Of all the plants that can be grown at higher elevations, trees are the most restricted. A survey of 66 mountain communities in Colorado showed that, with the exception of a few native trees, only three non-indigenous species (not native to the area) were found thriving above 9,000 feet. Of these, two (Pinon pine and Rocky Mountain juniper) are actually native but are considered to be above their natural range. The third, Green ash, was not reliably hardy above 8,500 feet except in protected locations.
The dividing line for a wide variety of trees seems to be at or near 8,500 feet. Above this elevation, consider locally native species as the primary source of trees. The following lists include trees considered reliably hardy for various elevations above 6,000 feet.
For a list of high altitude trees and more information, please contact your local Extension office. Also, check out our Fact Sheet 7.423 Trees and Shrubs for Mountain Areas