Site Code
Country: United Kingdom
Central coordinates: 51.11666667o [51o 7' 0" North], -1.68333333o [1o 40' 59" West]
Administrative region: South East (North Hampshire), South West (South Wiltshire)
Area: 1557 ha
Altitude: 92 - 159
Site Description
Porton Down constitutes the largest uninterrupted tract of semi-natural chalk grassland in Britain, a habitat which elsewhere has declined by more than 80% in the last 50 years. As well as the grassland, juniper scrub Juniperis communis of several age classes is widespread, and constitutes about 20% of the total southern English population. The site is also noted for its outstanding assemblages of lower plants (lichens), vascular plants and invertebrates.
Botanical Significance
Vascular plant interest. Four main types of grassland have been identified. Two of the communities are particularly rare in Britain. One, in which red fescue Festuca rubra and downy oatgrass Avenula pubescens occur as pronounced tussocks with litter-choked channels between, is virtually confined to Porton Down. The second uncommon community is characterised by sheep's-fescue Festuca ovina, mouse-ear hawkweed Hieracium pilosella and wild thyme Thymus praecox and has lichens prominent in the sward, in particular Cladonia rangiformis, C. impexa and Peltigera furescens may cover 80% of the ground surface. Other grassland communities include a type characterised by sheep's-fescue and meadow oat-grass Avenula pratensis, which has a particularly rich and intimate mixture of grasses and broadleaved herbs, and a type dominated by the coarse grass upright brome Bromus erectus, which has fewer herbs and is typical of undergrazed chalk downlands.Porton Down also supports a colony of meadow clary Salvia pratensis. Other rare species include early gentian Gentianella anglica, chalk milkwort Polygala calcarea, bastard toadflax Thesium humifusum and field fleawort Senecio integrifolius, all of which are confined to the southern chalk, and dwarf sedge Carex humilis, scrub and scattered trees are a feature of much of the grassland.
Management guidance notes
Vascular plant interest
Notes
None