Forest and tree line
The tree line is the edge of the habitat in which trees due to climatic factors ( Climatic forest boundaries ) or local or azonal site conditions ( Edaphic timberlines ) closed forests can form (that is, where the treetops just touch). This is to be distinguished from the tree line , beyond which no individual trees or groups of trees can appear.
In general usage , the two terms are primarily related to the climatic or extrazonal Alpine or upper forest and tree line , which characterize the transition area between the forested montane- free and the tree-free alpine vegetation level of the high mountains due to a too short vegetation period and too low temperatures ( mostly referred to as subalpine level).
In terms of global biogeography , the two polar forest and tree boundaries ( arctic or northern as well as Antarctic or southern ) are also temperature- related thermal forest and tree boundaries , the transition habitat of which is known as forest tundra (only occurring in the northern hemisphere ).
In addition, there is the hygric or lower tree line (differentiation of a similar tree line is very rare in the literature), another climatic forest line type of mountains . This boundary occurs in continental or arid climates in which forests can only thrive on more humid mountain slopes, while the climate of the valley locations is too dry for trees. The water shortage is too low for trees to grow below 400 mm of annual precipitation.
A fourth, (very rarely mentioned) upper climatic tree line is the exposure forest line , which refers to locations where strong winds prevent tree growth. On coasts and on isolated mountains , the tree line is therefore often much lower than in other mountains.
In addition to the climatic forest boundaries mentioned, there are locally very different locations that are called Edaphic forest boundaries (see also: edaphic ) due to unsuitable ( not directly climatically determined) soil conditions (too dry, too humid, too shallow, too rocky) .
Finally, there is sometimes talk of orographic forest boundaries (see also: Orography ) when barriers such as rock or glacier walls, avalanche channels and the like prevent forest growth.
Thermal forest and tree borders
At the thermal forest borders, tree growth is severely slowed down due to the lack of heat . Because of the shortness of the vegetation period, because of the stronger winds here and the pressure of snow for months , there are crippled tree shapes that only grow low and form dense bushes. The tree line, which is only a sharp line on a small scale, shows on closer inspection - like many other borders in nature - mostly sliding transitions: Trees grow less and less in the direction of the inhospitable climate until they finally fail completely. Different tree species penetrate furthest north in different sections of the tree line. Above all, this includes a group of cold-tolerant conifers , such as larches , pines , spruces and firs (forest tundra in Canada and Siberia ). Deciduous trees such as birch and alder only form the alpine and polar forest boundaries in oceanic zones (such as western Alaska , Greenland , Iceland , Lapland or Kamchatka ).
Polar boundaries
The decisive factor for the Arctic and Antarctic forest and tree borders is not the winter cold, but the duration and extent of the summer warming: If the air temperature is less than four months in the monthly average or less than three and a half months in the daily average below + 5 ° C or if not a month reached an average of more than + 10 ° C, respectively, the annual average of all daily temperature is above 0 ° C, then prevents the growth of trees: Seed germination is considerably more difficult and the young shoots of trees can not complete their growth to the Frosttrocknis of To survive winter.
The smooth transition from the forest to the tree line has created a forest tundra zone up to several hundred kilometers wide in the northern hemisphere . The associated subpolar climatic zone in the southern hemisphere lies exclusively over the oceans.
Alpine limits
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The highest height above sea level up to which forest or trees can grow. The (subalpine) space in between is known as the " Krummholzzone " or "-gürtel" or "Kampfzone" or "Kampfwald", in which upwards initially still forest islands, then only individual trees - also ever smaller, shrub-like and crippled forms - can be found before only dwarf shrub heaths and / or grass mats follow above the tree line . In the northern hemisphere , adapted woody species predominate in the forest border area, the growth forms of which are genetically determined, while in the tropics (in part) and in the southern hemisphere the same species at lower altitudes in the forest border area show dwarf and cripple growth due to climate (e.g. in the Andes Patagonia or New Zealand Alps ).
