Certainly, many people have noticed that the bark of some trees has turned a reddish, rusty color. Such trees can be seen in Bolesławiec, for example on Gdańska Street and in the area of the Bóbr River.
What causes some trees to “rust”? Is it some kind of tree disease? Is there cause for concern?
We found the answer to this question on a website for allotment and garden enthusiasts. As we read on dionp.pl:
The rusty coating on plants, usually on the lower parts of trunks, though also on larger branches, is caused by algae—a large group of unicellular and multicellular organisms that vary considerably in appearance and in the environmental conditions they inhabit. It is therefore not a fungal disease, a deposit from pollutants, or a deficiency of nutrients such as phosphorus or potassium—and certainly not paint deliberately applied to the plants.
These algae that colonize plants are known as aerophytes. They can also be found on dead matter, such as stones (a common sight, for example, in the Tatra Mountains), walls, pavements, and so on. The algae responsible for the rusty color on plants belong to Trentepohlia; one representative is the species known in Central Europe as Trentepohlia umbrina, which produces an orange-colored pigment. This pigment is responsible for the rust-like color of trunks and branches.
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