Habitat account - Rocky habitats and caves


8110 Siliceous scree of the montane to snow levels (Androsacetalia alpinae and Galeopsietalia ladani

Background to selection

Distribution of SACs/SCIs/cSACs with habitat 8110 Siliceous scree of the montane to snow levels (Androsacetalia alpinae and Galeopsietalia ladani).  Click image for enlarged map.
Distribution of SACs/SCIs/cSACs with habitat 8110 Siliceous scree of the montane to snow levels (Androsacetalia alpinae and Galeopsietalia ladani). Click image for enlarged map.

Description and ecological characteristics

 

Scree habitats consist of rock fragments covering the frost-shattered summits of mountains or accumulating on slopes below cliffs. Siliceous screes are made up of siliceous rocks such as quartzite, granite and sandstone. They may occur at any altitude, but screes in the lowlands are excluded from the Annex I definition. The scree may be colonised by a range of pioneer species. It also provides shelter for many species sensitive to frost, such as parsley fern Cryptogramma crispa, species requiring a humid microclimate such as Wilson’s filmy-fern Hymenophyllum wilsonii, and species sensitive to grazing such as stone bramble Rubus saxatilis.

 

Screes in the UK provide a habitat for plant communities with affinities to the Thlaspietea rotundifolii, as described from continental Europe. Both siliceous scree and 8120 Calcareous and calcshist screes of the montane to alpine levels (Thlaspietea rotundifolii) are important for their rich fern flora and act as refugia for a number of rare species.

 

Floristically the habitat type is principally characterised in the UK by two NVC types in which parsley fern Cryptogramma crispa and other ferns are prominent:

 

     

  • U18  Cryptogramma crispa – Athyrium distentifolium snow-bed community
  • U21  Cryptogramma crispa – Deschampsia flexuosa community

 

U18 Cryptogramma – Athyrium snow-bed community occurs principally in the Scottish Highlands above 600 m, where prolonged snow-cover provides suitable conditions for alpine lady-fern Athyrium distentifolium, the rare Newman’s lady-fern Athyrium flexile, and other montane vascular plants, bryophytes and lichens. U21 Cryptogramma – Deschampsia community extends to lower altitudes in mild oceanic climates in western Scotland, north-west England and north Wales, and has a less well-developed montane flora.

 

Other forms of siliceous scree are dominated by bryophytes and lichens and are not described in the NVC. In the west and, more locally at high altitude in the eastern Scottish Highlands, such screes provide an important habitat for Atlantic bryophytes, such as Anastrophyllum donnianum, Bazzania pearsonii, Herbertus aduncus, Scapania nimbosa and Scapania ornithopodioides, many of which have a restricted world distribution.

 

Siliceous scree of the montane to snow levels can occur in close association with Annex I type 8220 Siliceous rocky slopes with chasmophytic vegetation, while stabilised block screes may support a range of vegetation types including other Annex I types.

European status and distribution

 

This Annex I type has a fairly wide distribution in Europe. Vegetation resembling the Cryptogramma – Athyrium snow-bed community occurs in Scandinavia, although Cryptogramma crispa is largely confined there to western Norway. Vegetation related to the Cryptogramma – Deschampsia community occurs in the mountains of central Europe and in parts of western Norway.

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

 

Siliceous scree of the montane to snow levels is widely distributed in the UK. The Cryptogramma – Athyrium snow-bed community occurs throughout the Scottish Highlands, between Foinaven in the north and Ben Lui in the south. It is most common on the high Moine and Dalradian schist hills and on the hills that lie along the watershed of western Scotland. There are outliers in the Cairngorms and on Lochnagar.

 

The Cryptogramma – Deschampsia community is most common in the warmer parts of the oceanic west of the country, notably north Wales and the Lake District. It is especially associated with the hard volcanic rocks in these regions. Cryptogramma crispa is very scarce in south-west England, perhaps because the summers are too warm or dry, and in the Scottish Highlands it is largely confined to the Cryptogramma – Athyrium community in the shelter of snow-beds, except in the extreme west.

Site selection rationale

 

Sites have been selected to encompass the range of geographical, geological and ecological variation of siliceous scree in the UK. Generally the largest and most diverse examples with the best-developed structure have been selected. Low-altitude screes (including oceanic forms) and high-altitude, snow-influenced screes are represented. Forms of scree dominated by bryophytes and lichens have also been taken into account in site selection.