A sharply drawn tree line is also typical in the extra tropics of the southern hemisphere, so that there is no or only a very small space between the tree line and the tree line. Originally there was always a smooth transition in the northern hemisphere. The linear forest borders that can be found today are usually anthropogenic (clearing and cattle biting).
For several years it has been known that the natural tree line in the mountains - regardless of latitude - depends on the mean soil temperature (and not on extreme values!). If this temperature drops below a value of around +6.4 ° C at a depth of 10 cm (during the growing season), trees can no longer grow. Presumably, the absorption and transport of water and nutrients also deteriorates at low soil temperatures, which could explain the cripple growth. These findings also apply to the global thermal tree line.
The fact that the tree line in the southern hemisphere mountains is 200-300 meters lower with ground temperatures of a maximum of 8.9 ° to 9.5 ° C is explained by the lack of cold-tolerant conifers , or by an ecological niche not yet occupied by evolution .
An interesting phenomenon is the "self-shading" of trees in the border ecotone: tree seeds germinate and form young plants when the temperatures are above the threshold value mentioned. If the trees get bigger, however, your own shade can lower the mean soil temperature in the root area to such an extent that the tree can no longer grow or even dies.
The distance between the tree line and the tree line as well as the altitude is different and today is also influenced in many ways by humans .
The alpine timberline is also the dividing line between the underlying vegetation height levels - mainly from the vegetation be affected - and the overlying geomorphological altitude levels - subject to the priority physical processes.
Alpine forest / tree boundaries
In addition to the climatic factors mentioned, the alpine forest and tree line in one location also depends on local variables - such as the slope , the rain shadow and the like. Taking these factors into account, here is a list of the average heights from various points around the world:
| place | Approximate latitudes |
Approximate height of the tree line in meters |
Remarks |
|---|---|---|---|
| Santa Cruz Island , Galápagos | 0.5 ° S | 600 | isolated island without trees adapted to the climate |
| Kilimanjaro , Tanzania | 3 ° S | 3000 | |
| Puncak Trikora , New Guinea | 4 ° S | 3950 | |
| Kinabalu , Borneo | 6.5 ° N | 3400 | |
| Costa Rica | 9.5 ° N | 3400 | |
| Simien Mountains , Ethiopia | 13 ° N | 3000 | |
| Bolivian Andes | 17.5 ° S | 4100 | Polylepis forests, in places up to over 5000 m |
| USA , Hawaii | 20 ° N | 2800 | low rainfall above the trade winds |
| Mexico | 20 ° N | 4000 | Central high plateau |
| Himalayas | 28 ° N | 4400 | |
| United States, Yosemite | 38 ° N | 3200 | West side of the Sierra Nevada |
| United States, Yosemite | 38 ° N | 3600 | East side of the Sierra Nevada |
| Japanese Alps | 39 ° N | 2900 | Northern part |
| USA, Wyoming | 43 ° N | 3000 | |
| New Zealand Alps | 43 ° S | 1100 | Central South Island |
| Swiss Alps | 46 ° N | 2000 | the highest tree line in Europe is in Switzerland in the Mattertal |
| Altai ( Mongolia ) | 46 ° N | 2400 | Southern area, steppe zone |
| German Alps | 47.5 ° N | 1800 | |
| Altai ( Russia ) | 51 ° N | 1500 | Northern area, taiga zone |
| Tierra del Fuego ( Argentina ) | 54 ° S | 300 | |
| Kamchatka ( Russia ) | 56 ° N | 800 | |
| Chugach Mountains ( Alaska ) | 61 ° N | 900 | |
| Urals ( Russia ) | 65 ° N | 400 | Northern forest tundra zone |
| Swedish Lapland | 68 ° N | 750 |
The highest peaks of the Black Forest , the Bohemian Forest and the Brocken protrude above the tree line, with only the Brocken above the natural tree line. The freedom from forest on the peaks of Feldberg and Großem Arber is due to culture. Although the latter mountains are significantly higher than the Brocken, they are also more southerly and not as exposed as the Brocken.
