Ecoregions

Baltic mixed forests

June 9, 2012, 12:02 am
Content Cover Image

Edges of the western Baltic Sea and Kattagat(light green) are Baltic mixed forests. Source: NASAs

The Baltic mixed forests consist of broadleaf and mixed forests in northwestern continental Europe. Within the palearctic realm, the area of these forests is 116,600 square kilometers. This ecoregion lies within a temperate zone much farther north in latitude than comparable plant associations in the western part of the Eurasian continent or compared eastern North America. Baltic mixed forests are comprised of both forests and wetlands.

Baltic mixed forests have been exploited by man throughout the Holocene period; moreover, there are significant finds of sunken forests along the Baltic coastline, that reveal earlier forest composition, but that also suggest an early beginning of global warming and sea level rise, perhaps earlier than some realize. Presently, the ecoregion is being threatened by ongoing habitat destruction and water pollution discharge, especially from agricultural runoff to rivers and wetlands.

Geography

caption Occurrence of Baltic mixed forests (in yellow). Source: WWF

The Baltic mixed forests span an area of continental northwestern Europe from Denmark stretching eastward across northern Germany and Poland. In Denmark, the Baltic mixed forests are found on the eastern side of Jutland on the Danish peninsula; in Germany, the ecoregion is generally situated to the north of the Elbe River, and in Poland, north of the Oder River. In Sweden, the Baltic mixed forests occupy a very small area in the extreme south of Sweden rimmed by the Baltic Sea. North of the Baltic mixed forests ecoregion in Sweden lie the Sarmatic mixed forests.

Flora and fauna

caption Krogenberg Hegn, Denmark. Source: Dana Nau

This ecoregion encompasses many different habitats, and accordingly a broad diversity of species. Migrating and breeding water-birds, shorebirds, and wading birds visit this habitat each year, such that 32 Important Bird Areas have been designated within the ecoregion as a whole.

There is a number of threatened avian species found in this ecoregion; some of the threatened bird species breeding here are the Vulnerable Aquatic warbler (Acrocephalus paludicola), Vulnerable Great bustard (Otis tarda), Near Threatened Ferruginous pochard (Aythya nyroca), Near Threatened Black-tailed godwit (Limosa limosa), Vulnerable Steller's eider (polysticta stelleri), Near Threatened Red kite (Milvus milvus) . Great bittern (Botaurus stellaris) and Little bittern (Ixobrychus minutus) are found among the cover of reed beds preying upon fish, frogs and other small fauna. They and several other birds breed here and then migrate south for winter. Other large avafauna occurring in the Baltic mixed forests are gray heron and the mute swan. Raptors, including goshawks and buzzards, consume a gamut of birds, rodents, snakes, amphibians and other small to medium-sized animals. Many migratory birds fly through the ecoregion, utilising the rich wetlands of the coastal zones.

A number of other threatened fauna is found in the ecoregion including the Near Threatened European otter (Lutra lutra), that is found on the sea fringe as well as freshwater rivers tributary to the Baltic Sea and the Kattegat. Other threatened mammals include the European rabbit (Oryctolagus cuniculus). The Endangered European mink (Mustela lutreola), occurs chiefly in riparian zones; the risk of extinction of this mammal is mainly driven by riparian habitat destruction, but also exacerbated by introduction of the alien species American mink. Threatened bats found in the ecoregion include the Near Threatened Bechstein's bat (Myotis bechsteinii), the Near Threatened Western barbastelle (Barbastella barbastellus) and the Near Threatened Pond bat (Myotis cnerne)

The moor frog (Rana arvalis) and pool frog (Pelophylax lessonae), two amphibians found in this ecoregion, are classified as threatened species. Reptiles occurring in the Baltic mixed forests include the Near Threatened European pond turtle (Emys orbicularis)

Sunken forests from the early Holocene

The fringes of the Baltic Sea at the terrestrial edges of the Baltic mixed forests ecoregion have yielded important finds of sunken forests. At Puck Lagoon in Poland excavated stumpage from a depth of three meters was radiocarbon dated to 9370 years before present (BP), or about the same age as peat deposits from the lagoon bottom; Puck Lagoon itself is much younger, dating to the end of the Atlantic Period, indicating the forest was not inundated until about around 6000 to 5000 years BP.

Harff's recent discovery of tree stumps at the bottom of the Gulf of Gdansk along with peat deposits has augmented the understanding of these prehistoric sunken forests. This site is situated about six kilometres northeast of the Gdansk harbour in water depths of around 16 metres. Alder and oak trunks were sampled here, yielding radiocarbon dates of approximately 7940 years BP. The marine  intrusion into the ancient freshwater lake, preceding the formation of the Baltic Sea, occurred only around 8500 years BP. It is clear, therefore, that a warming trend and associated seawater rise was occurring well after the abrupt climate change accompanying the onset of the Holocene.

Justification of ecoregion delineation

caption Chorin Biosphere Reserve, Schorfheide region, Germany Source: WWF

The Baltic mixed forests ecoregion is equivalent to the DMEER unit of the same name. The ecoregion is composed predominantly of the lowland to submontane beech and mixed beech forests on the eastern side of the Danish peninsula and to the north of the Elbe and Oder Rivers.

References 

  caption Baltic mixed forests threatened by urbanization along the Baltic Sea at Karlshamm, Sweden. @ C.Michael Hogan

Glossary

Citation

Hogan, C. (2012). Baltic mixed forests. Retrieved from http://www.eoearth.org/view/article/150401

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