Habitat account - Natural and semi-natural grassland formations


6130 Calaminarian grasslands of the Violetalia calaminariae 

Background to selection

Distribution of SACs/SCIs/cSACs with habitat 6130 Calaminarian grasslands of the Violetalia calaminariae.  Click image for enlarged map.
Distribution of SACs/SCIs/cSACs with habitat 6130 Calaminarian grasslands of the Violetalia calaminariae. Click image for enlarged map.

Description and ecological characteristics

 

Calaminarian grasslands occur on soils that have levels of heavy metals, such as lead, zinc, chromium and copper, that are toxic to most plant species. The greatest extent of the habitat occurs on artificial sites associated with past mining activities. Near-natural examples are much more localised. There are three main situations where this habitat type has developed:

 

     

  1. Near-natural, open vegetation of serpentine rock and mineral vein outcrops with skeletal soils;
  2. Stable river gravels rich in lead and zinc and that are near-natural, although the heavy metal content may be partly an artefact of past mining activity in the river catchment;
  3. Artificial mine workings and spoil heaps, mainly on limestone; these are numerous (several thousand UK localities) and extensive, although few sites have a high species-richness.

 

Grasslands of this type are referable to the Thlaspion-Calaminariae alliance. The vegetation is typically species-poor but contains a number of species principally found in this habitat, most notably spring sandwort Minuartia verna and alpine penny-cress Thlaspi caerulescens. There is a genetically-adapted range of other species, such as sheep’s fescue Festuca ovina, bladder campion Silene vulgaris, sea campion Silene uniflora and thrift Armeria maritima. Heavy metal toxicity of the soils, perhaps combined with a low nutrient status, is believed to maintain the open vegetation, retarding succession. The rarer species are favoured by lack of competition from more vigorous colonists. The Annex I type also includes assemblages of metal-tolerant lower plants on mine waste, even if higher plant metallophytes are lacking.

 

In the UK some forms of this vegetation correspond to NVC type OV37 Festuca ovina – Minuartia verna community; other forms characterised by different metallophyte plant species or races and ecotypes are not described in the NVC.

 

Calaminarian grasslands and associated rock outcrops provide a habitat for several scarce plants, including northern rock-cress Arabis petraea, forked spleenwort Asplenium septentrionale and Young’s helleborine Epipactis youngiana. In northern parts of the UK there are local populations of boreal species that characterise these habitat conditions in Scandinavia, such as arctic sandwort Arenaria norvegica ssp. norvegica and the endemic Shetland mouse-ear Cerastium nigrescens. Some sites hold important populations of rare bryophytes and lichens.

European status and distribution

 

Outside the UK, calaminarian grasslands are very rare in the Atlantic Biogeographical Region.

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

 

Calaminarian grasslands are a locally widespread but uncommon habitat type in the north and west of Great Britain.

Site selection rationale

 

The SAC series includes examples of the three main situations where the habitat has developed, i.e. natural rock outcrops, river gravels, and mine spoil. Preference has been given to the selection of more natural types, particularly those which are important for the conservation of rare species, and all of the best examples of Calaminarian grasslands on near-natural substrates are included within the SAC series.

 

A more selective approach has been taken for artificial stands of the habitat. Examples of mine workings and spoil heaps containing the best stands of OV37, and those with distinctive representation of specialist higher plant, bryophyte and/or lichen assemblages have been included. The selected sites represent the range of geographical and ecological conditions in which the habitat is found in the UK.


