Three young German architects are designing structures made completely out of living trees, including a pavilion for concerts in downtown Stuttgart. But designing the ultimate treehouse turns out to be trickier than one might expect.
By Philip Bethge
Ferdinand Ludwig grows trees on trees. That’s what he does. And he has grafted together — trunk to top, top to trunk — seven young willow trees
At the moment a scaffold supports the young architect’s unusual tree tower. The roots of individual trees protrude sideways and into containers of soil. But soon the roots will be cut off. And “at that point,” the young architect says, “the trees will finally have merged into a single organism.”
Ludwig calls this technique “plant addition.” To do it, he uses one-year-old willows that are thin and flexible but at least 10 meters (33 feet) long. Once the willows have matured to full strength, the strands will be able to support the eight-meter (26-foot) tower that Ludwig plans to begin building near Lake Constance in southern Germany at the end of July, as though they were steel beams.
This is probably the biggest project to date within an innovative branch of architecture — no pun intended. Ludwig and fellow architects, Oliver Storz and Hannes Schwertfeger, call their new specialty “building botany.” As part of this the three men are building structures made from plants as well as studying the elasticity of plane trees and examining how effectively willows can grow around steel pipes at the University of Stuttgart’s Institute of Basics in Modern Architectural Design.
“In our opinion trees are high-tech material, which is why plant growth is part of our vision,” says Schwertfeger. “We start them off but the tree itself continues the building process,” Ludwig adds. “In architectural terms it’s very risky — but it’s a positive risk.”
Training trees to grow in all manner of decorative shapes is not new, it has been part of the skilled landscape gardener’s repertoire since the 13th century. And companies like the Israeli firm, Plantware, have perfected these techniques as they have shaped trees into fruit bowls, toilet paper holders and street lamps; they call their work “arborsculpture.” Now Stuttgart’s architectural rebels are taking the concept a step further. They consider the trees to be building materials similar to steel and concrete.
“The basic rule is this: All forces pass through the wood, from top to bottom,” Schwertfeger explains. And the trio has already built their first structures. For example on Lake Constance where a group of willows surround a metal walkway. And in the Bavarian Forest, trees form a “diagonal support frame” for a bird watching station. And now the pioneers are planning to build a “green room” in downtown Stuttgart. The project, dubbed “Satellite,” will consist of a 120-square-meter (1,290-square-foot) pavilion for exhibitions and concerts.
The basis of their work is always the same. First, the architects build a conventional support structure. Young, flexible trees are attached to the structure and bent into the desired shape. As the trees grow, they take on more and more of a load-bearing function. After a few years — and what Ludwig calls a “botanical certificate of fitness” inspection by a structural engineer — the support structure can be removed. At which point the roof and floors that have been inserted should be supported entirely by the trees.
But that’s not quite as easy as it sounds. For instance, there is the “risk of strangulation” if metal fasteners obstruct the flow of sap. The architects have already had to tack on “sap bypasses” made from branches to keep their botanical building material alive. In addition, just like an ornamental garden, a tree structure requires meticulous maintenance. “Or else everything turns back into shrubbery,” Ludwig says.
The architects are developing these methods on grounds belonging to a cultural association in northern Stuttgart. At the site, Ludwig is trying to figure out how best to “weld together” different trees while Storz tests the strength of basket willows. Two hundred trees are lined up in a straight row inside scaffolding that has concrete weights hanging from it. Four times a day, a system of computer-controlled winches use the weights to rock the trees back and forth in an elaborate pattern.
‘A Tree Doesn’t Want to Become a Wall’
The tree-bending experiment is designed to solve a problem that the botany builders didn’t expect. They noticed that when trees were attached to a frame, they no longer seemed to have any reason to develop their own strength. However, the stresses of being bent this way, with the concrete weights, artificially stimulates growth and improves stability.
“We have to subject ourselves to the tree’s own structural rules,” says Storz. For instance, trees are incapable of forming two-dimensional structures. “A tree doesn’t want to become a wall,” Ludwig adds.
In other words, anyone who expects your everyday residential structure or functional building from these builders of the botanical will be disappointed. But it is precisely this divergence from classic architecture that fascinates the Stuttgart architects.
The technique creates structures “that change quite considerably, that require one to adapt. Their uses change constantly too,” says Schwertfeger. “Each structure is a blend of fiction and reality,” notes the doctoral candidate, quickly adding that: “In our case, the fiction component is relatively high.”
Unfortunately, everyday reality keeps catching up with this fascinating, abstract theory. One example: for the past few weeks Ludwig has had a problem that someone embarking on a career in building with trees can certainly do without. He has somehow developed an allergy to plane trees.
Translated from the German by Christopher Sultan