Whether a tree line is natural can be seen from the presence of a Krummholzzone, which is present in the Brocken but is absent in the Feldberg and Großer Arber. In this regard, the 1214 meter high Fichtelberg almost seems to reach the natural tree line, because the trees on the summit already show a certain tendency to become crippled. The theoretical tree line would be there at 1,300 meters, i.e. as high as in the nearby Giant Mountains with the Schneekoppe protruding well beyond . Elsewhere in the Ore Mountains (in the statutes ) there are pines at an altitude of almost 900 meters.
In the Alps , the limit is between 1,800 and 2,200 meters above sea level. Culture-related, e.g. B. through alpine farming, the tree line in the Alps often appears lower than it is natural.
Types of tree line
An unsorted selection of typical tree line species:
- Antarctic beech ( Nothofagus antarctica )
- Arctic downy birch ( Betula pubescens subsp. Tortuosa )
- Mountain pine ( Pinus mugo ) or mountain pine , mountain pine, leg pine
- European larch ( Larix decidua )
- Foxtail Pine ( Pinus balfouriana )
- Awn pine ( Pinus aristata )
- Rumelian pine ( Pinus peuce ) or Macedonian pine
- Rowanberry ( Sorbus aucuparia )
- White-stemmed pine ( Pinus albicaulis )
- Swiss stone pine ( Pinus cembra )
See also
literature
- SF Arno, RP Hammerly: Timberline. Mountain and Arctic Forest Frontiers. The Mountaineers, Seattle, 1984, ISBN 0-89886-085-7 .
- Frank Hagedorn, Andreas Rigling, Peter Bebi: The tree line The Alps 9/2006.
- Conradin Burga, Frank Klötzli and Georg Grabherr (eds.): Mountains of the earth - landscape, climate, flora. Ulmer, Stuttgart 2004, ISBN 3-8001-4165-5 .
Web links
Remarks
- ↑ Google Books queries for “hygric tree line” with one hit (probably wrongly taken over from Wikipedia) and “hygric tree line” with two hits from older specialist literature, accessed on August 11, 2020.
- ↑ Google Books query for "exposed forest line" with one hit and "exposed tree line" without hits, accessed on August 11, 2020.
Individual evidence
- ↑ Christian Körner 2014: Why is there a tree line? Biology in Our Time 4: 250-257 (Wiley: PDF)
- ↑ Margarete Payer, Alois Payer (Ed.): Developing countries studies. Part I: Basic conditions. Chapter 4. Vegetation. HBI Stuttgart, 1998–1999, version dated February 7, 2001 (course Introduction to Developing Countries Studies ; online at payer.de).
- ↑ Karsten Grunewald and Jörg Scheithauer: Climate and Landscape History of Southeast Europe: Reconstruction based on geo-archives in the Pirin Mountains (Bulgaria) , Rhombos, Berlin 2008, p. 109.
- ^ S. Lipp, H. Steiner, J. Oettel, G. Frank: site protection forest in Austria. A study on the definition of terms and the allocation criteria using the example of natural forest reserves, BFW reports 150/2016, Federal Research Center for Forests, Vienna 2016, ISBN 978-3-902762-53-5 , online pdf version , accessed on August 11, 2020, Pp. 22, 26, 63-64.
- ↑ Keyword: tree line in the lexicon of biology on Spektrum.de, Heidelberg 1999, accessed on August 11, 2020.
- ↑ a b Jürgen Schultz: The ecological zones of the earth. 4th, completely revised edition, Ulmer UTB, Stuttgart 2008, ISBN 978-3-8252-1514-9 . Pp. 163-164.
- ↑ Burga, Klötzli u. Grabherr 2004, p. 37.
- ↑ Jörg S. Pfadenhauer and Frank A. Klötzli: Vegetation of the earth. Springer Spectrum, Berlin / Heidelberg 2014, ISBN 978-3-642-41949-2 . Pp. 73-78, 337-343.
- ↑ Werner Bätzing : Small Alpine Lexicon. Environment - economy - culture. CH Beck, Munich 1997, ISBN 3-406-42005-2 , pp. 104-108.
- ↑ http://link.springer.com/chapter/10.1007/978-3-642-76422-6_11