<P> The tree line is the edge of the habitat at which trees are capable of growing . It is found at high elevations and in frigid environments . Beyond the tree line, trees cannot tolerate the environmental conditions (usually cold temperatures or lack of moisture). The tree line should not be confused with a lower timberline or forest line, which is the line where trees form a forest with a closed canopy . </P> <P> At the tree line, tree growth is often sparse and stunted, with the last trees forming densely matted bushes, known as krummholz (German for "crooked wood"). </P>

Why do trees stop growing at a certain elevation