Whitehorse Hill

Also within

Oxfordshire County North Wessex Downs Scenic Area

Condition (Natural England)

Habitats

Mixed scrub, Montane scrub

Geology & landscape

Geological Feature: Karst · Geological Period: Quaternary · Rock Type: Chalk, Greensand

Landscape processes: Fluvial, Karst, Periglacial

Description

Area, 103.2 hectares 254.9 ac Description , a. Geographical and Physiographic The site covers the deep coombe of the Manger cut into the scarp face of the chalk escarpment where it rises to a crest at Whitehorse Hill and is representative of so many chalk coombes in the south of England. The scarp face below Whitehorse Hill is formed of Lower and Middle Chalk overlying the thin Upper Greensand, with Gault Clay flooring the valley to the north. The steep chalk slope is scored along much of its length by dry coombes and one of the most spectacular is The Manger which is on a fine example of the most distinctive landform of English chalk karst. The Manger coombe is a rounded, totally dry valley 500m long and over 50m deep. Its western side is scored by more than 10 tributary coombes each incised about 5m into the main coombe slope. Within The Manger bedrock is overlain by chalk silts and rubble up to 5m thick, capped by brown humic chalk silts up to 3m thick, with an upper layer of topsoil supporting sheep walk grassland. Though there is no surviving evidence of pre Devensian erosion, the scale of the coombe and the known Devensian sediments provide evidence of solifluction excavation during at least one cold stage of the Pleistocene. The existing dry coombe is evidence of the karstic fossilisation, by underground drainage, of a landform excavated under contrasting climatic conditions. b. Biological This site includes Uffington Castle, The White Horse, the steep slopes of The Manger, Dragon Hill and Uffington Wood. It contains a high proportion of the few remaining unploughed grasslands along the chalk escarpment in Oxfordshire. The slopes and crests of Whitehorse Hill have shallow, well drained calcareous silty soils of the Andover 1 series. Deep calcareous and non calcareous fine silty soils of the Wantage 1series are found in the valley bottoms. The species rich, unimproved grassland occurs on the thinner soils of the south facing slope of Dragon Hill. There is a light cover of upright brome Bromus erectus and sheep’s fescue Festuca ovina together with rock rose Helianthemum nummularium, dwarf thistle Cirsium acaule, wild thyme Thymus praecox, bird’s foot trefoil Lotus corniculatus, horseshoe vetch Hippocrepis comosa, yellow wort Blackstonia perfoliata, common milkwort Polygala vulgaris and glaucous sedge Carex flacca. The rare Chiltern gentian Gentianella germanica, a species confined to central southern England, occurs on some of the exposed slopes. The sparse chalk turf grades down to the lower slopes where there is an increase in cover of upright brome. Uneven ground with abandoned chalk works along the northern slopes of Dragon Hill support a diverse flora which includes chalk milkwort Polygala calcarea, small scabious Scabiosa columbaria, clustered bellflower Campanula glomerata, knapweed Centaurea nigra, oxeye daisy Leucanthemum vulgare and yellow rattle Rhinanthus minor. Twayblade Neottia ovata occurs on the northerly slope along with common spotted and pyramidal orchids Dactylorhiza fuchsii, Anacamptis pyramidalis. Large colonies of fragrant orchid Gymnadenia conopsea occur on the slopes northeast of The Manger. Grassland flanking the southern side of The Manger is mostly coarse and species poor with a dense mixture of upright brome, cock’s foot Dactylis glomerata, tor grass Brachypodium pinnatum and hogweed Heracleum sphondylium. This grades into a richer turf at the head of the valley. The open chalk grassland at the western end of the site contains The White Horse itself, together with an iron age hill fort, lynchets and mounds. Short sheep’s fescue turf tends to occur on the archaeological sites. The interior of Uffington Castle has a sward dominated by cock’s foot. Coarse grassland immediately westwards to the castle contains cowslips Primula veris and field fleawort Senecio integrifolius, an uncommon species strongly associated with the chalk of southern England. Sainfoin Onobrychis viciifolia has also been recorded from this locality. The two large areas of grassland along the escarpment are separated by Uffington Wood, an ash / hazel hanger with a rich ground flora. It is considered to be a north eastern outpost of a series of chalk slope woods dominated by ash; those further east tend to be dominated by beech. Some planting of conifers and beech has occurred since 1970. The ground flora, which is dominated by dog’s mercury Mercurialis perennis and common nettle Urtica dioica, includes herb paris Paris quadrifolia, a species almost wholly confined to ancient woodlands. Scrub is developing along the northern edge of Uffington Wood on the grassland dominated by upright brome and on the steep northern slope of Fallers Coombe. Sixteen species of snails have been found, including Helicella itala, a species restricted to dry calcareous grasslands. Butterflies which have been recorded from the chalk grassland include chalkhill blue, brown argus and marbled white.

Species mentioned

Plant communities