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Concept
Tree line
Summary
The tree line is the edge of the habitat at which trees are capable of growing. It is found at high elevations and high latitudes. Beyond the tree line, trees cannot tolerate the environmental conditions (usually low temperatures, extreme snowpack, or associated lack of available moisture). The tree line is sometimes distinguished from a lower timberline, which is the line below which trees form a forest with a closed canopy.
At the tree line, tree growth is often sparse, stunted, and deformed by wind and cold. This is sometimes known as krummholz (German for "crooked wood").
The tree line often appears well-defined, but it can be a more gradual transition. Trees grow shorter and often at lower densities as they approach the tree line, above which they are unable to grow at all. Given a certain latitude, the tree line is approximately 300 to 1000 meters below the permanent snow line and roughly parallel to it.
Due to their vertical structure, trees are more susceptible to cold than more ground-hugging forms of plants. Summer warmth generally sets the limit to which tree growth can occur, for while tree line conifers are very frost-hardy during most of the year, they become sensitive to just 1 or 2 degrees of frost in mid-summer. A series of warm summers in the 1940s seems to have permitted the establishment of "significant numbers" of spruce seedlings above the previous treeline in the hills near Fairbanks, Alaska. Survival depends on a sufficiency of new growth to support the tree. Wind can mechanically damage tree tissues directly, including blasting with windborne particles, and may also contribute to the desiccation of foliage, especially of shoots that project above the snow cover.
The actual tree line is set by the mean temperature, while the realized tree line may be affected by disturbances, such as logging. Most human activities cannot change the actual tree line, unless they affect the climate. The tree line follows the line where the seasonal mean temperature is approximately .
Official source
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