Salisbury Plain - Ecology - Vegetation

Vegetation

A diversity of soil types, slope, aspect and past and present land-use has given rise to various grassland communities. Historical evidence suggests that large areas of grassland are of great antiquity, and areas which were cultivated at the beginning of this century have experienced nearly 100 years of chalk grassland re-colonisation. Parts of East Salisbury Plain and the periphery of Central and West comprise areas of grassland currently managed for grazing pasture and hay-cutting, whilst the middle of Centre and West are ungrazed. A large proportion of Salisbury Plain supports upright brome (Bromus erectus) species-rich grassland, within which a continuous floristic variation is seen. A widespread type on the Plain is characterised by an abundance of red fescue (Festuca rubra), crested hair-grass (Koeleria macrantha), salad burnet (Sanguisorba minor), lady's bedstraw (Galium verum), rough hawkbit (Leontodon hispidus), common rock-rose (Helianthemum nummularium) and dropwort (Filipendula vulgaris). The high constancy of this last species is a distinctive feature of the upright brome grasslands on Salisbury Plain and is otherwise only known from one other site in Hampshire. Where upright brome is less dominating, plants such as small scabiosa (Scabiosa columbaria), clustered bellflower (Campanula glomerata), dyer's greenweed (Genista tinctoria), kidney vetch (Anthyllis vulneraria), sainfoin (Onobrychis viciifolia) and horseshoe vetch (Hippocrepis comosa) are characteristic associates.

The rare and notable plants which occur here include burnt orchid (Neotinea ustulata), slender bedstraw (Galium pumilum), field fleawort (Senecio integrifolius) and the nationally scarce British endemic early gentian (Gentianella anglica). Particularly associated with long established turf on thin rendzina soils, and rabbit-grazed areas of the eastern and central ranges, are low-growing perennials including squinancy-wort (Asperula cynanchica), chalk milkwort (Polygala calcarea), dwarf thistle (Cirsium acaule), wild thyme (Thymus praecox), the nationally scarce bastard toadflax (Thesium humifusum) and purple milk-vetch (Astragalus danicus) in its most southerly British station.

Devil's-bit scabious (Succisa pratensis), saw-wort (Serratula tinctoria) and betony (Stachys officinalis) are all abundant and exemplify the oceanic character of the chalk grassland on the Plain, a feature which is confined to south-west England. Similarly restricted is a community in which dwarf sedge Carex humilis forms a conspicuous component. This type of grassland has its stronghold in Wiltshire and occurs on the less disturbed areas of the central ranges. Herb diversity is generally lower in the tall, upright brome-dominated swards, but wild parsnip (Pastinaca sativa), hogweed (Heracleum sphondylium) and greater knapweed (Centaurea scabiosa) are characteristic. Parasitic on the latter species is knapweed broomrape (Orobanche elatior), occurring in greater quantity on the Plain than anywhere else in Britain. False-oat grass (Arrhenatherum elatius) grassland is also widespread, but is particularly a feature of the western ranges, often indicating areas of past cultivation.

On anthills, and in the more disturbed turf that is especially a feature of the impact area, mouse-ear hawkweed (Hieracium pilosella) is abundant together with sheep's fescue (Festuca ovina) and wild thyme. Annuals are also characteristic of this habitat, including common whitlowgrass (Erophila verna), rue-leaved saxifrage (Saxifraga tridactylites,) hairy rock-cress (Arabis hirsuta) and the nationally scarce dwarf mouse-ear (Cerastium pumilum) and fine-leaved sandwort (Minuartia hybrida). A very local community characterised by a lichen-rich turf (Cladonia species) and the broom moss (Dicranum scoparium) is found in some stabilised missile-impaction craters on the central ranges. This vegetation type is found elsewhere only on Porton Down SSSI and on the Brecklands.

Small areas of chalk-heath vegetation occur on superficial clay-with-flints deposits. Here chalk-loving plants such as salad burnet (Sanguisorba minor) and dropwort co-exist with plants typical of acid soils, including gorse (Ulex europaeus), heather (Calluna vulgaris) and the uncommon annual knawel (Scleranthus annuus). Two Red Data Book (RDB) plants occur on the Plain. The largest population in Britain of tuberous thistle (Cirsium tuberosum) occurs on the western ranges and is notable for the low incidence of hybridisation with dwarf thistle, a contributory cause of its decline in other localities. Meadow clary (Salvia pratensis) persists as a small colony in tall upright brome grassland.

Salisbury Plain supports a diverse bryophyte flora with seven nationally scarce species which have seen a general decline in other chalk grassland sites, including Barbula acuta, Phascum curvicolle, Pleurochaete squarrosa, Thuidium abietinum and Weissia sterilis.

Although there is some scrub development on the Plain, it is remarkable that large expanses of the chalk grassland remain open with very little invasion of woody species. Of particular interest are the large stands of juniper (Juniperus communis) on Bulford Downs and Beacon Hill. Both pyramidal and prostrate forms are present and this site, along with Porton Down SSSI to the south, supports the best remaining examples of the lowland type of juniper associated with chalk and mixed scrub in England.