Numerous older trees, not only in gardens and green spaces, are densely overgrown with lichens. In the following article we will clarify why they settle and whether this is harmful to the tree. You will also find out whether you need to take action against this collective of fungi and algae to protect the tree.
Is lichen infestation on trees harmful?
Lichen infestation on trees is not harmful because they only settle on the bark and do not penetrate into the interior of the tree. They provide themselves with nutrients and offer protection from other fungi and bacteria as well as shelter for useful small animals.
How do lichens form?
Lichens are among the longest-lived creatures on earth. They can live for several hundred years, and in exceptional cases even over a thousand years. Strictly speaking, these plants are not plants, but rather a community of algae and fungi.
The fungus that absorbs water and minerals from the environment and forms the body of the lichen cannot carry out photosynthesis on its own. The algae, which itself cannot absorb moisture or nutrients, is able to do this and produces vital sugars during this process. The fungus also offers the alga protection against drying out and mechanical damage.
Causes of lichen growth
Tree lichens, of which 25,000 species are known, often occur on the bark of deciduous trees and on some fruit trees. They require similar living conditions to mosses and prefer to thrive in shady places with high humidity.
Lichens depend on good air quality and are therefore considered indicator plants for pollutants present in the air. For this reason, trees with heavy lichen growth are rarely found on busy roads and in metropolitan areas.
Do the lichens harm the tree?
- Since they do not penetrate into the interior of the tree, lichens are not harmful.
- They are not an indication of the poor condition of an old tree.
- Thanks to their symbiotic properties, they provide themselves with water and nutrients.
- They only settle on the tree bark, which is thereby protected from other fungi and bacteria.
- Lichens provide shelter for numerous useful small animals.
When should lichen be removed?
This is only necessary as trunk care for older fruit trees, as the protective lichens provide protection for overwintering pests. The right time for this measure is the cold winter months. The lichens are brushed off with a special tree brush (€14.00 on Amazon), which you can get from garden shops. Please do not use a wire brush as this would permanently damage the bark of the tree.
Tip
Tree lichen can also be removed with a coat of lime. First scrape off the lichen and loose parts of the bark and then apply the preparation. The lichens die within a few weeks because their livelihoods are deprived. At the same time, the paint prevents fungal diseases and prevents frost cracks.
