forest line

The tree line, or timberline, is the upper limit of tree growth in mountainous regions or high latitudes. As elevation or latitude increases, trees become shorter and more spaced out until they disappear, giving way to tundra. This transition zone is influenced by temperature, wind, soil quality, and other factors.12

In mountainous areas, the tree line is generally higher closer to the Equator and lower near the poles. Temperature is the primary factor, with a general rule being that tree growth is possible where the average temperature for July is at least 10°C (50°F). The shape of trees also changes with altitude, with broad-leaved trees at lower elevations giving way to pines, spruces, and firs at higher elevations. The transition from forest to treeless land can be gradual, involving a zone of widening tree spacing and then a region of stunted, twisted trees called krummholz, which marks the end of the tree line.12