Area: 58.95 hectares, 145.67 acres.
A new site. Lies within the Dorset Area of Outstanding Natural Beauty (AONB).
Description and Reasons for Notification:
White Horse Hill forms part of the steep south-facing scarp at the southern edge of the Dorset chalk, overlooking the valley of the River Jordan, north of Weymouth. The site overlies bands of Upper, Middle and Lower Chalk on which herb-rich grassland communities have developed. These communities, unmodified by agricultural improvement, are now nationally rare and here support a wide range of uncommon butterfly species.
Over much of the site tor-grass Brachypodium pinnatum is dominant yet the swards remain herb-rich with horseshoe vetch Hippocrepis comosa, stemless thistle Cirsium acaule and squinancywort Asperula cynanchica amongst the many abundant herbs. Rarer plants in these areas include the nationally scarce bastard-toadflax Thesium humifusum and the local pale flax Linum bienne, sainfoin Onobrychis viciifolia and small-flowered buttercup Ranunculus parviflorus. There are also significant areas characterised by an abundance of red and sheep’s-fescue Festuca rubra and F. ovina and meadow oat-grass Avenula pratensis. Here the swards are particularly diverse.
In a few areas, the grazing pressure has been relaxed and the dominance of tor-grass has suppressed the herb content of the sward. Some herbs persist but there is much variation between different areas, horseshoe vetch being one of the few constant species. Gorse Ulex europaeus scrub has developed in some of these areas. The site includes a small area of meadow at the foot of the scarp. These swards are dominated by tall grasses and herbs, with meadow barley Hordeum secalinum, sweet vernal-grass Anthoxanthum odoratum, crested dog’s-tail Cynosurus cristatus and the nationally scarce corky-fruited water-dropwort Oenanthe pimpinelloides among many meadow and rich fen species.
The site provides excellent conditions for a variety of butterfly species which are favoured by the sheltered southern aspect of this downland. There are strong populations of two nationally scarce species, Adonis blue Lysandra bellargus and Lulworth skipper Thymelicus acteon as well as a number of local downland species including brown argus Aricia agestis, chalkhill blue Lysandra coridon, small blue Cupido minimus, dark green fritillary Argynnis aglaja and dingy skipper Erynnis tages.