Derg Valley Biodiversity Profile

In the following account of this LCA it should be noted that for consistency, the biodiversity section follows the standard order for all LCAs even though some of the communities discussed later may have more importance for biodiversity than those discussed earlier.

Key Characteristics

• little woodland in the LCA, less than 1% of the land cover compared with around 5.6% for Northern Ireland as a whole
• only a few small coniferous plantations; generally of low biodiversity
• the small amount of broadleaved woodland most commonly occurs as birch woodland on cut-over parts of bogs, but some rather poor, small upland oakwoods
• improved pastures of low biodiversity are widespread and dominate the landscape (about 75% of the land cover)
• a few lowland raised bogs on flat shelves in the north of the LCA; all have been cut over
• Moneygal Bog is the only large area of intact bog; often classed as lowland raised bog it is transitional to blanket bog. Of national and international importance for its vegetation and structural features and for wetland birds
• only a narrow band of blanket bog on the northern and southern borders - all cut-over
• rivers of importance for Priority Species and Atlantic salmon

Woodlands

There is little woodland in the LCA, less than 1% of the land cover compared with around 5.6% for Northern Ireland as a whole. Coniferous forest is confined to a few small plantations largely comprised of Sitka spruce but with some lodgepole pine, noble fir and Japanese larch. Fringes and thin compartments of hardwoods are also included. The biodiversity of these conifer forests is low, but red squirrel has been recorded in Aghyaran Forest.

The small amount of broadleaved woodland most commonly occurs on cut-over parts of bogs; birch is the dominant species where the peat remaining is drier and deeper, whereas around the wetter edges where most of the peat has been removed, willow and alder dominate (wet woodland). Examples of birch woodland on cut-over peat include the lower woodland at Bullock Park and that at Clara Wood/Clare Lodge where some of the birch appears to have been felled or coppiced in the past. The wood has been damaged by sheltering livestock and the lower part of the wood is being colonised by rhododendron. The woodland edge around cut-over bog at Lisnacloon is quite extensive.

There are some examples of upland oakwood, but all are rather poor. They include the upper part of Bullock Park which is bounded by old field boundaries and consists of a sparse oak canopy that is degenerating. The understorey contains scattered hazel and birch scrub with some holly. The wood is growing on a thin mineral soil with large boulders covering a lot of the ground and wet flushes in the hollows. The ground flora consists of 60-80% moss cover, with a few vascular plants. Dreenan Wood is located on a gentle south-facing slope on the north side of the Mourne Beg River valley. Birch is the predominant tree species with oak also common, although most is regenerating from cut stumps. The wood is open with grazing and rush-dominated areas.

Grassland and Arable

The Castlederg lowlands, especially east of the town, have long been recognised as one of the better farming areas in west Tyrone on account of their well-drained soils. Improved pastures are therefore widespread and dominate the agricultural landscape. Grassland accounts for about 92% of the land cover and four-fifths of that is improved pasture. With the exception of a few bogs on flat shelves, it is only in the northwest and extreme south of the LCA, as the land rises in altitude, that acid grassland and bog become predominant. On the deeper peat, purple moor grass may be dominant but as it thins downslope soft rush becomes the dominant. Such acid grasslands are of low biodiversity.

Improved pastures generally have low biodiversity as a result of relatively intensive management. Some of the pastures are sown grasslands dominated by ryegrass and few other species - low biodiversity is in-built. Other grasslands have been converted to improved pastures through management. High levels of grazing or repeated cutting for silage, high inputs of fertilizers and slurry, and selective herbicides serve to reduce diversity of both flora and fauna. Arable land - only c.2.5% of the land cover and that includes grass reseeding - lies alongside the River Derg to the east of Castlederg.

Biodiversity in areas of improved pastures and arable is often concentrated in hedgerows. Indeed, they may be the most significant wildlife habitat over much of lowland Northern Ireland, especially where there are few semi-natural habitats. Hedgerows are a refuge for many woodland and farmland plants and animals. In this LCA fields are enclosed by both stone walls and hedgerows and there are many hedgerow trees. Areas with small pastures tend to have a dense tree cover in the field boundaries, particularly where they are adjacent to the wet woodlands on the margins of the bogs. The larger fields on the valley floor are more open, with trees (often Scots pine and larch) grouped close to farm buildings; there has been some hedgerow removal in the valley floor and many fields are partially bordered by wire fences.

Despite the dominance of improved pastures, there is sufficient intermix of other cover types - small woods and hedges, damp pastures and bogs, and arable fields - to provide habitats for several of the bird Priority species. These include bullfinch, linnet, skylark, song thrush, spotted flycatcher and yellowhammer.

Heaths and Bogs

A few scattered lowland raised bogs occur on flat shelves and along some of the tributary streams, but all have been cut-over and several have been colonized by birch (see above).

