Hardwood meadow

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Hardwood floodplain in the Morava area

A Hartholzaue even Harte Au , Hard floodplain forest , hard floodplain or hardwood forest , is one of hardwoods existing riparian forest . Hardwood meadows are flooded once or twice a year for between 20 and 50 days with 0.5 m to 3 m areas of the rivers and streams of the middle and lower reaches or in silting oxbow lakes , e.g. B. cut meanders . Hardwood meadows are rarely found on the upper reaches of the low mountain range. They are replaced here by gray alder and red alder-ash riparian forests.

Like all alluvial forests, the hardwood floodplain is one of the azonal vegetation units of Central Europe .

Plant species

Tree layer

Due to the lower flow speed, duration of flooding and water depth compared to the softwood floodplain, woody plants , the alternating moisture, establish themselves in the hardwood floodplain . H. can tolerate the alternation between floods and drought. The most important tree species are English oak , field elm , flutter elm , common ash and sycamore maple , although the proportions of the species can vary greatly from region to region. The pedunculate oak ( Quercus robur ), which is characterized primarily by its resistance to flooding, is often a feature of the population . After the extensive loss of the elm due to the dying of the elm , it has taken over their habitat in many alluvial forests. However, the common oak is currently only slowly or not at all rejuvenating in many alluvial forests and is becoming less common in rejuvenation and in the shelter, its share is then mainly taken up by the ash.

The tree species of the hardwood floodplain forests are superior to the willow and poplar species of the softwood floodplain. However, these are not only less sensitive to long-lasting floods, they also tolerate mechanical damage better (e.g. from ice drift). The black alder is only involved in the population when the groundwater level is high (transition to the broken forest ).

Second layer of trees and bushes

The wild grapevine ( Vitis vinifera subsp. Sylvestris , Syn .: Vitis sylvestris ) has its original home in alluvial forests. The species occurs in Germany only in the warmest regions, in the Upper Rhine Plain. It is controversial whether it was native to the area or whether it was overgrown early on from the culture.

Herb layer

Common forest floor herbs and nutrient indicators are: wood anemone , celandine , yellow anemone , forest yellow star , real carnation root , Gundermann , forest ziest , giant fescue , forest twinkle , spotted dead nettle , ground elder .

Actual riparian forest species are rare and only found in a few stocks: winter horsetail , snake leek , regional two-leaved squill .

Hardwood Flooring Societies

The zonal societies of the mixed beech and oak forests are replaced in the floodplains by the azonal mixed oak forests of the hardwood floodplains regardless of the vegetation zone ( see: Forest Societies of Central Europe ).

In areas that are regularly flooded, populations are established that are associated with the elm-pedunculate oak forest Querco-Ulmetum minoris, named after the pedunculate oak ( Quercus robur ) and the field elm ( Ulmus minor ). This type of forest is the actual hardwood floodplain forest. Together with the stream floodplain forests, it forms the Alno-Ulmion association within the beech forests and beech forest-like deciduous forests of Europe (order Fagetalia) in the plant-sociological system. Types of separation between the elm-pedunculate oak and the floodplain forests are Acer campestre , Carpinus betulus , Crataegus laevigata and C. monogyna , Hedera helix , Ligustrum vulgare , Malus sylvestris , Populus alba , Pyrus pyraster , Quercus robur , Ulmus laevis and U. minor ; Strangely enough, only woody plants. The elm-pedunculate oak alluvial forest as an azonal forest community is very widespread in Europe. Accordingly, a distinction can be made between regional and soil-scientifically defined training courses.

  • Training with Ulmus laevis . Only on soils poor in lime.
  • Training with Populus alba , Malus sylvestris , common cobblestone ( Tamus communis ), Juglans regia , almond-leaved milkweed ( Euphorbia amygdaloides ), grapevine ( Vitis sylvestris ). Warmth-loving breed from the Upper Rhine region.
  • Training with Anemone ranunculoides , Glechoma hederacea , Sambucus nigra , wild garlic ( Allium ursinum ). On nutrient-rich soils (therefore lacking in the alluvial forests of the Alpine rivers).
  • Training with cane grass . On evenly wet gley or wet gley soils in the upper Danube region and on the Alpine rivers.

In particularly wet floodplain sections on the lower Danube, the Rhine and the Main, the elm-pedunculate oak floodplain forest is replaced by the black alder-ash floodplain forest (the Pruno-Fraxinetum ), which is otherwise particularly widespread in brook floodplains . In addition to the namesake bird cherry ( Prunus padus ) and ash ( Fraxinus excelsior ), black alder ( Alnus glutinosa ) and white elm ( Ulmus laevis ) are common here, while the common oak recedes. The black alder-ash alluvial forest, however, avoids the actual bank zone of the streams and larger rivers.

