Why are trees shedding their leaves now?
Created: 08/17/2022, 06:00
By: Franziska Kaindl
As early as August, many trees are losing their leaves and fruit.
Some gardens look as if autumn has already arrived.
Why is that?
Anyone who currently takes a look at the garden will not see much greenery, depending on the region.
The grass is yellow and dried up, and some of the trees have been shedding their first leaves since the end of July.
For some, it may seem like it's already October.
But where does this phenomenon come from and can something be done about it?
Heat and drought force trees to shed ballast
Even if it may appear so at first glance: the current behavior of the trees has nothing to do with the fall of leaves in autumn.
In fact, it is an acute reaction to the drought stress that nature is exposed to during a long period of heat, as
BR
reports.
What exactly is happening?
The leaves evaporate water and absorb CO₂ through small stomata on the underside.
At the same time, water is absorbed through the tree roots, which is distributed throughout the tree right down to the leaves - there it is an important part of photosynthesis, during which the absorbed CO₂ is bound.
Due to the drought, however, the trees lack water, which is absorbed through the plant roots.
The trees close their stomata in the afternoon to save water.
If the water supply finally fails completely, "the trees close the stomata completely to prevent further evaporation," says Lothar Zimmermann from the Bavarian State Institute for Forestry and Forestry, according to BR.
On the other hand, photosynthesis can no longer be carried out.
To survive,
Burnt foliage after exposure to direct sunlight during a heat wave and drought.
© Gottfried Czepluch/Imago
Are the trees recovering from the hot summer?
If trees already lose their leaves in summer, this can weaken the vitality of the trees, as the Freiburg forest scientist Rita Silva explains according to the German Press Agency.
According to Lothar Zimmermann, however, this depends on the severity of the damage.
Most of the time, trees would react the next year with fewer and smaller leaves and put more energy into the deep growth of the roots - so that they can absorb more water later.
According to studies by Henrik Hartmann from the Max Planck Institute for Biogeochemistry in Jena and international colleagues, trees die when the water conductivity of the trees falls below 40 percent.
This means that more than half of the tree's vascular tissue is too weak to transport the water from the ground up into all corners of the tree.
How much water do trees need to protect them from dying of thirst?
"Every drop that you bring to the roots is better than nothing," says Klaus Körber from the State Institute for Viticulture and Horticulture in Veitshöchheim, according to BR.
“But that can also be 200 liters.
A bucket is usually of little use.” When watering, the principle “rarely but plentifully” is best, especially with younger trees.
Because then the water would seep into deeper layers of soil and encourage the plants to root deeper.