Alvar (landform)

from Wikipedia, the free encyclopedia
Alvar shrinking after the onset of the summer dry season near Djupvik, Öland , 2004

The word Alvar in Old Swedish, as in today's Swedish , denoted an almost treeless land, unsuitable for agriculture , with a thin layer of vegetation on a rocky limestone subsoil . The scientific and now internationally used definition adds that the limestone rock was more or less planed by the ice of the Ice Age and that Alvar has a summer-dry, hemiboreal climate . An Alvar is a unique, differentiated biotope with characteristic flora and fauna .

Geographical distribution

Alvar area on Kelleys Island in Lake Erie in Ohio , USA

Most impressive is the Alvar landscape on the Ordovician limestone subsoil on the Swedish Baltic island of Öland . In its southern part, an area of ​​about 255 square kilometers bears the name Stora Alvaret (Great Alvar). Together with the adjacent farming landscape, it was declared a World Heritage Site by UNESCO in 2000 as the “ Agricultural Landscape of South Öland ” .

Smaller Alvar can be found in northern Öland, on the Silurian limestone of the neighboring island of Gotland and in the central Swedish province of Västergötland . Of the total of about 995 km² Alvar on earth , about 665 km² are in Sweden. The approximately 160 km² Alvar in Estonia are mainly located on the Silurian Limestone Islands Saaremaa ( German  "Ösel" ), Hiiumaa ( German  "Dagö" ) and Muhu . In Russia there is a small area southwest of Saint Petersburg . The approximately 110 km² in North America can be found in the Ordovician-Silurian Arc south of the Canadian primary rock shield in the Great Lakes area in Ontario , Michigan , Ohio , and New York .

The size information can only be approximate because the Alvar landscape is subject to constant changes, some of which are natural and some are of human origin. In Estonia, around 270 km² of Alvar has been lost since 1930 through state-planned land reclamation projects in connection with the collectivization of agriculture. But even Alvar landscapes left to their own devices would constantly change through natural processes, that is: bushes spread out until the first trees can gain a foothold. So the Alvar would eventually become forest if it were not exposed to the constant influence of humans. Stora Alvaret has been preserved in its character through extensive grazing since the Middle Ages .

vegetation

Example Stora Alvaret on Öland

The uniqueness of the Alvar vegetation is due to the effect of special climatic conditions on the rocky limestone subsoil. A winter with long frosts and strong winds is followed by relatively light rains in spring; the summer is hot and dry; autumn again brings little rain.

Orchid flower of the elder orchid ( Dactylorhiza sambucina ) in the Alvar near Knisa mosse on Öland, 2004

Thanks to increased photosynthesis , for example, many Alvar species are adapted to the short period of favorable growth and reproductive conditions, so that when the dry season soon sets in, their seeds have already matured. A conspicuous consequence is the colorful flowering period of numerous species over wide areas, compressed to a few weeks in spring, in the Stora Alvaret for example the chives ( Allium schoenoprasum var. Oelandicum ), which forms a magenta-colored lawn; the white little meadowsweet ( Filipendula vulgaris ); the yellow stonecrop ( Sedum acre ) and the white stonecrop ( Sedum album ), a number of orchid species , among which the yellow and red mixed stocks of the elder orchid ( Dactylorhiza sambucina , Swedish Adam och Eva ) are a tourist attraction.

Alvar vegetation a. a. with finger bush ( Potentilla fruticosa ) 's Small meadowsweet ( Filipendula vulgaris ) and White fat hen ( Sedum album ) along a column on Karst Öland

Another consequence of the interplay of climate and soil in the Alvar is the close coexistence of the most diverse biotopes. Almost invisible blue-green algae ( cyanobacteria ) species (e.g. Gloeocapsa spec. ) And up to a hundred lichen species live on the seemingly bare horizontal rock slabs . In the gaping crevices through which the slabs are traversed and in which weathered gravel and humus collect, up to 51 species of taller plants per square meter were found. On short stretches, the degree of weathering of the rock bed alternates between gravel , granular and fine gravel or the almost coal-black humus typical of lime weathering. Correspondingly, the thickness of the rock bedding varies between a few millimeters and several decimeters. As long as the layer of soil above the rock is thin, it is not only dried out by the summer heat, but also moved by frost in winter and, so to speak, tumbled through, so that hump-like or wave-like deformations of the soil occur. This process is another stress factor to which the species that live on such thin layers of soil are adapted.

