Tree line
The tree line is the edge of a habitat at which trees are capable of growing and beyond which they are not. 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).[1]: 51 The tree line is sometimes distinguished from a lower timberline, which is the line below which trees form a forest with a closed canopy.[2]: 151 [3]: 18
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").[4]: 58
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.[4]: 55 Given a certain latitude, the tree line is approximately 300 to 1000 meters below the permanent snow line and roughly parallel to it.[5]
Causes
Due to their vertical structure, trees are more susceptible to cold than more ground-hugging forms of plants.
The actual tree line is set by the mean temperature, while the realized tree line may be affected by disturbances, such as logging.[6] Most human activities cannot change the actual tree line, unless they affect the climate.[6] The tree line follows the line where the seasonal mean temperature is approximately 6 °C or 43 °F.[11][6] The seasonal mean temperature is taken over all days whose mean temperature is above 0.9 °C (33.6 °F). A growing season of 94 days above that temperature is required for tree growth.[12]
Types
Several types of tree lines are defined in ecology and geography:
Alpine
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 alpine tree line boundary is seldom abrupt: it usually forms a transition zone between closed forest below and treeless alpine zone 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".[16] Environmentally dwarfed shrubs (krummholz) commonly form the upper limit.
The decrease in air temperature with increasing elevation creates 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,[16] to 1.4 °F (0.78 °C) per 1,000 feet (300 m) in the moister mountains of the eastern United States.[17] Skin effects and topography can create microclimates that alter the general cooling trend.[18]
Compared with arctic tree lines, alpine tree lines may receive fewer than half of the number of degree days (above 10 °C (50 °F)) based on air temperature, but because solar radiation intensities are greater at alpine than at arctic tree lines the number of degree days calculated from leaf temperatures may be very similar.[16]
At the alpine tree line, tree growth is inhibited when excessive snow lingers and shortens the growing season to the point where new growth would not have time to harden before the onset of fall frost. Moderate snowpack, however, may promote tree growth by insulating the trees from extreme cold during the winter, curtailing water loss,[19] and prolonging a supply of moisture through the early part of the growing season. However, snow accumulation in sheltered gullies in the Selkirk Mountains of southeastern British Columbia causes the tree line to be 400 metres (1,300 ft) lower than on exposed intervening shoulders.[20]
In some mountainous areas, higher elevations above the condensation line, or on equator-facing and leeward slopes, can result in low rainfall and increased exposure to solar radiation. This dries out the soil, resulting in a localized arid environment unsuitable for trees. Many south-facing ridges of the mountains of the Western U.S. have a lower treeline than the northern faces because of increased sun exposure and aridity. Hawaii's treeline of about 8,000 ft (2,400 m) feet is also above the condensation zone and results due to a lack of moisture.[citation needed]
Exposure
On coasts and isolated mountains, the tree line is often much lower than in corresponding altitudes inland and in larger, more complex mountain systems, because strong winds reduce tree growth. In addition, the lack of suitable soil, such as along talus slopes or exposed rock formations, prevents trees from gaining an adequate foothold and exposes them to drought and sun.
Arctic
The arctic tree line is the northernmost latitude in the Northern Hemisphere where trees can grow; farther north, it is too cold all year round to sustain trees.[21] Extremely low temperatures, especially when prolonged, can freeze the internal sap of trees, killing them. In addition, permafrost in the soil can prevent trees from getting their roots deep enough for the necessary structural support.[citation needed]
Unlike alpine tree lines, the northern tree line occurs at low elevations. The arctic forest–tundra transition zone in northwestern Canada varies in width, perhaps averaging 145 kilometres (90 mi) and widening markedly from west to east,[22] in contrast with the telescoped alpine timberlines.[16] North of the arctic tree line lies the low-growing tundra, and southwards lies the boreal forest.
Two zones can be distinguished in the arctic tree line:[23][24] a forest–tundra zone of scattered patches of krummholz or stunted trees, with larger trees along rivers and on sheltered sites set in a matrix of tundra; and "open boreal forest" or "lichen woodland", consisting of open groves of erect trees underlain by a carpet of Cladonia spp. lichens.[23] The proportion of trees to lichen mat increases southwards towards the "forest line", where trees cover 50 percent or more of the landscape.[16][25]
Antarctic
A southern treeline exists in the New Zealand Subantarctic Islands and the Australian Macquarie Island, with places where mean annual temperatures above 5 °C (41 °F) support trees and woody plants, and those below 5 °C (41 °F) do not.[26] Another treeline exists in the southwesternmost parts of the Magellanic subpolar forests ecoregion, where the forest merges into the subantarctic tundra (termed Magellanic moorland or Magellanic tundra).[27] For example, the northern halves of Hoste and Navarino Islands have Nothofagus antarctica forests but the southern parts consist of moorlands and tundra.