Site accounts

Beinn Bhan Highland
The siliceous scree habitat at Beinn Bhan is relatively extensive and comprises areas of both scree and block scree, consisting of the highly siliceous Torridonian sandstone. The variation in the size of rock fragments tends to be reflected in the ecological diversity of the scree habitat. The block screes have an outstanding flora of Atlantic bryophytes, including examples of the Northern Atlantic hepatic mat. The screes are notable for the frequency of parsley fern Cryptogramma crispa, constituting a northerly outpost of the NVC type U21 Cryptogramma crispa–Deschampsia flexuosa community.
Ben Alder and Aonach Beag Highland
This site is one of the best sites for siliceous scree in the central Highlands. The site has extensive base-poor schistose screes developed at moderate to high altitude. Where snow lies late there is an extensive development of U18 Cryptogramma crispaAthyrium distentifolium snow-bed community. Within these snow-beds the endemic Newman’s lady fern Athyrium flexile occurs. The oceanic montane liverworts Scapania nimbosa, Lophozia opacifolia, Mylia taylorii and Bazzania tricrenata occur in one of their few eastern outliers in these rocky snow-beds. Siliceous scree also occurs extensively at lower levels.
Ben Nevis Highland
Ben Nevis is representative of high altitude siliceous scree in the north-west Scottish Highlands. The site contains extensive screes of quartzite and granite, with the most extensive known development in the UK of snow-bed screes with parsley fern Cryptogramma crispa, alpine lady-fern Athyrium distentifolium and other ferns (U18). The screes found in the site are diverse, with a range of characteristic species. There is an abundance of acid rock-loving species in high-altitude glacial troughs, corries and on summit ridges. These include a number of montane bryophytes and arctic-alpine vascular plants, such as curved wood-rush Luzula arcuata, wavy meadow-grass Poa flexuosa, hare’s-foot sedge Carex lachenalii, alpine tufted hair-grass Deschampsia alpina, starwort mouse-ear Cerastium cerastoides, alpine speedwell Veronica alpina and Highland saxifrage Saxifraga rivularis.
Cadair Idris Gwynedd
Cadair Idris is the most southerly site in the UK selected for high-altitude siliceous scree and as such is not as species-rich as more northerly examples. Much of the rock is dry and unstable, but on the extensive screes on steep slopes U21 Cryptogramma crispaDeschampsia flexuosa vegetation is well-distributed, and on the boulder screes, lemon-scented fern Oreopteris limbosperma can be found together with a range of characteristic bryophytes and lichens.
Cairngorms Aberdeenshire; Highland; Moray
The Cairngorms complex contains representative examples of high altitude siliceous scree communities characteristic of the eastern Scottish Highlands. Extensive areas of scree occur on granite at a range of altitudes in the Cairngorms. The scree communities in this site are very diverse. Of particular interest is the flora of high-altitude screes in the snowy corries, with parsley fern Cryptogramma crispa, alpine lady-fern Athyrium distentifolium and rare wavy meadow-grass Poa flexuosa (U18). The flora is rich in rare moss species, for example Dicranum glaciale, and rare liverworts, such as Tetralophozia setiformis and Marsupella adusta. These occur on rocks in and about the snow-beds. There are also several northern Atlantic bryophytes such as Scapania nimbosa, Scapania ornithopodioides and Anastrophyllum donnianum, which are restricted to areas of late snow-lie where they are protected from winter frosts.
Eryri/ Snowdonia Conwy; Gwynedd
Snowdonia is the largest site in Wales representative of siliceous scree. The site has extensive screes of igneous rocks with large stands of U21 Cryptogramma crispaDeschampsia flexuosa vegetation; associated species include fir clubmoss Huperzia selago. Bryophyte and lichen-dominated screes are also well-represented and include important populations of rare and local montane and oceanic species, such as Marsupella adusta, Marsupella stableri and Cornicularia narmoerica.
Foinaven Highland
Foinaven represents highly acid screes, made up mainly of quartzite, in the far north-west Highlands. The extensive quartzite screes are very species-poor. However, there is a flora of Atlantic bryophytes associated with block screes at high altitudes. There is an important crustose lichen assemblage on the rocks.
Glen Coe Highland
