|IPA Factsheet - St. Austell Clay Pits|
Site Description The site supports important populations of the internationally very rare liverwort western rustwort Marsupella profunda. The UK distribution of this species is restricted to china clay workings within the St Austell china clay district in east Cornwall and, former clay workings in west Cornwall at Tregonning Hill, Lower Bostraze, and Leswidden (within St Just Moors IPA). Internationally, western rustwort is rare throughout its range, it appears to have a restricted, strongly oceanic range, with records from Portugal, Madeira, and the Azores. In recognition of its rarity and vulnerability western rustwort is protected under UK and European Union legislation (Schedule 8 of the Wildlife and Countryside Act 1981 as amended, Annexes II & IV of the European Community Habitats and Species Directive, and it is the only Annex II 'priority' species listed which occurs in Britain) as well as being a priority BAP species and having Critically Endangered RDB status. This active clay workings site has been identified as an IPA due to the presence of an internationally rare bryophyte Western Rustwort, Marsupella profunda.
Botanical Significance The UK population of the internationally rare Western Rustwort - Marsupella profunda is restricted to china clay workings within the St Austell china clay district in east Cornwall and, former clay workings in west Cornwall at Tregonning Hill, Lower Bostraze, and Leswidden.
General Habitat Description In the St. Austell Clay Pits, western rustwort is generally found growing on clay waste substrates which are flat or gently sloping. Some patches occur on granitic rocks, usually where these are soft or crumbling. Western rustwort is a pioneer species, the largest populations being found on surfaces showing the early stages of colonisation by other bryophytes and by vascular plants.
Conservation Issues Unknown - Suitable habitat for M. profunda comprises open/ bare surfaces such as moist, crumbling, mica-rich granite and clays. Requires open conditions with no competition or shading. Site is in Unfavourable Declining state At Trethosa there is 55cm2 of Marsupella profunda overall, marked decrease since April 2007 due to increase of other vegetation cover on low ridge and absence from boulders on flay ground south of ridge. At Prosper there is 430 cm2 of Marsupella profunda overall but the upper ridge now much shaded, with ca 50 cm2 surviving only at west end. At Baal there is 800 cm2 of Marsupella Profunda overall, only 40 cm2 remaining within SSSI despite extensive Rhododendron clearance. Increased moss partly to blame for decline.