Technology against drought stress in trees

When scientists from different disciplines get together, something sensible can come out of it. This is especially good news when it comes to an emergency such as that caused by climate change. Because the patient’s situation is obvious, he is doing badly. A look at the trees shows that they are marked by drought stress in many locations. Or the latest storm has laid them flat because the roots cannot find a hold in the dried out soil. That left the physics professor Claus Mattheck from the Karlsruhe Institute of Technology (KIT) in no time. The bionics pioneer, who has received many awards and an expert on the mechanics and fracture behavior of trees, teamed up with a handful of like-minded people from the fields of mechanical engineering, biology and forestry and thought of solutions.

Lukas Weber

Editor in the “Technology and Engine” section.

What the experts have now presented as the result of their research is, like many good ideas, so obvious that one has to ask oneself why no one has thought of it yet. It is a method that is easy to implement, even for the layperson, to help individual trees in parks, cities or on the avenue. The effort is manageable, but it is not suitable for the quantities in the forest.

In essence, it’s about showing the roots how to get water. Every owner of a house in an area with heavy vegetation who has already had to deal with the renovation of his sewer pipes knows this: The roots of the plants are drawn to where it is moist and nutritious, if necessary they squeeze through the smallest crack and settle the cross-section increases over time. In doing so, they develop considerable strength, roots are able to blow up walls and lift stone slabs. And they are tensile, with a root four centimeters in diameter you can lift two elephants, says Mattheck. If the tree is knocked over by the storm, it is usually because the earth and stones have been torn out with it.

Inconspicuous: the hole filled with split and Inca earth is hardly visible.

Inconspicuous: the hole filled with split and Inca earth is hardly visible.

Image: KIT

A lot of moisture near the surface, for example through constant watering, tempts the plant not to go deep, which is undesirable with a view to the anchoring. Instead, the scientists’ solution is to show the roots the way down, to where the soil is still moist during drought. This also works for species that naturally have rather shallow roots. For this purpose, a hole 20 to 30 centimeters in diameter is made next to the tree with an auger. This entry gate for rain and air is as deep as possible that the dry layer is pierced, the moist earth then still sticks to the drill when it is pulled out. It is filled with a mixture of split and Inca earth (terra preta).

As tests at the Karlsruhe Institute have shown, a grain size of 20 to 40 millimeters is ideal, as this is where the roots can best anchor themselves. In addition, there is about enough Inca soil that the cavities between the stones are just filled, which prevents sagging. Then it is poured on several times. Inca soil consists for the most part of biochar, which is porous and can therefore absorb a lot of water, and it also contains nutrient-rich components. The coal can be produced from organic material such as green waste, straw or grain husks using modern pyrolysis processes.

Cartoon: Science in a loose package

Cartoon: Science in a loose package

Photo: C. Mattheck

When the nutrients are used up after a few years, the Inca soil can be recharged. As soon as the roots have penetrated the cylinder, they grow further down where the earth is more humid, which is also desirable in terms of firmness. Experiments at the institute with maize show that the method works. There are also first attempts with large trees, long-term experience is of course still lacking. In places where the soil is already very permeable to water, the split cylinder is of no use, and even in the opposite case the possibilities of use are limited, for example if the cylinder overflows in the clay soil, the roots can suffocate.

Where is the best place to make the hole? This requires knowledge of the underground growth of the trees, because the split cylinder should seduce the fine roots and not cut the anchoring of the tree. We are looking for the edge of the root plate, which is roughly in the eaves area. Several cylinders per tree are possible, but one can also supply two trees, it is attached between them and rooted through by both of them. This method can not only restore old trees, it can also be used for new plantings. The authors suggest placing the young tree on split stilts over several cylinders in the planting hole.

The best way to create the split cylinders can be found in the book “Climate-proof tree?” With many other information on the subject, in which, under Mattheck’s leadership, science is packaged in humorous presentations. It is available in electronic form for around 10 euros on Amazon.


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