CYNGOR CEFN GWLAD CYMRU

COUNTRYSIDE COUNCIL FOR WALES

SITE OF SPECIAL SCIENTIFIC INTEREST CITATION

VALE OF GLAMORGAN OLD CASTLE DOWN

Date of Notification: 1981, 1983

National Grid Reference: SS 805758

O.S. Maps: 1:50,000 Sheet Number: 170

1:25,000 Sheet Number: SS 87

Site area: 79.8 ha

Description:

A site of national nature conservation importance for its range of limestone heath and calcareous grassland vegetation composed of plant species that reflect its western location. The soils have been described by Crampton (1972) as being of the Lulsgate series of Brown Earths on Carboniferous Limestone. The steeper slopes have a rendzina soil similar to that on chalk downs and the plateau soils have a proportion of clay leading to more poorly drained and acidic soils.

The variation in calcium carbonate content of these soils results in a range of vegetation types from limestone grasslands through to a very interesting limestone heath which occupies most of the site.

On the west side of the B4265 is a SE facing slope with a Festuca grassland with Thymus drucei, Helianthemum chamaecistus, Galium verum and Linum catharticum common. Within this very characteristic calcareous grassland are Calluna vulgaris, Galium saxatile and Potentilla erecta which are more characteristic of grass/heath associations. This area is, therefore, a limestone heath comparable with the chalk heaths of Lullington, Sussex (L6) and Martin Down, Hampshire (L24). Unlike the chalk heaths and possibly because of its western situation, the uncommon sedge Carex montana is present along with the very typical S. west of Britain heath species, Agrostis setacea.

The main area of the site lies to the east of the B4265 and consists of a plateau which has east, west and north facing slopes. A broad band of Ulex occurs towards the top of the west facing slope and below it is a Festuca/Molinia grassland with Erica tetralix and Pedicularis sylvatica. Towards the southern end there are areas of thin soil giving a typical limestone flora but Pteridium aquilinum has colonised the deeper soils. The plateau is an Agrostis setacea grassland with some minor agriculturally improved grasslands around the southern edge. On the eastern side is an oak, hazel, ash scrub woodland separated from the A. sectacea grassland by a narrow belt of limestone grassland.

Invertebrate interest in the site is now known to be considerable.