When a meander is cut and an oxbow is formed, hardwood floodplains merge into swamp forests . With constant overflow, alder breaks occur .

Only in the highest parts of the hardwood floodplain does the European beech manage to gain a foothold in oceanic climates, as it is sensitive to waterlogging and fluctuating groundwater levels, floods and the associated reductive soil conditions. Pedunculate oak , hornbeam and elm tolerate these conditions better than the common beech.

The low flow rate at high water events resulting in hardwood floodplain forest mostly to the deposition of finer sediments such as clay and clay ( floodplain Vega Clay and Vergleyung ). The exception here are the Alpine rivers, where gravel also forms the subsoil in the hardwood floodplain forest. It is usually assumed that the alluvial clay deposits are caused by humans (increased erosion in the catchment area, mainly due to arable farming). By nature, the rivers of the low mountain ranges also have gravel-shaped floodplains.

Landscape ecological value

“Of all of our Central European forest communities, the oak-elm floodplain forest is the most diverse in terms of structure, number of species and small-scale alternation of different forms of training. With several species-rich tree and shrub layers and thus a high proportion of phanerophytes , with an irregular canopy in which individual giant trees can exceed 35 m in height, with lianas and a warm, humid stand climate, our alluvial forest deviates significantly from the forests of Central Europe, which are mostly poor in tree species and stands in the vicinity of warm, even tropical wet forests ”( Erich Oberdorfer ). Hardwood meadows are rich in large-volume dead wood because of the frequent natural disturbances ; the different development phases of the forest can occur side by side in small spaces and thus offer a great variety of habitats. Hardwood meadows form a pronounced second tree layer or shrub layer, which is dominated by the old trees and is disturbed by prolonged floods. This creates forests with old oaks and elms exposed to the sun, which are the ideal habitat for stern species such as the large oakbuck . Since oaks and elms have lighter crowns than the common beech, the development of a very dense undergrowth is encouraged.

Species of the hardwood meadows

Other animal species are bats , v. a. the water bat , otter , beaver , hedgehog .

Causes of decline and legal protection

The hardwood meadows are among the most endangered biotopes in Central Europe; their natural forest communities are also threatened with extinction or extinct in certain areas. Originally, hardwood floodplains were on all rivers and streams, v. a. Widespread on the Elbe , Danube and Rhine and also has a major impact. In addition, there were all the smaller rivers of the hill and lowlands, provided that there were no bogs , softwood meadows, bodies of water and breaks.

The overflow and the long-term wetness promote the development of floodplain Vega soils. These very fertile soils made the floodplains popular for settlements as early as Roman times. Through the settlement activities and the use as a hut forest , forest fields, later pastures and fields; and due to the need for wood, the hardwood meadows were probably already in decline in the High Middle Ages . In modern times the guard was widened and further forests cleared, from the 18th century hardwood meadows were used for forestry .

The conversion of hardwood meadows into grassland and arable land continued in Central Europe until the late 20th century. In the 19th and 20th centuries, human interventions, v. a. Construction, river straightening and afforestation with other tree species are the strongest factors of decline. The fungus ( Ceratocystis ulmi ) transmitted by the great elm splint beetle ( Scolytus scolytus ) leads to extensive death of the elms (especially Ulmus minor ) and to a change in the natural forest communities even in natural hardwood meadows.

According to the Habitats Directive , Annex I, hardwood alluvial forests are “natural habitats of community interest, for the conservation of which special protected areas must be designated”. In Germany they are "legally protected biotopes" according to § 30 BNatSchG , which are subject to special protection even without further instructions (observe state laws).

literature

Individual evidence

  1. ^ Manfred A. Fischer, Karl Oswald, Wolfgang Adler: Excursion flora for Austria, Liechtenstein and South Tyrol . 3rd, improved edition. Province of Upper Austria, Biology Center of the Upper Austrian State Museums, Linz 2008, ISBN 978-3-85474-187-9 , p. 1276 .
  2. ^ Judith Gläser: Historical alluvial forest development in the Leipzig alluvial forest (PDF) ( Memento from December 24, 2013 in the Internet Archive ). Dissertation TU Dresden , 2002.
  3. ↑ Carlo Becker, Jörg Putkunz, Klaus-Peter Lange, Doris Long, John Crane: restore former watercourses of the billet. Preliminary investigation / feasibility study (PDF) ( Memento from September 24, 2015 in the Internet Archive ). bgmr landscape architects / Ecosystem Saxonia, Leipzig 2006.
  4. ↑ Erich Oberdorfer: South German Plant Societies. Part IV: Forests and bushes. 2nd Edition. Gustav Fischer, Jena / Stuttgart / New York 1992, ISBN 3-334-60385-7 .