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Expert explains

That’s why birch bark is white

Birch trees can be recognized from afar by their striking white bark
Birch trees can be recognized from afar by their striking white bark Photo: Getty Images

October 10, 2024, 10:46 am | Read time: 3 minutes

Nature can sometimes be quite clever. Some plants defend themselves against predators with spines or scents, or they form runners to ensure their survival and spread. But why does a birch actually have white bark? myHOMEBOOK asked Sebastian Mühlemann from Bauer Baumschulen AG.

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You can sometimes see trees painted white along streets and avenues. There is a reason for this. Birch trees can also be recognized from afar thanks to their characteristic coloring. But why is birch bark actually white? It’s for the same reason that avenue trees are painted white.

Why birches are white

Birch trees developed the white bark to compensate for temperature fluctuations, explains Sebastian Mühlemann from Bauer Baumschulen AG. “Especially in winter, when the sun shines on the trunks, the trunks heat up less. The temperature is lower due to the reflection.”

A low temperature in winter is necessary to set certain processes in motion, explains the expert: “Below minus five degrees, the trees begin to build sugar complexes into their cell walls in order to survive longer periods of frost. The cell membranes are thereby compacted, and water can no longer pass back and forth. Above this temperature mark, the water in the stems is reasonably mobile and can still supply the cells sufficiently. However, this also means that the cells should remain cool during longer periods of frost to prevent them from drying out.”

But the white color of birch trees, which is called betulin, has even more advantages: “It has a water-repellent effect. This means that less water can adhere to the trunks, which would freeze and cause frost damage. During frost hardening, woody plants transport the water to the inside of the trunk to prevent this frost in the cells. Expansion due to freezing would destroy the cells,” explains Mühlemann. In addition, the white color on the birch tree is a protection against pests, as it has an antibacterial effect.

More on the topic

Why don’t all trees have white bark?

Mühlemann describes birches as “pioneer trees”. This means that they are usually the first of their kind to live in unprotected places. “They grow comparatively quickly but also age quickly and then make way for slower-growing woody plants,” explains the expert. They are, therefore, exposed to the weather and sunlight without protection.

However, rapid growth also has disadvantages: “Rapid growth also means losses. Creating fast cells means having to sacrifice resistance. Birch trees have a few damaging fungi, such as hallimash or birch spores, which require felling if they can multiply in the birch tree.”

The tree cannot defend itself against the fungal infestation as it has not specialized in it. “The bark helps to protect it a little from this danger. Other woody plants, on the other hand, can form very dense cells through slow growth and thus partially evade decomposition.”

This article is a machine translation of the original German version of MYHOMEBOOK and has been reviewed for accuracy and quality by a native speaker. For feedback, please contact us at info@petbook.de.

Topics Trees
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