Tree species near tree line
Some typical Arctic and alpine tree line tree species (note the predominance of
Australia
- Snow gum (Eucalyptus pauciflora)
Eurasia
- Dahurian larch (Larix gmelinii)
- Macedonian pine (Pinus peuce)
- Swiss pine (Pinus cembra)
- Mountain pine (Pinus mugo)
- Arctic white birch (Betula pubescens subsp. tortuosa)
- Rowan[28] (Sorbus aucuparia)
North America
- Subalpine fir (Abies lasiocarpa)[15]: 106
- Subalpine larch (Larix lyallii)[29]
- Mountain hemlock (Tsuga mertensiana)
- Alaska yellow cedar(Chaemaecyparis nootkatensis)
- Engelmann spruce (Picea engelmannii)[15]: 106
- Whitebark pine (Pinus albicaulis)[29]
- Great Basin bristlecone pine (Pinus longaeva)
- Rocky Mountains bristlecone pine (Pinus aristata)
- Foxtail pine (Pinus balfouriana)
- Limber pine (Pinus flexilis)
- Potosi pinyon (Pinus culminicola)
- Black spruce (Picea mariana)[1]: 53
- White spruce (Picea glauca)
- Tamarack (Larix laricina)
- Hartweg's pine (Pinus hartwegii)
South America
- Antarctic beech (Nothofagus antarctica)
- Lenga beech (Nothofagus pumilio)[30]
- Alder (Alnus acuminata)
- Pino del cerro (Podocarpus parlatorei)
- Polylepis (Polylepis tarapacana)
- Eucalyptus (not native to South America but grown in large amounts in the high Andes).[31]
Worldwide distribution
Alpine tree lines
The alpine tree line at a location is dependent on local variables, such as
Averaging over many locations and local microclimates, the treeline rises 75 metres (245 ft) when moving 1 degree south from 70 to 50°N, and 130 metres (430 ft) per degree from 50 to 30°N. Between 30°N and 20°S, the treeline is roughly constant, between 3,500 and 4,000 metres (11,500 and 13,100 ft).[32]
Here is a list of approximate tree lines from locations around the globe:
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 | [32] |
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, United Kingdom | 57°N | 500 | 1,600 | Strong maritime influence serves to cool summer and restrict tree growth[33]: 79 |
Northern Quebec | 56°N | 0 | 0 | The cold Labrador Current originating in the arctic makes eastern Canada the sea-level region with the most southern tree-line in the northern hemisphere. |
Southern Urals | 55°N | 1,100 | 3,600 | |
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 | [34] |
Mount Katahdin, Maine, United States | 46°N | 1,150 | 3,800 | |
Eastern Alps, Austria, Italy | 46°N | 1,750 | 5,700 | More exposure to cold Russian winds than Western Alps |
Sikhote-Alin, Russia | 46°N | 1,600 | 5,200 | [35] |
Alps of Piedmont, Northwestern Italy | 45°N | 2,100 | 6,900 | |
New Hampshire, United States | 44°N | 1,350 | 4,400 | Grand Monadnock and Mount Chocorua .
