fashion. What are thetotal impacts of a built environment on the naturalcapital, and do they satisfy fixed constraints? Twonotable examples of attempts to quantify and integratesuch impacts are the ecological footprint (Wackernageland Rees, 1996), and The Natural Step (TNS) for com-munities (Holmberg and Robert, 2000; James andLahti, 2004). Both entail quantitative procedures forassessing the total flows associated with different econ-omies, including different types of built environments,and for valuing the total flows in terms that relate tofixed constraints imposed by the planetary ecosystems.The ecological footprint converts flows into the area ofproductive ecosystems required to sustain such flowsindefinitely. In a world with shrinking ecologicalresources and a growing population, exceptionallylarge ecological footprints are unsustainable bothbecause they exceed carrying capacity, and because therepresent an unfair appropriation of limited communalresources. TNS compares the measured flows with‘system limits’ based upon global capacity for generatingresources and assimilating wastes. Any economic activitythat exceeds these limits is deemed to contribute to thelong-term failure of natural and economic systems.Both ecological footprints and TNS offer a popular heur-istic for imposing long-term, fixed constraints on therelationships between built and non-built environments– especially at the urban scale. It becomes possible fordecision-makers to ‘backcast’ from sustainable relations(an equitable footprint or the system limits) to currentconditions, and then to explore options for managingthe often difficult transitions or ‘critical path’.However, such approaches are absolutely dependentupon standardized and rigorous methods for environ-mental accounting, especially when comparing onelocation to another, monitoring performance overtime, or formulating backcasting and forecasting scen-arios. As more and more cities and regions attempt toadopt these new metrics for sustainability, the result islikely to be a much greater interest in what might consti-tute a formal and practical method for stock aggregationusing hybrid MFA profiling (Barrett et al., 2002, p. 108).

Towards a new conceptualization of time forbuilt environmentsA review of current themes has identified many chal-lenges to conceptualizing the built environment as a

social ecological system. Two issues stand out asespecially problematic. Firstly, the impact of spatialrelationships, at different scales, is largely ignored bythe physical models. Secondly, concepts of time seeminadequate, especially with respect to longer-term pat-terns and consequences. In both cases, it is interestingto explore how the framework might be expanded toaddress these issues.

Incorporating spatial dynamicsSpatial scales for built environments are typically por-trayed as a nested hierarchy. Although terms may vary,the hierarchy grows from the building footprint orparcel, through block, cluster, neighbourhood, cityand region. In addition, some spatial elements maybe more linear, like rights-of-way or rivers, and helpto connect and define the nested scales. An expandedframework would initially need to consider howthese spatial elements affect the understanding ofrelationships between the built environment and thematerial world, on one side, and between the builtenvironment and society, on the other. Figure 3 illus-trates the nested hierarchy, and possibleinterrelationships.

Material relationships include two types of builtenvironment effects: those that aggregate as onemoves from local scale outwards, and those that maybe relevant only at specific scales. The site-specificeffects can vary significantly, both in terms of thenature of impacts and the threshold of concern. Forexample, what is diverse at one scale becomes repetitiveand monotonous if repeated many times at the nextscale up. Localized effects, such as noise or odours,may become immaterial when assessing impacts at thescale of a region or the larger economic system.

The social relationships also appear to have two typesof spatial interaction, here referred to as ‘localization’and ‘synergization’. Localization means that thesearch for creative design solutions ideally begins atthe most local scale – building or parcel, withprimary responsibility on the local actors anddecision-makers. It is they who first explore designoptions, and thus have the greatest freedom to inno-vate. What is passed on to the scale above are onlythose service or performance requirements thatcannot be successfully satisfied locally (due to techni-cal, economic or other practical reasons). Thus, like abaton in a relay race, the responsibilities move out-wards, except that the baton gets much lighter ateach stage until, at the regional scale, there may belittle or no need for policy or investment. In this way,the built environment can emulate the self-organizingand self-reliant properties of natural ecologies.

