Lichens

On the concrete piles along the road you can see gray-green, rust-colored to orange-yellow spots: these are lichens.
A lichen is a form of society of a weed and a fungus. They need each other to live. The fungus absorbs water and minerals from the environment, the seaweed ensures the production of sugars.
Lichens are adapted to fairly dry, often even extreme environmental conditions. They are pioneers, you can even find them on stone. Lichens can grow very old. In archaeology, they are sometimes an aid in age determinations.
The bush-shaped lichens on the trunks of the poplars are very sensitive to air pollution. They are used as bio-indicators and tell you something about the quality of the air.

Departement Omgeving