• Tree line

    Tree line

    • The tree line is the edge of the habitat at which trees are capable of growing. It is found at high elevations and in frigid environments. Beyond the tree line, trees cannot tolerate the environmental conditions (usually cold temperatures or lack of moisture). The tree line should not be confused with a lower timberline or forest line, which is the line where trees form a forest with a closed canopy.

      At the tree line, tree growth is often sparse and stunted, with the last trees forming densely matted bushes, known as krummholz (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.

      There are several types of tree lines defined in ecology and geology:

      An alpine tree line is the highest elevation that sustains trees; higher up it is too cold, or the snow cover lasts for too much of the year to sustain trees. The climate above the tree line of mountains is called an alpine climate, and the terrain can be described as alpine tundra. In the northern hemisphere treelines on north-facing slopes are lower than on south-facing slopes because the increased shade on north-facing slopes means the snowpack takes longer to melt. This shortens the growing season for trees. In the southern hemisphere, the south-facing slopes have the shorter growing season.

      The alpine tree line boundary is seldom abrupt: it usually forms a transition zone between closed forest below and treeless alpine tundra above. This zone of transition occurs “near the top of the tallest peaks in the northeastern United States, high up on the giant volcanoes in central Mexico, and on mountains in each of the 11 western states and throughout much of Canada and Alaska”. Environmentally dwarfed shrubs (krummholz) commonly forms the upper limit.

      The decrease in air temperature due to increasing elevation causes the alpine climate. The rate of decrease can vary in different mountain chains, from 3.5 °F (1.9 °C) per 1,000 feet (300 m) of elevation gain in the dry mountains of the Western United States, to 1.4 °F (0.78 °C) per 1,000 feet (300 m) in the moister mountains of the Eastern United States. Skin effects and topography can create microclimates that alter the general cooling trend.

