Boundaries

The Northern Baltic Drainages ecoregion encompasses the drainages of Fennoscandia that flow into the Baltic Sea and eastern North Sea. It is bounded to the west by the Scandinavian Mountains that separate Norway and Sweden. It also includes the Åland Islands (Finland); Gotland, Öland (Sweden); and Sjælland (Denmark) in the Baltic Sea.

Topography

The ecoregion is part of the Fennoscandian or Baltic Shield, which is an area of exposed Precambrian crystalline metamorphic rocks that are the oldest on the European continent. Many of the ecoregion’s lakes and streams were formed by glaciers that scoured and compressed the landscape (Malmqvistet al. 2009). The Vänern, the largest lake in the ecoregion, was formed by tectonic depression. The relief throughout much of the ecoregion is low, with elevations rising from sea level to more than 2400 m at Galdhøpiggen and Glittertind in the Scandanavian Mountains (Hijmans et al. 2004).

Freshwater habitats

This ecoregion is dissected by rivers draining the Fennoscandian Shield and the tens of thousands of lakes carved by multiple glaciations. Many of the rivers are driven by snowmelt and have high gradient streams characterized by rapids, waterfalls and gorges. The westernmost large river is the Glomma, which flows into Lake Mjøsa (L’Abée-Lund et al. 2009). To the northeast is the Dal River, whose rapids connect numerous lakes in the lower portion of the catchment. Dividing Sweden and Finland is the Torne, which has a gentle gradient and no major falls. In southern Finland nearly half of the landscape is covered in water through chains of lakes interlinked by short rivers. Of these, the Saimaa lakes complex is the largest with more than 120 lakes and 13,710 islands (Malmqvist et al. 2009). These lakes are mostly oligotrophic and in a natural state. They empty into Lake Ladoga via the Vuoska River (Kottelat & Freyhof 2007).

Some of the largest and deepest lakes in Europe occur in this ecoregion. The largest of these is Lake Vänern (5655 km²), which is the largest lake in Sweden and third largest lake in Europe. This is followed by the Saimaa (4377 km²), Vättern (1893 km²), Päijänne (1081 km²), and Mjøsa (365 km²), which at a depth of 468 m is one of the deepest lakes in Europe.

Mires are a common feature across the boreal landscape, occupying 10-30% of the terrain on average, and up to 50% in some areas. Raised mires dominate southern Sweden, aapa mires are common across northern Sweden and Finland, and mire complexes occur in southern Finland. Notable mires that have been designated as Ramsar sites include Store Mosse-Kävsjön, Sjaunja, Tavvavouma, Martimo, and Koitelaiskaira (Pakarinen 1995). There are also numerous wetland areas, peat bogs, marsh meadows, and fens (Wetlands International 2002).

Terrestrial habitats

Most rivers flow through the boreal vegetation zone through coniferous forests and taiga of the Fennoscandian Shield. South of the Dal drainage are mixed deciduous and conifer forests dominated by oak (Quercus spp), Norway spruce (Picea abies), and Scots pine (Pinus sylvestris) (WWF 2001). European black alder (Alnus glutinosa) is the dominant tree in the riparian zone (Malmqvistet al. 2009). North of this river the forests are dominated by Norway spruce, Scots pine and downed birch (Betula pubescens). These species also dominate the riparian zone.

Description of endemic fishes

The only endemic in the ecoregion is the storsik (Coregonus maxillaris), which occurs in deeper waters of lakes such as lakes Vänern, Löcknesjön, and Siljan (Kottelat & Freyhof 2007).

Other noteworthy fishes

The Baltic cisco (Coregonus albula), found as far north as Lake Inari, is distinguished from other cisco species by its autumn spawning, which occurs around October in central Finland (Kottelat & Freyhof 2007).

Ecological phenomena

The ecoregion contains migratory populations of brown trout (Salmo trutta), Atlantic salmon (S. salar), and the catadromous European eel (Anguilla anguilla). The Torne is the most important salmon river in the Baltic due to its low gradient, which allows spawning up to 450-500 km from the sea (Malmqvistet al. 2009).

Justification for delineation

Northern and eastern European ecoregions were delineated through a top-down process using major basins as a starting point and incorporating traditionally recognized zoogeographic patterns where appropriate (Abell et al. 2008).

Level of taxonomic exploration

Good to Fair