Mountain Ash tree seems to be dying - why? I have a 30 yrs old Mountain Ash tree that has always been an attractive specimen in my back yard then all of a sudden in mid July - the leaves of 2/3's of the tree started to turn brown and the beautiful red berries looked dehydrated. The tree looks like if it's dying. 1/3 of the tree is green and healthy but the rest....awful!!! What can I do to save my tree?? I would be grateful for any advice that will help me. Follow-Up Postings: RE: Mountain Ash tree seems to be dying - why? That doesn't sound promising :-(. 25-30 years is an average lifespan for a Mountain Ash - sounds like yours is on the far side of average. They can live to be 50-70 years under ideal conditions (acidic, peaty soil with excellent drainage), but most of us don't have those idea conditions - especially those of us in southern Ontario and Quebec. Probably it is old and weak and something stressed it beyond its ability to thrive (insects, rot, fungus...). Given its age, and the fact that 2/3 of it is dying, I'd say it's best to hire an arborist to come take it down and replace it with a new tree. One of the reason Mountain Ash is so popular is because it's a fast growing tree (that also means it's a short lived tree). A new one will quickly grow to a nice height.