Force of nature: as the world confronts the current environmental crisis, landscape design assumes a new evangelising power.

What price the natural world? A mature plane tree in London's Berkeley Square was recently 'valued' at [pounds sterling]750 000, making it the most expensive specimen in the city. Factors in the calculation of its worth included age (it dates from the nineteenth century), size, location, condition and importance in the landscape ensemble of the square. Ascribing a monetary value to a tree as an estate agent would to a house might seem absurd, but it makes the point that the historic presence of nature, especially in cities, is precious. And if putting a price tag on it is the only way to bring this truth home to landowners, developers and councils, all shiftily eyeing their chainsaws, then perhaps it does not seem so unhinged.

Yet in a saga that echoes the wider despoiling of the global environment, trees in London are under increasing assault. Estimates suggest that over 40 000 were culled in the last five years. Shockingly, nearly half of those were consigned to municipal woodchippers by an implacable alliance of insurance agents spooked by subsidence claims and pettifogging borough councils that see leaves as a public nuisance and branches as a potential liability. Depressingly such attitudes have come to epitomise the current strained relationship between humankind and the natural world. Now; for the first time in history more people live in towns than in the countryside, and this has fuelled a general sense of alienation towards nature. The passive neglect and active destruction of the environment can be seen as being indirectly linked to this sense of detachment and anomie. If people lose touch with nature, they no longer acknowledge its importance or care about, its fate.

Yet as history shows, the consequences of environmental degradation can topple civilisations. As Peter Buchanan points out, (1) the fertile crescent of Mesopotamia withered to a desert as salts leached by irrigation sterilised its once abundant fields. Imperial Rome's North African breadbasket turned into the Sahara, Spain's rainfall was reduced by the rapacious felling of its forests to build ships, while in ancient Greece, overgrazing and olive roots destroyed its soil. At the time, such catastrophes were geographically limited, so their effects were contained, but the current environmental crisis is of well documented global proportions. From pole to melting pole it impacts upon and implicates both the developed and developing worlds.

The rise of ecological awareness and environmentalism has put landscape, and our responses to it, squarely back centre stage. Reclaimed from the margins of watercolour feyness, it is now an effective and evangelising force. Landscape has always figured prominently in human cultural imagination, oscillating between a real place and the representation of it as promulgated by artists and writers. Yet throughout history the appropriation of land and the taming of landscape-for agriculture, building, hunting, recreation, waste disposal, or manicured just-so for the gentry's pleasure-has been motivated by ideology. Power, money and politics have always trailed in its wake, so it's a tough call to try to wrest it back for some nebulous greater good. How then, might ideas about landscape become a force for reconciliation and progress in these dislocated times?

Landscape has traditionally designated terrain that is not urbanised, but this convention is being rapidly usurped, as the city becomes understood as an ecosystem in its own right and the countryside falls prey to corruption and delinquency. Neither could exist without the other and an understanding of their symbiotic dependence chisels away at the simplistic polarity of the urban and the rural. Today, with the environment imperilled, traditional canons of scenic beauty are being rewritten. Ecology now coexists with engineering and moral meaning-has assumed renewed significance. This has implications for cities as well as the countryside. As James Corner observes, there is now 'a deep concern with landscape's conceptual scope; with its capacity to theorize sites, territories, ecosystems, networks and infrastructures and to organize larger urban fields. In particular, thematics of organization, dynamic interaction, ecology and technique point to a looser, emergent urbanism more akin to the real complexity' of cities and offering an alternative to the rigid mechanisms of central planning'. (2) The complexity of the metabolism that drives the modern city demands a conflation of professional disciplines into a new synthetic art capable of addressing the challenges of the urban ecosystem with critical insight and imaginative depth. This new and evolving field of landscape urbanism breaks down the traditional rigid disciplines of the architect, planner and landscape architect in favour of a more fluid, hybrid form of collaboration and practice. The outcome of such collaborations suggests new approaches to the integration of landscape and buildings. Beyond their civic roles, spaces such as parks, esplanades, gardens and green ways can also function as important ecological vessels and pathways, creating and sustaining a healthy urban infrastructure. Rather than being sell-contained and self-satisfied interventions surrounded by a flimsy veil of 'landscaping', buildings can be re-conceived as part of a much wider' urban ecology, or become the landscape itself, as witnessed by the topographic experiments of Foreign Office, Diller and Scofidio, MVRDV el at. In this issue, for instance, Renzo Piano transforms the huge roof of the California Academy of Sciences (p32) into a living, thriving plot of the local flora and fauna. In Hamburg, EMBT nimbly implant spaces and weave linkages on the former tabula rasa of the city's rotting docklands (p42). And in Venice, Gustafson Porter reclaim an abandoned and overgrown site in the outer reaches of the Arsenale and transmute it into an allegorical quest for paradise and enlightenment (p54).

So more than ever, landscape has a role to play in shaping the future of human civilisation, mediating between place and modernity nature and artifice, permanence and transience. As Kenneth Frampton concludes: 'The dystopia of the megalopolis is already an irreversible historical fact: it has long since installed a new life, not to say a new nature ... I would submit that instead we need to conceive of a remedial landscape that is capable of playing a critical and compensatory role in relation to the ongoing destructive commodification of our man-made world'. (3) Every surface of the earth contains the possibility of manipulation by human hand, so the potential clearly exists for a new generation of landscape practitioners to investigate, challenge, reinvigoratc and reconfigure existing realities and to act as a transformative resistance against the forces of environmental homogenisation and degradation. And you thought it was just about trees.

(1.) Essay by Peter Buchanan 'Imitation to the Dance: Sustainability and the Expanded Realm of Design' from Nature, Landscape and Building for Sustainability, edited by William S. Saunders. Minneapolis: University of Minnesota Press. 2008. p114.

(2.) Essay by James Corner 'Terra Fluxus', from The Landscape Urbanism Reader, edited by (Charles Waldheim, New York: Princeton University Press, 2006. p23.

(3.) 'Towards an Urban Landscape', Columbia Documents no 4, 1994. pp83-93.