Site accounts

Caenlochan Eastern Scotland, North Eastern Scotland
Caenlochan in north-east Scotland represents natural, open Calaminarian grasslands over serpentine debris, occurring at about 850870 m altitude on Meikle Kilrannoch, the highest representation of the habitat in the UK. The site is notable for the large population of the rare alpine catchfly Lychnis alpina, which occurs at only one other locality in the UK (the other station being in the English Lake District). Other characteristic plants of the debris include thrift Armeria maritima, mossy cyphel Minuartia sedoides and scurvygrass Cochlearia sp. This is the only known site for the Scottish endemic subspecies of common mouse-ear Cerastium fontanum ssp. scoticum.
Coyles of Muick North Eastern Scotland
Coyles of Muick represents the second-largest extent of near-natural, open serpentine debris with Calaminarian vegetation in Scotland. The habitat occurs at high altitude (450-600 m), exceeded in altitude only by Meikle Kilrannoch on Caenlochan. The serpentine here is more calcareous and less toxic than on other serpentine sites in north-east Scotland, perhaps favouring certain species that do not normally occur on serpentine. The Calaminarian community occurs in open serpentine debris on the summit and upper slopes, and is unusual in including alpine mouse-ear Cerastium alpinum (but not spring sandwort Minuartia verna). Other species include northern rock-cress Arabis petraea, mossy saxifrage Saxifraga hypnoides, yellow mountain saxifrage S. aizoides, thrift Armeria maritima, field gentian Gentianella campestris and sea campion Silene uniflora. There are transitions to grassland and fen habitats, and dry heath dominates the lower slopes of the site.
Elenydd East Wales, West Wales and The Valleys
Heavy metals have been extracted from the Ystwyth Valley for over 1000 years. At Cwm Ystwyth this activity has left extensive areas of rock outcrop, scree, spoil-heaps and abandoned shafts, adits and buildings variously affected by heavy metals available for colonisation by heavy metal-tolerant plant species. Lichens and bryophytes are a notable component of the developing flora and include a number of scarce species such as Vezdaea cobria, Lecanora handelii, Gyalidea subscutellaris and Ditrichum plumbicola.
Gang Mine Derbyshire and Nottinghamshire
Gang Mine is an example of Calaminarian grasslands in an anthropogenic context in northern England. Natural limestone outcrops supporting species typical of calaminarian grasslands are rare and small, with a very impoverished flora. This site is included to provide an example of the habitat type on sedimentary rocks; it has colonised the large area of mine workings and spoil heaps on limestone. These are notable for the wide variations in slope, aspect and soil toxicity. Floristically the site contains the richest anthropogenic Calaminarian grasslands in the UK, with abundant spring sandwort Minuartia verna and alpine penny-cress Thlaspi caerulescens. Other species of grassland vegetation present include early-purple orchid Orchis mascula and dyer’s greenweed Genista tinctoria. Many of these species are likely to be distinct genotypes adapted to soils rich in heavy metals.
Green Hill of Strathdon North Eastern Scotland
Green Hill of Strathdon represents Calaminarian grasslands on open serpentine debris within Calluna moorland at low altitude in the eastern Scottish Highlands. There are a number of small, scattered areas of serpentine debris similar in character to those on Hill of Towanreef. The vegetation includes frequent spring sandwort Minuartia verna, scurvygrass Cochlearia officinalis, mossy saxifrage Saxifraga hypnoides and thrift Armeria maritima.
Grogwynion West Wales and The Valleys
At Gro Ystwyth, waste from past heavy metal mining has combined with natural river gravel to create the foundations of an extensive area of shingle heath on the flood plain of the River Ystwyth below Grogwynion. As the river reworks the gravel in a series of braided channels fresh material is deposited, and a range of seral stages in the development of heath and scrub are found at this site. Lichens are locally dominant in the heath, with a number of uncommon species present including Cladonia fragilissima and C. uncialis ssp. uncialis. Normally montane species, such as Stereocaulon condensatum and Epilichen scabrosus, occur here at an unusually low altitude. Metallophyte lichens of open ground are well-represented, with nationally scarce species, such as Vezdaea acicularis, Gyalidea subscutellaris and Thelocarpon impressellum, occurring amongst patches of sea campion Silene uniflora.
