Inland Rock Outcrop and Scree Habitats (Uk Bap Priority Habitat)

INLAND ROCK OUTCROP AND SCREE HABITATS (UK BAP PRIORITY HABITAT)

Summary

This priority type includes plant communities that are confined or almost confined to inaccessible ledges on cliffs and crags or to screes and boulders. The predominant controlling factor is the base-status of the rock which determines what the vegetation consists of. There are communities of smaller ferns on small ledges, and in crevices, on screes and boulder-fields, and boulder-scree on sheltered slopes where snow lies late in spring.

The habitat is common throughout the uplands where extensive glaciation has resulted in steep cliffs and outcrops, screes and block litter, though there are also examples on river cliffs in the lowlands, and the small fern communities can occur on walls and buildings. This priority habitat occurs throughout Scotland from just above sea level to over 1000 m on our highest hills.

Rock and scree habitats are home to many rare and uncommon species. Boulder-fields, screes and high ledges where snow lies very late are habitats for snow-tolerant species. This priority habitat is also very important for lichens which are often the dominant life-form. Inland crags are the preferred nesting sites of golden eagle Aquila chrysaetos, sea eagle Haliaeetus albicilla, raven Corvus corax and peregrine falcon Falco peregrinus, whilst snow buntings Plectrophenax nivalis nest among boulders in high corries. The vegetation is near- natural.

Being out of the reach of all grazing animals apart from goats, and being difficult to burn, these communities are not threatened by many human activities apart from some disturbance by climbers.

What is it?

These are the plant communities associated primarily with natural exposures of rock, whether it occurs as cliffs, outcrops, boulder-fields or screes. The predominant plants are either ferns or tall herbs or both, but lichens and bryophytes are also important and may be dominant. Fern communities vary from the crevice assemblages of small species such as wall rue Asplenium ruta-muraria, maidenhair spleenwort A. trichomanes, black spleenwort A. adiantum-nigrum (OV39), green spleenwort A. viride and brittle bladder fern Cystopteris fragilis (OV40) to tall swards of male fern Dryopteris filix-mas, broad buckler fern D. dilatata and lemon-scented fern Oreopteris limbosperma (U16) and the scree community of parsley fern Cryptogramma crispa (U21). Consolidated block scree at high altitudes is home to the snowbed fern community U18 with Alpine lady fern Athyrium distentifolium, Cryptogramma crispa and, at a few sites, mountain bladder fern Cystopteris montana. Tall herb vegetation is very variable. On acid cliffs it may consist of little more than great wood-rush Luzula sylvatica swards interleaved with bilberry Vaccinium myrtillus and dotted with a few ferns (U16). On basic ledges it can consist of tall grasses, ferns and herbs (U17). In summer the flowering swards of wild angelica Angelica sylvestris, roseroot Sedum rosea, common valerian Valeriana officinalis, globe flower Trollius europaeus, meadow buttercup Ranunculus acris, water avens Geum rivale, dropwort Filipendula vulgaris, wood crane’s-bill Geranium sylvaticum and smooth lady’s mantle Alchemilla glabra are very colourful. There is also an array of smaller species such as primrose Primula vulgaris, Alpine lady’s mantle Alchemilla alpina, lesser clubmoss Selaginella selaginoides, common butterwort Pinguicula vulgaris, yellow saxifrage Saxifraga aizoides, purple saxifrage S. oppositifolia and Alpine meadow-rue Thalictrum alpinum.

How do I recognise it?

Differentiation from other priority habitats

Inland rock outcrop and scree habitats are assemblages of ferns or tall herbs or both. This distinguishes them from the Upland heathland, Mountain heaths and willow scrub that can also occur on cliff ledges and among scree. The Upland heathland has a canopy of dwarf shrubs such as ling Calluna vulgaris, bell heather Erica cinerea or Vaccinium myrtillus, or mixtures of C. vulgaris, cross-leaved heath Erica tetralix, E. cinerea, deergrass Scirpus cespitosus and purple moor-grass Molinia caerulea; the Mountain heaths may consist of mixtures of any or all of crowberry Empetrum nigrum, Vaccinium spp., mosses Racomitrium lanuginosum, Rhytidiadelphus loreus or montane willows.

