Question
oak tree 1
We are concerned about an oak tree in our back yard. We love our trees, but this one is completely hollow inside. There is a crack or opening on one side and when you peer inside, you can see the inside is hollowed out. When we look way up into the tree, we see another hole. It leafs out every year nice and green, the same as our other trees, but we are concerned about it being weak and coming down on the neighbor's house. The diameter of the tree is 36", but we can stick a tape measure inside the tree 23". We don't know what to do, we don't want to hastily cut down a tree if it is okay, but we want to be safe.
AnswerA tree that is living but hollowed out has
experienced heart rot. Just because a tree
has heart rot does not mean it is
hazardous. The rate of recent diameter
growth is a useful index of the probable
safety of any tree with heart rot or
hollowness. Trees that are making good
growth will have thicker sapwood than
those growing slowly and should be less
likely to fail. The condition of callus growth
around wounds is also an indicator. If
growth of the tree is good, callusing will be
good and the bark over the callus will be
thin and healthy in appearance. The crown
of the tree also will be thrifty.
The hazard of a tree with heart rot is
commonly overrated. A tree can stand for
decades, even though hollow or showing
rot, and can suffer up to one-third loss in
strength--equivalent to approximately a 70
percent loss in total wood diameter inside
bark--without materially affecting its safety,
if the weakening defect is heart rot
uncomplicated by other defects. This
standard can be applied most conveniently
in the field after finding the thickness in
inches of sound wood outside of the rot
column or hollow. A 36 inch diameter tree should have a sound wood thickness of 5.5 inches or more. Oaks are generally a low hazard tree.
If the tree foliage and limbs look healthy and the tree is generally up right (not leaning) I would not be too concerned. To make sure you would need to get a Certified Arborist or Forester to take a look at the tree. In the US the State Agencies have Urban Foresters that should be able to help you determine the health of the tree. their number should be in your local phone book. Also some larger cities have Urban Foresters that deal with this on city trees and can help. Before I cut the tree I would get one of these to come take a look. BUT If the tree is not leaning or has not dieback in the crown I would not cut it. Normally a tree this size will start having large limbs break off long before the tree will fall.
