The tree canopy as blueprint

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As the opportunities for new territories become more limited, the only way is up. Mitchell Schwarzer explores the dizzying heights of the ‘last biotic frontier of arboreal architecture with its high platforms, walkways and canopy craft. Challenging in construction and engineering terms, the tree canopy also requires engaging with a different atmospheric and climatic range to those conditions encountered at ground level.

Imagine a time in the not so distant future when cities resemble the forest tree canopy. Oil has run out. Coal has been banned. Greenhouse emissions have so overheated the planet that surface temperatures in temperate latitudes match those of the tropics. The seas have risen. To escape the torrid inundation, society migrates skyward. Structures are reinforced. Additions pile up.

Cantilevers strut into gaps. The rich claim the city’s overstorey, safely beneath the blazing crown where roof gardens suck in sunlight and moisture, and energy farms harvest the winds and solar radiation. Below the wealthy the middle classes reside midcanopy in a cooler, shadier, if less productive environment. On the lowest floors, their litter becomes the housing medium for the poor, the dark scabbard of scavengers.

For much of modern history the drone of a machine sounded sweet no matter what its effect on nature. No longer. Given widespread evidence that proliferating machines are engineering global warming and as massive species die off, architecture, often self-professed as a machine for living, faces a challenge. Practically every past architectural revolution sprang from the invention of construction technologies intended to advance societal transformations. The environment, from quarried stone to iron ore, was something to be used and abused for the betterment of humans. While many architects have responded to the current environmental crisis by touting green building technologies and sustainable development practices, it is worth asking whether we can build our way out of this predicament. Can the old stand-bys, better building machines, be the solution? Or do we need to contemplate a new blueprint for design?

Within the last years one such blueprint has been grasped at by research in architecture and science that seeks insights from the forest tree canopy. Less understood than other terrestrial environments, the tree canopy has been described as the ‘last biotic frontier’. Because of its richness of life, scientists are avidly seeking out its secrets. As they have sought to gain a footing in the trees they have engaged architecture: literally, in the construction of high platforms, walkways and canopy craft; and metaphorically, through the ideas and associations the canopy provokes for rethinking the construction of human environs insulated from atmospheric variations in sunlight, temperature, rainfall and humidity.

In the tree canopy, change occurs within a set of parameters, many of which are understandable to an architect. Like a building, a tree canopy consists of structure, space and meteorological/luminary conditions. Its crown, the atmospheric interface, appears from the sky as a topography of ridges and ravines. Its understorey, the vast area beneath the crown, demonstrates an increase in morphological size and complexity as one descends. But whereas a building’s systems are programmed to operate steadily for their human occupants, the tree canopy grows and changes its internal conditions in response to ongoing biotic and atmospheric fluctuations. The high zones of the tree canopy that seem upon first glance to be more precarious – small twigs that cannot support much weight – and less commodious, subject to intensive fluctuations of sunlight, temperature and moisture, sustain copious life.

In 1981, entomologist Terry Erwin’s research on beetles in the Panamanian tree canopy launched a species rush. Erwin found so many new species he extrapolated that the number of potential species on the planet was not somewhere between three and five million as previously thought, but rather closer to 30 million. A fantastic percentage of the earth’s biodiversity occurred just below the location in the crown where sunlight was transformed into plant material. Comprehensive study was called for. How did the canopy’s microclimates – caused by variations of temperature and humidity, rainfall and solar radiation – influence species diversity and creation? How did spatial patterns on light transmittance within the canopy’s strata impact plant growth?

Historically, most scientific knowledge of the forest’s upper reaches was gleaned from leaf litter, faunal droppings and fallen branches found on the floor below. A few intrepid scientists climbed freehand into the canopy to obtain living samples. Some researchers, wary of the shaky, unstable altitudes, sent up macaque monkeys as collectors. Others brought the ecosystem down to earth, chainsawing trees to study the otherwise inaccessible branches, twigs and leaves. After Erwin’s tantalising projections, scientists needed to conduct more extensive work in the canopy’s varied strata: the overstorey of crowns fully illuminated from above; the midcanopy of transition from light to shadow; the understorey of the lowest shady layers.

The simplest structures were assemblages of ladders, ropes and pulleys fixed by iron rods to trees. They were effective for moving scientists upwards, but insufficient for bringing down collected items. A better approach was to lift scientists into the canopy on hydraulic cranes or cherry pickers. But since such cranes functioned best at the edge of a forest, new types of towers – resembling those stanchions used for skyscraper window cleaning – had to be devised. Instead of moving diagonally, they could be raised vertically. Once within the chosen area of the tree canopy their long arms could be extended horizontally to afford a peek and grab at arboreal animals and insects, epiphytes (plants living on other plants) and lianas (or vines), and the morphology of tree and leaf.