Halkyn Mountain/ Mynydd Helygain East Wales
Halkyn Mountain has the most extensive recorded area of the metalliferous NVC type OV37 Festuca ovinaMinuartia verna grassland community in Wales. Stands of this vegetation type are associated with a number of old lead and zinc ore mines, which date back to Roman times and were intensively worked during the 19th century. They include relatively open, lichen-rich swards, as well as more closed examples with abundant wild thyme Thymus polytrichus. The stands are scattered over an extensive undulating plateau of Carboniferous limestone, most of which is unenclosed common land. They are associated with more extensive areas of open and closed calcareous and acidic grassland and dwarf shrub heath vegetation vegetation, some of which is upland in character.
Hill of Towanreef Highlands and Islands, North Eastern Scotland
Hill of Towanreef represents Calaminarian grasslands at low altitude in the eastern Scottish Highlands. This low-lying hilly area of dolomitic serpentine is similar to the Green Hill of Strathdon but is more extensive. Serpentine debris vegetation occurs amongst more extensive areas of serpentine-influenced vegetation, in particular 4030 European dry heath. The serpentine debris community has abundant spring sandwort Minuartia verna, common scurvygrass Cochlearia officinalis and eyebright Euphrasia officinalis with thrift Armeria maritima. Also present are the moss Grimmia ungeri, a species of dry serpentine rock known from only two or three sites in north-east Scotland, and a serpentine form of black spleenwort Asplenium adiantum-nigrum. Other habitats on the site associated with serpentine include 5130 Juniperus communis formations and base-rich flushes, which locally support 1528 Marsh saxifrage Saxifraga hirculus.
Keen of Hamar Highlands and Islands
Keen of Hamar has the largest surviving area in the UK of near-natural Calaminarian grasslands on serpentine. The site is rich in rare northern species, such as arctic sandwort Arenaria norvegica ssp. norvegica and northern rock-cress Arabis petraea, and includes the endemic Shetland mouse-ear Cerastium nigrescens, found only on serpentine rocks at this site. The site has ecological features and floristic composition similar to those of serpentine grasslands in Scandinavia, where the habitat type is also rare.
Moor House - Upper Teesdale Cumbria, Tees Valley and Durham
This site contains an example of Calaminarian grassland on lead-mine spoil associated with the Carboniferous limestone at high altitude in the Pennines of northern England. Much of the spoil is unvegetated and has a variety of particle sizes ranging from coarse rubble to fine sediment, and several steep, unstable slopes. The metallophytes spring sandwort Minuartia verna, alpine penny-cress Thlaspi caerulescens and Pyrenean scurvygrass Cochlearia pyrenaica occur along with lichens such as Cladonia rangiformis, C. chlorophaea and Coelocaulon aculeatum.
Mwyngloddiau Fforest Gwydir/ Gwydyr Forest Mines West Wales and The Valleys
This site includes a series of scattered disused lead and zinc mines with spoil-heaps of varying extent, set among extensive conifer plantations and some agricultural land. The calaminarian assemblage of Gwydir Forest includes forked spleenwort Asplenium septentrionale and alpine penny-cress Thlaspi caerulescens, together with several lichen taxa, but it is especially notable for the local frequency of the near-endemic moss Ditrichum plumbicola.
Ox Close North Yorkshire
Ox Close is a large site representing Calaminarian grassland in the central Pennines. The site is unusual in that it encompasses the three main situations in which this habitat occurs in the UK, including near-natural forms on cliffs and scars, old spoil-heaps from past lead-mining, and metal-enriched river alluvium. This site supports a rich metallophyte flora with substantial populations of five species of higher plant metallophytes: thrift Armeria maritima, moonwort Botrychium lunaria, Pyrenean scurvygrass Cochlearia pyrenaica, spring sandwort Minuartia verna and alpine penny-cress Thlaspi caerulescens. The site shows the full succession from open sparsely-vegetated spoil to closed turf. Transitions from Calaminarian grassland to 6210 semi-natural dry grassland and flushes also occur.