Synergization refers to the spatial interactions that arebeing driven in the opposite direction – from the region

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back to the parcel. The primary responsibility is at themacro-scale, where a big picture perspective can helpin defining constraints or targets, and in enabling coor-dinated solutions that achieve positive synergies.At each scale the enabling function may includeinformation transfer to the more local scales, includingtraining, certification, requests, recommendations, feestructures, incentives, pricing signals and continuousfeedback systems. Enabling functions may alsoinvolve the design and operation of systems for con-necting more local scales – creating networks, forexample, that allow surplus resources at local scalesto be transferred, shared and stored. In theory, a com-bination of localization and synergization can producean efficient, diverse built environment, where the wholesystem is much greater than the sum of the parts.

The concept of synergy may also be something to con-sider when exploring how frameworks portray phys-ical relationships. Reductionist methods like MFAand LCA are convenient for modelling, but fail toaddress the potential for a more symbiotic relationshipbetween built and natural environments, where, forexample, built environments regenerate ecologies,and adapt and respond to environmental changes.A balance of flows is not necessarily a balancedrelationship, especially when so many synergies arepossible between built and natural at the local scale.Part of the difficulty is the historical perspectives thatstill influence design and management decision-making.

Environmental accounting emerged out of the19th-century industrial engineering perspective, thatsees nature as a bank of commodities and thatassumes ‘economies of scale’ and societal progressjustify urban systems that are large, centralized,

supply oriented and single purpose. This perspectivenow co-exists with a number of others. In response toenvironmental regulations in the 1960s and 1970sthe design philosophy for basic infrastructure servicesexpanded to include ‘environmental engineering’(initially referred to as sanitary engineering). Environ-mental engineers addressed the externalities by meansof ‘end-of-pipe’ systems for waste control, treatmentand disposal. Interestingly, the concept of ecologicalengineering was also introduced in energy termsduring the early 1960s with the seminal work ofH. T. Odum (1963). However, the concept did notbecome well understood in practice until the late1980s. Even now, there tends to be some confusionaround the scope of what may be included. Allapproaches to ecological engineering use quantitative,science-based design methods, and employ self-organizing ecosystems to remove, transform orcontain pollutants. The level of human interventionmay vary. Regardless, by using natural systems (con-structed wetlands, bio-swales, composting) to cleanand regulate flows, ecological engineering can savecapital and operating costs relative to constructedsystems, and provide multiple ancillary benefits.

If ecological engineering is designing with nature, thenext shift in paradigms is designing ‘like’ nature.A number of seminal articles in the early 1990s out-lined a new approach to urban design, building uponthe ecological theories developed by pioneers likeEugene Odum (Odum, 1989; Brugmann, 1992;Thompson and Steiner, 1997) By the late 1990s theseconcepts had coalesced into a renewed approach tolandscape architecture, that reconnects with the eco-logical roots of the early regional planning movement.In essence, from ecological systems a set of principlesare distilled, with working examples, that are then

Figure 3 As spatial scales change, somephysical effects are aggregated,while others are scale speci¢c; some decision-making beginsat the most local scale and seeks to maximize self-reliance, while other decision-making begins at the macro-scale and seeks to enablepositive synergies

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applied to design projects at scales from the building tothe urban region. The many principles of ecologicaldesign – elegance, food chains, functional adaptation,feedback systems, redundancy, multi-purpose struc-tures, and so on – provide a rich pallet for the designand management of built systems, based on amplenatural precedents. Koh (2005) argues that thescience of ecology provides a basis for post-modernlandscape architecture because it reintroduces to aes-thetics a measure of constraint and a sense of morality.He points out that ecology is a science fundamentallyabout intelligent, self-organizing systems, whichmakes it the most appropriate science for guidingdesign of the larger built environment. At the urbanscale especially, it would seem that this perspectiveemphasizes a different type of relationship, movingfrom ‘big architecture’, industrial engineering, andcoping with externalities, to the stewardship of land-scapes and integration of both social and ecologicalvalues into design and management. In theory, allbuilt systems have the capacity to enhance ecologicalproductivity, and complement the environmental ser-vices upon which society depends. However, it is notyet clear how any framework can accommodate suchpotentially complex and dynamic relationships.

