South Uist Machair

General site character

• Tidal rivers, Estuaries, Mud flats, Sand flats, Lagoons (including saltwork basins) (8.7%)
  
• Coastal sand dunes, Sand beaches, Machair (52%)
  
• Inland water bodies (Standing water, Running water) (21%)
  
• Bogs, Marshes, Water fringed vegetation, Fens (10%)
  
• Improved grassland (5%)
  
• Other land (including Towns, Villages, Roads, Waste places, Mines, Industrial sites) (3.3%)
  

Annex I habitats that are a primary reason for selection of this site

• 21A0 Machairs (* in Ireland)

  South Uist in the Outer Hebrides has the most extensive cultivated machair system in Scotland, extending the whole length of the island and up to 2 km inland. There is extensive grazing, and rotational cultivation, mainly to provide cattle fodder. The area is very diverse in physical form and is extremely rich in plant species. Extensive areas of wet machair include transitions to machair lochs or wet heath, marshes and peatland. The site is selected for several of these Annex I habitat types in their own right. The standing waters within the site exhibit a wide range of pH and salinity. The Annex II species 1833 Slender naiad Najas flexilis occurs in a number of them, for which the site is also selected.

• 3110 Oligotrophic waters containing very few minerals of sandy plains (Littorelletalia uniflorae)

  This site encompasses a series of oligotrophic lochs on the machair plains of the west coast of South Uist in the Outer Hebrides. It is considered to be the most important site in the UK for the conservation of this habitat type, owing to the diversity and extent of the habitat type and because these lochs contain all three characteristic plant genera (water lobelia Lobelia, shoreweed Littorella and quillwort Isoetes). The oligotrophic lochs form one element of a series of lochs, which range from dystrophic lochs on inland peat bogs, through oligotrophic lochs of this type in areas of transitions between peat and calcareous sands, to calcareous lochs of the main machair plain and brackish sea lochs closest to the sea. Oligotrophic waters in this composite site are Lochs Fada, na Tanga, na Cuithe Mòire, a’Phuirt-ruaidh, a’Chnoic Bhuidha and Schoolhouse Loch.

• 3130 Oligotrophic to mesotrophic standing waters with vegetation of the Littorelletea uniflorae and/or of the Isoëto-Nanojuncetea

  South Uist Machair includes the largest machair system in the British Isles and contains excellent examples of transition from marine to freshwater habitats including oligotrophic freshwaters. At this site, oligotrophic conditions are present within lochs that receive drainage from the acidic blacklands, hills and moors. The principal oligotrophic loch in this site is Loch Druidibeg which has a catchment that lies over Lewisian gneiss, a rock type which weathers to produce acid and nutrient-poor soils. Loch Druidibeg is a large, shallow loch that supports a flora typical of its nutrient-poor status.

• 3140 Hard oligo-mesotrophic waters with benthic vegetation of Chara spp.

  South Uist in the Outer Hebrides contains oligo-mesotrophic waters of the machair loch type which derive the calcium content of their nutrient-poor waters from calcareous shell-sand. This complex of high-quality calcareous machair lochs occurs in an intermediate zone between the oligotrophic inland lochs and the eutrophic lochs found nearer the coast. As a result the site is selected for several Annex I habitat types. The lochs are the most extensive and diverse examples of calcareous machair lochs in Scotland and support a number of stoneworts, including the scarce Chara aspera and C. hispida. A strong maritime influence is discernible from their water chemistry and all sites have extensive areas of shell-sand substrate. Owing to their location, these lochs are subject to a mixture of influences from peat and shell-rich sand. The lochs of this type within the South Uist Machair are: Loch Hallan, Grogarry Loch, Loch an Eilean, Mid Loch Ollay and Loch Toronish.

• 3150 Natural eutrophic lakes with Magnopotamion or Hydrocharition - type vegetation

  South Uist in the Outer Hebrides contains a series of coastal natural eutrophic lakes formed on calcareous marine sediments on the machair plain. These lakes are the best examples of their type in the UK, owing to the richness of their flora. Stoneworts Chara spp. and pondweeds Potamogeton spp. dominate the aquatic community, and shorelines contain spike-rush Eleocharis associations. Lochs of this type within the site are: Loch Roag; West Loch Ollay; Loch Ardvule; Loch Stilligarry; and Loch na Liana Móire. The South Uist machair supports a unique transition from oligotrophic lochs on peatland towards the centre of the island, through mixed oligotrophic and mesotrophic lochs where peat ‘blackland’ meets machair, to eutrophic lochs over calcareous sand and brackish lochs on the west coast. This site has been selected for many of these Annex I habitat types in their own right.

Annex I habitats present as a qualifying feature, but not a primary reason for selection of this site

• 1150 Coastal lagoons  * Priority feature
• 1210 Annual vegetation of drift lines
• 2120 "Shifting dunes along the shoreline with Ammophila arenaria (""white dunes"")"
• 2130 "Fixed coastal dunes with herbaceous vegetation (""grey dunes"")"  * Priority feature
• 2190 Humid dune slacks

Annex II species that are a primary reason for selection of this site

• 1833 Slender naiad Najas flexilis

  The west coast machair plain of South Uist in the Outer Hebrides contains a cluster of eleven lochs supporting slender naiad Najas flexilis, the largest cluster of lochs with the species in the UK. The site is considered to be the best in the UK for slender naiad, holding nearly one-third of UK lochs with recent (post-1980) records for this species. It has been recorded in South Uist since the 1930s. The freshwater lochs within the South Uist machair are of diverse types, with a transition from oligotrophic waters situated on the peatlands to more nutrient-rich, calcareous lochs on shell-sand near the coast. Lochs of an intermediate type occur at the junction of peat and sandy substrates. Slender naiad occurs in both the oligotrophic and intermediate loch types. Water quality is high and conditions are particularly favourable for the species.

Annex II species present as a qualifying feature, but not a primary reason for site selection

• 1355 Otter Lutra lutra