Yet another idea was to approach the canopy from above. In 1987, tropical botanist Francis Halle, architect Gilles Ebersolt, and Dany Cleyet-Marrel, a hot-air balloonist, unveiled Le Radeau des Cimes (the Raft of the Tree Crowns). Manoeuvered to any site by a hot-air balloon, a frame of inflatable rubber pontoons supported a synthetic-fibre structure that could gently rest atop the canopy crown without disturbing the vegetation. Ebersolt developed several variations of the structure, including the Solvin Bretzel used to study the canopy of rainforests in French Guyana. In the early 2000s, Ebersolt came up with the similar yet more durable Ikos Flexible Research Station, a 20-sided sphere (icosahedron) that hangs lightly from the branches accommodating three scientists for up to five days.

Not only was this cheaper than fixed crane structures; the station also focused attention on the least understood and most productive zone of the canopy – the top landscape composed of a bushy vegetation of small leafy twigs. Resembling a contraption from a Hollywood adventure flick, the mobile qualities of the Ikos station also recall the plug-in craft designed by Archigram and the Metabolists during the 1960s. But this lightweight, winged version is more elastic, flexible and adaptable to a variety of situations or sockets.

Scientific discoveries in the tree canopy stimulated efforts to take the general public up to the high climes. Endeavours of this kind have generated a new subset of building – canopy towers or walkways. In 1987, the first tree walkway in the world was opened to the public at Australia’s Lamington National Park. In the years since, such arboreal high-wire acts have become a popular attraction at national and botanical parks – no doubt in part to inject a bit of dazzle into the public’s experience of trees. In 2008, the Treetop Walkway and Rhizotron opened at the Royal Botanic Gardens at Kew, outside London. A circuit of 18-metre (59-foot) steel pylons support a 200-metre (656- foot) oval path set into a forest of chestnut, plane and oak trees. Designed by Marks Barfield Architects, the weathered steel structure seeks to blend into the forest; pylons arc gracefully like tree trunks and likewise branch, this time as supports, beneath the walkway.

A visit to the Treetop Walkway and Rhizotron begins underground in darkness and ascends to bright views of London that alternate with the confines of tree canopies. Its goal is to elevate the public into natural worlds (of leaves, epiphytes, lianas, butterflies, insects, birds and small mammals) they have rarely, if ever, encountered before and to allow them to experience the strikingly different atmospheric effects – like the decrease of shade and humidity – one experiences in the upper crown. This didactic encounter with ‘wild nature’ occurs in a forest planted by the 18th-century landscape designer Capability Brown. In his day, Brown revolutionised garden design by turning from rigid, geometric plans modelled on French palace gardens to those undulating curves, inclines and irregularities of the British countryside. A couple of centuries later, canopy architects went beyond these pleasantly spaced and picturesque vistas, and cast visitors into the claustrophobic, mysterious boughs of the tree canopy. Yet truly, this 21st-century ecological journey to a nature unknown harkens back to the spirit of 18thcentury Romanticism; for it was in those days that adventurers sought inspiration for original creation in the otherworldly terrain of underground caverns and glacial peaks. Then, as now, the modern spirit finds nature most tantalising when in the throes of discovery.

Most treetop stations provide a neutral vantage point to view the trees. Most seek to disguise their architecture within that of the forest. In 2009, SeARCH took a different approach, merging perceptual conditions with those of the environment being perceived. The Bostoren, or forest tower, is a futuristic structure set within an arboretum on the Schovenhorst Estate in Putten, the Netherlands. Rather than a promenade about the high canopy, a single steel-truss structure supports a winding path up through a sequence of viewing platforms – branching towards the tree canopy’s various strata. On one station, visitors look out through a wooden lattice that resembles a bird’s nest.

Upon reaching the top circular platform, they will be faced, when the trees grow, with a planted forest that filters their view of the tree canopy’s crown. While walking skyward, a shiny copper plate at the bottom of the top platform reflects both the structure and surrounding woods, confusing artificial and organic. SeARCH’s tower does not imitate the appearance of the forest and forthrightly asserts its formal presence. The correspondence with the environment occurs via perception, in that the built structure borrows from the tangled and sometimes glistening (when one sees leaves freshly coated with precipitation) world of the canopy to complicate and enrich vision. The mystery of visiting an alien world thus boomerangs back to one’s own senses and the architectural armature through which they expand.

Walkways that weave into the canopy cause one to ponder the ways in which architecture crosses paths with trees. Usually when trees on a building site are preserved or planted, considerations revolve around their ability to enhance views or provide shade. Of late, environmentalists stress the benefits of shade for reducing indoor temperatures, on leaves for capturing and storing carbon dioxide, and on roots for harvesting storm runoff. The results, alas, remain similar. Trees enhance building, but such improvements in architecture’s rapport with nature do not go far enough in a time of escalating environmental collapse.

