Seeing the other threads here on tree selection, thought I'd open it up a bit more.
Twelve odd years ago, I used the Soil Conservancy to pick up hundreds of bare-root trees and shrubs to plant a noise/wind/visual border as I live on the corner of two busy county roads. The trees are Scots Pine and Green Ash - the pine is getting hammered by bark beetle, I lose a few each year, and there are several that are, for all intents and purposes, dead already but still look green. And the Ash may well get hit by the borer, if it makes it's way over to the western slope.
So I wish to replace them, slowly and as they die off, with inexpensive bare-root selections. I'd also like to have several different species to avoid what I have now, a mono-culture susceptible to a single bug or disease.
I have lavish irrigation, but that isn't really the direction I want to go - I think it reasonable to assume that in the future 50 years, the available amount will go down, but still have some water available.