Burrs (Nature Tour)

A burr, this rounded "bump" seen on this tree trunk, are seen commonly on tree trunks that have suffered damaged from a number of different causes: fungi, viruses, weather, animals, and insects. Most people don't know that trees have a number of different mechanisms to combat damage, burrs being one of them, which is simply a mass of shoot and bud tissue that wraps around the damage attempting to isolate it from the rest of the tree, creating this "bump."

The red pigment seen in the photograph is lichen, which doesn't harm the tree, it just found a home here which suited its environmental conditions.