Nature wants people to perceive trees

How do the trees know that autumn is coming?

It's about life and death. Like every autumn. When oaks blush, the maple turns yellow and the next gust of wind blows the last leaves from the trees. “As the temperatures drop, trees begin to draw all usable nutrients from their leaves and store them. The chlorophyll, which makes the leaves appear green to us, is first broken down, and the red and yellow colorings of the leaves become visible, ”explains forest policy officer Stefan Adler from the Naturschutzbund Deutschland (NABU).

Ultimately, the tree eats the usable components of its leaves, because it needs “strength” to survive the winter and does not want to “give anything away”. When all the nutrients in the leaf are used up, a kind of bark forms between the leaf base and the branch to protect the tree from frost. If a wind now comes up, the leaf is separated from the branch at this point. However, there are also cold periods in summer. The trees don't shed their leaves. Besides the air temperature, what shows the trees that it is autumn now?

"A second important factor that shows the trees that autumn is coming is the length of the day," says Stefan Adler. So plants can actually sense how long the days and nights are in relation to one another. Strictly speaking, the length of the dark period, i.e. the night, is the decisive factor. The trees measure the length of the night using special proteins in their leaves, which perceive dark red light. Ultimately, this is how deciduous trees ensure their survival. Because if they had leaves in winter too, sooner or later they would dry up. Why? Trees evaporate much of the water that the roots take in through their leaves. In winter they cannot stay in this “evaporation mode” because the water freezes in the ground.

Conifers, on the other hand, cannot even be chased into the fenugreek in autumn. They are evergreen and do not shed their needles, because these are equipped with an insulating layer of wax that protects them from the cold and can store the water inside.