How Much Decay in Trees Is Too Much Before Taking a Tree Down?

Cavities or Open Wounds

• If there are cavities or open wounds, these indicate where decay has started but do not indicate how far into the tree the decay has progressed. Check the bark around these areas, and if it is loose there may be more decay underneath. External decay usually means internal decay is extensive.

Look for Insects

• Carpenter ants are often present when the interior of a tree is decaying. Also, look for wood boring insects; they leave "frass" at their entry locations. These are often at the tree's base or in tree crotches. Insects attack trees under stress or decline, so their presence is a good indicator of decay.

Presence of Mushrooms, Conks or Fungi

• If you see mushrooms growing at the base, or conks on the trunk, large branches or roots, these are very good indicators that decay organisms are at work. This presence can be confusing, as they may come and go with the seasons.

Presence of Birds and Bees

• Small cavities in trees often serve as home for birds, and are not a problem. The presence of birds, however, may mean that insects are inside the tree and they are feeding on them. Bees will also make their home inside cavities, and if the opening is as large as the cross-section of the trunk, this is a warning sign.

Check Soundness

• Sometimes you can tell how much of the tree trunk is hollow by tapping with a rubber mallet. This will not help with the percentage calculation, but if a significant portion of the trunk does sound hollow, you can assume decay is extensive.

Consult a Professional

• If the tree is of significant size and value to you, hiring a certified arborist is a good idea before actually cutting the tree down. They have the education and experience to determine if a tree is a risk hazard and needs to be removed.