Phoenix United Mine and Crow`s Nest Cornwall and Isles of Scilly
This site on the south-eastern edge of Bodmin Moor supports internationally-important Calaminarian grassland metallophyte communities. The legacy of a long history of copper and tin extraction survives as mine spoil which has been colonised by a number of metallophytic bryophytes. In particular, the site supports the only known site in the world for the endangered Cornish path-moss Ditrichum cornubicum. Other notable metallophytes include the Red Data Book liverworts Cephaloziella massalongi and the endemic C. nicholsonii, both associated with copper-rich substrates, and the mosses Pohlia andalusica and Scopelophila cataractae, the latter possibly an introduction into this country on imported ore. Many other notable bryophytes have colonised the spoil, including the liverworts Cephaloziella integerrima, C. stellulifera, Lophozia sudetica, Gymnomitrion obtusum and Marsupella funckii, and the moss Ditrichum lineare. The vulnerable liverwort Cephaloziella calyculata grows on derelict mine buildings.
Rum Highlands and Islands
Rum is one of the best sites in the UK for open rocky Calaminarian vegetation characterised by the presence of arctic sandwort Arenaria norvegica ssp. norvegica and northern rock-cress Arabis petraea, similar to that on Keen of Hamar. The habitat, which represents Calaminarian grasslands of the Violetalia calaminariae, is developed on rocky areas of debris and erosion terraces on the peridotite of Ruinsival eastwards towards Sgurr nan Gillean. A. norvegica is the rare ultramafic species represented, while other uncommon basiphiles include purple saxifrage Saxifraga oppositifolia, mossy cyphel Minuartia sedoides and moss campion Silene acaulis. This is one of the most maritime-influenced sites of the series and the maritime species sea campion Silene uniflora, sea plantain Plantago maritima and thrift Armeria maritima are especially frequent.
Tyne and Allen River Gravels Northumberland and Tyne and Wear
This site in north-east England encompasses the most extensive, structurally varied and species-rich examples of riverine Calaminarian grasslands in the UK. The river gravels contain a range of structural types, ranging from a highly toxic, sparsely vegetated area with abundant lichens through to closed willow/alder Salix/Alnus woodland. In addition, the site is of considerable functional interest for the series of fossilised river channel features. Spring sandwort Minuartia verna and thrift Armeria maritima are particularly abundant, and there are several rare species, including Young’s helleborine Epipactis youngiana, which has its main UK population at this site. The site is also of great importance for its lichen communities. A number of rare and scarce species are present, including the Red Data Book-listed Peltigera venosa.
Tyne and Nent Cumbria
At this site in the north-west Pennines, Calaminarian grassland occurs in association with lead mine waste and river shingles of the rivers South Tyne and Nent. This site supports a rich metallophyte flora with substantial populations of six species of higher plant metallophytes: thrift Armeria maritima, moonwort Botrychium lunaria, Pyrenean scurvygrass Cochlearia pyrenaica, spring sandwort Minuartia verna, alpine penny-cress Thlaspi caerulescens and mountain pansy Viola lutea. The site is also of great importance for its lichen communities associated with both spoil and river shingle. A number of rare and scarce species are present, including Peltigera venosa, P. neckeri and Sarcosagium campestre var. macrosporum. The site shows the full succession from open sparsely vegetated shingle and spoil to closed turf. Transitions from Calaminarian grassland to both calcareous grassland and dry heath also occur.

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

Craven Limestone Complex North Yorkshire
Lendalfoot Hills Complex South Western Scotland
North Pennine Moors Cumbria, North Yorkshire, Northumberland and Tyne and Wear, Tees Valley and Durham
Peak District Dales Derbyshire and Nottinghamshire, Shropshire and Staffordshire
 

Many designated sites are on private land: the listing of a site in these pages does not imply any right of public access.