Definition in relation to other habitat classifications

Classification Habitat types belonging to this UK BAP priority habitat OV38 (examples not within limestone pavements), OV39 (examples on natural rock but not in/on limestone pavements), OV40 (examples not in/on limestone pavements), OV41 NVC (examples on natural rock outcrops), U16-17 (examples on cliffs), U18 and U21 (all examples). OV40 and U16-18 are included in the Scottish Biodiversity List. OV38 and OV41 are not known to occur in Scotland. The Inland rock outcrop and scree habitats priority habitat Phase 1 includes three Phase 1 habitat types: C2 (examples which are NVC CG11-12 and CG14), C3 (examples on inland cliffs and screes) and I1 (examples which are not limestone pavements). All examples of Inland rock outcrop and scree habitats priority UK BAP broad habitat in Britain belongs in the UK BAP broad habitat – Inland habitat Rock.

Definition in relation to legislative classifications

Classification Habitat types belonging to this UK BAP priority habitat The Inland rock outcrop and scree habitats priority habitat Habitats Directive includes four Annex I habitats: H6430 (examples in rocky Annex I habitats, especially on cliffs), H8110, H8120 and H8220 (all examples). Rocky slopes (includes inland cliff, rocky outcrops, chasmophytic vegetation): Natural outcrops with NVC OV39-40 (= same as Annex I type H8210) or U21(= same as Annex I type H8220).. Calcareous scree: Screes with NVC OV38 or OV40 (= same as Annex I type H8120). SNH SSSI habitat features Siliceous scree (includes boulder fields): Non-montane acid screes including those with NVC U21. Tall herb ledge: NVC U16, U17 and U19 (= same as Annex I type H6430). This priority habitat can also be part of a mosaic of two or more SSSI habitat features classed together as the Upland assemblage SSSI habitat feature.

Where is it?

Cliffs and screes are products of glaciation and subsequent weathering. They are most common in the uplands, where the rocks are hard and have resisted erosion over the millennia since they were formed. So most of the Inland rock outcrop and scree habitats experiences an upland climate with cool summers, cold winters, heavy and frequent rain, and strong winds.

The vegetation of rock habitats depends largely on the base-status of the rock. On many hard, acid rock exposures the ledge vegetation consists of fragmentary stands of the surrounding upland heath or montane heath communities, and the specialised assemblages of herbs and ferns simply do not occur. Many cliffs of granite, acid schist and gneiss and acid sedimentary rock such as slate and shale are like this. Where there is more distinctive vegetation on acid ledges it consists of mixtures of ferns, Vaccinium myrtillus and Luzula sylvatica, with few if any herbs. The full expression of tall-herb vegetation occurs only on base-rich cliffs, especially where the rock has a friable texture easily weathered into mineral- rich soil. The mica-schists of the Breadalbane hills and the basalt of the Inner Hebrides are the best examples of this, although there are also some fine swards on base-rich exposures of Moine schist and Lewisian gneiss.

The most luxuriant tall-herb vegetation develops on ledges that are not only formed of base- rich rock, but that are kept continuously moist by flushing with base-rich water. This is why many of the characteristic species, such as meadowsweet Filipendula ulmaria, Geum rivale, marsh hawk’s-beard Crepis paludosa, Trollius europaeus, Angelica sylvestris and Valeriana officinalis are also wetland species, and why the best examples of herb-rich vegetation are on damp, shaded slopes facing between north-west and east. Drier, sun-exposed rocks, or free-draining porous ones such as limestones, tend to have less luxuriant ledge vegetation. They are home to the assemblages of small ferns, which root deeply into moist crevices.

