Habitat account - Natural and semi-natural grassland formations


6170 Alpine and subalpine calcareous grasslands 

Background to selection

Distribution of SACs/SCIs/cSACs with habitat 6170 Alpine and subalpine calcareous grasslands.  Click image for enlarged map.
Distribution of SACs/SCIs/cSACs with habitat 6170 Alpine and subalpine calcareous grasslands. Click image for enlarged map.

Description and ecological characteristics

 

This habitat occurs on lime-rich soils and consists of short, often grazed, species-rich mixtures of mountain avens Dryas octopetala, arctic-alpine cushion herbs, grasses and sedges. In the UK this habitat occurs close to sea level, as well as at high altitudes. This is unusual in a European context and is due to the harsh northern oceanic climate of north-west Scotland. At low altitude, colonisation of the grasslands by trees and shrubs is prevented by a combination of exposure and grazing. At high altitude the grasslands are maintained by the harsh climate, though grazing may also alter species composition. This is one of the most important upland habitats in the UK for rare arctic-alpine plants and other rare montane or northern plants and animals, including the endemic Scottish primrose Primula scotica. Indeed, areas with this habitat form a large proportion of the localities in the Highlands traditionally regarded as important for their arctic-alpine flora.

 

Arctic-alpines that are characteristic of this habitat include moss campion Silene acaulis, alpine lady’s-mantle Alchemilla alpina, sibbaldia Sibbaldia procumbens, spiked wood-rush Luzula spicata, cyphel Minuartia sedoides, purple saxifrage Saxifraga oppositifolia, dwarf willow Salix herbacea, alpine bistort Persicaria vivipara, hair sedge Carex capillaris, yellow saxifrage Saxifraga aizoides, alpine meadow-rue Thalictrum alpinum, net-leaved willow Salix reticulata and green spleenwort Asplenium viride. The habitat also supports populations of nationally rare species, such as alpine mouse-ear Cerastium alpinum, rock sedge Carex rupestris, hoary whitlowgrass Draba incana, rock whitlowgrass D. norvegica, dark-red helleborine Epipactis atrorubens, alpine forget-me-not Myosotis alpestris, purple oxytropis Oxytropis halleri, alpine meadow-grass Poa alpina, alpine cinquefoil Potentilla crantzii, alpine speedwell Veronica alpina and rock speedwell Veronica fruticans. There are also rare or uncommon calcicolous bryophytes, including Aulacomnium turgidum, Amblystegium compactum, Seligeria trifaria and Lescuraea incurvata.

 

Alpine and subalpine calcareous grasslands comprise three NVC types, one of which is confusingly referred to as heath. They are:

 

     

  • CG12  Festuca ovina – Alchemilla alpina – Silene acaulis dwarf-herb community
  • CG13  Dryas octopetala – Carex flacca heath
  • CG14  Dryas octopetala – Silene acaulis ledge community

 

Variation within the habitat type is due to differences in altitude, climate and the intensity of grazing. The low-altitude CG13 Dryas – Carex grasslands are dominated by mountain avens Dryas octopetala. This community occurs in the north and west of Scotland from near sea level up to an altitude of 500 m, mainly on Durness limestone and wind-blown shell-sand. Within Dryas – Carex heath, mountain avens occurs mixed with lowland species and a relatively small complement of other arctic-alpine species. In some forms of the community the calcifuge (lime-hating) arctic-alpines crowberry Empetrum nigrum ssp. nigrum, hermaphrodite crowberry E. nigrum ssp. hermaphroditum and bearberry Arctostaphylos uva-ursi, occur mixed with calciphile (lime-loving) species such as mountain avens. This is highly unusual and is perhaps due to surface leaching in the wet climate.

 

At high altitudes the habitat type occurs in two forms with a much larger assemblage of arctic-alpine species. Dominance of mountain avens is maintained on steep rocky ground, on rock ledges, and among boulders out of reach of grazing animals, forming CG14 Dryas – Silene ledge community. Within this sub-type, mountain avens occurs mixed with a wide range of arctic-alpine species. On open slopes, montane cushion herbs, especially moss campion Silene acaulis, and other small herbs replace mountain avens to form CG12 Festuca – Alchemilla – Silene dwarf-herb community. Arctic-alpines also dominate here, usually moss campion and alpine lady’s-mantle, sometimes with cyphel.

