What is a Burr?
You may have noticed that some old trees have large lumps on the trunk which gives it a disfigured look. These lumps are known as Burrs.
What Causes Burrs?
Burrs are a reaction to damage from a number of causes:
When A Tree Is Under attack
Trees can defend themselves and fight back from attack. Burrs are a visible response to attack.
A large knobbly growth that grows on the trunk sometimes two can be easily seen.
Why Do They Appear
Burrs usually form over a wound which heals over during the period of irregular growth. The burr protects the tree from any further damage at that site. This wood is called reaction wood.
Burrs are nothing more than unsightly to some people. They do not harm the tree.