Scree is a challenging habitat for vascular plants because it is unstable, consists of large fragments, a lot of air space, and is very free-draining. One species that can tolerate such conditions well is the fern Cryptogramma crispa, and this forms characteristic bright green swards on screes. At higher altitudes, consolidated scree and boulder-fields may be covered with snow for long periods in the winter. This suits ferns such as Athyrium distentifolium (and also C. crispa) as dormant buds are protected from winter frosts by the insulating blanket of snow, and the deep cool soils that accumulate between the boulders sustain the growth of the ferns during the summer.

Inland rock outcrop and scree habitats occur throughout Scotland, mostly in the uplands but descending near to sea level in the north and west. Vegetation belonging to this priority habitat covers only a very small amount of the total rock habitat in Scotland. Reliable extent data are not available but the UK Second Report on the Implementation of the Habitats Directive (http://www.jncc.gov.uk/page-4060) gives the following broad estimates for the Habitats Directive Annex I habitats: tall-herb ledge vegetation H6430 at 100-300ha; siliceous rock and scree types H8110 and H8220 at 87,000-123,000ha; calcareous rock and scree types H8120 and H8210 at 800-1,700 ha.

There is similar vegetation in Ireland, in the Faroe Islands, Iceland, Greenland, Norway and Sweden.

What is special about it?

Some species of special conservation status recorded in this priority habitat in Scotland are listed below.

