Karlsruhe Institute of Technology: Climate-resistant tree

Tree roots are attracted to moist areas of the soil, a phenomenon known as hydrotropism. Superficial watering therefore means that roots stay close to the surface instead of growing deep. Biomechanics at the Karlsruhe Institute of Technology (KIT) have developed an easy-to-use process, using the split cylinder method, with which the tree roots are lured into deeper, more humid soil layers. This should make the trees more resistant to the effects of climate change.

City and park trees, but also trees on the properties of private homeowners, are suffering more and more from drought stress due to climate change and the resulting lower rainfall. Plant roots normally grow in the direction of higher soil moisture through so-called hydrotropism. “Regular superficial watering leads to the roots being pulled towards the surface instead of deeper where they find more moisture,” explains Professor Claus Mattheck from the Biomechanics Department at the KIT Institute for Applied Materials Science. “So we have to give the roots an incentive to grow downwards.” More modern irrigation methods bring water into the deeper soil layers with vertically inserted pipes, thus luring roots down where the soil does not dry out so quickly.

With gravel against drought

With the split cylinder method now developed at KIT, street trees in the city, existing trees in parks or in the home garden could better arm themselves against drought with a simple process. The basis for this is a mixture of coarse grit and terra preta, a fertile black soil originally from the Amazon region. This mixture should be introduced as deep as possible into the earth, for example by drilling a 20 to 30 centimeter wide hole.

“We assume that the roots of the trees will be attracted by the well-ventilated, terra preta-enriched gravel column, which is barely compressible by traffic vibrations, and will increasingly root through it,” says Mattheck, describing the aim of the process. Experiments with maize plants confirm this hypothesis. Studies on trees are ongoing at several locations.

The idea of ​​using Terra preta as a fertilizer here came from Siegfried Fink, Professor of Forest Botany at the University of Freiburg, who did research in the Amazon.

Now the deeper soil layers are usually a little more humid and thus attract the roots. “If the root density in the lower end of the split cylinder becomes too high, it is to be expected that the roots will spread in this deep and moister soil layer outside the given cylinder. Permanent irrigation is then no longer necessary, ”says Mattheck. In the greater depths, the roots find more water even in drought.

“For the trees, the split cylinder is, so to speak, a feeding place and root dipping station in one and thus a help for self-help,” says the scientist, satisfied with the new process. “But the rooting of the split cylinders takes some time and therefore the tree lover needs patience.” However, clay soils are unsuitable for this method, because heavy rain would cause them to run full of water and suffocate the roots.