Ecologyas a source of new timing toolsAccording to Elias, conceptions of time fall into twobasic camps: either time is viewed as a natural flow,outside of mankind (Newton) or time is considered asan inherent part of human perception and identity(Kant) (Elias, 1992/2007). In reality, a multitude oftime conceptions exist throughout history, and fromone location or discipline to another: linear con-ceptions of time coexist with cyclic conceptions,some disciplines measure time (physics), others con-sider time as a form of social relation (sociology ofknowledge) or as a social construct. They all offerdifferent views of a complex notion which is perma-nently changing. Elias calls it Wandlungskontinuum(change continuum) arguing that what one considersas time today is the result of a long social and individ-ual learning process required to deal with social andtechnical environments that have become increasinglycomplex. Whitrow (1980, p. 120) points out that it ispointless to try to define time:

The very essence of time is its transience, and this isa fundamental concept that cannot be explained interms of something more fundamental.

Both Elias and Whitrow agree that time concepts arenot a fixed ingredient of reality or culture, but arerather a kind of reference language used for synchroni-zation and orientation. Mythic time helped earlyhumans synchronize their society to the eternallyrepeating cycles of the natural world. Mythic timealso oriented society through the unceasing rehearsal

of the same primordial myths, each a piece of aneternal moment that resonates with all other suchmoments – a kind of eternal present. Modern timewas invented to help society synchronize to theprecise and unsleeping world of the machines. It alsoprovided a new orientation: modernity, in which allof humanity became swept up in ‘waves of society pro-gress’ (Graham and Marvin, 2001) As the relationshipof built environments to ecosphere is conceptualized inthe 21st-century, one of the challenges appears to behow society can adapt or create timing concepts, inte-grating the recent time concepts resulting from trans-disciplinary approaches (Constanza et al., 2007).

Ecological time presents a very different set of conceptsfor modelling and decision-making, and over the pastfew years ecologists and other scientists have exploredthe implications on the entire socio-ecological system(Gunderson and Holling, 2001). From an ecologicalperspective the long-term value or integrity of thesystem can be defined by its ability to provide continu-ously the ecological services upon which humans (andother species) depend. Time periods are defined on acontextual basis where the organism or dynamicunder investigation provides the temporal scale, nothuman needs or values. Each organism and objectwithin the environment has its individual time, and aclass of similar objects has a generalized time arche-type, providing ecology with a time structure that isbuilt up of qualitatively different periods, which areinseparable from the discipline itself. The strength orrobustness of an ecosystem depends upon the inter-action between the nested time scales for the ‘keystone’species that maintain order within the system, and thatcontribute to the succession of events that allow thesystem to evolve and adapt.

The time rings for keystone species can range frommonths to centuries. Some species respond quickly tochange and shocks, others more slowly. The timerings allow the system as a whole to be reconstructedat any time scale, should gaps occur. From this ecologi-cal perspective, discounting of time makes no sense,and is not a concept that is used. Rather the challengeis balancing short-term and long-term processes acrossthe time rings. Ecologies purposely mix the time scalesbecause, as Brand (1999) says: ‘Fast learns, slowremembers’ (Cole, 2000). All durable and sustainablesystems have this sort of structure; it is what makesthem adaptable and robust. Figure 4 shows how thetime rings of the natural world might interface withthe time rings of society. Society is composed ofelements ranging from the short-lived cells in ourbodies to Homo sapiens to the entire biosphere, eachof which has a very different lifetime and, hence, adifferent time preference. Loyalties are divided acrossthese time rings, which helps to create a balanced per-spective on time (Dyson, 1979). Where the natural andsocial overlap is in the built environment, which

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encompasses the fast changing, short-term processes –like design and management systems – within the con-straints imposed by the features of long-lived buildingsand infrastructure systems and the underlying land usepatterns. Essentially the time rings for builtenvironments provide a more systemic and graduatedperspective on how time is valued (norms) and howelements of the built environment and ecosphereinteract and influence each other.

