Area: 7.89 hectares.
New site. Adjacent to Isle of Portland SSSI.
Description and Reasons for Notification:
Nicodemus Heights forms part of a complex range of habitats including limestone grasslands, cliffs and quarries found on the Isle of Portland. The limestone geology, southern maritime position and land use history give the Island a unique ecological character and rich biodiversity and make Portland one of the key limestone areas in Britain.
Nicodemus Heights lies in the north-eastern part of the Island. The southern part of the site has been disturbed by past quarrying activity and the plant communities are the result of natural recolonisation of the calcareous substrates. In the north grassland has developed on thin soils over upper Portland beds. The site is important for limestone grassland communities; for Nationally Rare and Scarce bryophytes and higher plants; for the endemic plant early gentian Gentianella anglica*; and for the Nationally Scarce butterfly silver-studded blue Plebejus argus cretaceus.
The unimproved limestone grassland is of high quality and two distinct communities are present. The most extensive type is characterised by abundant upright brome Bromus erecta, and also contains frequent or abundant sheep’s fescue Festuca ovina, kidney vetch Anthyllis vulneraria, bird’s-foot-trefoil Lotus corniculatus, black medick Medicago lupulina and wild carrot Daucus carota. Horseshoe vetch Hippocrepis comosa is locally frequent, and the Nationally Scarce slender tare Vicia parviflora is also present. The second type of unimproved grassland, which has a very restricted distribution nationally, occurs on thin and well-drained soils which have developed over old limestone spoil heaps. This vegetation is short and open with areas of bare rock, and amongst the abundant sheep’s fescue there is frequent squinancywort Asperula cynanchica, wild thyme Thymus polytrichus and mouse-ear hawkweed Pilosella officinarum. The Nationally Scarce dwarf mouse-ear Cerastium pumilum also occurs here, together with a variety of small bryophytes, including two Nationally Rare liverworts Cephaloziella baumgartneri and green blackwort Southbya nigrella, and a Nationally Scarce moss Luisier’s tufa moss Gymnostomum viridulum.
These grasslands also support substantial colonies of the endemic and Nationally Scarce plant early gentian Gentianella anglica*. Numbers of plants vary greatly from year to year but the site has recently held over 50% of the total early gentian population on Portland.
Small areas of scrub occur within the site, often associated with hollows, boulders and rocks left behind by historic quarrying activity. Ivy Hedera helix growing here provides a host for the Nationally Scarce parasitic plant ivy broomrape Orobanche hederae. Wild privet Ligustrum vulgare and traveller’s joy Clematis vitalba are frequent in these areas, which also contain occasional introduced species such as fig Ficus carica and reflexed stonecrop Sedum rupestre.
In the southern part of the site is an area of open vegetation on a stony substrate which contains a variety of plants associated with unimproved calcareous conditions, including marjoram Origanum vulgare and wild parsnip Pastinaca sativa. This part of the site forms the core of a large population of the Nationally Scarce butterfly silver-studded blue Plebejus argus cretaceus. This butterfly has suffered population declines throughout its range and the cretaceus race is now confined to Portland. Nicodemus Heights SSSI supports one of the three largest colonies on Portland.
The site also supports a large population of small blue Cupido minimus, a declining butterfly for which Portland is a stronghold.
*Species listed on Annex II to Council Directive 92/43/EEC on the Conservation of Natural Habitats and of Wild Fauna and Flora, and on Schedule 8 of the Wildlife and Countryside Act 1981.