 

On most upland sites, Alpine and subalpine calcareous grasslands form intimate mosaics with other upland Annex I habitats, and there are complex transitions to a range of montane communities. They are often associated with 4080 Sub-Arctic Salix spp. scrub and 6430 Hydrophilous tall herb fringe communities of plains and of the montane to alpine levels on inaccessible rocky ground. On more siliceous soils, they give way to 6230 Species-rich Nardus grasslands, on siliceous substrates in mountain areas (and submountain areas in continental Europe) or more species-poor forms of Nardus grassland. Where snow lies late they give way to late snow-bed communities, and on the more windswept and leached summits they are replaced by moss-heaths, both habitats belonging to 6150 Siliceous alpine and boreal grasslands. Where there is strong base-rich flushing they grade into 7240 Alpine pioneer formations of the Caricion bicoloris-atrofuscae and on rocky ground to 8210 Calcareous rocky slopes with chasmophytic vegetation or 8220 Siliceous rocky slopes with chasmophytic vegetation.

European status and distribution

 

In the EU, Alpine and subalpine calcareous grasslands are largely restricted to the Alpine and Boreal Biogeographical Regions. The UK examples represent western and oceanic outliers of this habitat type.

UK status and distribution Click to view UK distribution of this habitat

 

Alpine and subalpine calcareous grasslands are extremely scarce in the UK. Only about 500 ha of this habitat are found in the SSSI and ASSI series, and this is thought to be a very high proportion of the total UK resource of the habitat, which occurs primarily in the Scottish Highlands. High-altitude alpine calcareous grassland is almost entirely restricted to those upland areas in the central and north-western Highlands where base-rich rocks are found. Examples of the habitat at low altitude are very localised, being largely restricted to calcareous rocks in north-west mainland Scotland and on Skye.

Site selection rationale

 

Site selection has ensured that a high proportion of the Alpine and subalpine calcareous grassland resource is included in the SAC series. The sites selected are the largest and structurally and functionally most complete examples of the habitat type. Such sites have the greatest variety of sub-types, and the highest diversity of vegetation mosaics and transitions to other communities. The sites encompass the ecological variation and geographical range of the habitat type.

 

Site selection has also aimed to represent all of the rarer species and the largest populations of the characteristic species associated with Alpine and subalpine calcareous grassland.