Wildlife EC Scottish and UK BAP Habitats Bio- Red Country- Common priority Directive diversity Data side Act Group name Latin name list Annex II List List (1981) Troglodytes birds St Kilda wren troglodytes subsp. y y y hirtensis ferns holly-fern Polystichum lonchitis y y y oblong ferns Woodsia ilvensis y y y y woodsia flowering Arran Sorbus arranensis y y y plants whitebeam flowering Arran service- Sorbus y y y plants tree pseudofennica flowering mountain Cochlearia micacea y y plants scurvy-grass flowering Arctic mouse- Cerastium arcticum y y y plants ear flowering Alpine blue- Cicerbita alpina y y y y plants sow-thistle flowering Alpine Erigeron borealis y y y y plants fleabane flowering mountain Minuartia rubella y y y plants sandwort flowering snow Sagina nivalis y y y plants pearlwort flowering drooping Saxifraga cernua y y y y plants saxifrage flowering tufted Saxifraga cespitosa y y plants saxifrage flowering Alpine milk- Astragalus alpinus y y y plants vetch flowering cyphel Minuartia sedoides y y y plants Wildlife EC Scottish and UK BAP Habitats Bio- Red Country- Common priority Directive diversity Data side Act Group name Latin name list Annex II List List (1981) flowering frog orchid Coeloglossum viride y y y plants flowering eyebright Euphrasia ostenfeldii y y y plants flowering small-white Pseudorchis albida y y y plants orchid flowering Hieracium sect. hawkweed y y plants Alpestria flowering Arctic Arenaria norvegica y y y plants sandwort subsp. norvegica flowering juniper Juniperus communis y y plants flowering Norwegian Artemisia norvegica y y y plants mugwort purple flowering ramping- Fumaria purpurea y y plants fumitory flowering small cow- Melampyrum y y y plants wheat sylvaticum flowering pyramidal Ajuga pyramidalis y y y plants bugle flowering basil thyme Clinopodium acinos y y y plants flowering a hawkweed Hieracium backhousei y y plants flowering a hawkweed Hieracium calvum y y plants flowering a hawkweed Hieracium graniticola y y y plants flowering a hawkweed Hieracium grovesii y y y plants flowering a hawkweed Hieracium insigne y y y plants flowering a hawkweed Hieracium kennethii y y y plants flowering a hawkweed Hieracium larigense y y y plants flowering a hawkweed Hieracium leptodon y y y plants flowering Hieracium a hawkweed y y y plants macrocarpum flowering a hawkweed Hieracium notabile y y y plants flowering a hawkweed Hieracium optimum y y y plants flowering Hieracium a hawkweed y y y plants pseudocurvatum flowering Hieracium a hawkweed y y y plants pseudopetiolatum Shetland flowering Pilosella flagellaris mouse-ear- y y y plants subsp. bicapitata hawkweed flowering rock cinquefoil Potentilla rupestris y y y y plants flowering annual knawel Scleranthus annuus y y y plants stalked fungi Tulostoma niveum y y puffball bordered lacewings brown Megalomus hirtus y y lacewing lichen a lichen Porina sudetica y y y Stereocaulon lichen a lichen y y y symphycheilum lichens a lichen Calicium corynellum y y y lichens a lichen Lecania chlorotiza y y y lichens tarn lecanora Lecanora achariana y y y lichens a lichen Peltigera venosa y y y Wildlife EC Scottish and UK BAP Habitats Bio- Red Country- Common priority Directive diversity Data side Act Group name Latin name list Annex II List List (1981) lichens a lichen Poeltinula cerebrina y y y lichens a lichen Sticta canariensis y y y lichens elm gyalecta Gyalecta ulmi y y y y lichens a lichen Brodoa intestiniformis y y lichens a lichen Gyalidea roseola y y y ear-lobed dog- lichens Peltigera lepidophora y y y y lichen lichens a lichen Collema fragile y y y Phaeophyscia lichens a lichen y y y endococcina lichens a lichen Stereocaulon delisei y y y lichens a lichen Synalissa symphorea y y y lichens a lichen Toninia sedifolia y y Barbilophozia liverworts bog paw-wort y y kunzeana Joergensen`s Anastrophyllum liverworts y y y notchwort joergensenii liverworts Arctic rustwort Marsupella arctica y y y Scottish mammals Felis silvestris y y y y wildcat mammals pine marten Martes martes y y y y cross whorl molluscs Vertigo modesta y y snail long-leaved mosses Anomodon longifolius y y y y tail-moss Scottish Bryoerythrophyllum mosses y y y beard-moss caledonicum elegant Eurhynchium mosses y y y feather-moss pulchellum brown mosses Grimmia elongata y y y grimmia snow brook- Hygrohypnum mosses y y y moss styriacum Alpine hump- Plagiobryum mosses y y y moss demissum brown Pseudoleskea mosses mountain y y y incurvata leskea blunt-leaved mosses Pohlia obtusifolia y y y thread-moss sheathed mosses Timmia austriaca y y y timmia mosses Irish daltonia Daltonia splachnoides y y reptiles common lizard Zootoca vivipara y y y

Cliff ledge vegetation occupies inaccessible situations because of the lack of grazing. This means that many species persist here that otherwise would be grazed out, or reduced to non-flowering rosettes in a grassy sward. Tall-herb vegetation accounts for only a small fraction of the total vegetation of an upland area, but can hold much of the species diversity and nature conservation interest. There are many rare species associated with this habitat, including Alpine bartsia Bartsia alpina, Alpine woodsia Woodsia alpina, oblong woodsia W. ilvensis, drooping saxifrage Saxifraga cernua, Highland saxifrage S. rivularis, S. nivalis, S. cespitosa, Alpine blue sow-thistle Cicerbita alpina, alpine forget-me-not Myosotis alpestris, purple colt’s-foot Homogyne alpina, black alpine sedge Carex atrata, yellow oxytropis Oxytropis campestris and the bryophytes Bryoerythrophyllum caledonicum, Mnium thomsonii, Molendoa warburgii, Hymenostylium insigne, Paraleptodontium recurvifolium and Herbertus stramineus.

