Why do knots form in wood?

Knots form around these branches, building up trunk material as the tree continues to expand. Since the branches are still growing as they are overtaken by the trunk, the knot that forms is solid and contains living wood throughout. read more

In order to supply the branches with water and nutrients, and to support all of that weight, the structure of the wood is very different around the base of the branch, forming a knot. In particular the orientation of the fibers is different, transitioning from side/straight grain to end grain. read more