Another parameter that varies everywhere is the water permeability of the soil. Rainwater soon seeps away on karst subsoil, leaving the surface to dry out more quickly. Elsewhere, water can not penetrate deeper into the soil, is not on the horizontal drainage by radicals of silicate - moraines prevented. So damp patches created with lush grass and bush vegetation Kalksümpfe with muddy lawn of mosses Scorpidium scorpioides and pseudo Calliergon turgescens at the bottom and large stocks of sedges (z. B. Stiff sedge ( Carex elata )), reed ( Phragmites australis ) and bins cutting ( Cladium mariscus ), even shallow lakes like Möckelmossen between Resmo and Stenåsa or Knisa mosse near Sandvik . In summer such wetlands get smaller, but none of them dry out completely, except in the disaster summers, which come about every seven to ten years. They are often breeding grounds for sea and shore birds and resting places for cranes .

A wide variety of species groups with different survival strategies against competitors, stress factors (temperature extremes, nutrient deficiency, dehydration) as well as human impact, for example through grazing or deforestation, settle along the parameters of the depth and moisture penetration of the soil .

The interaction of the climate typical of the Alvar (hard winters, moderate precipitation, hot dry summers) with the geological factors outlined results in geobotanically conspicuous phenomena, namely the increased occurrence of endemics (only occurring here) and of relic species (i.e. species that live on Were widespread at the end of the Ice Age and in post- Ice Age warm periods, but are now only found in the Alvar, isolated from their present occurrences). The list of these species is remarkable.

Endemic species

Sparse Alvar vegetation with Arenaria gothica and several Sedum species on the Kinnekulle (Sweden)

The abbreviations “Ö” and “G” following the species names in the following list of endemic species indicate the respective occurrence on Öland and / or Gotland .

Relic species

The abbreviations “Ö” and “G” following the species names in the following list of relict species identify the respective occurrence on Öland and / or Gotland .

Arctic-alpine:

South West European:

Mediterranean:

Southeast European:

Continental / Siberian:

Circumpolar:

fauna

An equally special insect fauna lives together with the Alvar special flora .

Alvar am Kinnekulle - The net-like vegetation along rock crevices that are still covered by the ground is a characteristic of many karst areas .
Shrubby Alvar area in the south of Öland

Sociological aspects of vegetation history

Today's image of Alvar has a dynamic that is hidden from the eye and which, in its stages, is only revealed to the historical view. In the 19th century the Alvar was almost devoid of bushes and trees. This was not just due to extensive grazing. Another factor was the poverty of the landless cottagers who, descended from the non-inheriting sons of the village farmers, were living a poor life in a kind of slum (Swedish: malm ) in steadily increasing numbers on the edge of the village . To warm their primitive huts and to cook their meager meals, they had to rely on what day-long collective hikes out to the Alvar could bring: if they were lucky, real firewood from a leftover tree, but mostly only bundles of brushwood and cow dung to be dried.

With the turn of the 20th century that changed. Some of the Malm residents found work in the emerging industry on the mainland; many left with the great wave of emigration to America . A little later, mechanization and intensification began in agriculture. But an attempt was made to reclaim land using the new methods only in the margins of the Alvar. The real Alvar was more and more left to its own devices, initially to the advance of the equally aggressive and tough juniper , the ever thicker bushes and the eventual emergence of forest.

In the second half of the 20th century, nature conservation put a stop to these tendencies, which threatened to reduce the biodiversity of the Alvar. Controlled forest fires (although this is only used in North America) and de-bushing projects and government grazing subsidies have proven to be effective means of returning the Alvar to its open state . H. the farmers are paid to keep grazing cattle on the Alvar.

UNESCO world heritage

Efforts to protect the Alvar have been motivated and intensified since 2000 by the fact that the villages on the Stora Alvar were awarded the UNESCO World Heritage seal as the “ Agricultural Landscape of South Öland” (or “Farming Landscape of Southern Öland”) . The brief justification for the award shows that UNESCO recognizes what is worth preserving about this piece of earth in its character as a cultural (and not, for example, a natural heritage relatively untouched by humans):

“Today's landscape in southern Öland is shaped as much by its long cultural history as it is by geological and topographical conditions. The farming landscape ( odlingslandskap ) of southern Öland is a unique example of how humans use the multiform landscape (...) in an optimal way. "

The Alvar appears here as an integral part of an ensemble that is grouped around the Zeilendörfer on the western and eastern edge of the Alvar. These impress with their wonderfully simple, solid wooden courtyard buildings painted in ox blood color. Beyond this, the fertile farmland sloping west to Kalmarsund , on the other side of the island first farmland, then the productive pastureland of the sea meadows that run flat into the Baltic Sea ( sjömarker ). These are one of the ornithologists treasured bird sanctuary , which from the Ornithological Ottenby is monitored at the southern tip of the island. It is as exceptionally rich in species in birds as the Alvar in plants.