      Location Approx. latitude Approx. elevation of tree line Notes
      (m) (ft)
      Finnmarksvidda, Norway 69°N 500 1,600 At 71°N, near the coast, the tree-line is below sea level (Arctic tree line).
      Abisko, Sweden 68°N 650 2,100
      Chugach Mountains, Alaska 61°N 700 2,300 Tree line around 1,500 feet (460 m) or lower in coastal areas
      Southern Norway 61°N 1,100 3,600 Much lower near the coast, down to 500–600 metres (1,600–2,000 ft).
      Scotland 57°N 500 1,600 Strong maritime influence serves to cool summer and restrict tree growth
      Canadian Rockies 51°N 2,400 7,900
      Tatra Mountains 49°N 1,600 5,200
      Olympic Mountains WA, United States 47°N 1,500 4,900 Heavy winter snowpack buries young trees until late summer
      Swiss Alps 47°N 2,200 7,200
      Mount Katahdin, Maine, United States 46°N 1,150 3,800
      Eastern Alps, Austria, Italy 46°N 1,750 5,700 more exposure to Russian cold winds than Western Alps
      Sikhote-Alin, Russia 46°N 1,600 5,200
      Alps of Piedmont, Northwestern Italy 45°N 2,100 6,900
      New Hampshire, United States 44°N 1,350 4,400 Some peaks have even lower treelines because of fire and subsequent loss of soil, such as Grand Monadnock and Mount Chocorua.
      Wyoming, United States 43°N 3,000 9,800
      Rila and Pirin Mountains, Bulgaria 42°N 2,300 7,500 Up to 2,600 m (8,500 ft) on favorable locations. Mountain Pine is the most common tree line species.
      Pyrenees Spain, France, Andorra 42°N 2,300 7,500 Mountain Pine is the tree line species
      Wasatch Mountains, Utah, United States 40°N 2,900 9,500 Higher (nearly 11,000 feet or 3,400 metres in the Uintas)
      Rocky Mountain NP, CO, United States 40°N 3,550 11,600 On warm southwest slopes
      3,250 10,700 On northeast slopes
      Japanese Alps 36°N 2,900 9,500
      Yosemite, CA, United States 38°N 3,200 10,500 West side of Sierra Nevada
      3,600 11,800 East side of Sierra Nevada
      Sierra Nevada, Spain 37°N 2,400 7,900 Precipitation low in summer
      Khumbu, Himalaya 28°N 4,200 13,800
      Yushan, Taiwan 23°N 3,600 11,800 Strong winds and poor soil restrict further grow of trees.
      Hawaii, United States 20°N 3,000 9,800 Geographic isolation and no local tree species with high tolerance to cold temperatures.
      Pico de Orizaba, Mexico 19°N 4,000 13,100
      Costa Rica 9.5°N 3,400 11,200
      Mount Kinabalu, Borneo 6.1°N 3,400 11,200
      Mount Kilimanjaro, Tanzania 3°S 3,950 13,000
      New Guinea 6°S 3,850 12,600
      Andes, Peru 11°S 3,900 12,800 East side; on west side tree growth is restricted by dryness
      Andes, Bolivia 18°S 5,200 17,100 Western Cordillera; highest treeline in the world on the slopes of Sajama Volcano (Polylepis tarapacana)
      4,100 13,500 Eastern Cordillera; treeline is lower because of lower solar radiation (more humid climate)
      Sierra de Córdoba, Argentina 31°S 2,000 6,600 Precipitation low above trade winds, also high exposure
      Australian Alps, Australia 36°S 2,000 6,600 West side of Australian Alps
      1,700 5,600 East side of Australian Alps
      Andes, Laguna del Laja, Chile 37°S 1,600 5,200 Temperature rather than precipitation restricts tree growth
      Mount Taranaki, North Island, New Zealand 39°S 1,500 4,900 Strong maritime influence serves to cool summer and restrict tree growth
      Tasmania, Australia 41°S 1,200 3,900 Cold winters, strong cold winds and cool summers with occasional summer snow restrict tree growth
      Fiordland, South Island, New Zealand 45°S 950 3,100 Cold winters, strong cold winds and cool summers with occasional summer snow restrict tree growth
      Torres del Paine, Chile 51°S 950 3,100 Strong influence from the Southern Patagonian Ice Field serves to cool summer and restrict tree growth
      Navarino Island, Chile 55°S 600 2,000 Strong maritime influence serves to cool summer and restrict tree growth
      Location Approx. longitude Approx. latitude of tree line Notes
      Norway 24°E 70°N The North Atlantic current makes Arctic climates in this region warmer than other coastal locations at comparable latitude. In particular the mildness of winters prevents permafrost.
      West Siberian Plain 75°E 66°N
      Central Siberian Plateau 102°E 72°N Extreme continental climate means the summer is warm enough to allow tree growth at higher latitudes, extending to northernmost forests of the world at 72°28'N at Ary-Mas (102° 15' E) in the Novaya River valley, a tributary of the Khatanga River and the more northern Lukunsky grove at 72°31'N, 105° 03' E east from Khatanga River.
      Russian Far East (Kamchatka and Chukotka) 160°E 60°N The Oyashio Current and strong winds affect summer temperatures to prevent tree growth. The Aleutian Islands are almost completely treeless.
      Alaska 152°W 68°N Trees grow north to the south facing slopes of the Brooks Range. The mountains block cold air coming off of the Arctic Ocean.
      Northwest Territories, Canada 132°W 69°N Reaches north of the Arctic Circle because of the continental nature of the climate and warmer summer temperatures.
      Nunavut 95°W 61°N Influence of the very cold Hudson Bay moves the treeline southwards.
      Labrador Peninsula 72°W 56°N Very strong influence of the Labrador Current on summer temperatures as well as altitude effects (much of Labrador is a plateau). In parts of Labrador, the treeline extends as far south as 53°N.
      Greenland 50°W 64°N Determined by experimental tree planting in the absence of native trees because of isolation from natural seed sources; a very few trees are surviving, but growing slowly, at Søndre Strømfjord, 67°N.

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