A tree burl is an abnormal growth caused by stress, injury, or infection from a virus, fungus, or insects.
Cause
A burl is an abnormal growth on a tree, with swirled grain.
Triggers
- Stress or injury.
- Viral, fungal or bacterial infection.
- Insect damage.
- Genetic factors.
Is it harmful
Usually not. Most trees live with burls.
Value
Burl wood is prized for furniture and bowls because of its grain.
Harvest
Take care not to kill the tree.
Formation
A burl is a rounded outgrowth on a tree trunk or branch with swirling, distorted grain. It forms when cells grow abnormally in response to stress, such as injury, fungal or viral infection, insect damage or environmental stress. Burls contain dormant buds, which is why they sometimes sprout shoots.
- Coast redwood burls form at the base of trunks, and the trees can regenerate from them.
- Burls are common in redwood, maple, walnut, oak and cherry trees.
- Most burls do not kill the tree, though large ones can weaken a branch.
Value and harvest
Burl wood is prized for furniture, bowls, guitars, clock faces and veneers because of its figured grain. Prices for large burl slabs can reach thousands of dollars. Harvesting from redwood parks is illegal in many places, such as California state parks, and rules apply to burl poaching, which damages ancient trees. Buy from certified or salvaged sources.
Formation
A burl is an abnormal growth on a tree trunk or roots. Causes include viral or fungal infections, insect damage, injury, or stress, which make cells grow in a disordered way, producing swirling grain. Redwoods can form burls from dormant buds.
Value and harvest
Burl wood is prized for furniture and veneer, with patterns such as bird’s eye and quilting. Harvesting from living trees can harm them; sourcing from licensed suppliers is important. Burls usually do not kill the tree.
Types of burl and wood
Burls form on many species, with burl wood from walnut, maple, redwood, cherry and elm. Redwood burls (lignotubers) can produce new trees. The patterns include eyed, bird’s eye and flame. A large redwood burl slab can sell for hundreds to thousands of dollars.
Harvest and ethics
Cutting burls from living trees can leave wounds that allow disease. Many harvest from fallen or dead trees. Poaching of redwood burls in California state parks is a crime with penalties, and has damaged old growth. Burl wood is difficult to work because grain direction changes, and is stabilized with resin for use in pens, bowls and veneer.
Based on data from the US Forest Service and California State Parks
