Question
Hello Jim, thanks for reading my question.

I have a 75 yr old flowering cherry in the front of my house.. 燭oday I noticed one of the nodes that used to have a limb which either was cut or broke off at some point had rotted wood inside so I pulled it apart and scooped out the rotted wood which was moist and well composted. 燭he rot went maybe 3 inches deep (horizontally inside the tree) and the entire hole about 8inches long and 4inches wide.  I am wondering if the tree will "heal" itself and compartmentalize the wound and if this should be a cause for concern.  Other than this hole, the tree appears healthy and sturdy.  

Thanks,
Michelle

Answer
If the foliage is green and full the tree is healthy. It sounds like the wood in the center of the tree is decaying and the tree may have some hollow places in the trunk. The living part of a tree is just under the bark and the bark protects the cells from decay fungi. When there is a wound to the bark decay fungi can get into the woody cells and start the eat away at the cells. carpenter ants some times make their nests in these decaying areas. The woody cells are dead cells and not associated with the healthy of the tree except for strength.
Trees can and do live many many years with their trunks completely hollow. Trees have the capability to seal off the decay fungi and slow the growth of the decay.

I would fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter and water it in  good, or wait just before a rain storm and fertilize and you will not have to water. This will increase the health of the tree and help slow the decay fungi. I would do this now and again after the leaves fall in the Fall.

The wound may not seal over but the tree on the inside will grow guard cell to compartmentalize off the fungi.  Trees do not become hollow overnight - it can take decades - and while the center of the tree (the heartwood) may be decaying, the tree continues to lay down healthy wood (sapwood) around the outside of its trunk.  This results in the formation of a cylinder, the strength of which depends upon the percentage of healthy to unhealthy tissue.
Plugging or sealing tree cavities or treating tree wounds with wound dressings is not advised. Such treatments are unnecessary and will slow down any healing process.