Anything described as montane has something to do with mountains. If you move to the Rockies, you can call your new house a montane home.
You're most likely to find the adjective montane in a scholarly book or article about the ecosystem known as a montane forest. These are forests found at high altitudes, but not high enough for growth to be so limited that trees can't take root there. When there's a timberline or forest line on a mountain, that's typically the highest part of a montane forest. The Latin root of montane is the Latin mons, or "mountain."