Habitat account - Rocky habitats and caves

8220 Siliceous rocky slopes with chasmophytic vegetation 

Background to selection

Distribution of SACs/SCIs/cSACs with habitat 8220 Siliceous rocky slopes with chasmophytic vegetation.  Click image for enlarged map.
Distribution of SACs/SCIs/cSACs with habitat 8220 Siliceous rocky slopes with chasmophytic vegetation. Click image for enlarged map.

Description and ecological characteristics


Chasmophytic vegetation consists of plant communities that colonise the cracks and fissures of rock faces. The type of plant community that develops is largely determined by the base-status of the rock face. Siliceous communities develop on acid rocks whereas calcareous sub-types develop on lime-rich rocks such as limestone and calcareous schists. The presence of calcareous bands within otherwise mainly siliceous rocks often brings the two types together on the same rock outcrop. As a result, Siliceous rocky slopes with chasmophytic vegetation may occur in close association with Annex I type 8210 Calcareous rocky slopes with chasmophytic vegetation, and some sites are listed for both types. Lowland examples are included in the Annex I definition only where they include cliffs supporting distinctive crevice communities; coastal examples are referable to Annex I type 1230 Vegetated sea cliffs of the Atlantic and Baltic coasts.


Both forms of chasmophytic vegetation in the UK correspond to the rock fissure communities described from Europe (Asplenietea trichomanis). Siliceous rock crevice vegetation is poorly covered by the NVC, although some forms can be referred to U21 Cryptogramma crispa Ė Deschampsia flexuosa community. The habitat type typically comprises mixtures of bryophytes, such as Amphidium mougeotii and Racomitrium spp., and vascular plants, such as wavy hair-grass Deschampsia flexuosa and fir clubmoss Huperzia selago.


Altitude and geographical location account for a large part of the ecological variation exhibited by this habitat type. High-altitude examples in northern Scotland are particularly important for a range of rare species, such as alpine speedwell Veronica alpina and Highland cudweed Gnaphalium norvegicum, that have an arctic-alpine or boreal distribution.


In western localities, especially close to the coast, the habitat type is enriched by oceanic species, such as Wilsonís filmy fern Hymenophyllum wilsonii and sea spleenwort Asplenium marinum, as well as rich assemblages of Atlantic bryophytes. In the southern uplands of Wales and England, northern floristic elements are reduced. Although some species, such as dwarf willow Salix herbacea, have their most southerly occurrence in this habitat type, southern species, such as forked spleenwort Asplenium septentrionale, tutsan Hypericum androsaemum and wood bitter vetch Vicia orobus, also occur.

European status and distribution


Siliceous rocky slopes with chasmophytic vegetation are widely distributed in the mountains of the EU.

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


Siliceous rocky slopes with chasmophytic vegetation are widespread in upland areas of the UK. Although both siliceous and calcareous types are widely distributed in the uplands of the UK, siliceous rocks predominate and calcareous chasmophytic vegetation is of more limited overall extent.

Site selection rationale


Sites have been selected to take account of the range of floristic assemblages characteristic of acidic rock crevices in the UK. Preference has been given to the largest areas with the most diverse populations of characteristic montane plants. Sites that host important populations of arctic-alpine or western species have been favoured in site selection.

