Habitat account - Rocky habitats and caves


8120 Calcareous and calcshist screes of the montane to alpine levels (Thlaspietea rotundifolii

Background to selection

Distribution of SACs/SCIs/cSACs with habitat 8120 Calcareous and calcshist screes of the montane to alpine levels (Thlaspietea rotundifolii).  Click image for enlarged map.
Distribution of SACs/SCIs/cSACs with habitat 8120 Calcareous and calcshist screes of the montane to alpine levels (Thlaspietea rotundifolii). 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. Calcareous and calcshist screes consist of base-rich rocks including limestone, calcareous-schists and the more basic igneous rocks, such as serpentine and basalt. They may occur at any altitude, but screes in the lowlands are excluded from the Annex I definition. The scree is colonised by a range of pioneer species and provides shelter for many species sensitive to frost or grazing. Similar species may be found in the habitat known as ‘fell field’. Screes in the UK provide a habitat for various plant communities with affinities to the Thlaspietalia rotundifolii described from continental Europe. Both Calcareous and calcshist screes and 8110 Siliceous scree of the montane to snow levels are important for their rich fern flora and act as refugia for a number of rare species.

 

The vegetation consists of assemblages of calcicole and basiphilous species, the composition of which is heavily influenced by altitude. Characteristic species at high altitude include purple saxifrage Saxifraga oppositifolia, holly-fern Polystichum lonchitis and alpine meadow-grass Poa alpina, while at lower altitude limestone fern Gymnocarpium robertianum, herb-robert Geranium robertianum and wall lettuce Mycelis muralis are more usual. A large number of calcicolous mosses occur in the habitat type. Some low-lying examples are referable to NVC type OV38 Gymnocarpium robertianum – Arrhenatherum elatius. OV40 Asplenium viride – Cystopteris fragilis community is usually associated with rock crevices but is occasionally developed in scree. Other forms of calcareous and calcshist scree vegetation are not described by the NVC.

 

This habitat type may occur in close association with Annex I type 8210 Calcareous rocky slopes with chasmophytic vegetation, or grade to other Annex I types where the scree is stable.

European status and distribution

 

In mainland Europe, Calcareous and calcshist screes of the montane to alpine levels mainly occur in the Alps and locally in peri-alpine mountains.

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

 

This habitat type is widely distributed in the uplands of the UK, but is local in its occurrence.

Site selection rationale

 

Sites have been selected to take account of the importance of the habitat type as a refugium for rare plant species, and to cover ecological, altitudinal and geological variation and geographical range. Sites with the largest and most diverse examples of scree vegetation have been selected. Large upland sites generally contain more varied and extensive examples of the habitat type, and this is reflected in the SAC series. Sites that host important populations of arctic-alpine species have been favoured in site selection.


Site accounts

Caenlochan Eastern Scotland, North Eastern Scotland
Caenlochan is representative of communities on calcareous and calcshist screes at high altitude in the eastern Scottish Highlands. Although the habitat type is localised within the site, Caenlochan has a variety of different screes with an unusual flora. Fern-rich screes on calcareous-schist rocks support holly-fern Polystichum lonchitis, buckler-fern Dryopteris spp., roseroot Sedum rosea and mountain sorrel Oxyria digyna, while porphyritic screes have alpine penny-cress Thlaspi caerulescens and alpine speedwell Veronica alpina.
Inchnadamph Highlands and Islands
Inchnadamph is representative of calcareous and calcshist screes at low altitude in the north of Scotland. Screes of Durness limestone are extensive and support a diverse calcicolous flora. Species present include the limestone fern Gymnocarpium robertianum, holly-fern Polystichum lonchitis, hard shield fern Polystichum aculeatum, herb-Robert Geranium robertianum, the lady’s-mantle Alchemilla glabra, alpine lady’s-mantle Alchemilla alpina and, unusually in this context, primrose Primula vulgaris. Many calcicolous bryophytes are also found.
Keen of Hamar Highlands and Islands
Keen of Hamar, in the north of Shetland, is the most northerly site selected to represent calcareous and calcshist screes in Scotland. It is highly unusual in that the communities have developed on serpentine rock debris, which occurs extensively throughout the site and forms a mosaic with 6130 Calaminarian grasslands of the Violetalia calaminariae at low altitude. The scree supports a flora that is unique in the number of endemic races and subspecies it contains. These include moss campion Silene acaulis, northern rock-cress Arabis petraea, arctic sandwort Arenaria norvegica ssp. norvegica and Shetland mouse-ear Cerastium nigrescens.
Moor House - Upper Teesdale Cumbria, Tees Valley and Durham
This site is representative of the communities of calcareous and calcshist screes in the north of England up to an altitude of 760 m. This site has the most extensive areas of calcareous and calcshist scree in the UK, consisting of Carboniferous limestone. Communities are diverse and there is a mix of northern and southern floristic elements, including holly-fern Polystichum lonchitis, rigid buckler-fern Dryopteris submontana, limestone fern Gymnocarpium robertianum, musk thistle Carduus nutans and mossy saxifrage Saxifraga hypnoides. Hairy stonecrop Sedum villosum occurs where scree is flushed by springs.
Rum Highlands and Islands
Rum is representative of mildly calcareous and calcshist screes up to moderately high altitude in oceanic western Scotland. Rum has screes of various types, some of which are relatively small areas composed of ultra-basic rocks. Gravelly screes are widespread and unusual in supporting Scottish asphodel Tofieldia pusilla, which is usually associated with fens. Associated species include mountain everlasting Antennaria dioica, moss campion Silene acaulis, mossy cyphel Minuartia sedoides, thrift Armeria maritima, sea plantain Plantago maritima and purple saxifrage Saxifraga oppositifolia. Other species found in scree of larger rock fragments include northern rock-cress Arabis petraea, alpine penny-cress Thlaspi caerulescens, mountain sorrel Oxyria digyna and stone bramble Rubus saxatilis. Many ferns such as hay-scented buckler-fern Dryopteris aemula, northern buckler-fern D. expansa and male-fern D. filix-mas find a refuge from grazing animals in scree. Also there is a rich community of lower plants.
Trotternish Ridge Highlands and Islands
Trotternish Ridge is representative of mildly calcareous and calcshist screes at moderately high altitude in the oceanic west of Scotland. Although there is a mixture of scree types on the site, the calcareous screes are relatively restricted in extent. However, the mildly calcareous screes that are present have a rich flora, including northern rock-cress Arabis petraea, mountain sorrel Oxyria digyna, moss campion Silene acaulis, alpine lady’s-mantle Alchemilla alpina, stone bramble Rubus saxatilis, lesser clubmoss Selaginella selaginoides, the oceanic mosses Campylopus setifolius, Ulota phyllantha and Racomitrium ellipticum, and liverworts Plagiochila carringtonii and Lepidozia pearsonii. There is a rich fern flora, including green spleenwort Asplenium viride, scaly male-fern Dryopteris affinis and holly-fern Polystichum lonchitis. Flushed scree and the similar stony fell-field are habitats for the rare Iceland-purslane Koenigia islandica, growing with spiked wood-rush Luzula spicata and the montane liverwort Anthelia juratzkana.

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

Beinn Iadain and Beinn na h' Uamha Highlands and Islands
Ben Nevis Highlands and Islands
Berwyn a Mynyddoedd de Clwyd/ Berwyn and South Clwyd Mountains East Wales, West Wales and The Valleys
Binevenagh Northern Ireland
Peak District Dales Derbyshire and Nottinghamshire, Shropshire and Staffordshire
 

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