Saturday, December 22, 2012

Central European Mixed Forests (6)

 The Central European mixed forest ecoregion, on the lowland plains of northern Europe, is the main zone within which the Early Medieval Slavic-speaking communities will have spread.  It extends from eastern Germany to northern Moldova and northeastern Romania. The ecoregion thus covers large portions of Poland, Lithuania, Belarus, and Ukraine, as well as a portion of the Czech Republic. It is bordered by the lowland-colline subcontinental meadow steppes and dry grassland vegetation on the eastern side, hemiboreal spruce and pine-spruce forests to the north, beech and mixed beech forests of the Carpathians to the south, and the beech and mixed beech forests of the Baltic and Western Europe to the west.

Current extent of Central European mixed forests (after the Encyclopedia of the Earth)

This area was strongly affected by the Pleistocene glaciations (the largest ice sheet advanced as far south as 47°N) the flora and fauna became impoverished as a result of repeated glaciations. After the  last ice sheet  retreated about 10 000 years BP, mixed and deciduous forests became re-established on the cover of glacial, fluvioglacial, and glacio-lacustrine deposits left by the glaciations across the plain. The proportion of loamy deposits gradually increases southward and loess is typical of the southern areas. These more loamy substrata developed stands of deciduous trees, while the sandy and silty deposits generally supported pine and mixed stands. In the west of the region, brown forest soils developed in the regions dominated by Beech. In areas with a more continental climate, grey forest soils developed, usually under oak and lime forests. Under the mixed forests however podsols developed. With the climatic changes of the postglacial period there were considerable changes in flora and fauna.

The climax vegetation today is dominated by a complex mosaic of dynamic mixtures of coniferous and deciduous tree stands, consisting of lowland to submontane acidophilous oak and mixed oak forests, mixed oak-hornbeam forests, as well as lowland to submontane hemiboreal and nemoral pine forests on the North European glaciated plain. Among coniferous tree species, Picea abies and P. obovata prevail on loamy substrata and Pinus sylvestris on sandy substrata. Among deciduous species, Fagus sylvestris and Carpinus betulus are typical of the western regions and Quercus robur and Tilia cordata of the centre and the east. Today, much of the ecoregion has been cleared for agriculture, plantations and urban areas.  The whole ecoregion belongs to the most densely populated and altered parts of Europe. Much of the original forest vegetation was long ago transformed into arable fields, meadows, and pastures.The percentage of forested area as well as the current forest composition varies among countries of the region, the mean forest cover in the entire region is now below 30%, and most of that is either secondary forest or forest plantations.

According to the Encyclopedia of the Earth:
The ecoregion consists of vast plains in the middle, hilly moraines with lakes in the north, and upland areas in the south. The highest elevation within the region does not exceed 600 meters (m), and most of the area lies between 100 and 300 m above sea level. Mean annual temperatures are quite uniform throughout the region and range between 7 and 9°Celcius (C); the climate is more mild in the west and more continental in the east. The mean January temperatures range from -1°C in Germany to -6°C in Belarus. Annual precipitation is between 500 and 700 millimeters (mm); most of which falls during the growing season, with maximum rainfall in July. Snow cover in the NE part of the region lasts over 3 months, but the accumulation of snow is not very high; in the south and in the west of the region snow cover in winter is ephemeral. 
The average July temperature is 17.5°C to 19.5°C.

The makeup of the forst is probably a little different from that of the past, today Scots pine (Pinus sylvestris) is now the most common forest tree species of the ecoregion (up to 90% in western Poland for example), but in the past it was confined to less productive habitats, primarily sandy soils in areas of low precipitation, but has spread throughout the region, even into more fertile habitats, due to extensive 19th and 20th century planting.
The deciduous and mixed deciduous forests have been decimated, primarily due to the fact that that they used to occur on habitats suitable for agriculture. That refers especially to the lowland mixed deciduous forests (Quercus robur-Carpinus betulus-Tilia cordata), which now cover less than 10% of their original range. Mixed deciduous forests in the western part of the region (Germany, Czech Republic, W Poland) contain an admixture of European beech (Fagus sylvatica), or even small pure beech stands. In the north-eastern part of the region (Lithuania, Belarus, NE Poland) Norway spruce (Picea abies) occurs as an admixture in mixed deciduous stands on fertile habitats, often as a canopy emergent. This is especially pronounced in the Bialowieza Forest, where the old-growth spruces in good habitats can exceed the height of 50 m, they are the tallest trees in North European lowlands. Waterlogged sites are dominated by black alder (Alnus glutinosa), and to a lesser extent by downy birch (Betula pubescens) and various species of willows (Salix spp.). The former poplar (Populus sp.) and elm (Ulmus laevis) forests on river terraces has been largely replaced by willow (especially Salix purpuraea) thickets. 
Of particular note in the region is the ecosystem of the Białowieza forest (a UNESCO World Heritage Site) located just in the middle of the ecoregion on the border between Poland and Belarus:
one of the largest and definitely the best preserved forest tract in the lowlands of Europe. It still contains a wide array of old-growth forest stands representing all the major habitat types, a rich variety of wildlife and a still not sufficiently studied numerous lower plants, fungi and slime moulds. One of the most distinct features of the ecoregion is the presence of extensive wetland habitats. Common in early mediaeval times, they have since largely disappeared because of intensive draining of marshes and river valleys.

Despite the extensive post-Medieval clearance, semi-natural habitats (like extensively used meadows and traditional pastures) still support important plant and animal communities that include many of the original faunal inhabitants. That diversity is now largely threatened by the changes in land use pattern, namely by more intense management in some areas, and abandonment of traditional management (associated with secondary succession) in others. The forest cover in the entire region is now slowly increasing at the expense of arable land.
However, some of the forest habitats have been dramatically reduced and altered. This refers especially to the riparian forests on river terraces, which have been mostly wiped out and replaced by meadows, pastures or willow plantations. The remaining riparian forests are prone to biological invasions, and their ground vegetation layer is now dominated by a few very expansive alien plants. Also mixed deciduous oak-hornbeam forests have been reduced to a tiny fraction of their original distribution range. [...] Two complexes of marshes, peat-bogs and fens – the Polesie region on the border between Belarus and Ukraine, and the Biebrza valley in the NE Poland – are now among the largest remaining tracts of semi-natural wetlands in Europe. They provide habitat for numerous rare and endangered species, especially birds. The Biebrza valley is now protected within a national park (the largest one in Poland), while the wetlands of the Polesie region are, for the most part, not protected in any way. 
These forests supported a wider faunal range than today. The largest grazing anuimal was the European bison (Bison bonasus) now only present in a few reserves such as Bialowieza Forest. Wolves (Canis lupus) and bears inhabited the forests in the past, other carnivores  included the lynx (Lynx lynx) and some eagles (such as the white-tailed eagle (Haliaeetus albicilla) and the greater spotted eagle (Aquila clanga)). All these are now threatened species, as is the Black grouse (Tetrao urogallus), the largest European woodland grouse.

Source:World Wildlife Fund, 'Central European mixed forests', August 23, 2008
See also:  Mixed and Deciduous Forests of the East European Plain


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