The tree line is the edge of the habitat at which trees are capable of growing. Beyond the tree line, they are unable to grow because of inappropriate environmental conditions (usually cold temperatures or lack of moisture). Some distinguish additionally a deeper timberline or forest line, where trees form a forest with a closed canopy.
At the tree line, tree growth is often very stunted, with the last trees forming low, densely matted bushes. If it is caused by wind, it is known as krummholz formation, from the German for 'twisted wood'.
The tree line, like many other natural lines (lake boundaries, for example), appears well-defined from a distance, but upon sufficiently close inspection, it is a gradual transition in most places. Trees grow shorter towards the inhospitable climate until they simply stop growing.
Famous quotes containing the words tree and/or line:
“A tree swayed overwater.
A voice said:
Stay. Stay by the slip-ooze. Stay.”
—Theodore Roethke (1908–1963)
“Men are not to be told anything they might find too painful; the secret depths of human nature, the sordid physicalities, might overwhelm or damage them. For instance, men often faint at the sight of their own blood, to which they are not accustomed. For this reason you should never stand behind one in the line at the Red Cross donor clinic.”
—Margaret Atwood (b. 1939)