|
Wyoming, United States | 43°N | 3,000 | 9,800 | |
Caucasus Mountains | 42°N | 2,400 | 7,900 | [37] |
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
|
Steens Mountain, Oregon, US | 42°N | 2,500 | 8,200 | |
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 | [32] On warm southwest slopes |
3,250 | 10,700 | On northeast slopes | ||
Yosemite, CA, United States | 38°N | 3,200 | 10,500 | Sierra Nevada
|
3,600 | 11,800 | [38] East side of Sierra Nevada | ||
Sierra Nevada, Spain | 37°N | 2,400 | 7,900 | Precipitation low in summer |
Japanese Alps | 36°N | 2,900 | 9,500 | |
Himalaya
|
28°N | 4,200 | 13,800 | [32] |
Yushan, Taiwan
|
23°N | 3,600 | 11,800 | [39] Strong winds and poor soil restrict further grow of trees. |
Hawaii, United States | 20°N | 3,000 | 9,800 | [32] Geographic isolation and no local tree species with high tolerance to cold temperatures. |
Pico de Orizaba, Mexico | 19°N | 4,000 | 13,100 | [34] |
Costa Rica | 9.5°N | 3,400 | 11,200 | |
Mount Kinabalu, Borneo | 6.1°N | 3,400 | 11,200 | [40] |
Mount Kilimanjaro, Tanzania | 3°S | 3,100 | 10,200 | [32] Upper limit of forest trees; woody ericaeous scrub grows up to 3900m |
New Guinea | 6°S | 3,850 | 12,600 | [32] |
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, New South Wales, Australia | 36°S | |||
1,800 | 5,900 | Despite the far inland location, summers are cool relative to the latitude, with occasional summer snow; and heavy springtime snowfalls are common[41] | ||
Andes, Laguna del Laja, Chile | 37°S | 1,600 | 5,200 | Temperature rather than precipitation restricts tree growth[42] |
Mount Taranaki, North Island, New Zealand | 39°S | 1,500 | 4,900 | Strong maritime influence serves to cool summer and restrict tree growth |
Northeast Tasmania, Australia | 41°S | 1,200 | 3,900 | Although sheltered on the leeward side of the island, summers are still cool for the latitude. |
Southwest Tasmania, Australia | 43°S | 750 | 2,500 | Exposed to the westerly storm track, summer is extraordinarily cool for the latitude, with frequent summer snow. Springtime receives an extreme amount of cold, heavy precipitation; winds are likewise extreme. |
Fiordland, South Island, New Zealand | 45°S | 950 | 3,100 | Very snowy springs, strong cold winds and cool summers with frequent summer snow restrict tree growth[citation needed] |
Lago Argentino , Argentina
|
50°S | 1,000 | 3,300 | Nothofagus pumilio[43] |
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[44] |
Navarino Island, Chile | 55°S | 600 | 2,000 | Strong maritime influence serves to cool summer and restrict tree growth[44] |
Arctic tree lines
Like the alpine tree lines shown above, polar tree lines are heavily influenced by local variables such as
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 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, United States | 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. Along the coast the northernmost trees are at 58°N in Napartok Bay. |
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. There is one natural forest in the Qinngua Valley. |
Antarctic tree lines
Trees exist on Tierra del Fuego (55°S) at the southern end of South America, but generally not on subantarctic islands and not in Antarctica. Therefore, there is no explicit Antarctic tree line.
Antarctic Peninsula is the northernmost point in Antarctica (63°S) and has the mildest weather—it is located 1,080 kilometres (670 mi) from Cape Horn on Tierra del Fuego—yet no trees survive there; only a few mosses, lichens, and species of grass do so. In addition, no trees survive on any of the subantarctic islands near the peninsula.
Southern Rata forests exist on Enderby Island and Auckland Islands (both 50°S) and these grow up to an elevation of 370 metres (1,200 ft) in sheltered valleys. These trees seldom grow above 3 m (9.8 ft) in height and they get smaller as one gains altitude, so that by 180 m (600 ft) they are waist-high. These islands have only between 600 and 800 hours of sun annually. Campbell Island (52°S) further south is treeless, except for one stunted Spruce, planted by scientists.[45] The climate on these islands is not severe, but tree growth is limited by almost continual rain and wind. Summers are very cold with an average January temperature of 9 °C (48 °F). Winters are mild 5 °C (41 °F) but wet. Macquarie Island (Australia) is located at 54°S and has no vegetation beyond snow grass and alpine grasses and mosses.[citation needed]
See also
- Trees portal
- Montane ecosystems
- Ecotone: a transition between two adjacent ecological communities
- Edge effects: the effect of contrasting environments on an ecosystem
- Massenerhebung effect
- Snow line
References
- ^ ISBN 978-0-521-55986-7.
- ^ ISBN 978-0-444-53466-8.
- ISBN 978-3-0348-0396-0.
- ^ ISBN 978-1-55566-171-7.
- ^ "Why treelines?".
- ^ S2CID 235999977.
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- ISBN 978-1-4612-4902-3.
- S2CID 59025355.
- S2CID 8752987.
- ISBN 978-3-540-00347-2.
- ^ "Alpine Tundra Ecosystem". Rocky Mountain National Park. National Park Service. Retrieved 2011-05-13.
- ^ ISBN 978-0-521-55986-7.
- ^ ISBN 978-0-89886-085-6.
