Natural Heritage - SNH in West Highland

SNH’s West Highland Area stretches from Rannoch Moor and Glen Coe in the south to Gruinard Bay in the north, extends eastwards from the west coast to include Glen Spean, Glen Garry and Glen Carron, and encompasses the Small Isles and Skye. It is an area of rich and diverse natural environments, with habitats extending from beneath the Atlantic into the coastal zone and on through a variety of grassland, bog and woodland types up onto mountain summits, including that of Britain’s highest mountain, of rock, scree and montane heath.

Much of the Area experiences a generally cool, humid, ‘oceanic’ climate, characterised by high rainfall, moderate temperatures, and strong westerlies which make the western seaboard one of the windiest places in Britain. In the easternmost part of the Area the oceanic influence is reduced, and conditions are drier and more ‘continental’. On the high ground, precipitation as snow is significant. Snow lies above 800m on Ben Nevis for about five months of the year, and in sheltered, north-facing corries and gullies it can last all year.

The combination of the cool and wet conditions and the generally acidic geology has given rise to a predominance of peaty soils, and there are extensive areas of deep peat at places such as Kentra Moss, Sligachan and Inverasdale. Rannoch Moor is a particularly large and spectacular undulating plateau of deep peat studded with lochs and lochans. These areas support internationally important blanket bog vegetation, such as sphagnum mosses and the Rannoch rush – found only on Rannoch moor – and are home to rare birds such as the greenshank and dunlin. However, base-rich areas occur in several locations, such as the basalts of Troternish and the extensive exposures of limestone at Strath Suardal on Skye or Rassal in Wester Ross. The limestone supports distinctive crevice vegetation surrounded by species-rich grasslands and calcareous mires, and gives rise to a distinctive species-rich flora.

Throughout West Highland, moorland and upland habitats are widespread. The sub-montane habitats, below about 700m, consist of heather moorland, rough grassland, bog and fern rich communities on some scree slopes. On the mountain summits these habitats merge into montane vegetation represented by low-growing, wind-clipped grasslands, heaths and willow scrub; bare rock and scree is a common feature and cliff ledges provide lush, ungrazed habitats. The West Highlands contain some of the most extensive patches of late lying snow in Britain and support a wide range of snow-bed plant communities, some of which are amongst the finest of their type, and encompass a number of rare mosses, liverworts, lichens and fungi which are only associated with snow beds. The arctic-alpine plant Diapensia lapponica and the montane lichen Nephroma arctica and liverwort Herbertus borealis occur on just one mountain summit each; Alpine rock cress is found in only one location on Skye, and Icelandic purslane is confined to gravel screes on Skye and Mull.

In addition to such rare plants and bryophytes, the high tops are also the haunt of rare and distinctive breeding birds such as dotterel, ptarmigan and snow bunting. Here too golden eagles hunt mountain hares, and merlin and peregrine range extensively over the hill slopes.

A range of native woodland types occur within the area, but it is only a small remnant of the one-time forest cover that blanketed the west coast. The woods are dominated by birch, oak and Scots pine with alder, ash, hazel and rowan. A number of the woods are particularly important examples of their type, such as the alder-ash wood at Carnach, the Leven Valley birch woods, the Sunart oak woods and the Scots pine at Beinn Eighe, Coille Phuiteachain, and Ardgour. Uncommon tree-line Alpine willow scrub is well represented in Glencoe and on Ben Nevis and its neighbouring mountains. Associated with the woodlands, especially those of oak, hazel and ash, are internationally important communities of mosses, liverworts and lichens, many of which are affiliated with and/or confined to west Atlantic coasts.

Native woodlands support a distinct range of wildlife including conservation priority species such as red squirrel, here at the north west of its range, black grouse and Scottish crossbill, and rare insects such as the chequered skipper butterfly, which has a stronghold in the oak and birch woods of Lochaber. Other invertebrates for which the Area is important include the marsh fritillary and pearl-bordered fritillary butterflies, two rare flies and the Scottish Wood Ant; all priority species under the UK Biodiversity Action Plan programme.

Coastal grasslands also support rare invertebrates such as slender scotch burnet and the New Forest burnet moth, the latter being another species with its sole British population within West Highland Area. Around the coast the spectacular white-tailed eagle is slowly re-establishing itself after its re-introduction to Rum in the 1980s. Here too otters are widespread, with particularly high densities inhabiting the sea lochs, and both common and grey seals can be seen, though the latter is relatively uncommon.

The coastline itself is dominated by rock, much of which is fairly sheltered, and this extends underwater to form extensive sub-marine rocky reefs. Soft coastal habitats such as saltmarsh, machair, sand dune and mud flats occur more locally, such as at the head of sea lochs or on sheltered parts of islands. For example there are large mudflats at Kentra and Moidart and there is machair on Eigg. The Area’s high rainfall creates much run-off which, in sheltered sea lochs, often floats on the surface of the sea water forming a brackish layer up to 12 m deep. The range of substrates in the sea lochs includes gravel, bedrock, sand and mud, creating a range of habitats which in turn support a rich variety of species such as sea pens, brittle stars, prawns, scallops, crabs and horse mussel beds.

The West Highland marine environment is very diverse and of considerable natural importance. The sea lochs harbour some of the deepest underwater cliffs in Scotland, with sides plunging down over 100 metres. The tidal range is also large and at Lochs Duich, Long and Alsh for example, it is 6 metres, one of the largest such ranges in Scotland. The large volumes of water passing over the shallows sills in these, and other, sea lochs, creates the distinctive ‘tidal torrents’ habitat. The Sound of Arisaig is home to yet another unusual sub-tidal habitat: maerl beds. Maerl is a corral-like seaweed which is very slow growing and has a restricted European distribution as it has very specific ecological requirements, which include clear, unpolluted waters. Some of the most sheltered bays are home to a rare floating form of egg-wrack, a seaweed which normally grows attached to rock.

An important feature of the Area’s marine environment is that it is at the meeting place of colder, northern currents and the warmer waters of Gulf Stream. Hence there is an interesting mixture of marine species, some of which are at their southern limit and others at their northern limit. As well as a rich and diverse benthic, or sea-bed fauna, the waters are important for fish, with the sea lochs and near shore waters being nursery areas for a number of commercial fish species such as saithe, cod, plaice, sprat and herring. More unusual marine vertebrates around the coast include basking sharks and leatherback turtles.

West Highland’s freshwater environment is also significant and is a key component in the ecology and character of the Area. Much of the ground is frequently waterlogged and there are several thousands of kilometres of streams, rivers and burns. Many of these are high energy systems with steep gradients, small catchments and rapidly fluctuating water levels. Some support the internationally scarce and endangered freshwater pearl mussel. In recent years, Atlantic salmon and sea trout numbers in West Highland rivers have decreased markedly.

Freshwater lochs are significant West Highland habitats too and cover many thousands of square kilometres. Loch Morar is the deepest freshwater body in Britain, with a maximum depth of 310 metres and an average depth of 87 metres. Most of the Area’s lochs are nutrient poor, with characteristic plants such as water lobelia, quill wort and shore weed. The rare pipewort grows in some shallow lochs and lochans and the semi-aquatic pigmy weed is found nowhere else in Britain. Important bird species dependent on the freshwater bodies include black and red-throated divers and common scoter. Arctic charr and brown trout are notable fish species found in these waters.