Site accounts

Beinn Dearg Highlands and Islands
Beinn Dearg, with Ben Nevis, is selected as representative of the high-altitude sub-types of this habitat type in the western Scottish Highlands. It supports both CG12 Festuca ovina – Alchemilla alpina – Silene acaulis dwarf-herb community and CG14 Dryas octopetala – Silene acaulis ledge community. The habitat type is moderately extensive and well-developed, and supports a rich flora of arctic-alpines, including alpine mouse-ear Cerastium alpinum, arctic mouse-ear Cerastium arcticum, alpine meadow-grass Poa alpina, alpine cinquefoil Potentilla crantzii and net-leaved willow Salix reticulata.
Ben Alder and Aonach Beag Highlands and Islands
Ben Alder and Aonach Beag is representative of high-altitude Alpine and subalpine calcareous grasslands in the central Highlands, where the habitat is very local owing to the infrequent occurrence of calcareous rocks at high altitude. Both CG12 Festuca ovina – Alchemilla alpina – Silene acaulis dwarf-herb and CG14 Dryas octopetala – Silene acaulis ledge communities are well-represented, especially the latter. The widespread arctic-alpines purple saxifrage Saxifraga oppositifolia and yellow saxifrage S. aizoides are frequent, while rarer species that are widespread on the site include cyphel Minuartia sedoides, alpine meadow-grass Poa alpina, hair sedge Carex capillaris, black alpine-sedge C. atrata and alpine speedwell Veronica alpina. Unusually, grazing levels appear to be low enough to allow the development of mountain avens heath on slopes open to grazing animals. The low grazing levels also allow the exceptional development of moderately large populations of montane willows, including woolly willow Salix lanata, conforming to Annex I type 4080 Sub-Arctic Salix spp. scrub, for which the site is also selected. The transition between these two habitat types is unusual.
Ben Heasgarnich Eastern Scotland, Highlands and Islands
Ben Heasgarnich is one of four sites selected in the Breadalbane Hills of the southern Highlands to represent high-altitude Alpine and subalpine calcareous grasslands. Ben Heasgarnich has moderately extensive CG12 Festuca ovina – Alchemilla alpina – Silene acaulis dwarf-herb community on high corrie slopes. There are also some well-developed areas of high-altitude CG14 Dryas octopetala – Silene acaulis ledge community on steep, rocky slopes. The habitat type supports an outstanding arctic-alpine flora, with many rare species, including alpine mouse-ear Cerastium alpinum, hoary whitlowgrass Draba incana, cyphel Minuartia sedoides and hair sedge Carex capillaris. There are transitions to 6230 Species-rich Nardus grasslands, on siliceous substrates in mountain areas (and submountain areas in continental Europe) and to other alpine plant communities.
Ben Lawers Eastern Scotland
Ben Lawers has the most extensive development of Alpine and subalpine calcareous grasslands in the UK, representing high-altitude forms of the habitat. The main sub-type, CG12 Festuca ovina – Alchemilla alpina – Silene acaulis dwarf-herb community, is found on the open hill, and is dominated by moss campion Silene acaulis. CG14 Dryas octopetala – Silene acaulis ledge community also occurs and is largely confined to crags because of heavy grazing pressure. The site has an exceptional arctic-alpine flora, including a wide range of characteristic species and many rarities. These include cyphel Minuartia sedoides, sibbaldia Sibbaldia procumbens, mountain pansy Viola lutea, alpine forget-me-not Myosotis alpestris, alpine fleabane Erigeron borealis, alpine gentian Gentiana nivalis, mountain sandwort Minuartia rubella, rock speedwell Veronica fruticans, blue moor-grass Sesleria caerulea, alpine meadow-grass Poa alpina, alpine pearlwort Sagina saginoides and alpine saxifrage Saxifraga nivalis. There are well-developed transitions to a wide range of other alpine plant communities, including snow-beds and 7240 Alpine pioneer formations of the Caricion bicoloris-atrofuscae.
Ben Lui Eastern Scotland, Highlands and Islands
Ben Lui is one of four sites selected in the Breadalbane Hills of the southern Highlands to represent high-altitude Alpine and subalpine calcareous grasslands. Ben Lui has extensive areas of the open hill sub-type CG12 Festuca ovina – Alchemilla alpina – Silene acaulis dwarf-herb community. CG14 Dryas octopetala – Silene acaulis ledge community also occurs in profusion on steep, rocky ground. This supports an outstanding arctic-alpine flora, including alpine bartsia Bartsia alpina, mossy saxifrage Saxifraga hypnoides, cyphel Minuartia sedoides, rock sedge Carex rupestris, and hair sedge C. capillaris. The quality and diversity of this community and the range of transitions to other habitat types are similar to those on Ben Lawers, but less extensive.
Ben Nevis Highlands and Islands
With Beinn Dearg, Ben Nevis represents high-altitude sub-types of Alpine and subalpine calcareous grasslands in the western Scottish Highlands. The site contains moderately extensive areas of both CG12 Festuca ovina – Alchemilla alpina – Silene acaulis dwarf-herb community and CG14 Dryas octopetala – Silene acaulis ledge community. There is a moderately rich arctic-alpine flora including alpine mouse-ear Cerastium alpinum, arctic mouse-ear Cerastium arcticum, rock sedge Carex rupestris, hair sedge C. capillaris, mossy saxifrage Saxifraga hypnoides and alpine meadow-rue Thalictrum alpinum. There are relatively low grazing levels on the northern slopes of Ben Nevis, enabling the high-altitude Dryas heath community to survive on the open hillside, rather than being restricted to inaccessible ledges.
Durness Highlands and Islands
