Normally, lichens are considered beneficial, serving as food for animals, and producing soil on bare rock, providing a foothold for other plants, but in at least one case, the National Park Service actively seeks it out and destroys it. Why do they do that?
Answer:
The National Park Service goes to considerable trouble to get rid of lichens growing on Mt. Rushmore. Since lichens slowly break down the rock they are growing on, they contribute to the erosion of the carved faces.
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