The Mountain Ash tree is susceptible to the fungal disease Fire Blight. Once the tree is weakened the upper branches will die back. Insects will bore into the trunk followed by Woodpeckers. The orderly spaced holes are from bird damage. Contacting a local ISA Certified Arborist to prune the diseased branches might be possible. The multiple holes in the trunk are not a good sign. Below is a brief description of diseases that effect Mountain Ash from Penn State Extension. https://extension.psu.edu/mountain-ash-diseases