Site accounts

Ballochbuie North Eastern Scotland
Situated on the north slopes of the Dee valley below the foothills of the Lochnagar massif, the geology at Ballochbuie is dominated by granites of various degrees of acidity, but with complex of siliceous and calcareous metamorphic rocks in the west of the site, in the vicinity of the Lionís Face and Creag Clunie. Cliffs of siliceous rocks occur in various parts of the site, both within and above the 91C0 Caledonian forest which is the dominant habitat on the site. These cliffs give rise to areas of block scree. These rocky slopes support a number of specialised bryophytes and, in particular, lichens, along with occasional ferns. At the Lionís Face the assemblage of lichens associated with siliceous rocks contrasts with the adjacent calcareous rocky slopes. Rare species, such as Protoparmelia nephaea and Umbilicaria nyladeriana (both Nationally rare) are present, along with two recently-described species. Stabilised block screes and associated outcrops on Creag Clunie also support a number of rare lichens, such as Lecanora cenisia and Pyrrhospora rubigans (both Nationally rare). Rare mosses are also present including Cynodontium polycarpon (Vulnerable) and Grimmia incurva (Nationally scarce).
Beinn Dearg Highlands and Islands
Beinn Dearg is representative of high-altitude Siliceous rocky slopes with chasmophytic vegetation in north-west Scotland. On Beinn Dearg the habitat type occurs on large crags of siliceous metamorphosed sandstones. There is a rich flora of characteristic montane acid-loving and base-indifferent arctic-alpines, such as three-leaved rush Juncus trifidus, spiked wood-rush Luzula spicata, dwarf willow Salix herbacea, mountain sorrel Oxyria digyna, northern rock-cress Arabis petraea, stone bramble Rubus saxatilis and the rare Highland cudweed Gnaphalium norvegicum. The associated montane bryophyte flora contains a rich assemblage of species characteristic of the north-west Highlands.
Ben Nevis Highlands and Islands
Ben Nevis is representative of high-altitude Siliceous rocky slopes with chasmophytic vegetation in north-west Scotland. Crevice communities occur extensively on acidic crags up to a very high altitude and have a diverse flora, with characteristic examples of the commoner arctic-alpine species. The site also supports a number of rare species, including hareís-foot sedge Carex lachenalii, spiked wood-rush Luzula spicata and alpine speedwell Veronica alpina.
Brecon Beacons/ Bannau Brycheiniog East Wales
The Brecon Beacons support Siliceous rocky slopes with chasmophytic vegetation on a number of cliffs and rock-faces. The more siliceous sites are often towards the top of the cliffs, where the calcareous cements have been leached out, with a transition to more calcareous chasmophytic vegetation lower down the face. Species found in this habitat include fir clubmoss Huperzia selago, serrated wintergreen Orthilia secunda and the nationally scarce bryophytes Brachydontium trichodes and Rhabdoweisia crenulata.
Cadair Idris West Wales and The Valleys
Cadair Idris is one of three Welsh sites representing Siliceous rocky slopes with chasmophytic vegetation. Cliffs and rock outcrops are abundant on the site, with many supporting characteristic assemblages of lichen and bryophyte communities, particularly on the steep, moist, north-facing cliffs. Vascular plants include Wilsonís filmy-fern Hymenophyllum wilsonii, starry saxifrage Saxifraga stellaris and fir clubmoss Huperzia selago.
Cairngorms Highlands and Islands, North Eastern Scotland
The Cairngorms represent high-altitude Siliceous rocky slopes with chasmophytic vegetation in the eastern Scottish Highlands. Crevice communities occur widely on acidic granite rocks and support an abundance of characteristic species. Rare species include Highland cudweed Gnaphalium norvegicum, alpine speedwell Veronica alpina, spiked wood-rush Luzula spicata and hareís-foot sedge Carex lachenalii.
Eryri/ Snowdonia West Wales and The Valleys
Snowdonia, north Wales, is representative of Siliceous rocky slopes with chasmophytic vegetation at the southern edge of the range of the habitat type. Acidic crevice communities occur throughout the site on igneous outcrops and include populations of stiff sedge Carex bigelowii, fir clubmoss Huperzia selago and forked spleenwort Asplenium septentrionale. Atlantic species, including Wilsonís filmy-fern Hymenophyllum wilsonii and a wide range of bryophytes, are also well-represented.
Foinaven Highlands and Islands
Foinaven in north-west Scotland is the most northerly site selected for Siliceous rocky slopes with chasmophytic vegetation. The site has a cool oceanic climate and the crevice communities are developed widely on extensive outcrops of quartzite, Lewisian gneiss and schist, which occur from low to moderately high altitude. Characteristic species that occur are black spleenwort Asplenium adiantum-nigrum, fir clubmoss Huperzia selago and starry saxifrage Saxifraga stellaris, while rarer species, such as rock whitlowgrass Draba norvegica, and oceanic ferns, such as Wilsonís filmy-fern Hymenophyllum wilsonii, with associated oceanic bryophytes, may occur.
Glen Coe Highlands and Islands