Durness is one of four sites representing the low-altitude Alpine and subalpine calcareous grasslands that are restricted to the north-west mainland of Scotland. Durness contains the largest stands of CG13 Dryas octopetala – Carex flacca heath in the UK, developed on dolomitic limestone at 0–60 m. The site has an outstanding representation of characteristic species, including wild thyme Thymus polytrichus, ribwort plantain Plantago lanceolata, sea plantain Plantago maritima, purging flax Linum catharticum and common bird’s-foot-trefoil Lotus corniculatus. The endemic Scottish primrose Primula scotica is present, and other uncommon species include mountain everlasting Antennaria dioica, hair sedge Carex capillaris, lesser meadow-rue Thalictrum minus, frog orchid Coeloglossum viride and hart’s-tongue Phyllitis scolopendrium. Locally, the calcifuge species crowberry Empetrum nigrum occurs, giving rise to an unusual sub-type of Dryas heath. There are transitions to a wide range of other communities, including coastal dunes, other types of base-rich grasslands, and a range of dwarf-shrub heaths.
Inchnadamph Highlands and Islands
Inchnadamph is one of five sites representing low-altitude CG13 Dryas octopetala – Carex flacca heath, and has the second most extensive development of this sub-type of Alpine and subalpine calcareous grasslands in the UK. Dryas – Carex heath at Inchnadamph occurs from 100 m up to around 450 m, similar to Rassal. The site is the best example of the transition from low to high altitude alpine calcareous grassland. As the site is at a higher altitude than Durness there are more arctic-alpines in the flora, including purple saxifrage Saxifraga oppositifolia, yellow saxifrage S. aizoides, moss campion Silene acaulis, alpine meadow-rue Thalictrum alpinum and hair sedge Carex capillaris, while some low-altitude species are lacking. The site shows the transition between low- and high-altitude Alpine and subalpine calcareous grassland, and occupies a key position in the range of variation shown by this habitat type in the UK.
Invernaver Highlands and Islands
Invernaver is one of five sites representing low altitude CG13 Dryas octopetala – Carex flacca heath, and this is the only site with extensive development of Alpine and subalpine calcareous grasslands on wind-blown calcareous shell-sand, from near sea level to about 100 m. On the other four low-altitude examples, the heath is developed chiefly on limestone outcrops. The site has an unusually extensive representation of a sub-type of Dryas heath in which the Dryas is mixed with ericaceous and other woody plants, including crowberry Empetrum nigrum, bearberry Arctostaphylos uva-ursi, creeping willow Salix repens ssp. argentea and juniper Juniperus communis. This sub-type is better represented here than on any other site selected. The abundance of woody plants may be partly attributable to lower grazing pressure. The diversity of arctic-alpine species is relatively low compared with high-altitude sites, but mountain avens, crowberry Empetrum nigrum ssp. hermaphroditum and bearberry Arctostaphylos uva-ursi are abundant, and other species, such as purple saxifrage Saxifraga oppositifolia, yellow saxifrage S. aizoides and hair sedge Carex capillaris, are frequent. The site is unusually exposed for a low-altitude site, and this is reflected by the occurrence of dwarf juniper Juniperus communis ssp. nana. There are transitions to calcareous coastal habitats to seaward, while inland there are transitions to a unique form of mixed Calluna – Juniperus – Arctostaphylos heath on more acid soils, and to oceanic Calluna – Erica cinerea heath, calcareous grassland and base-rich mires.
Meall na Samhna Eastern Scotland
Meall na Samhna is one of four sites selected in the Breadalbane Hills of the southern Highlands to represent high-altitude Alpine and subalpine calcareous grasslands. The CG12 Festuca ovina – Alchemilla alpina – Silene acaulis dwarf-herb community is moderately extensive, and there are some well-developed areas of CG14 Dryas octopetala – Silene acaulis ledge community on steep, rocky slopes. The habitat supports an outstanding arctic-alpine flora, which includes alpine bartsia Bartsia alpina, alpine mouse-ear Cerastium alpinum, alpine saw-wort Saussurea alpina, hair sedge Carex capillaris and net-leaved willow Salix reticulata. There are transitions to 6230 Species-rich Nardus grasslands, on siliceous substrates in mountain areas (and submountain areas in continental Europe) and other alpine communities.
Strath Highlands and Islands
Strath is one of four sites representing low-altitude Alpine and subalpine calcareous grasslands in north-west Scotland. Although the areas of CG13 Dryas octopetala – Carex flacca heath on this site are relatively small, they occur widely wherever there are outcrops of Dalradian Durness limestone from near sea level up to around 250 m. This habitat type is part of a complex mosaic with other Annex I habitat types on the limestone, 8240 Limestone pavements and 8210 Calcareous rocky slopes with chasmophytic vegetation. The site contains a diverse range of characteristic species, including wild thyme Thymus polytrichus, ribwort plantain Plantago lanceolata, purging flax Linum catharticum, spring sedge Carex caryophyllea and common bird’s-foot-trefoil Lotus corniculatus. A sub-type of the Dryas heath containing the calcifuge dwarf shrubs crowberry Empetrum nigrum and bearberry Arctostaphylos uva-ursi is well-developed. Rarer species include dark-red helleborine Epipactis atrorubens and alpine bistort Persicaria vivipara. Unusually, there are transitions to one of the most floristically-rich areas of 8240 Limestone pavements in Scotland.

SACs/SCIs/cSACs where this Annex I habitat is a qualifying feature, but not a primary reason for site selection

Eryri/ Snowdonia West Wales and The Valleys
Glen Coe Highlands and Islands
Rassal Highlands and Islands
Trotternish Ridge Highlands and Islands
 

Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.