- JSTOR 1943534.
- ^ Geiger, R. (1950). The Climate near the Ground. Cambridge, MA: Harvard University Press.
- JSTOR 2446122.
- ^ Shaw, C.H. (1909). "The causes of timberline on mountains: the role of snow". Plant World. 12: 169–181.
- ISBN 978-1-4020-2126-8.
- JSTOR 40511186.
- ^ JSTOR 1550141.
- JSTOR 213287.
- doi:10.1139/b78-243.
- ^ "Antipodes Subantarctic Islands tundra". Terrestrial Ecoregions. World Wildlife Fund.
- ^ "Magellanic subpolar Nothofagus forests". Terrestrial Ecoregions. World Wildlife Fund.
- ISBN 978-3-642-76424-0.
- ^ a b "Treeline". The Canadian Encyclopedia. Archived from the original on 2010-12-03. Retrieved 2011-06-22.
- hdl:10533/134794.
- JSTOR 2561632.
- ^ S2CID 8647814.
- ^ "Action For Scotland's Biodiversity" (PDF).
- ^ a b Körner, Ch. "High Elevation Treeline Research". Archived from the original on 2011-09-27. Retrieved 2010-06-14.
- ^ "Physiogeography of the Russian Far East".
- ^ "Mount Washington State Park". New Hampshire State Parks. Archived from the original on 2013-04-03. Retrieved 2013-08-22.
Tree line, the elevation above which trees do not grow, is about 4,400 feet in the White Mountains, nearly 2,000 feet below the summit of Mt. Washington.
- ^ "Georgia's natural resources and conservation" (PDF). geostat.ge (in Georgian). National Statistic Office of Georgia. Retrieved 2023-04-13.
- ^ ISBN 978-0-520-06922-0.
- ^ "台灣地帶性植被之區劃與植物區系之分區" (PDF). Archived from the original (PDF) on 2014-11-29.
- ^ "Mount Kinabalu National Park". www.ecologyasia.com. Ecology Asia. 4 September 2016. Retrieved 6 September 2016.
- ^ "Alpine trees | ANU Research School of Biology".
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- hdl:11336/141218.
- ^ hdl:11336/40918.
- ^ kimberleycollins (2012-04-12). "The Lone Tree of Campbell Island". Toroa. Retrieved 2021-09-05.
Further reading
- Arno, S.F.; Hammerly, R.P. (1984). Timberline. Mountain and Arctic Forest Frontiers. Seattle: The Mountaineers. ISBN 978-0-89886-085-6.
- Beringer, Jason; Tapper, Nigel J.; McHugh, Ian; Chapin, F. S. III; et al. (2001). "Impact of Arctic treeline on synoptic climate". .
- Ødum, S (1979). "Actual and potential tree line in the North Atlantic region, especially in Greenland and the Faroes". .
- Ødum, S (1991). "Choice of species and origins for arboriculture in Greenland and the Faroe Islands". Dansk Dendrologisk Årsskrift. 9: 3–78.
- Singh, C.P.; Panigrahy, S.; Parihar, J.S.; Dharaiya, N. (2013). "Modeling environmental niche of Himalayan birch and remote sensing based vicarious validation" (PDF). Tropical Ecology. 54 (3): 321–329.
- Singh, C.P.; Panigrahy, S.; Thapliyal, A.; Kimothi, M.M.; Soni, P.; Parihar, J.S. (2012). "Monitoring the alpine treeline shift in parts of the Indian Himalayas using remote sensing" (PDF). Current Science. 102 (4): 559–562. Archived from the original (PDF) on 2013-05-16.
- Panigrahy, Sushma; Singh, C.P.; Kimothi, M.M.; Soni, P.; Parihar, J.S. (2010). "The Upward Migration of Alpine Vegetation as an Indicator of Climate Change: Observations from Indian Himalayan region using Remote Sensing Data" (PDF). NNRMS(B). 35: 73–80. Archived from the original on November 24, 2011.
{{cite journal}}
: CS1 maint: unfit URL (link) - Singh, C.P. (2008). "Alpine ecosystems in relation to climate change". ISG Newsletter. 14: 54–57.
- Ameztegui, A; Coll, L; Brotons, L; Ninot, JM (2016). "Land-use legacies rather than climate change are driving the recent upward shift of the mountain tree line in the Pyrenees" (PDF). Global Ecology and Biogeography. 25 (3): 263. hdl:10459.1/65151.