Lowland raised bog is a rare habitat in the UK, and Northern Ireland has a large proportion of that remaining; in particular it has much of the intact lowland bog. In the best examples there is a diversity of structural features including hummocks and hollows and pools that give rise to micro-habitats related especially to the height of the water table. The plant species are adapted not only to the generally waterlogged, acid and low nutrient conditions, but also to these small-scale variations in topography and water level. Typical plant species include bog mosses, deer sedge, cotton sedges, bog asphodel, sundews, cross-leaved heath and common heather.

Moneygal Bog ASSI (also Moneygal FNR, Moneygal Bog SAC) is the only extensive intact lowland raised bog, but there is some doubt whether this is a true raised bog because the underlying topography is of a low ridge over which peat has accumulated. That is, the 'dome' may originate from the subsurface rather than from the internal mechanisms of raised bog growth. The site is a large one with the hummock-forming species Sphagnum imbricatum and Sphagnum fuscum common - species not widespread in the UK bogs. Moneygal Bog Part II ASSI comprises the old hand cut margins and provides additional habitat diversity. The cuttings are dominated by a mosaic of regenerating bog, drier, raised banks dominated by common heather and occasional pockets of flushed acid grassland. The area provides an important habitat for birds. Snipe, woodcock and meadow pipit have all been recorded, in addition to other wildfowl and waders from the bog, including mallard, golden plover, curlew and redshank.

Blanket bog is confined in Europe to the northwest margins of the continent, so that Northern Ireland contains not only a large proportion of the UK's and of Ireland's total area of blanket bog, but also is of major importance at a European scale. Blanket bog, and particularly intact blanket bog, in any LCA is therefore of national and international significance. It is home to plant species adapted to the acidic, low nutrient conditions - including common heather, cross-leaved heath, cotton sedges, bog asphodel, deer sedge, bog mosses (Sphagnum species) and sundews. It is also important for over-wintering birds and for breeding birds, including waders. Blanket peat is also important as a store for carbon and as a repository of information on past environments (as are raised bogs).

Blanket peat is limited in the LCA to the northern and southern borders and all has been cut-over. Nevertheless it can be of biodiversity interest because the different depths of peat left by past cutting provide several micro-habitats including wetter areas for dragonflies, drier peat banks with common heather and more nutrient rich flushes and soakaways with greater plant species diversity.

Wetland and Lakes

There are no priority lakes recorded in the LCA, nor are then any significant areas of fen or reedbeds. The River Derg, Mourne Beg River and Fairy Water have river water crowfoot and, being part of the Foyle system, are important for Atlantic salmon.

Key Issues

General actions for UK and NI Priority Habitats and Priority Species are detailed in the Habitat Action Plans and Species Action Plans.

WOODLANDS

Issue: low woodland cover of variable biodiversity value

Actions:

• further study of the history of broadleaved woodlands particularly any ancient and long-established, as a key to future managementen
• courage control of grazing in broadleaved woodlands to foster regeneration and if necessary, encourage replanting of canopy species; remove invasive species (e.g. rhododendron)
• encourage planting of native broadleaved plantations through appropriate grant schemes, rather than the small conifer plantations which are of poor biodiversity and landscape value
• ensure retention of birch and wet woodlands on and around bogs - limit drainage, land-fill, fly-tipping

GRASSLAND AND ARABLE

Issue: poor biodiversity of farmland

Actions:

• maintain and improve field boundaries especially hedgerows - where traditional in the landscape. This may be achieved through adoption of correct cutting cycles; hedge laying and replanting where necessary; leaving saplings uncut to develop into hedgerow trees; avoidance of spraying with fertilizers, slurry, herbicides; provision of wildlife strips and conservation headlands around fields; and limitation of field amalgamation.
• encourage (through participation in Environmental Schemes) adoption of less intensive management of pastures to allow reversion to more species-rich grassland and protect areas of species-rich wet grassland
• promote further study of grasslands to establish their species diversity more fully - as a key to future managementleave stubble over winter, rather than autumn ploughing, to increase food resources for farmland birds; spring sown cereals are beneficial to breeding farmland birds.

HEATH AND BOGS

Issue: raised bogs and blanket bogs are of national and international importance

Actions:

• maintain the integrity of existing lowland raised bogs (including cut-over surrounds and cut-over bogs) by for example, preventing infilling, fly-tipping, fires, new drainage and new peat cutting
• consider restoration of raised bog habitats through appropriate water level management, removal of individual colonizing trees and phasing out peat cutting
• prevent new forest planting on raised/blanket bog

WETLANDS

Issue: important rivers for Priority species and Atlantic salmon

Actions:

• protect water quality of rivers through nutrient management and by reducing suspended sediments from peat cutting/forestry operations, thus
• promote and encourage existing good farming practices so that streams are not polluted by run-off from agricultural land or seepage from silage pits
• monitor streams for pH, nutrient enrichment, sediment load and deposition arising from forestry and peat cutting, noting that operations outside the LCA can affect rivers, and operations in the LCA can affect water bodies and rivers downstream
• monitor streams in relation to expansion of rural/urban housing and associated septic tanks/sewage treatment plants

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