|IPA Factsheet - St. Just Moors (Lower Bostraze and Leswidden)|
Site Description This former 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 in Cornwall. The former clay working site in west Cornwall supports important populations of the internationally very rare liverwort western rustwort Marsupella profunda. The UK distribution of this species is restricted to this site as well as the clay workings within the St Austell china clay district in east Cornwall (St Austell Clay Pits 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. The two discrete parts of this site, notified for the presence of a very rare liverwort, are located approximately 8 km west of Penzance. The site has been extensively worked for china clay until recent years. Both areas are located within disused china clay workings, consisting of pits, benches, spoil tips and granitic debris with sparse vegetation cover. The colony at Lower Bostraze is in the southern half of a disused china-clay quarry where extraction ended around 1991. There are many exposed clay surfaces with little or no colonisation by bryophytes and vascular plants. Filamentous green algae are however widespread on the clay. Most vascular plants present are only immature individuals, with heather Calluna vulgaris and bell heather Erica cinerea the most common species. Lower Bostraze supports the largest population of western rustwort, with an estimated 4,000 cm2 cover, while Leswidden supports an estimated 200 cm2. Leswidden is also a former china-clay quarry, where working ceased before 1965. Banks of clay spoil have been exposed more recently during work to clear and flatten the area to the south now used as a coal merchantís yard. As at Lower Bostraze, the clay surfaces are colonised by filamentous green algae and, very sparsely, by calcifuge vascular plants such as heather Calluna vulgaris and bell heather Erica cinerea. Western rustwort Marsupella profunda is presently known from only one other location in Britain (St Austell Clay Pitts IPA), also in west Cornwall. Internationally, it is known from Portugal, the Canaries, Azores and Madeira, but it is rare throughout its range. At Lower Bostraze and Leswidden, western rustwort is generally found growing on micaceous or clay waste substrates which are flat or gently sloping. Some patches occur on granitic rocks, usually where these are soft or crumbling. It appears to be a pioneer species, the largest populations being found on surfaces showing the early stages of colonisation by other bryophytes and by vascular plants.
General Habitat Description Both areas are located within disused china clay workings, consisting of pits, benches, spoil tips and granitic debris with sparse vegetation cover.
Conservation Issues Suitable habitat for Marsupella profunda is being lost through natural succession. Current small scale management is only sufficient to slow this process. Potential new habitat is currently only created through occasional rock falls. Bare surfaces may be colonised by this species at any time.