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:
“It never had been inside the room,
And only one of the two
Was afraid in an oft-repeated dream
Of what the tree might do.”
—Robert Frost (1874–1963)
“Our job is now clear. All Americans must be prepared to make, on a 24 hour schedule, every war weapon possible and the war factory line will use men and materials which will bring, the war effort to every man, woman, and child in America. All one hundred thirty million of us will be needed to answer the sunrise stealth of the Sabbath Day Assassins.”
—Lyndon Baines Johnson (1908–1973)