On mountains, the timberline is primarily determined by the elevation. In the Arctic, trees cannot grow normally north of the timberline.
Timberlines are not well-defined. They may be higher on southern mountain slopes and lower on northern facing slopes.
Slightly north or above the timberline, the trees are shrubby, small and scattered. Some may appear to be low shrubs or bushes. This area is sometimes called the tree line.
Above the timberline, the temperature is too low for normal tree growth. The soil may be permanently frozen, the precipitation inadequate, the growing season too short and the exposure to wind, snow, sun and ice too great.
