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:
“There was not a tree as far as we could see, and that was many miles each way, the general level of the upland being about the same everywhere. Even from the Atlantic side we overlooked the Bay, and saw to Manomet Point in Plymouth, and better from that side because it was the highest.”
—Henry David Thoreau (1817–1862)
“As for conforming outwardly, and living your own life inwardly, I do not think much of that. Let not your right hand know what your left hand does in that line of business. It will prove a failure.... It is a greater strain than any soul can long endure. When you get God to pulling one way, and the devil the other, each having his feet well braced,—to say nothing of the conscience sawing transversely,—almost any timber will give way.”
—Henry David Thoreau (1817–1862)