I have two native mountain ash trees that up until this year would produce a ton of berries. This year there were no berries and worse still the limbs are being reduced to skeletons - no leaves just the stems. Here is a pic with the affected areas highlighted in red. What could be causing this? They've been getting regular water.
Did you see some mountain ash sawfly larvae there? They could be the culprit of the damage. Mountain ashes don't have plentiful berries each year. It is rather usual, that some years they bear almost no fruits at all. I think, I see leaves from your photo, not limbs only, but the blades of the leaflets are eaten completely, only midribs have remained.
A friend has the sawfly appearing and doing this damage every year. So you may likewise be stuck with them unless you identify a control method.
Yes, only the midribs have remained. I didn't see any larvae, but it sure sounds like they're the culprits. Apparently they were just noticed in Vancouver a few years ago where they ate 90% of the foliage! https://pnwisa.org/2017/09/update-mountain-ash-sawfly-larvae-eat-their-way-into-year-three/
