Why do trees shed their foliage?

During the onset of cold weather, the leaves begin to freeze. The water inside the foliage cells freezes and the crystals destroy the cell structure. Therefore, the leaves will not be able to survive the winter. But not only because of this, plants shed their leaves. This has an important role in the removal of harmful and toxic substances from plants that accumulate in the plant body. Because of these substances, the leaves change color, since if you pick a green leaf, it will not turn yellow or turn red, but will slightly lose its bright green color and dry out.