Fig Limbs Hollow and Not Because of Borers

Q. I have a fig tree that is close to 30 years old. It was getting out of control so I have been pruning it. I noticed some holes in the trunk but as I am cutting the branches I find that some are completely hollow inside.  Other than a few dead areas that I am pruning out, the tree looks generally ok and is putting out new growth, even from the hollow branches. Since the main trunk seems to be involved I can’t really cut out all the part that is affected.  Can you tell me what is causing this and if there is anything that I need, or can do about it???  I noticed the hollow where I had cut out a branch from the trunk a long time ago, but did not worry about it.    I would like to save the tree, it has sentimental value and provides needed shade.   I have attached some photos.  

Readers fig tree with hole in the trunk

A. Your pictures through me for a loop a bit. I have not seen that on fig before but I have seen something similar on other trees. I knew it was not from borers but I was not sure why you lost the center of your fig trees.

            When trees grow, they grow both upward and in girth. We know that upward growth is from the buds on trees. Growth in girth is not as obvious. Growth in girth is from some cylindrical layers just under the bark.

            As a fig tree gets fatter, the center of the tree dies. As it continues to grow fatter and fatter, the dead wood in the center of the tree gets larger and larger. As long as the tree remains healthy and doesn't get any infections, the deadwood in the center of the tree remains intact.

            On some occasions, organisms such as fungi and bacteria can invade the center of a tree and begin feeding on this dead wood. These organisms are almost always feeding only on deadwood and not the living parts of the tree.

Fig limb hollow

            So these organisms technically are not disease organisms but wood-rotting organisms. Since the center of a tree is dead, these organisms continue to feed on this dead center of the tree and can hollow out a tree very effectively. I think we have all seen pictures or cartoons of animals living inside of trees. Well, this can actually happen.

               The center of the larger trunk and branches of a fig tree are filled with dead wood that is fairly soft and pithy. Once these wood-rotting organisms get going they will clean out that central core of large branches and the trunk. The living portion of the tree is unaffected.

               What you have is not a borer problem but a wood rotting process going on. There is nothing you need to do about it but keep in mind that these branches may snap more easily than branches which do not have the central core hollowed out.

            This is one of the reasons I emphasize so strongly to clean your pruning saws and pruning shears before you start pruning. It is best to clean and sanitize them between each tree, not necessarily between each cut unless you know the limb is diseased.