A very special tree house

Architects at the University of Stuttgart not only copy constructive and functional principles from nature, they also use plants whilst they are still growing to create buildings that will become green areas in the truest sense of the word. The first large construction, a tower made from willows, is almost fully grown. Further constructions are planned in the near future.

There is a long tradition of architectural work with biological structures at the University of Stuttgart. From 1984 to 1995, the plant physiologist Prof. Dr. Ulrich Kull and the architect Frei Otto worked together on the collaborative research centre 230 (SFB 230), which targeted the development of “buildings from nature”. Ferdinand Ludwig resumed this tradition as part of his doctorate, although not in exactly the same way. Ludwig studied architecture at the University of Stuttgart where he developed an interest in living constructions using ‘designer’ plants during his initial university studies.

Ferdinand Ludwig from the "Construction Botany" workgroup at the University of Stuttgart © private

"There are examples of living constructions in all historical periods. In the Middle Ages, dance floors were built around a tree whose branches bore the weight of a wooden dancing platform," explains Ludwig.

Ludwig was so fascinated by these natural constructions that he joined the "Construction Botany" (Baubotanik) research group at the Institute for the Theory of Modern Architecture and Design (IGMA) under Prof. Dr. Gerd de Bruyn. The IGMA specifically focuses on interdisciplinary cooperation beyond the borders of architecture with the aim of combining technology, the natural sciences and the humanities. Ludwig's mentor, Gerd de Bruyn, put Ludwig in contact with Prof. Dr. Thomas Speck at the University of Freiburg. Prof. Dr. Speck works in the field of bionics, which uses nature as a model for technical constructions. "Speck became the botanical co-supervisor of my doctoral thesis and together we investigated the biomechanical properties of plant branches, shoots and stems," said Ludwig.

Creating space with topiary plants

Ludwig’s doctoral thesis focuses primarily on the construction of a three-storey tower from living white willows (Salix alba). The tower is nine metres high and has a base area of around eight square metres. At present, the tower consists mainly of a steel scaffold which supports the trees, enabling them to grow in the required way. Several hundred willow plants were grown on the ground in baskets, and once the shoots reached two metres in height, the plants were subsequently spread around the different floors of the tower.

The plant tower was constructed in cooperation with Cornelius Hackenbraucht (Neue Kunst am Ried) © Ferdinand Ludwig, University of Stuttgart

The plants are not just left to grow as they wish, but instead are trained to follow a pattern designed by Ludwig and his colleagues. The construction botanists base their constructions on long-standing knowledge. Using traditional grafting methods, the scientists have developed a way to merge the delicate branches and stems of the same species into one organism.

The objective is that the individual plants will eventually become a single organism and form a stable truss. When the living structure is solid enough to carry the load of both the steel platforms and the working load, the temporary steel scaffolding and plant containers will be removed. The willows will then spread to form a green wall; the plants on the ground will develop a strong root system that will firmly anchor the entire construction in the soil. The tower was not built on massive foundations, instead other solutions had to be found to enable the structure to bear the weight of several tons of plant baskets as well as its own weight. Ludwig's solution was screw foundations. "We used conical tubes manufactured by the company Krinner. A metal coil welded to the tubes helps to firmly anchor the ground screws into the soil," explains Ludwig.

Detailed insights: how does the plants’ metabolism react?

In order to predict the moment that the plant tower will be able to support itself, Ludwig has done numerous calculations, for example relating to the increase of the soil mass: “We believe that it will take between eight and ten years before the tower is stable enough to support itself. However, these are only estimates. We are about to carry out further research to find out more about how willows grow.” Another decisive and exciting issue relates to how the plants’ substance flows develop. Ludwig will work with botanists to find an answer to this issue.

Parallel intergrowth of a one-year old sycamore tree. © Ferdinand Ludwig, University of Stuttgart

Ludwig has recently started working with Prof. Dr. Manfred Küppers, head of the Ecophysiology workgroup at the University of Hohenheim. The researchers have submitted a joint application to the Baden-Württemberg Landesstiftung foundation in the hope of receiving the financial support required to carry out comprehensive plant physiological analyses. How do the substances flow, how can they be measured in the complex wattle and how can these flows be controlled? The researchers hope to find answers to these questions in a three-year research project that will only be possible if they receive financial support. The decision on their application is expected to be made in April 2010.

Ludwig also has plans for other projects. In cooperation with the architect and town planner Daniel Schönle, Ludwig is planning to develop a living construction with sycamore trees for the Baden-Württemberg Horticultural Show (Landesgartenschau) in 2012. "Sycamore trees are very robust and have excellent intergrowth properties. In addition they are excellently suited for use in heavily built-up areas," said Ludwig explaining the advantages of sycamore trees. Although the plans are not yet finalised, the young plants that will be used for the construction in Nagold have been purchased and are being grown by a plant cultivation company. "We are working with Helix Pflanzen GmbH in Kornwestheim. We cannot use just any plants, they have to be special, very slim and vital plants of an extreme flexibility that can be shaped according to our purposes," said Ludwig who is not yet sure what the final construction will look like. Ludwig's initial idea is to construct a spatial structure with terraces; he will come up with concrete plans over the next few months.

Plant constructions with great development potential

Ludwig is not a lone soldier in the field of construction botany; two other doctoral students at the IGMA are focusing on constructive and architectural aspects of three-dimensional living constructions. The construction botanists do not envisage replacing traditional constructions with living constructions. Their aim is to enrich the building trade and push back frontiers. Ludwig envisages that potential applications will be situated initially at the interface between landscaping and architecture. “For example, we would like to create structures with particularly broad, shady treetops which will bind particulate matter, amongst other things.”

Ludwig is aiming to change the way we perceive trees; he wants to create three-dimensional green areas in parks and building complexes. “My idea is that pedestrians will use the upper floors and cyclists will be able to use the lower areas,” said Ludwig expounding on his vision. Another of his projects focuses on using plant constructions in order to extend balconies to merge buildings with gardens. “This resembles espalier fruit, with the difference that we will also be working in the third dimension,” said the imaginative researcher.

Further information:

University of Stuttgart
Institute for the Theory of Modern Architecture and Design (IGMA)
Prof. Dr. Gerd de Bruyn
Dipl. Ing. Ferdinand Ludwig
Keplerstrasse 11
70174 Stuttgart
Tel.: +49 (0)711 685-83319 oder 0711 4084111
E-mail: ferdinand.ludwig[at]igma.uni-stuttgart.de

Website address: https://www.bio-pro.de/en/fachartikel/a-very-special-tree-house/