A unique and defining aspect of ecological systems istheir focus on the future. Life systems are goaldriven, and future oriented. In fact, all the relationalcharacteristics of life systems can only be understoodin terms of final causes. The final cause of an ecosys-tem, for example, is to optimize welfare (e.g. biomassand stored energy and information) over time (Fathet al., 2001). First described by Fantappie (1991) asthe law of syntropy, the goal driven nature of lifesystems has been explored with some difficulty bymany scientists. The concept of a future-orientedaction conflicts with the law of causality, a lawwhich underlies the scientific method. Basically, theperformance of life systems is a function of some pre-dicted future state. Rosen (2000) describes this asanticipatory behaviour and points out that such beha-viour is based upon a ‘model’ in the broadest sense.Thus, models lie at the root of organic systems, fromthe molecular scale to the societal, from the survivalbehaviour of organisms to the theory of evolution.The norms or goals that drive these models help todefine a preferred end-state, the precise nature ofthese goals, and the choice of rational strategies toachieve such goals, becomes the focus for ethical andpolitical discourse. This ecological perspective suggeststhat time concepts for built environments must include

this characteristic relational approach, where modelsat all scales guide behaviour to achieve long-termgoals.

In essence, ecological science offers a wealth of newconcepts and timing tools, and a view of time that ismarkedly different from economic time. Adoptingsuch a perspective as part of a new theoreticalapproach may represent a possible cultural adaptationto the challenge of sustainability for built environments(Moffatt, 2007). What is not so clear is whether suchconcepts, on their own, can succeed in the face ofincreasingly high time preferences throughout society.

Long-term ecological research and resiliency for builtenvironmentsAnother approach that emerges from an ecological per-spective is to look back in time at how differentsocieties have defined and managed the relationshipbetween the built environments and their surroundingecosystems (Sieferle, 1997; Reichholf, 2007). Longi-tudinal studies suggest that ecological context andclimate have shaped and mediated the rise and fall ofcivilizations, wars, and human achievement. Thecapacity of any social–ecological system to surviveand prosper may depend very much on its ability tounderstand these past patterns and respond appropri-ately (Constanza et al., 2007). Diamond (2005) hasanalysed historical patterns of survival of societiesand proposed an explanation about why societies failor succeed. He identifies five factors that contributeto collapse: climate change, hostile neighbours, tradepartners, environmental problems, and a society’sresponse to its environmental problems. Diamondclaims that the fifth factor is always significant, in the

Figure 4 Robust and adaptable systems require interaction across the time rings (logarithmic scale). For ecosystems, the rings areoccupied by keystone species that provide responsiveness and continuity. For society, the rings re£ect the simultaneous loyalties forhumans, as individuals, and as members of larger collectives. For built environments, the material and cultural realms are combined, withthe fast pace of the social processes (design, assessment, contracting, management) balanced by the longer-term in£uences ofbuildings and landscapes

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sense that it is completely within its control (somethingnot always true for the other four factors). In otherwords, societies can ‘choose to fail’.

Discussion on sustainable built environments is cur-rently focused on how to harmonize rates of consump-tion with constraints imposed by natural systems.4 Theimplicit assumption is that a steady-state relationship ispossible and desirable. This mind-set tends to obscurethe inevitable cycling over time of both natural andbuilt environments. It also ignores the many, diverseand increasing threats that can undermine the perform-ance of the built environment and the security of cul-tural systems. A more reasonable assumption is thatbuilt environments will encounter many differenttime cycles of collapse and renewal, and that the goalfor design and management is to achieve some degreeof security in the face of changing circumstances.From this perspective, all proposals for sustainabledesign and management may need to first be assessedin terms of their affect on future threats and vulner-ability. Is it possible to design systems that mitigatethreats, and that are inherently more capable ofwithstanding surprise and shocks?

