I have a beautiful three trunk Black Walnut that the bark has been falling off of. Two of the three trunks have lost 50-75% of the bark up to seven feet off of the ground. In some area's now exposed the wood is a fairly light in color and spongy/damp. The tree looks healthy other than this area. We bought the property last fall and I'm not certain how long the tree has been this way. Any ideas on what has caused this, or what can be done? I have roughly 25 large Walnuts, I'd hate to lose this one but I'm not going to spend a lot of money to save it. Thanks for your help.

The dead bark probably indicates a root problem. The exposed wood is subject to decay once the bark dies. This is the reason the exposed wood is soft and damp.

You will probably have to remove at least the two injured trunks. I strongly urge you to contact a Registered Consulting Arborist (American Society of Consulting Arborists ) or a Certified Arborist ( International Society of Arboriculture). Get the tree inspected. Hopefully, it is not something that will spread or affect the other walnuts. Investigation of the root system will be necessary, and possibly some lab tests to determine the cause of root loss.

Good luck.

Sounds like severe root damage. This sort of damage is often man made. When you purchased your property had there been any landscaping or construction done? Any new driveways, freshly turfed uniform banks, new planting, does the tree trunk have a lack of taper towards the base,any new buildings nearby? If so is the dead bark closest to/facing any of the afforementioned. Often is the case that roots are chopped off by a digger then the soil replaced raising the level suffocating the remaining roots and the covered stem causing rot and more death of the bark. Like Russ said get someone to look at it, surgery may save the tree, but even if you don't want to spend a lot of money you may find out the person who sold you the house sold you doomed trees.