The tree line is the edge of the habitat at which trees are capable of growing. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions (usually cold temperatures or associated lack of available moisture). The tree line is sometimes distinguished from a lower timberline or forest line, which is the line where trees form a forest with a closed canopy.
At the tree line, tree growth is often sparse, stunted, and deformed by wind and cold krummholz(German for “crooked wood”).
The tree line often appears well-defined, but it can be a more gradual transition. Trees grow shorter and often at lower densities as they approach tree line, above which they cease to exist.