Part of the challenge in achieving a secure builtenvironment is the scale of physical inter-dependenciesthat characterize cities and their stocks and systems in acomplex global society. Urban regions can no longer beperceived as polygons on a road map. Cities every-where are nodes connected by hierarchical, global net-works upon which they depend for critical suppliesincluding energy, food, information, consumer pro-ducts, employment and even human reproduction(Hall and Pfeiffer, 2000). The chains of resources andservices create a house of cards where one failure – acity or system collapse – can cascade (Mileti, 1999).The support systems for cities include elements oftheir ecological footprints – the productive and some-time remote areas of agriculture, forests and fisheries.How secure is a built environment if remote tradingpartners and associated ecological infrastructure aredeteriorating or facing collapse, and how can suchrisks be managed?

Traditionally the concept of disaster is based onuncontrollable external forces that impact the builtenvironment. Hence, the common term ‘natural disas-ter’. In reality, the same hazard can produce remark-able different outcomes in different locations, becausethe risk of disaster is more a function of the vulner-ability of the built environment and culture, than thephysical hazard per se (Hewitt, 1997; Spence andKelman, 2004; Spence, 2004; White, 2004; Wisneret al., 2004; Hassler, forthcoming). Lack of foresightleads to ‘unnatural’ disasters and to domino effectswhere for example logging of hillsides might provokein turn flash floods, landslides, collapse of buildings,toxic pollution and disease. The rate and cost of

urban disasters is increasing, despite years of UnitedNations effort on disaster reduction. Poverty is afactor that often leads to crowding, poor constructionand inadequate medical supplies. But such problemsare compounded by the increasing size and complexityof the built environment, and by systems that areplanned and designed without much attention to eventhe most likely changes. The future will almostcertainly be punctuated by an increasing frequencyand variety of city-based disasters and societal col-lapse. Hence, the common ‘fortress world’ scenarios,where pockets of wealth and privilege are surroundedby chaos and deprivation (Lempert et al., 2003,p. 55). In a fast changing world that is home toover 1 million towns and cities, it is likely that manysuch fortresses will play out at different times andplaces.

Economic, social and environmental threats are the‘dark-side’ or shadow threats that lie behind visionsof sustainability. Design and management of builtenvironments should be partly an exercise in preparingfor such disaster scenarios. Perhaps the theoreticalassumption should be that society and material worldare locked in a very dynamic and uncertain relation-ship, and that the road to sustainability is all about resi-liency for built environments.

One likely disaster scenario is surprise itself, or, inLinstone’s (1994, p. 325) words, the ‘surprising sur-prises’ that cast no shadow:

For complex systems, disorder is as normal asorder and everything interacts with everything.Thus the prediction capability of science andtechnology is constrained, and so, too, is ourimagination. Surprises will therefore be certainin our future.

Complexity, with its element of chaos, is double edged.It can contribute to long-term resiliency because – as isapparent in all ecological systems – the added redun-dancy and diversity provide a larger number ofoptions when the system must adapt to new conditions.At the same time the many indirect consequences ofactions become obscure, and this undermines effortsto control or predict system behaviour, and achievekey goals and targets. All well-managed systems –even those based entirely upon incentives – requiresome understanding of cause and effect relationshipsin order to ‘set the rules’. Nowadays the cause andeffect chains are many and long, and understandingkey connections often impossible. A traditional engin-eering approach – where a reasonable margin of safetyis established for each design element within a con-trolled situation – may no longer suffice. Essentiallyany surprise is assumed away. This is exactly wrongwhen designing complex systems (Lovins, 1982).