Glen Coe is representative of communities on siliceous scree derived from igneous rocks at a range of altitudes in the western Scottish Highlands. The characteristic species parsley fern Cryptogramma crispa occurs throughout the site, and tends to be found with alpine lady-fern Athyrium distentifolium in snowy corries at high altitude (U18). There is an abundance of ferns on the boulder screes within the site. These include lemon-scented fern Oreopteris limbosperma, and a number of oceanic species such as Wilson’s filmy-fern Hymenophyllum wilsonii. Atlantic mosses and liverworts such as Anastrophyllum donianum and Scapania nimbosa are also abundant in screes on steep, shady, humid slopes. The rare Highland saxifrage Saxifraga rivularis occurs in springs and flushes amongst high-altitude scree.
Lake District High Fells Cumbria
This complex is representative of siliceous scree communities found at high altitude in north-west England. The site has the most extensive development of screes with parsley fern Cryptogramma crispa in the UK. The main rock, the Borrowdale Volcanic Series (but more locally Skiddaw Slates), varies much in base-status, but the screes are chiefly base-poor. Siliceous screes are one of the most extensive habitats within the Lake District High Fells, covering large areas on moderately steep ground, always interspersed with other habitats. The screes vary from recently-formed loose scree in lower sections of gullies and below cliffs to stable areas colonised by grasses, bryophytes and ferns. The main scree NVC type present is U21 Cryptogramma crispaDeschampsia flexuosa community. It is found throughout the complex, but major scree areas occur in Wasdale Screes, Helvellyn and Fairfield, Buttermere Fells, Scafell Pikes, Pillar and Ennerdale Fells and Skiddaw Group. The communities are well-developed and diverse with a wide range of characteristic species, including an abundance of parsley fern Cryptogramma crispa with associated species such as alpine lady’s mantle Alchemilla alpina, stone bramble Rubus saxatilis, heath bedstraw Galium saxatile, sheep’s fescue Festuca ovina and common bent Agrostis capillaris. Lemon-scented fern Oreopteris limbosperma is also found on the screes within Pillar and Ennerdale Fells. Bryophytes such as woolly hair-moss Racomitrium lanuginosum, R. fasciculare, Rhytidiadelphus loreus and R. squarrosus can be frequent. The screes provide a suitable microclimate for many oceanic moss and liverwort species such as Scapania ornithopiodes and Kiaeria starkei, found in Helvellyn and Fairfield.
Loch Maree Complex Highland
Loch Maree Complex is representative of vegetation communities on siliceous scree, mainly of quartzite and sandstone, in north-west Scotland. Screes are extensive and the communities they support are well-developed and diverse, with a range of characteristic species. Parsley fern Cryptogramma crispa is locally abundant, northern rock-cress Arabis petraea is frequently found and alpine lady-fern Athyrium distentifolium occurs in high-altitude areas where snow lingers. Other ferns occur frequently in the screes, including mountain male-fern Dryopteris oreades, beech fern Phegopteris connectilis, lemon-scented fern Oreopteris limbosperma and the oceanic Wilson’s filmy-fern Hymenophyllum wilsonii. The most outstanding feature of the vegetation on these sites is the abundance of northern Atlantic mosses and liverworts, which include Plagiochila spinulosa, Anastrophyllum donnianum and Scapania nimbosa, which are chiefly developed on steep, shady and humid slopes. The screes form a significant part of the habitat complex on this site, which is the most important single area in the UK for communities of these lower plants.
Moor House - Upper Teesdale Cumbria; Durham
Moor House – Upper Teesdale is representative of communities on both low and high altitude siliceous scree in northern England. Screes are extensive, with diverse plant communities. Cross Fell is a southern outlier of high-altitude gritstone scree, with a flora including rare lichens and some widespread montane vascular plants. Ferns including parsley fern Cryptogramma crispa and holly fern Polystichum lonchitis occur on extensive whin-sill screes at lower altitudes.

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

Beinn a`Ghlo Perth and Kinross
Beinn Dearg Highland
Ben Lui Argyll and Bute; Stirling
Ben Wyvis Highland
Caenlochan Aberdeenshire; Angus; Perth and Kinross
Creag Meagaidh Highland
Cuilcagh Mountain Fermanagh
Drumochter Hills Highland; Perth and Kinross
Eastern Mournes Down
Fannich Hills Highland
Inverpolly Highland
Merrick Kells Dumfries and Galloway; East Ayrshire; South Ayrshire
Moffat Hills Dumfries and Galloway
North Harris Western Isles / Na h-Eileanan an Iar
North Pennine Moors Cumbria; Durham; Northumberland; North Yorkshire
Ronas Hill - North Roe Shetland Islands
Rum Highland
Strathglass Complex Highland
 

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