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Calaminarian Grasslands


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UK Biodiversity Action Plan

Priority Habitat Descriptions

Calaminarian Grasslands



From:

UK Biodiversity Action Plan; Priority Habitat Descriptions. BRIG (ed. Ant Maddock) 2008.

For more information about the UK Biodiversity Action Plan (UK BAP) visit

http://www.jncc.gov.uk/page-5155

Calaminarian Grasslands

Correspondence with existing habitat/s


  • UK BAP broad habitat: Inland rock

  • Phase 1: I1.2 Scree pp; I2.2 Spoil pp

  • NVC: OV37 and other un-described types, i.e. not fully covered by NVC

  • Annex I: synonymous with H6130 Calaminarian grasslands of the Violetalia calaminariae (see http://www.jncc.gov.uk/ProtectedSites/SACselection/habitat.asp?FeatureIntCode=H6130)

Description


Calaminarian grasslands include a range of semi-natural and anthropogenic sparsely vegetated habitats on substrates characterised by high levels of heavy metals such as lead, chromium and copper, or other unusual minerals. These are associated with outcrops of serpentine and river gravels rich in heavy metals, as well as with artificial mine workings and spoil heaps. Seral succession is slowed or arrested by the toxicity of the substrate. Open-structured plant communities, sometimes known as ‘Calaminarian grasslands’, typically occur, composed of ruderal/metallophyte species of lichens, bryophytes and vascular plants, such as spring sandwort Minuartia verna, alpine pennycress Thlaspi arvense, and genetically adapted races of species such as thrift Armeria maritima and bladder campion Silene maritima. Notable species include Epipactis youngiana, Asplenium septentrionale, Ditrichum cornubicum, Marsupella profunda, Cephaloziella nicholsonii and Ditrichum plumbicola. In northern parts of the UK there are local populations of boreal species which characterise these habitat conditions in Scandinavia, such as Scottish sandwort Arenaria norvegica and the endemic Shetland mouse-ear Cerastium nigrescens.

Vegetation on metalliferous substrates is found in three distinct settings in the UK:



  • Near-natural substrates;

  • Mine spoil, in situations where naturally occurring metalliferous outcrops have been quarried away;

  • Metalliferous river gravels, sometimes derived from washed-out mine workings. In many localities the metalliferous outcrops which would have been the natural habitat for the species referred to above have been quarried away but the mine spoil still provides suitable habitat.

Although this habitat occurs widely across the north and west of the UK, its extent is restricted because of the limited occurrence of suitable rock types. Near-natural examples are highly localised on outcrops and scree of serpentine and related rock types, mostly in the Scottish Highlands and Islands. Metalliferous mine spoil and river gravels are more widespread, but still local, in certain urban and post-industrial areas, particularly in parts of England and Wales. A map of known and potential distribution of the Annex I type 6130 is given below.

No comprehensive data are available on the UK extent, but estimates are given in the table below: This is based mainly on NVC and Phase 1 surveys undertaken over the last 15-20 years, but accurate survey data are lacking for many areas. A total of 326 ha is thought to occur in SACs. Forms referable to the Festuca ovina - Minuartia verna community (OV37) are estimated to cover less than 100 ha in Britain (David Stevens, pers. comm.). In Scotland, most of the resource appears to occur within SSSIs (Dave Horsfield, pers. comm.).



Map 1: UK distribution of Annex I type 6130 Calaminarian grasslands of the Violetalia calaminariae. Current distribution shown in green (from Rodwell and others. 2007) The European Context of British Lowland Grasslands. JNCC Report in press). The potential distribution shown in red is an amalgamation of the distributions of indicator species Minuartia verna, Thlaspi caerulescens, Lychnis alpina, Cerastium nigrescens (Preston and others, 2002) and Ditrichum plumbicola (Hill and others., 1992).



Extent of H6130 Calaminarian grasslands of the Violetalia calaminariae in the UK:




Area (ha)

Reliability of measure/estimate

England

<200

Estimate based on areas on SACs and expert opinion

Scotland

<200

Estimate based on areas on SACs and expert opinion

Wales

50

Estimate based on areas on SACs & Stevens & others. (2002) (areas of OV37 in Wales)

Northern Ireland

absent



Total UK extent

<450

Estimate calculated from different data sources, incomplete inventory data & expert opinion



References:
Hill, M.O., Preston, C.D. and Smith, A.J.E. (1992). Atlas of the bryophytes of Britain and Ireland. Harley Books, Colchester.
Northumberland County Council. Calaminarian Grassland Habitat Action Plan. In Working for wildlife; the Northumberland Biodiversity Action Plan.
Preston, C.D., Pearman, D.A. and Dines, T.D. (2002). New atlas of the British flora. Oxford University Press.

Rodwell, J.R., Moss, D., Morgan, V. and Jefferson, R.G. (2007). The European Context of British Lowland Grasslands. JNCC Report in press).


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