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Extended time scales and time cycles make possible agreat number of strategies which are rarely or neverconsidered by conventional teams of emergency plan-ners. More specifically, it becomes possible to designbuildings, roads, critical infrastructure systems, andinstitutional structures that are less vulnerable tofuture trends and threats. For this reason long-termthinking is fundamental to the success of mitigationstrategies and is:

by far the broadest and most potentially effectiveof all the strategies available under the currentparadigm.

(Mileti, 1999)

Ecological perspectives offer a variety of strategies forachieving resilient built environments. Adaptive man-agement or ‘active learning’ is an approach first devel-oped for resource management that assumes surpriseand failure, and thus builds in the frequent feedbackloops and experiments that help managers learn andquickly adjust. Adaptable design is an approach thatborrows techniques from ecologies to increase theflexibility, durability and shock resistance of builtenvironments. Examples from ecological theoryinclude cellular design (modularity) and compartmen-talization, redundancies, self-reliance for criticalneeds, a diversity of resource sources and supplyroutes, the use of non-hierarchical self-organizingsystems, and buffering (or creating capacity in excessof needs) (Levin, 1999; Pelling, 2003).

Foresight can help to plan succession strategies.Although rarely practised, succession planning isespecially relevant to large urban systems, since theselong-lived elements set the context for so many otherdecisions. Succession is achieved through threedynamics: facilitation, tolerance and inhibition.Urban systems at present can be likened to young eco-systems, where the energy (or nutrient) invested inprimary production of biomass exceeds the amountof energy invested in the maintenance of the system(Odum, 1983; Brugmann, 1992). In order to achievehigh growth rates, nutrient cycles are open, and theexchange of nutrients and energy between organismsin the system is very rapid. Food chains are simple,and species diversity and biochemistry diversity arelow. The lack of specialized species limits the resourceefficiency and stability.

From this ecological perspective the design challenge isto facilitate succession to a mature system where thefocus changes to system maintenance and quality,cycles become closed, the role of waste material as anutrient source becomes more important, food websor resource exchange networks become complex,diversity increases, and so does specialization of func-tion and efficiency of resource use. Information flowsplay an increasingly important role in this progression,

helping the mature system to become more cyberneticand adaptive.

Succession from young to mature ecosystems may offera meta model for 21st-century urban system design.However, in natural ecosystems the growth continuesuntil the maintenance requirements equal themaximum local energy input. For urban systemstoday the energy inputs are no longer local, and infact are mostly imported as food, fossil fuels and man-ufactured products. As Decker et al. (2000) conclude:

If modern urban systems are undergoing someform of succession, it is now at the earth systemlevel. The climax will occur when global energyresources are marginally utilised, energy flux isat a steady state, and infrastructure growth hasceased.

(p. 721)

Conclusion: complementarymethods,common challengesConventional definitions of ‘built environment’ tend toview it in isolation. In fact, the built environment onlyexists in relation to the ‘non-built’ environment, i.e. tothe ecosphere. This distinction refers to the historicallychanging dichotomy between ‘society’ and ‘nature’.

An examination of dominant themes and methods forconceptualizing the built environment suggests that itis possible to build models of the built environmentthat allow changes in social, economic and environ-mental conditions to be assessed. These models canbe used to understand better the impact of differentmanagerial and social policies at both the macro- andmicro-levels.

A combination of approaches appears to provide a suit-able method for understanding the basic physical andeconomic relationships between the built environmentand the ecosphere. In particular, it should be possibleto relate building and infrastructure descriptions,based on life cycle-oriented product models, to a multi-tude of metabolic representations, including differentflows and variable scales. A shared framework canallow many different potential users to model the mul-tiple relationships at each stage of the process and tounderstand better the dynamics of the broader system(Kohler et al., 2004). The environmental effects, andflow quantities derived from micro-modelling, can beaggregated to assess the performance of entire stocksof buildings and their associated infrastructure. Physicalflows for any built environment can be valued to deter-mine whether they satisfy a range of fixed constraintsover time. The net performance can be measured interms of combined natural, social and cultural capital.

