Birch polypore fungus (Piptosporus betulinus) on the trunk of a birch tree (Betula sp.). This is a bracket fungus, and the structure seen here is the bracket-shaped fruiting body (mushroom) of the fungus. The fungus attacks weakened trees, causing intensive brown rot. Fruiting bodies appear after the death of the tree. Photographed in October, in Abernethy Forest, Cairngorms National Park, in the Highland region of Scotland.