This ensemble has a very old cultural history. Agriculture was practiced here as early as the Stone Age (around 3000 BC), as evidenced by the impressive remains of refuges and settlements in and on the Alvar. The districts of the Zeilendörfer were essentially determined during the Middle Ages. Today the ensemble of Alvar, Seewiesen, farmland and rural villages is a perfect example of how stylishly one understands in Sweden how to complement an old rural tradition full of simple dignity with an unobtrusively elegant, efficient modernity.

literature

  • N. Albertson: The great southern Alvar of the island of Öland. Svensk Botanisk Tidskrift 44 (2). 1950.
  • PM Catling: The extent of confinement of vascular plants to alvars in southern Ontario. Canadian Field Naturalist 109 (2): pp. 172-181. 1995.
  • PM Catling, VR Brownell: A review of the alvars of the Great Lakes region: Distribution, floristic composition, biogeography and protection. Canadian Field Naturalist 109 (2): pp. 143-171. 1995.
  • U. Ekstam, N. Forshed: Svenska alvarmarker - historia och ekologi. Naturvårdsverket Förlag, Stockholm 2002. ISBN 91-620-1222-3 .
  • MOG Eriksson, E. Rosén: Management of Natura 2000 habitats. 6280 Nordic alvar and precambrian calcareous flatrocks. (PDF; 688 kB) European Commission. 2008.
  • A. Johansson, P. Larsson: Ölands stora alvar. Männniskor och miljöer. Carlssons Bokförlag, Stockholm 1992. ISBN 91-7798-581-8 .
  • M. Pärtel, R. Kalamees, M. Zobel, E. Rosén: Alvar grasslands in Estonia: Variation in species composition and community structure. Journal of Vegetation Science 10: pp. 561-568. 1999.
  • C. Reschke, R. Reid, J. Jones, T. Feeney, H. Potter: Conserving Great Lakes alvars. Final technical report of the international alvar conservation initiative. The Nature Conservancy Chicago. 1999.
  • E. Rosén: Periodic droughts and long-term dynamics of alvar grassland vegetation on Öland, Sweden. Folia Geobot. Phytotax. 30: pp. 131-140. 1995.
  • H. Rydin, P. Snoeijs, M. Diekmann: Swedish plant geography. Acta Phytogeographica Suecica 84. Svenska Växtgeografiska Sällskapet, Uppsala 1999. ISBN 91-7210-084-2 .
  • R. Sterner: Öland's kärlväxtflora. 2nd rev. Ed. Å. Lundqvist from flora of the island of Öland . Acta Phytogeographica Suecica 9 (1938). 1985. ISBN 91-86344-36-6 .

Web links

Commons : Alvar  - collection of images, videos and audio files

Individual evidence

  1. ↑ Hemiboreal is the ecozone in which coniferous and deciduous forest occur mixed, in contrast to the northern boreal zone with pure coniferous forest and the southern nemoral zone with pure deciduous forest.
  2. ↑ Ekstam and Forshed 2002, p. 61
  3. ↑ Ekstam and Forshed 2002, p. 86
  4. ↑ This complex process is described in detail in Ekstam and Forshed 2002, p. 94 ff.
  5. ↑ A classification in the plant societies established by plant sociology is offered by Ryden et al. 1999, pp. 124-130
  6. ^ On the concept of survival strategies see: JP Grime: Evidence for the existence of three primary strategies in plants and its relevance to ecological and evolutionary theory. The American Naturalist 111: pp. 1169-1194. 1977.
  7. ↑ a b c See Rydin et al. 1999, p. 126. A detailed discussion of the types of relics can be found in Ekstam and Forshed 2002, pp. 38–46.
  8. ↑ Illustrated descriptions of the insect fauna can be found in Ekstam and Forshed 2002, passim .
  9. ↑ In detail Johansson and Larsson 1992
  10. ↑ In older literature one occasionally finds the view that the noticeably greater biodiversity in limestone areas with their higher pH value compared to that in low-pH silicate soils is based on the fact that limestone soils are rich in nutrients precisely because of their lime content. In contrast, more recent research assumes that the lime content means that limestone soils are particularly poor in mineral plant nutrients, especially phosphorus. The calcicolen (“lime-loving”) plants could have adapted to this deficiency in the course of their evolution. Their survival strategy is not that they are better able to use a certain resource, namely lime, than their competitors, but that their stress tolerance is greater under conditions of nutrient poverty. It is undisputed that calcicole species are unable to adapt to more nutrient-rich conditions. The same applies to the fact that the proportion of calcicoler plant species in the flora of Sweden, for example, is much larger than the proportion of limestone soils in the total area of ​​the country. This becomes apparent as soon as one has left the mainland, which is determined by the “acid” granite, and enters the “basic” limestone islands of Öland and Gotland with their great biodiversity. (cf. Ekstam and Forshed, 2002, pp. 47–48)
  11. ↑ Världsarvet Södra Ölands odlingslandskap ( Memento from August 30, 2007 in the Internet Archive ), on the website of the provincial government of Kalmar län (Swedish)