Tree line 463469 223281499 2008-07-03T11:30:11Z Ghirlandajo 147410 /* References */ [[Image:Tree line.jpg|thumb|300px|In this view of an alpine tree line, the distant line looks particularly sharp. The foreground shows the transition from trees to no trees. These trees are stunted and one-sided because of cold and winds.]] The '''tree line''' or '''timberline''' is the edge of the habitat at which [[tree]]s are capable of growing. Beyond the tree line, they are unable to grow because of inappropriate environmental conditions (usually cold temperatures, insufficient air pressure, or lack of moisture). 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 language|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. Trees grow shorter towards the inhospitable climate until they simply stop growing. == Types of tree lines == There are several types of tree lines defined in [[ecology]] and [[geology]]: * '''Alpine tree line''' The highest [[elevation]] which sustains trees; higher up, it is too cold or snow cover persists for too much of the year, to sustain trees. Usually associated with [[mountain]]s, the [[climate]] above the tree line is called an [[alpine climate]], and the terrain can be described as [[alpine tundra]]. Mountains of the [[Pacific Northwest]] of North America exhibit lower treelines on north-facing slopes than south-facing slopes, because increased shade means the deep [[snowpack]] takes longer to melt, which shortens the growing season for trees. * '''Desert tree line''' The driest places that trees can grow; drier [[desert]] areas having insufficient [[rainfall]] to sustain trees. These tend to be called the "lower" tree line and occur below about 5000 ft (1500 m) elevation in the Desert [[Southwestern United States]]. The desert treeline tends to be lower on pole-facing slopes than equator-facing slopes, because the increased shade on a pole-facing slope keeps those slopes cooler and prevents moisture from evaporating as quickly, giving trees a longer growing season and more access to water. * '''Desert-Alpine tree line''' In some mountainous areas, higher elevations above the [[condensation]] line or on south-facing in the northern hemisphere and north-facing in the southern hemisphere, or 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. The slopes of [[Mauna Loa]] above 10,000 ft in [[Hawaii]] are an example of this. 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. * '''Exposure tree line''' On [[coast]]s and isolated mountains, the tree line is often much lower than in corresponding altitudes inland and in larger, more complex mountain systems, because strong [[wind]]s reduce tree growth. In addition, the lack of suitable soil, such as along [[scree|talus slopes]] or exposed rock formations prevent trees from gaining an adequate foothold and expose them to drought and sun. * '''Arctic tree line''' The furthest [[north]] in the [[Northern Hemisphere]] that trees can grow; further north, it is too cold to sustain trees. Extremely cold temperatures can result in freezing of the internal sap of trees, killing those trees. In addition, [[permafrost]] in the soil can prevent trees from getting their roots deep enough for the necessary structural support. * '''Antarctic tree line''' The furthest [[south]] in the [[Southern Hemisphere]] that trees can grow; further south, it is too cold to sustain trees. It is a theoretical concept that does not have any defined location. No trees occur on [[Antarctica]] or the [[sub-antarctic islands]], and there are no land masses to the north that have a true treeline. * '''Other tree lines''' The immediate environment is too extreme for trees to grow. This can be caused by geothermal exposure associated with hot springs, such as at [[Yellowstone]], or near [[volcanoes]], high soil acidity near [[bog]]s, high salinity associated with [[playas]] or [[salt lakes]], or ground that is too saturated by ground water which excludes [[oxygen]] from the soil, which most tree [[root]]s need for growth. The margins of [[muskeg]]s and bogs are common examples of these types of open areas. However, no such line exists for [[swamp]]s, where trees, such as [[Taxodium|Bald cypress]] and the many [[mangrove]] species, are adapted to growing in permanently waterlogged soil. == Typical vegetation == [[Image:Jojo-Maly Szyszak 2005.jpg|thumb|Severe winter climate conditions at alpine tree line causes stunted ''krummholz'' growth. [[Karkonosze]], Poland.]] [[Image:Larix gmelinii0.jpg|thumb|[[Dahurian Larch]] growing close to the Arctic tree line in the Kolyma