Mullaghcarn ASSI

The area is of special scientific interest because of its earth science features, and its upland habitat mosaic of peatland, lakes and woodland together with associated flora and fauna. Mullaghcarn ASSI displays important examples of glacial landforms. The landform within the Gortin delta complex is one of the largest and best examples of a proglacial delta landform assemblage in Northern Ireland. The main landform dates from the end of the last glacial period when the Owenkillew Valley was part of an extensive lake formed between the high ground of the Sperrins and an ice sheet blocking the Foyle valley. The lake was fed by water from the melting ice sheets which also fed huge quantities of gravel, sands and clays into the lake.

An area of oakwood, known as Boorin Wood, covers a steep, north-facing slope towards the most northerly perimeter of Mullaghcarn ASSI.

The earth science interest at Mullaghcarn occurs as features formed by the interaction of ice, rock and water towards the end of the last Ice Age, some 17,000 to 13,000 years ago. At this time, the climate was beginning to warm after the prolonged cold period that had allowed the ice to accumulate.

Mullaghcarn ASSI contains the Gortin deltaic complex on the northern slopes of Mullaghcarn. This is composed of sand, gravel and clay deposited as ice retreated towards the Omagh Basin. The Gortin deltaic complex is known as a ‘Gilbert’ type delta and is one of the largest examples of a proglacial delta landform assemblage in Northern Ireland. It contains a range of landforms associated with the standard model for such depositional environments including flat-topped delta, subglacial surfaces, steep delta foreslopes, post-depositional dissection channels, subglacial Nye-type feeder channels and a series of kettle holes that are now the dystrophic lakes south of Boorin Wood. Kettle holes were formed when large blocks of ice were left stranded by the retreating ice mass. Sediments were then deposited around the blocks by glacial meltwater. The blocks themselves eventually melted, leaving the kettle holes. The presence of the delta itself indicates that a proglacial lake filled the Owenkillew River Valley, into which the sediments were deposited. The flat tops of the delta series record varying water levels within this lake.

Near the summit of Mullaghcarn, a number of small lakes known as tarns are found. The lakes sit in the base of near circular depressions made in the rock by ice. Evidence suggests these depressions represent a time when the main ice mass had retreated from the area, but the climate was cold enough for snow and eventually ice to accumulate as small glaciers. Small moraines associated with the downhill movement of these minor glaciers can also be seen. The position of these steep sided depressions, in some instances, within sub-glacial feeder channels, indicates that they post date the presence of the main ice front with which the Gortin delta was associated. This suggests that these localised upland glaciers may date from the Nahanagan Stadial, the last cold phase of the last Ice Age, some 11,000 years ago.

Biological interest relates to the size, quality and diversity of the upland habitats overlying the glacial landforms, in addition to the presence of plant and animal species of note. The vegetation on the intact bog surface is characterised by a bog-moss. carpet, ericoid dwarf-shrubs, sedges and associated species. The composition and abundance of these depends upon local environmental conditions, particularly structural features on the bog surface and the height of the water table. Much of the bog plain is dominated by heather and hare’s-tail cottongrass, with cross-leaved heath, deergrass, bilberry and crowberry. The moss carpet beneath generally consists of red bog-moss and papillose bog-moss with associated pleurocarpous mosses, primarily heath plait- and liverworts such as Taylor’s flapwort. The easily recognisable leafy liverwort purple spoonwort is frequent across the area and is a characteristic species in the west of the British Isles.

Mullaghcarn ASSI incorporates Boorin National Nature Reserve which is comprised of very wet blanket bog communities adjacent to the kettle hole lakes; wet and dry heathland mosaics on shallow peats over the sand and gravel deposits and oakwood. The area of deep peat within the NNR, primarily to the north of Lenamore Road, is very wet, and along with the peatland compartment to the east of the Nature Reserve, supports floating mats of bog-mosses interspersed with areas of flushing and poor acid fen. The luxuriant moss carpet is dominated by red bog-moss with papillose bog-moss, flat-topped bog-moss and occasional Magellanic bog-moss. Higher plants associated with these wetter blanket bog plains include, bogbean and the insectivorous round-leaved sundew. The fungi rose bloom, a species rarely recorded in the UK, occurs on its host cranberry in this area.

On steeper slopes where the peat thins over sand, gravel and mud deposits, blanket bog frequently forms a mosaic with wet heath. The moss layer is generally much more diverse, with bog-moss. intermixed with a variety of pleurocarpus mosses including heath plait-moss, little shaggy-moss and red-stemmed feather-moss.

On the shallowest peats, most often on the upper slopes of the sand and gravel deposits, there is a further transition to dry heath communities where bell heather generally replaces cross-leaved heath in the sward. Where high rocky outcrops occur the arctic/alpine cowberry was recorded together with the fir clubmoss. On the most exposed summit ridge of Mullaghcarn Mountain, there are localised patches of montane heath characterised by woolly fringe-moss.

On the lower slopes, around the periphery of Mullaghcarn ASSI, cutover bog and wet heath frequently form a mosaic with upland grassland communities dominated by common bent with velvet bent, mat-grass, sheep’s-fescue, and the herbs heath bedstraw and tormentil.

Boorin Wood occurs in the most north-easterly area of Mullaghcarn ASSI covering the steep, north facing valley slope. The canopy of the wood is dominated by Sessile oak, Pedunculate oak with occasional downy birch and rowan. The latter two species along with hazel and hawthorn form a sparse understorey. The lower slopes have been inter-planted with beech. Further diversity is provided by a small area of mature willow carr in the north eastern corner. The ground flora associated with the oakwood is dominated by greater wood-rush with occasional wood-sorrel, broad buckler-fern and bluebell. Where greater wood-rush is less dense, the ground flora displays greater diversity with a rich herb, grass and moss component. In the most acidic areas of the oakwood, bilberry occurs locally as dominant stands. On the lower, beech dominated, the woodland floor is characterised by dense leaf litter, scattered herbs and a carpet of woodland mosses.

The mature trees support a rich epiphytic growth of ferns, mosses and lichens while climbers are sparse. The lichen flora associated with the oak trees is generally very acid in character with species such as dot lichen and the lichen indicating woodland continuity. Further diversity is associated with the mature beech, hazel and especially the old willow carr where the lichen species indicate little disturbance and a stable microclimate over a long period of time.

Several dystrophic (peaty) lakes occur within the kettle holes of the outwash complex. They have a very impoverished plant assemblage only occasionally characterised by aquatic mosses such as feathery bog-moss and cow-horn bog-moss. The floating and marginal vegetation is also very limited to a poor acid fen fringe, generally dominated by bottle sedge and common sedge.

Mullaghcarn also provides an extensive area of undisturbed upland habitat that is very valuable for associated invertebrates, birds and animals such as red grouse and common lizard.

Site Related Documents

Site map (.PDF 3.7Mb) and Combined Citation and Views about Management document (.PDF 664Kb).