Answer: There are a couple of possibilites that come to mind: Bronze birch borer, or a fungal disease. These problems usually affect trees that are in a weakened state, due to poor growing conditions or extreme weather. The only way to find out for sure is to have a professional arborist take a look at the trees and make a diagnosis. You will have to at least cut out the dying portions of the trees, and treat them with great care to restore them to health. Best of luck!
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