Timberline is the ecological zone that lies between the boreal forest and tundra at high mountainous elevations. It is characterized by trees of stunted growth (often affected by the prevailing wind) and by low, dense matted bushes.
In the southern Sierra Nevada of California and Nevada, the Foxtail pine, Pinus balfouriana, grows in this zone. It is notable for having an upright growth habit, in contrast to other trees in the area, which are only stunted krummholz. It is gradually increasing its range to the north in the current interglacial period.
The analogous location at high latitudes is called the treeline.