Glen Coe is representative of high-altitude Siliceous rocky slopes with chasmophytic vegetation in west Scotland. The habitat type is developed on massive outcrops of siliceous igneous rocks with crags up to very high altitude. The rock type varies across the site, leading to variation in the plant species. The crags support many of the commoner arctic-alpine species of acidic rocks, which are widespread across the site. The very rare drooping saxifrage Saxifraga cernua occurs in small pockets of calcareous material within predominantly acidic rocks, together with such species as brittle bladder-fern Cystopteris fragilis, roseroot Sedum rosea and mountain sorrel Oxyria digyna. The fern flora of this site is extremely diverse and westerly influences on the site are shown by the extensive development of oceanic bryophytes associated with the crags.
Lake District High Fells Cumbria
Lake District High Fells represent high-altitude siliceous slopes with chasmophytic vegetation in northern England. These communities are found throughout the complex, but predominantly in Helvellyn and Fairfield, Wasdale Screes, Scafell Pikes, Pillar and Ennerdale Fells, Honister Crag, Buttermere Fells and Armboth Fells. The communities have developed on long lines of cliffs and coves formed largely of acidic rocks of the Borrowdale Volcanic Series, with considerable amounts of calcite in the eroding gullies. On the predominantly acid crags, there are extensive communities of silicicolous vegetation. The species present are characteristic of north-west England and include alpine ladyís mantle Alchemilla alpina, starry saxifrage Saxifraga stellaris and stiff sedge Carex bigelowii. Crevices and wet rock faces support a number of uncommon ferns including green spleenwort Asplenium viride, brittle bladder fern Cystopteris fragilis and Wilsonís filmy fern Hymenophyllum wilsonii. Scattered trees on crags include aspen Populus tremula and rock whitebeam Sorbus rupicola. Wasdale Screes also has many more typical lowland species such as royal fern Osmunda regalis.
Loch Maree Complex Highlands and Islands
Loch Maree Complex is representative of the acid Siliceous rocky slopes with chasmophytic vegetation in north-west Scotland. The habitat occurs widely on extensive crags of Torridonian sandstone and quartzite at low to moderately high altitudes. The site contains a characteristic north-western flora, with many of the commoner montane vascular plants, including Wilsonís filmy-fern Hymenophyllum wilsonii, sea spleenwort Asplenium marinum, three-leaved rush Juncus trifidus, dwarf willow Salix herbacea and spiked wood-rush Luzula spicata. Rarer species include the characteristic black spleenwort A. adiantum-nigrum. Oceanic influence is shown by the widespread development of oceanic ferns. Of particular importance is the outstanding flora of Atlantic mosses and liverworts in the crevices of the more shady crags.
Moor House - Upper Teesdale Cumbria, Tees Valley and Durham
Moor House Ė Upper Teesdale, which includes the highest point of the Pennines, has a mixed geology of Carboniferous sandstones, mudstone and limestones, that have influenced the important plant communities that are found there. This cSAC is one of only a very few sites in England supporting Siliceous rocky slopes with chasmophytic vegetation. The most extensive occurrences of this community type are where the Whin Sill outcrops at Falcon Clints, Ravenscar, Holwick Scars and High Force. Some examples also occur at Middle Tongue and alongside Cash Burn. Characteristic species present include parsley fern Cryptogramma crispa, mountain male-fern Dryopteris oreades and northern buckler-fern D. expansa. Bearberry Arctostaphylos uva-ursi and starry saxifrage Saxifraga stellaris also occur in this community.
North Pennine Moors Cumbria, North Yorkshire, Northumberland and Tyne and Wear, Tees Valley and Durham
Acidic rock outcrops and screes are well-scattered across the North Pennine Moors and support vegetation typical of Siliceous rocky slopes with chasmophytic vegetation in England, including a range of lichens and bryophytes, such as Racomitrium lanuginosum, and species like stiff sedge Carex bigelowii and fir clubmoss Huperzia selago.
Strathglass Complex Highlands and Islands
Strathglass Complex has some of the most extensive outcrops of siliceous rock in the UK. This is one of eight sites representing this habitat in the western Highlands between Glen Coe in the south and Foinaven in the far north. A characteristic flora occurs up to very high altitude including parsley fern Cryptogramma crispa, three-leaved rush Juncus trifidus, least willow Salix herbacea, starry saxifrage Saxifraga stellaris, beech fern Phegopteris connectilis and the nationally rare Highland cudweed Gnaphalium norvegicum. Crevices in the more shady rocks support a flora of Atlantic mosses and liverworts.

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

Beinn a' Ghlo Eastern Scotland
Beinn Bhan Highlands and Islands
Ben Alder and Aonach Beag Highlands and Islands
Ben Heasgarnich Eastern Scotland, Highlands and Islands
Ben Lawers Eastern Scotland
Ben Lui Eastern Scotland, Highlands and Islands
Ben Wyvis Highlands and Islands
Borrowdale Woodland Complex Cumbria
Caenlochan Eastern Scotland, North Eastern Scotland
Creag Meagaidh Highlands and Islands
Cuilcagh Mountain Northern Ireland
Drumochter Hills Eastern Scotland, Highlands and Islands
Eastern Mournes Northern Ireland
Fannich Hills Highlands and Islands
Inverpolly Highlands and Islands
Merrick Kells South Western Scotland
Moffat Hills South Western Scotland
North Harris Highlands and Islands
Rum Highlands and Islands

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