Small ledges and high-altitude screes have sparse vegetation that is not a good fit for any NVC community, but can include some notable rarities such as Alpine rock-cress Arabis alpina, Alpine fleabane Erigeron borealis, mountain sandwort Minuartia rubella, rock speedwell Veronica fruticans, Highland cudweed Gnaphalium norvegicum, Poa flexuosa and bryophytes such as Blindia caespiticia and Barbilophozia quadriloba.

Boulder-fields and shaded slopes at high altitudes are home to some notable snow-bed species such as Polytrichum sexangulare, Kiaeria glacialis, Andreaea nivalis, A. blyttii, A. sinuosa, Pleurocladula albescens, Moerckia blyttii and Marsupella condensata.

These communities are important examples of near-natural upland vegetation owing more to geology, soil, water, climate and natural geomorphological processes than to human activity.

Cliff ledge vegetation is a rich habitat for invertebrates, especially beetles, flies and spiders, with Leistus montanus, Nebria nivalis, Tipula spp., Thricops spp., Helina vicina and Pardosa traillii among the more interesting species.

Vegetated ledges are used as habitat by cliff-nesting birds including golden eagle, raven and peregrine.

How do we manage it?

These communities persist because of the absence of active management, including grazing. Sheep and deer are unable to reach the ledges unless they fall onto them from above. Goats are more of a threat because they are able to climb cliffs where the other animals cannot. Human climbers can disturb nesting birds, although protocols are now in place to discourage climbing near known nest sites during the breeding season. Clearing vegetation to expose new climbing routes can also be a problem on popular cliffs.

Natural erosion such as rockfall and landslips can eliminate populations of cliff plants in a single incident, though there is nothing that can be done to prevent this.

References, links and further reading

Averis, A., Averis, B., Birks, J., Horsfield, D., Thompson, D., & Yeo, M. 2004. An Illustrated Guide to British Upland Vegetation. Peterborough, JNCC. http://jncc.defra.gov.uk/page-2463

Ellis, N.E. and Munro, K. 2004. A preliminary review of the distribution and extent of BAP priority habitats across Scotland. Scottish Natural Heritage Commissioned Report No.044 (ROAME No. F00NA02). https://www.nature.scot/information-library-data-and-research/information-library

Rodwell, J.S. ed. 1991 et seq.. British Plant Communities. 5 volumes: Vol. 1 (1991) - Woodlands and Scrub; Vol. 2 (1991) - Mires and Heaths; Vol. 3 (1992) - Grasslands and montane communities; Vol. 4 (1995) - Aquatic communities, swamps and tall-herb fens; Vol. 5 (2000) - Maritime Cliffs, Sand Dunes, Saltmarshes and Other Vegetation. Cambridge, Cambridge University Press. http://jncc.defra.gov.uk/page-4268

Rodwell, J.S., Dring, J.C., Averis, A.B.G., Proctor, M.C.F., Malloch, A.J.C., Schaminee, J.H.J. & Dargie, T.C.D. 1998. Review of coverage of the National Vegetation Classification. Joint Nature Conservation Committee contract report F76-01-170. Coordinated by the Unit of Vegetation Science, Lancaster University.

UK BAP 2008. http://jncc.defra.gov.uk/pdf/UKBAP_BAPHabitats-19-InlandRockOutcrop.pdf

Usher, M.B., Bain, C. and Kerr, A. eds. 2000. Action for Scotland's Biodiversity. Scottish Biodiversity Group. Edinburgh, The Scottish Executive and The Stationery Office.

Common Standards Monitoring guidance: documents (pdf files) available to download from http://www.jncc.gov.uk/page-2199

National Biodiversity Network (NBN) Gateway https://data.nbn.org.uk/

Scottish Government website – information about agricultural grants, subsidies and services: http://www.scotland.gov.uk/Topics/farmingrural/Agriculture/grants/A-Z/Intro

Scottish Natural Heritage website: http://www.nature.scot

UKBAP information on JNCC website: http://jncc.defra.gov.uk/default.aspx?page=5155