timberline

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timberline,

elevation above which trees cannot grow. Its location is influenced by the various factors that determine temperature, including latitude, prevailing wind directions, and exposure to sunlight. In general, the timberline is highest in the tropics and descends in elevation toward the polar regions; in the north it intersects the land surface approximately at the Arctic Circle. For example, the timberline is at about 2,500 ft (750 m) on Denali (Mt. McKinley), Alaska; 6,500 ft (1,950 m) on Mt. Shasta, Calif.; and 11,500 ft (3,450 m) in the San Francisco Mts., Ariz. These figures represent elevations on the sunny side of the mountains; the timberline is lower on the shaded sides. The timberline is roughly marked by the location of the 50°F; (10°C;) isotherm (see isoplethisopleth
, line drawn on a map through all points of equal value of some measurable quantity. In many meteorologic, oceanographic, or geologic studies some physical or chemical property is examined that varies from place to place on a map.
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) during the warmest month.

timberline

[′tim·bər‚līn]
(ecology)
The elevation or latitudinal limits for arboreal growth. Also known as tree line.
References in periodicals archive ?
The timberline is located at altitudes of 370-440 m a.s.l., and the annual mean temperature ranges between 607 and 696 d.d.
Each of the 13 localities consists of 3-4 rows of three circular monitoring plots along an altitudinal gradient from forest to timberline to tree line (Fig.
Pine tree density was similar in the forest and at the timberline, but it decreased sharply at the tree line (Fig.
Spruce seedling density almost doubled up to the timberline, and at the tree line it was close to the level in the forest zone (Fig.
Although regional variation was relatively low in the forest and at the timberline (1.2-4.1 [m.sup.2]/ha) (Table 2), the basal area of mountain birch varied strongly among the localities within the regions (data not shown).
The pine seedling densities decreased slightly in the different zones from the early 1980s to 1999, but the overall decreases (24% for forest, 28% for timberline, and 4% for tree line) were not significant.
The number of pine seedlings increased on 42%, 39%, and 25% of the plots in the forest, timberline and tree line, respectively.
Therefore, seeds are also produced to some extent in average years in northern timberline areas.
The difference was especially clear at the timberline, where reduction in seedling density occurred in the southern localities, especially between 1983 and 1994 (Fig.
Pine tree density increased by 23% in the forest, 31% at the timberline, and 29% at the tree line.
According to Kullman (1997; see also Kullman, 2000), Scots pine seedlings from the 1950s and even the 1930s did not attain tree size until the 1980s and 1990s, and therefore the timberline and tree line have risen.
The increase in the total basal area was higher at the timberline than in the forest zone.