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It can be assessed from differentiated value systems (useand non-use values, and bequest values) expressed bymaterial and immaterial criteria. While all themethods are challenged with methodological problems,it is also true that considerable progress appears to haveoccurred in that last few years, and that practical toolsmay soon emerge for use in daily practice.

At the same time, it would appear that the new per-spectives reveal the need for a broader perspective,and additional methods and models for analysingbuilt environments. Two deficiencies especially standout. Firstly, the spatial perspective is mostly absentwhen considering physical flows, even though it cansignificantly affect the types of flows and their effects.None of the information generated by currentmethods is sensitive to spatial characteristics, despitethe very significant implications. Any social–ecologicalsystem framework needs to emphasize the critical needfor integrating morphological and physiological pro-cesses within analytical methods and decision-makingprocesses.

Secondly, the temporal perspective adopted by allcurrent methods appears to be misleading andespecially inadequate. Despite the importance givento sustainable development by all professional associ-ations and also by most local governments, and themajor effort that has been given to developing LCAmethods that extend time horizons, almost no effectivemethods are available for long-term analysis of howbuilt environments relate to the ecosphere, past orfuture. No alternatives exist to economic discounting.With few exceptions, the building industry as awhole has no ability to develop forecasting and back-casting scenarios for different investment options, orto consider the likely impacts of key external forcessuch as technological development, climate change,demographics, resource scarcities, natural disasters,and globalization. It appears that simplistic conceptsof time are the single greatest obstacle at present todeveloping an effective conceptualization of the builtenvironment.

A historical analysis shows that the relation between thebuilt environment and the ecosphere has been in thecentre of scientific work long ago, and emerged out ofattempts to cope with scare resources. The universalavailability of cheap energy throughout most of the20th century has led to a nearly unlimited belief in thepossibilities of technology, and to a complete separationof economic models from the underlying physicalreality. For the past three decades, this world view is dis-integrating and a system–ecological as well as human–ecological interpretation of the present situation is nowbecoming the centre of transdisciplinary research.

Social–ecological systems thus become the basis of thepresent understanding of the complex relation between

the built environment and the ecosystem. A combi-nation of new accounting methods, including lifecycle product modelling and environmental account-ing, can be used to represent a systems perspective,where multiple-related metabolisms define the builtenvironment at varying scales. A formalized structurefor these models and subsystems is needed tocombine flow-based and capital (resource)-basedmodels for building and infrastructure stocks. Ulti-mately, such a model may presage a fundamentalchange in design practice, where a rational imperativeis the preservation of capital over time, and the satis-faction of fixed constraints. The management of thelong-term evolution of this social–ecological systemcan only be assured through appropriating ecologicalconcepts of time, including resilience-based models,and through integrating the history of nature with thehistory of human culture.

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Endnotes1In common use in the literature since the mid-1970s. The originis clearly in anthropological and behavioural studies concerningthe influence of form and space on the individual and social beha-viour (Rapoport, 1976). The concept has evolved in anthropologyand in more recent research the built environment is understoodas the result of a process of social construction (Lawrence andLow, 1990, p. 455).

2A quotation from Wikipedia (November 2007), as one typicalexample of conventional usage.

3Risk information, for example, is available from the ChemicalAccident Risk Assessment Thesaurus (CARAT; Rosenthal et al.,2003), and through European legislation on the ‘Registration,Evaluation, Authorisation and Restriction of Chemicals’(REACH, 2006).

4For example, the high-profile ICLEI (International Council forLocal Environmental Initiatives) programmes, The ZeroEnergy Development projects, and the Natural Step Commu-nities all focus on reducing ecological footprints to levels thatreflect a responsible and fair allocation of estimated globalresources.

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