Burls

A burl on a tree at Connequot River State Park.

The tumor-like growth on this tree trunk is known as a burl. They develop when a tree is stressed from an insect infestation, fungi, or mold. The tree trunk pictured above also has woodpecker holes. Although burls were once believed caused by woodpeckers, this apparently is not the case, because they will also grow on trees in areas not inhabited by woodpeckers. However, insects causing stress to a tree could also attract woodpeckers looking for a meal. The good news is that burls are harmless to trees (although what is causing the stress might not be). The wood inside them is prized by woodworkers for its intricate patterns and vivid colors, which result from its complex grain.