Lowland calcareous grassland

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Abridged version taken from the Wiltshire Biodiversity Action Plan (BAP)

Introduction

Lowland calcareous grasslands have developed on shallow lime-rich soils generally overlying limestone rocks, including chalk. The thin, well-drained, nutrient-poor soils support a characteristic variety of herbs and grasses. These grasslands are now largely restricted to distinct topographic features such as escarpments, dry valley slopes or ancient earthworks, in landscapes strongly influenced by the underlying limestone and chalk geology. Unusually there are a number of extensive areas remaining on flat ground as on Salisbury Plain and Porton Down, where the grasslands have survived due to military occupation where there has been limited agricultural intensification. Small remnants also occur along road verges and in woodland glades.

Calcareous grasslands are typically managed as components of pastoral or mixed farming systems, supporting sheep, cattle or occasionally horses; a few are cut for hay.

Importance

“Dry grasslands and scrublands on limestone” (including Chalk) and “Juniper on heaths or calcareous grasslands” are listed in the European Habitats Directive as habitats of importance. As such, three sites in Wiltshire: Pewsey Downs, Prescombe Down and Salisbury Plain (which includes Parsonage Down and Porton Down Sites of Special Scientific Interest - (SSSI) are designated as Special Areas of Conservation (SAC) for these habitats and the species of (European) community importance which they support (early gentian, marsh fritillary and orchid communities).

There are 62 SSSIs within Wiltshire, which contain areas of calcareous grassland. It is estimated that over 18,000 hectares are protected in this way with a further 1,600 hectares recognised as County Wildlife Sites (sites of County Importance).

Extent and distribution

There are estimated to be 40,000 to 50,000 hectares of calcareous grassland remaining in the UK, with the majority of this on chalk. The major concentrations are in Wiltshire, Dorset and the South Downs (UK Biodiversity Action Plan). Wiltshire has between 18,000 and 24,000 hectares of calcareous grassland, the majority of which is on chalk, with approximately 500 hectares on limestone. This equates to approximately 50% of the total UK calcareous grassland resource.

Salisbury Plain Training Area alone has approximately 12,000 hectares of chalk grassland, which represents over 40% of the resource of chalk grassland in North West Europe

Trends

No definitive figures exist for decline in calcareous grassland in Wiltshire, however a study in Dorset found that over 50% had been lost between the mid 1950s and the early 1990s. Recent DEFRA data on land use, however, suggests that the area of permanent grassland in the county is now relatively stable.

Key Species

• Bastard toadflax
• Burnt-tip orchid
• Chalk milkwort
• Dwarf sedge
• Field fleawort
• Round-headed rampion
• Early gentian
• Juniper
• Tuberous thistle
• Stone curlew
• Quail
• Skylark
• Grey partridge
• Merlin
• Hen harrier
• Linnet
• Corn bunting
• Wheatear
• Barn owl
• Duke of burgundy
• Adonis blue
• Marsh fritillary
• Chalkhill blue
• Silver spotted skipper
• Hornet robber fly
• Shrill carder bee
• Brown banded carder bee
• Narrow-bordered bee hawk moth
• Chalk carpet moth
• Pale shining brown moth
• Trichopteryx polycommata - a micro moth
• Wartbiter cricket
• Brown hare

Last updated: 23 June 2009