Boundaries

This ecoregion encompasses Scotland, a small area in northeastern England, Ireland, Shetland Islands, Orkney Islands, Hebrides, Isle of Man, and Faroe Islands (Denmark).

Topography

The geology of the British Isles is highly complex, formed by the action of tectonic plates, earthquake and volcanic activity, and glaciations. Northwest Scotland and the Outer Hebrides reveal outcrops of bedrock comprised of Lewisian gneisses, which are some of the oldest rocks on earth (2700 mya). The bedrock is overlain by folded sedimentary rocks. Glaciation during the Quaternary helped shape the islands, forming numerous headlands, peninsulas, inlets, and bays, particularly on the western coasts. The topography is varied, ranging from the lowlands in central Ireland and Scotland to the rugged elevations of the Scottish Highlands. Ben Nevis (1344 m) in the Grampian Mountains is the tallest peak, followed by Macdui (1309 m), Braeriach (1296 m), and Cairn Toul (1291 m) in the Cairngorm Mountains. There are also mountainous areas in Wales and Ireland that exceed 1000 m. The highlands of Scotland and Ireland form part of the Caledonian mountain chain that extends to Scandanavia (Soulsby et al. 2009).

Freshwater habitats

The ecoregion contains many diverse habitats including lakes, ponds, rivers, streams, wetlands, marshes, mires, swamps, fens, floodplain grasslands and peatlands. It is distinguished by the high proportion of temperate upland rivers, such as the Tay and Spey. The Spey is also distinguished by the Insh Marshes, one of the largest and least disturbed floodplain fens in the UK (Soulsby et al. 2009).  Forming ecotones between terrestrial and aquatic systems, mires (bogs) are some of the more noteworthy features of this ecoregion. Hydrology, geomorphology, base content, nutrient availability, and plant communities influence the different types of mires, which have various classifications such as floodplain, valley, soligenous, basin, and ombrogenous (which is further divided into raised or blanket mires) (Tansely 1949). Some notable examples are Ramsar sites such as Lough Barra bog, Fairy Water bogs, Clara bog, and Mongan bog in Ireland; Caithness and Sutherland peatlands, Silver Flowe, and Rannoch moor in Scotland; and Crymlyn bog in Wales (Wetlands International 2002).

Terrestrial habitats

Although natural areas have largely been modified to grasslands, plantation forests, or drained peatland, several terrestrial ecoregions were historically dominant across this landscape. The largest is the Celtic broadleaf forests [PA0409] in southeastern Ireland, southeastern Scotland, and Wales. This largely consisted of lowland to submontane acidophilous oak and mixed oak forests, mixed oak-ash forests, and small areas of western boreal, nemoral-montane birch forests, and fen and swamp forests. There are also floodplain, estuarine, and freshwater polder vegetation and ombrotrophic mires (bogs) in southern Scotland and northern England. A small area of Caledonian conifer forests [PA0503] remains in the Highlands of Scotland with hemiboreal pine forests, Atlantic dwarf shrub heaths, and one area of ombrotrophic mires. The North Atlantic moist mixed forests [PA0429] extended along the western coastal areas and islands of Ireland and Scotland, including the Shetland, Hebrides, and Orkney islands. It is composed of moist lowland forests, lowland to submontane acidophilous oak and mixed oak forests, as well as floodplain vegetation and ombrotrophic mires. Faroe Islands boreal grasslands consists of Atlantic dwarf shrub heaths [PA0807] (Bohn et al. 2000 in WWF 2001).

Description of endemic fishes

There are nearly 20 endemic freshwater fishes in the ecoregion, a majority of which are in the Salmonidae family. The high number of salmonids reflects the classification of genetically isolated populations of brown trout (Salmo trutta) into separate species, such as the gillaroo (S. stomachicus) that occurs in Lough Melvin (Kottelat & Freyhof 2007). However, it has been debated whether these should be regarded as one species with separate sub-species, thus potentially reducing the number of endemics. Most of the endemics fall within the genus Salvelinus with species such as Faroe charr (S. faroensis), Coomasaharn charr (S. fimbriatus), and Melvin charr (S. grayi).  Other endemics include the powan (Coregonus clupeoides), gwyniad (C. pennantii), and pollan (C. pollan) in the family Salmonidae; Killarney shad (Alosa killarnensis) in the family Clupeidae; and Western ninespine stickleback (Pungitius laevis) in the family Gasterosteidae.

Other noteworthy fishes

Several notable fish include the strictly freshwater race of the normally anadromous river lamprey (Lampetra fluviatilis) in Loch Lomond, and threatened species like the Killarney shad (Alosa killarnensis, CR), gwyniad (Coregonus pennantii, CR), pollan (C. pollan, EN), Melvin charr (Salvelinus grayi, CR), and blunt-snouted charr (S. obtusus, CR) (Freyhof & Kottelat 2008; Maitland & Lyle 1996; Quigley & Flannery 1996).

Ecological phenomena

One of the important features of this ecoregion is that it has only recently emerged from glaciation, resulting in low species diversity that is dominated by generalists. This has also resulted in the transfer of relatively large amounts of nutrients from young soils to freshwater systems. Other features characterizing this ecoregion include a cool wet climate that favors peat formation and carbon storage, open freshwater systems (no endorheicity and salinization), and the conversion of most of the ecoregion from biome to anthrome.

Justification for delineation

Northern 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). Lough Melvin has three sympatric species of the genus Salmo. The ecoregion contains a number of endemic species of Salmonidae. Many species have small isolated ranges, and a number of them are unnamed (M. Kottelat pers comm. 2006).