Most engagements of building and tree still tend towards obliteration – the use of bulldozers, chainsaws, lawnmowers and pesticides to create a cordon sanitaire between architecture and wild nature. In 1993, Roche DSV & Sie – now R&Sie(n) – reversed the line of attack and proposed strangling a house with trees in the Compiègne Forest outside Paris. House in the Trees envisioned a plastic-walled dwelling raised on steel piloti above 15 saplings. Instead of clearing the ground and disturbing the site, the architects elevated the building above it. Instead of surrounding the building with docile nature, they created circumstances where the trunks and branches would grow, contort themselves around the house, punch into walls, block doors and warp floors. The project posed a vivid metaphor for how worldwide construction relentlessly destroys forest habitats.

As a means for understanding how building might engage the ecology of the forest, however, it fell short; the architect’s design of nature’s ways determines the course of disturbance. Learning from the forest has not come easily to architects. Architecture’s Urform (its primal form), the primitive hut, epitomises what happens when architects consider trees philosophically. Seeking a basis for architecture in nature before recorded history, 18th-century theorist Marc-Antoine Laugier noted the resemblance of columns to tree trunks and roof gables to leaf-covered boughs. The resemblances were hammered into a Neoclassical design logic (of the post and lintel and pediment) in which arboreal elements were abstracted and ossified. In the 21st century, increased exposure to the ecology of the tree canopy has shown architects how its biodiversity results from myriad interactions of energy, material and organic life, but has not changed the way they tend to regard natural phenomena as formal models. In the project Holiday House on a Farm (2002), AMID (cero9) scattered the rooms of a house within a small forest, subjecting them to intensified atmospheric conditions. Given that the residential shapes resemble clouds resting amid the tree canopy, one wonders whether the primary design aim was interaction within an ecological system or the fashioning of a tantalising message/image.

More than most architects, Philippe Rahm has tried to shift attention from form to atmosphere, arguing that Modernism’s asymmetrical buildings contain within paradoxically symmetrical thermal atmospheres deadening to the senses.

Rahm advocates architecture ‘open to meteorological permutations and the passage of time, to seasonal changes, to the alternation of night and day and moreover to the sudden appearance of unanticipated functions and forms. To this extent, he builds from Le Corbusier’s insight of architecture as the ‘play of masses brought together in light’ into a design approach where the play of building volumes is felt within heat distribution. His critique of architecture’s drift towards vision, to the neglect of the other senses – in particular, the haptic and olfactory – starts to map out how architecture might better engage ecologies like the tree canopy.

Once it was a given that the forest provided woodland societies with a site and materials for building as well as a source of symbols linking back to nature. Nowadays, led by scientists and environmentalists, postindustrial societies are learning once more from the forest. Hopefully, the increasing role of architecture in structuring the ascent of the tree canopy will encourage architects to extend experiments beyond recent environmental projects in which trees and other natural elements appear as instrumental features, invasive elements or mere ornaments.

Time spent in the forest canopy confronts us with perspectives impossible within the media din of architectural culture, where each building endeavour flails its forms for our attention. Rising up from the forest floor we are pulled away from a sense of this tree or that tree, this shape or that shape. Above us are trunks surging to heights out of sight. Around us are branches angling out (and usually upwards) into an indistinguishable net. Sometimes the spread of foliage hovers overhead in a thick unified layer. Other times, especially during the climb into the canopy, we find ourselves passing, as in an arcade, through separate strata of leaves. For the birds, small mammals and innumerable insects up could just as easily be down. High twigs leap towards the bright yonder atop the crown; inside they are practically outside. Below in the understorey biotic communities content themselves in the moist shade; outdoors in this penumbra they are somehow indoors. The hard line between life and death in modern human society softens.

Detritus accumulates on the flatter surfaces and it is plain to see that dead trees stand for decades decaying – death not consigned beneath the ground or sawed and varnished into the building, but active within the living forest, and sustaining of it. Off the ground we forsake our grassland viewpoint of underworld, surface and heaven for a space tangled up in parallax. Like our simian ancestors we scramble on a path whose sky is rich in soil, the air dank with humus that reeks sweet and foul. No horizon line or long vista guides us. Sightlines peel into peripheries that seem to search, like shoots and stems, for spaces of illumination. Where hierarchies, geometries and visibilities change, so too can mentalities. The tree canopy indicates a blueprint for design where plan is not drawn into a closed system or on a blank sheet, but rather set lightly into a living environment, where elevation does not lose face, and where section, instead of gobbling up space, realises that architectural design must be imposed into nature in a manner sustaining of each.

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