Inland Rock Outcrop & Scree Habitats

These habitats occur throughout the uplands. They are found on stony ground on cliff ledges, crags, ridges, summits, scree slopes, and amongst cracks and fissures of rock faces. Although particularly characteristic of high altitudes, rock and scree habitats are also found at lower elevations, notably in northern Scotland. They grow on a wide range of substrates, from acidic to highly calcareous and base-poor to base-rich.

 

A wide range of vegetation communities can be found on inland rock outcrops and screes. Some are very sparse, some are very species-rich; some are well-vegetated, whilst others are species-poor; some are dominated by ferns or grasses and herbs, whilst others are dominated by low-growing cryptogams.

 

Summary details of major vegetation types (as described in the National Vegetation Classification) associated with inland rock outcrop and scree are given below.

 

NVC type

Main locations

Description

U16 Luzula sylvatica-Vaccinium myrtillus tall-herb community

Confined to exposed, base-poor rocks and screes in the Scottish uplands, with outliers in the Lake District and Cheviots

Typically dominated by mixtures of great wood-rush Luzula sylvatica and bilberry/blaeberry Vaccinium myrtillus, which sometimes grow to considerable stature. It is confined to cold, wet, upland areas, on ledges, in crags, over screes, on top of boulders or on rocky lake islands where protected from grazing and burning. Some flushing with moderately base-rich waters can occur.

 

U17 Luzula sylvatica-Geum rivale tall herb community

Confined to exposed, base-rich rocks and screes, or acid rocks flushed with base-rich waters, in the Scottish Highlands and Isles, with outliers in northern England and north Wales

Confined to inaccessible situations, such as ledges on cliffs and crags in ravines, or ground among or on top of boulders, or on islands in lakes, where livestock and deer rarely, if ever, penetrate. It is associated with flushed locations and persistently wet conditions of the north-west. Major species include great wood-rush Luzula sylvatica, roseroot Rhodiola rosea, tufted hair-grass Deschampsia cespitosa, sheep’s fescue/viviparous sheep's-fescue Festuca ovina/vivipara, water avens Geum rivale, wild angelica Angelica sylvestris, and the moss Hylocomium splendens. This is a varied community, with, for example, isolated stands on ledges of the same cliff face often having markedly different plants. It can be very species-rich and supports many extremely localised plant species.

 

U18 Cryptogramma crispa-Athyrium distentifolium snow-bed

Confined to high altitude, base-poor snow-beds in the Scottish uplands

Confined to high-altitude snow-beds, on rocky ground with base-poor, humic soils. It is usually dominated by Alpine lady-fern Athyrium distentifolium and, especially on lower slopes, parsley fern Crytogramma crispa, together with Alpine lady's mantle Alchemilla alpina, Alpine marsh violet Viola palustris, common sorrel Rumex acetosa, heath bedstraw Galium saxatile, starry saxifrage Saxifraga stellaris, tufted hair-grass Deschampsia cespitosa, and wavy hair-grass Deschampsia flexuosa.  Mosses are numerous and varied, such as Barbilophozia floerkii, Hylocomium splendens, Hypnum callichroum, Kiaeria starkei, Polytrichum alpinum, and Rhytidiadelphus loreus (which sometimes forms carpets among the rocks). Lichens, such as Cladonia bellidiflora, are characteristic.

 

U21 Cryptogramma crispa-Deschampsia flexuosa community

Mostly exposed, base-poor rock and screes at relatively low to moderate altitudes

Comprises pioneer vegetation of acidic screes and tumbled boulders, typically with parsley fern Crytogramma crispa the dominant species. Young stands often only have patches of encrusting mosses such as Andreaea rupestris and Racomitrium fasciculare. Nevertheless, heath bedstraw Galium saxatile, sheep's-fescue Festuca ovina, wavy hair-grass Deschampsia flexuosa, and the mosses Campylopus paradoxus and Polytrichum formosum are all characteristically present.

 

OV38 Gymnocarpium robertianum-Arrhenatherum elatius community

Mostly exposed, base-rich screes and rocky limestone slopes, in southern Britain

Typically comprises more or less open stands of limestone fern Gymnocarpium robertianum and false oat-grass Arrhenatherum elatius, together with herb robert Geranium robertianum, red/sheep’s fescue Festuca rubra/ovina, wood sage Teucrium scorodonia, and the moss Ctenidium molluscum. Other common plants include wall-lettuce Mycelis muralis, dog’s mercury Mercurialis perennis and the feather moss Homalothecium sericeum. Whilst mosses are frequently numerous and can be locally plentiful, lichens are scarce.

 

OV39 Asplenium trichomanes-Asplenium ruta-muraria community

Mostly exposed, base-rich rocks and screes at relatively low to moderate altitudes in the west

Characteristic of crevices in lime-rich bedrocks and wall-mortar, especially toward the more humid west of Britain. It generally comprises very open, fragmentary stands of low-growing ferns and bryophytes, such as Asplenium trichomanes, Asplenium ruta-mutaria, Homalothecium sericeum, and Porella platyphylla. However, biting stonecrop Sedum acre, thyme-leaved sandwort Arenaria serpyllifolia, sheep’s fescue Festuca ovina, wild thyme Thymus praecox, and a range of lime-loving grassland species can also feature.

 

OV40 Asplenium viride-Cystopteris fragilis community

Confined to exposed, base-rich rock and scree habitats in upland Britain

Open, often fragmentary vegetation of rock crevices, narrow ledges, and amongst screes, where a variety of ferns characteristically assume prominence. Green spleenwort Asplenium viride is most characteristic, particularly in the mountains of Scotland and northern England. Maidenhair spleenwort Asplenium trichomanes and wall-rue Asplenium ruta-mutaria are common, but decline rapidly at higher altitudes. Brittle bladder-fern Cystopteris fragilis is generally found throughout, whereas hart's-tongue fern Phyllitis scolopendrium is typical of lower altitudes, and northern
holly fern Polystichum lonchitis of the mountains of Scotland. Few other vascular plants occur, although sheep’s fescue Festuca ovina is usually present. Bryophytes can be abundant, notably Ctenidium molluscum, Fissidens cristatus and Tortella tortuosa. Lichens are generally scarce.

 

 

Lichens and bryophytes are one of the most notable features associated with inland rock outcrop and scree habitats. Many hundreds of individual species have been recorded growing on rock faces and scree, with different communities associated with acidic rock and limestone. Two groups of lichen species are of outstanding conservation interest: 1) species of western oceanic areas; and 2) species of calcareous rock at high altitudes.

 

Animal life

Inland rock outcrop and scree habitats are important for a range of animals. Inland crags in the Scottish uplands provide important nesting sites for golden eagle, sea eagle, raven and peregrine falcon. Snow buntings nest among boulders in high corries.  Botanically-rich rock habitats support a number of notable invertebrate species. Key groups include beetles, such as the ground beetles Leistus montanus and Nebria nivalis, flies such as Tipula and Thricops species and Helina vicina, and spiders, such as the highly localised Pardosa traillii.