Plant stems as building material for living plant constructions
Ferdinand Ludwig1, Gerd de Bruyn1, Marc Thielen2, Thomas Speck2

1Research Group Baubotanik, Institute for Theory of Modern Architecture, University of Stuttgart, Germany
2Plant Biomechanics Group Freiburg, Botanic Garden, University of Freiburg, Germany


The German term 'Baubotanik' describes a kind of architecture where natural growth processes are used to create living plant constructions. In 'Baubotanik'-projects the stems of young woody plants are interconnected to an artificial tree-like construction or building. Due to secondary growth processes these in the beginning delicate structures are developing a high mechanical load capacity in the course of time. The plants used to form the initial structure have to comply physiological and especially morphological and biomechanical constraints. For constructing, the employed stems have to be bent with narrow radii and it is advantageous if they are very slender and un-branched.

In order to achieve such a stem form and structure it is investigated under which cultivation conditions plant stems that show a high degree of slenderness at an adequate length, a low Young's modulus and a high tensile strength, can be grown. As a model plant, one year old seedlings of Platanus acerifolia are used. To control the form and structure of the stems, the plants are grown under different, artificially adjusted environmental conditions in special growth chambers. As key-factors influencing form, structural and mechanical parameters of the stems in one set of parallel experiments the photosynthetic active radiation (PAR) and the relative rate of red (R) and far red (FR) radiation are altered by using light filters to filter out specific bands of the wavelength of the radiation, causing reactions of the plants know as 'shade avoidance' and 'phytochrome effect'. In a second set of parallel experiments PAR is reduced without changing the spectral composition of irradiation by using shading cloth. In another experimental series the stems are wrapped in different light-filtering films while the leaves are exposed to full sunlight. Due to the fact that only the light quality at the stem is altered different aspects of the shade avoidance reaction can be separated.

Our results show correlations between light conditions and morphological, anatomical and biomechanical characters of the examined plant stems. These correlations are yet only sparsely investigated in woody plants. For the field of 'Baubotanik' the results represent fundamental information to describe and produce the stems of woody plants as a living construction material.


Keywords: Baubotanik, shade avoidance, Platanus acerifolia