region, Arctic northeast Siberia.]] Some typical Arctic and alpine tree-line tree species (note the predominance of [[conifer]]s): *[[Subalpine fir]] (''Abies lasiocarpa'') *[[Subalpine Larch]] (''Larix lyallii'') *[[Engelmann Spruce]] (''Picea engelmannii'') *[[Whitebark Pine]] (''Pinus albicaulis'') *[[Great Basin Bristlecone Pine]] (''Pinus longaeva'') *[[Rocky Mountains Bristlecone Pine]] (''Pinus aristata'') *[[Foxtail Pine]] (''Pinus balfouriana'') *[[Dahurian Larch]] (''Larix gmelinii'') *[[Potosi Pinyon]] (''Pinus culminicola'') *[[Macedonian Pine]] (''Pinus peuce'') *[[Swiss Pine]] (''Pinus cembra'') *[[Mountain Pine]] (''Pinus mugo'') *[[Hartweg's Pine]] (''Pinus hartwegii'') *[[Betula pubescens|Arctic White Birch]] (''Betula pubescens'' subsp. ''tortuosa'') *[[Polylepis]] (''Polylepis tarapacana'') *[[Eucalyptus pauciflora|Snow Gum]] (''Eucalyptus pauciflora'') *[[Nothofagus antarctica|Antarctic Beech]] (''Nothofagus Antarctica'') *[[Nothofagus pumilio|Lenga Beech]] (''Nothofagus pumilio'') *[[Black spruce]] (''Picea mariana'') ==Worldwide distribution== ===Alpine tree lines=== The alpine tree line at a location is dependent on local variables, such as [[aspect (geography)|aspect]] of slope, [[rain shadow]] and proximity to either [[geographical pole]]. In addition, in some tropical or island localities, the lack of biogeographical access to species that have evolved in a sub-alpine environment, can result in lower tree lines than one might expect by climate alone. Given this caveat, here is a list of approximate tree lines from locations around the globe: {| class="wikitable" !align="left" rowspan="2"|Location !align="left" rowspan="2"|Approx. latitude !colspan=2|Approx. elevation of tree line !rowspan="2" |Notes |- !align="center"|(m) !align="center"|(ft) |- |[[Sweden]] |68°N |align="center"|800 |align="center"|2600 | |- |[[Norway]] |61°N |align="center"|1100 |align="center"|3600 |Lower near the coast |- |[[Olympic Mountains]] WA, [[USA]] |47°N |align="center"|1500 |align="center"|5000 |Heavy winter snowpack buries young trees until late summer |- |[[Swiss Alps]] |46°N |align="center"|2100 |align="center"|7000 | Higher on the southern side of the Alps. |- |Alps of [[Piedmont]], Northwestern [[Italy]] |45°N |align="center"|2100 |align="center"|7000 | |- |[[Rila]] |42°N |align="center"|2300 |align="center"|7700 | [[Mountain Pine]] is the most common tree line species |- |[[Mount Katahdin]], [[Maine]], [[USA]] |46°N |align="center"|1158 |align="center"|3800 |- |[[New Hampshire]], [[USA]] |44°N |align="center"|1220 |align="center"|4000 | Some peaks have even lower treelines because of fire and subsequent loss of soil, such as [[Grand Monadnock]] and [[Mount Chocorua]]. |- |[[Wyoming]], [[USA]] |43°N |align="center"|3000 |align="center"|10000 | |- |[[Wasatch Mountains]], [[Utah]], [[USA]] |40°N |align="center"|2900 |align="center"|9500 |Higher (nearly 11,000 feet) in the [[Uintas]] |- | rowspan="2" |[[Rocky Mountain National Park|Rocky Mountain NP]], [[USA]] | rowspan="2" |40°N |align="center"|3500 |align="center"|11500 |On warm southwest slopes |- |align="center"|3250 |align="center"|10800 |On northeast slopes |- |[[Japanese Alps]] |39°N |align="center"|2900 |align="center"|9500 | |- | rowspan="2" | [[Yosemite National Park|Yosemite]], [[USA]] | rowspan="2" |38°N |align="center"|3200 |align="center"|10500 |West side of [[Sierra Nevada (U.S.)|Sierra Nevada]] |- |align="center"|3600 |align="center"|11800 |East side of Sierra Nevada |- |[[Popocatepetl]], [[Mexico]] |28°N |align="center"|4000 |align="center"|13000 |- |[[Himalaya]] |28°N |align="center"|4400 |align="center"|14400 | |- |[[Hawaii]], [[USA]] |20°N |align="center"|2800 |align="center"|9000 |Precipitation low above the [[trade wind]]s |- |[[Costa Rica]] |9.5°N |align="center"|3400 |align="center"|11200 | |- |[[Mount Kilimanjaro]], [[Tanzania]] |3°S |align="center"|3000 |align="center"|10000 |Example of a tropical location lacking biogeographical access to species that are evolved for living in a subalpine environment. Thus, the tolerance of the indigenous species is lower and it results in a lower tree line |- |[[New Guinea]] |6°S |align="center"|3900 |align="center"|13000 | |- |[[Andes]], [[Peru]] |11°S |align="center"|3900 |align="center"|13000 |East side; on west side tree growth is restricted by dryness |- | rowspan="2" |[[Andes]], [[Bolivia]] | rowspan="2" |18°S |align="center"|5200 |align="center"|17000 |Western Cordillera; highest treeline in the world on the slopes of Sajama Volcano (Polylepis tarapacana) |- |align="center"|4100 |align="center"|13000 |Eastern Cordillera; treeline is lower because of lower solar radiation (more humid climate) |- |[[Sierra de Córdoba]], [[Argentina]] |31°S |align="center"|2000 |align="center"|6500 |Precipitation low above [[trade winds]], also high exposure |- | rowspan="2" |[[Australian Alps]], [[Australia]] | rowspan="2" |36°S |align="center"|2000 |align="center"|6500 |West side of Australian Alps |- |align="center"|1700 |align="center"|5500 |East side of Australian Alps |- |[[South Island]], [[New Zealand]] |43°S |align="center"|1200 |align="center"|4000 |Strong maritime influence serves to cool [[summer]] and restrict tree growth |} ===Arctic tree lines=== Like the alpine tree lines shown above, polar tree lines are heavily influenced by local variables such as [[aspect (geography)|aspect]] of slope and degree of shelter. In addition, [[permafrost]] has a major impact on the ability of trees to place roots into the ground. When roots are too shallow, trees are susceptible to windthrow and erosion. Trees can often grow in river [[valleys]] at latitudes where they could not grow on a more exposed site. Maritime influences such as [[ocean currents]] also play a major role in determining how far from the equator trees can grow. Here are some typical polar treelines: {| class="wikitable" !align="left"|Location !align="left"|Approx. longitude !colspan=1|Approx. latitude of tree line !Notes |- |[[Norway]] |24°E |align="center"|70°N |The [[North Atlantic current]] makes Arctic climates in this region warmer than other coastal locations at comparable latitude. In particular the mild winters prevents [[permafrost]]. |- |[[West Siberian Plain]] |75°E |align="center"|66°N | |- |[[Central Siberian Plateau]] |102°E |align="center"|72°N |Extreme [[continental climate]] means the summer is warm enough to allow tree growth at higher latitudes, extending to 72°30'N at Ary-Mas (102° 27' E) in the [[Novaya River]] valley, a tributary of the [[Khatanga River]]. |- |[[Russian Far East]] ([[Kamchatka Peninsula|Kamchatka]] and [[Chukchi Peninsula|Chukotka]]) |160°E |align="center"|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 |align="center"|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 |align="center"|69°N |Reaches north of the Arctic Circle because of the continental nature of the climate and warmer summer temperatures. |- |[[Nunavut]] |95°W |align="center"|61°N |Influence of the very cold [[Hudson Bay]] moves treeline southwards. |- |[[Quebec]] |72°W |align="center"|56°N |Very strong influence of the [[Labrador Current]] on summer temperatures. In parts of [[Labrador]], the treeline extends as far south as 53°N. |- |[[Greenland]] |50°W |align="center"|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. |- |} ===Antarctic tree lines=== [[Kerguelen Island]], [[Île Saint-Paul]], [[South Georgia]], and other Sub-Antarctic islands are all so heavily wind exposed and marginal in climate, that none have any indigenous tree species, although many such islands receive enough rainfall that they would otherwise be capable of hosting [[temperate rain forest]]. However, these are not directly related to the Antarctic tree line, but are related to exposure. [[Image:BeagleChannelGlacier.jpg|thumb|Trees growing along the north shore of the [[Beagle Channel]], 55°S.]] ==See also== *[[Ecotone]]: a transition between two adjacent ecological communities *[[Edge effect]]: the effect of contrasting environments on an ecosystem *[[Massenerhebung effect]] *[[Tundra]]: an area where tree growth is inhibited by low temperatures and short growing seasons ==References== *Arno, S. F. & Hammerly, R. P. 1984. ''Timberline. Mountain and Arctic Forest Frontiers.'' The Mountaineers, Seattle. ISBN 0-89886-085-7 *Ødum, S. 1979. Actual and potential tree line in the North Atlantic region, especially in Greenland and the Faroes. ''Holarctic Ecology'' 2: 222-227. *Ødum, S. 1991. Choice of species and origins for arboriculture in Greenland and the Faroe Islands. ''Dansk Dendrologisk Årsskrift'' 9: 3-78. *Beringer, J., Tapper, N. J., McHugh, I., Lynch, A. H., Serreze, M. C., & Slater, A. 2001. Impact of Arctic treeline on synoptic climate. ''Geophysical Research Letters'' 28 (22): 4247-4250. [[Category:Trees]] [[Category:Conifers]] [[Category:Forestry]] [[Category:Climate]] [[da:Trægrænse]] [[de:Waldgrenze]] [[es:Línea arbolada]] [[eo:Arbarolimo]] [[fr:Limite des arbres]] [[it:Linea degli alberi]] [[nl:Boomgrens]] [[ja:森林限界]] [[pl:Granica drzew]] [[pt:Linha das árvores]] [[ru:Альпийский пояс]] [[simple:Tree line]] [[fi:Puuraja]] [[sv:Trädgränsen]]