Buckinghamshire & Milton Keynes Biodiversity Action Plan Lowland Calcareous Grassland Habitat Action Plan Lowland Calcareous Grassland Key associated species Chalk Carpet Moth Chalkhill Blue Chiltern Gentian Duke of Burgundy Early Gentian Glow Worm Green Hairstreak Hornet Robber Fly Horseshoe Vetch Juniper Linnet Meadow Clary Pasque Flower Roman Snail Silver-spotted Skipper Snail Abida secale Stone Curlew Striped Lychnis Moth Yellow Meadow Ant This habitat includes all semi-improved grassland and unimproved grassland occurring on shallow lime-rich soils normally underlain by chalk or limestone rocks. Calcareous grassland is associated with distinct topographic features such as escarpments or dry valley slopes and ancient earth works. Lowland calcareous grassland supports a very rich flora with many nationally rare and scarce species together with a diverse invertebrate fauna such as Chalkhill Blue and Duke of Burgundy butterflies. Scrub, such as Juniper and Box, is associated with calcareous grassland and contributes to local biodiversity. 1 Current status in the UK Biological status 1.1 Calcareous grassland is a rich grassland type in terms of the diversity of plant and invertebrate species supported. Many species are confined to calcareous grassland in the UK, including those that are on the northern edge of their European range. 1.2 Lowland calcareous grasslands are defined by the UK Biodiversity Group as the first nine communities in the National Vegetation Classification CG grouping. These communities are largely restricted to the warmer and drier climate of southern and eastern areas of the UK. 1.3 The amount of calcareous grassland has undergone a significant decline over the last 50 years. Although there are no detailed figures available for the UK as a whole, local statistics demonstrate the overall decline eg 50% lost in Dorset between the mid-1950s and the early 1990s, 25% lost in Sussex between 1966 and 1980. No figures are available for Buckinghamshire. 1 Buckinghamshire & Milton Keynes Biodiversity Action Plan Lowland Calcareous Grassland Habitat Action Plan 1.4 Current estimates for lowland calcareous grassland in the UK are between 33,000 and 41,000 ha with less than 1,000 ha in Wales and none in Scotland. The majority of this is associated with chalk (25,000 to 32,000 ha) with the key concentrations in Wiltshire, Dorset and the South Downs. 2 Current status in Buckinghamshire Cover and distribution 2.1 Buckinghamshire has over 350 ha of calcareous grassland, the majority of which occurs in the Chilterns though it is also found on the Cornbrash and Oolitic limestone in the north of the County. Approximately 100 ha of Local Wildlife Sites are currently attributable to Lowland Calcareous Grassland. 2.2 The distribution of calcareous grassland is linked to the geology of the County, developing on shallow, lime-rich, nutrient-poor soils derived from chalk and limestone rocks. In Buckingham-shire, the largest areas occur along the Chilterns escarpment such as the Ivinghoe Hills, Coombe Hill, Kimble Warrens, Grangelands and Pulpit Hill. As a result of scrub encroachment and agricultural improvement a large proportion of the remaining calcareous grassland occurs on inaccessible land on steep scarp slopes, in dry valleys, on railway cuttings and on old earth workings such as Aston Clinton Ragpits. These areas often occur within a larger mosaic of scrub, woodland and hedgerows. Alternatively, it may be isolated in large tracts of intensively managed farmland. 2.3 This habitat supports indigenous populations of grasses and wildflowers and includes some of the most diverse plant communities in Britain. The resource is of international importance. National Vegetation Classification (NVC) CG 2,3 and six communities are recorded on calcareous grassland. 2.4 A special feature of the calcareous grassland in the Chilterns is that it is frequently found in an intimate mosaic of large blocks of woodland and valuable hedgerows. In some areas such as at Coombe Hill SSSI the lower slopes of calcareous grassland link to the plateau which is capped with a shallow layer of clay-with-flints. Where the plateau remains free from woodland cover and agricultural improvement, this may give rise to acidic grassland and even chalk heath. 2.5.1 The occurrence of calcareous grassland as a mosaic with scrub and woodland results in a diversity of habitats, which combined, are of high conservation value. Indeed, scrub often acts as a key feature which links grassland and wooded areas. Scrub communities also have 2 Buckinghamshire & Milton Keynes Biodiversity Action Plan Lowland Calcareous Grassland Habitat Action Plan inherent ecological value, particularly for invertebrates, for example, the Duke of Burgundy butterfly. This means that any proposals for scrub clearance should be thought through carefully and an assessment made of its existing value. Clearly, a balance needs to be determined as excessive scrub encroachment and the dominance of vigorous grass species can significantly reduce the conservation value of a site. Trends 2.6 A significant decline in the extent and quality of calcareous grassland has occurred this century, principally as a result of scrub encroachment and agricultural development. Conversion of large areas of pasture to arable land has been followed by the loss of remaining grassland to scrub and secondary woodland, usually small unmanageable areas along the scarp or valley sides. The latter was exacerbated by the crash in rabbit populations following the introduction of myxomatosis in the 1950s, although rabbit populations have subsequently recovered. 3 Current factors affecting the habitat Agricultural intensification 3.1 Agricultural improvement through fertiliser and herbicide applications, ploughing and seeding has been driven by a combination of technological improvements but latterly by the Common Agricultural Policy and its associated subsidies. Lack of management 3.2 Undergrazing, or cessation of management results in a rank sward and eventually scrub and secondary woodland. Fluctuating rabbit populations have an important role in grazing intensity. Built development 3.3 Industrial and urban development leads to losses. This includes the infilling of abandoned chalk and limestone quarries where calcareous grassland has become established after cessation of work. Recreation use/pressures 3.4 Conflicting land uses such as pony paddocks, tree planting and golf courses can lead to a deterioration in habitat. Lack of public understanding over conservation management, especially removal of scrub should be addressed in order to increase awareness of the need for management. High levels of public access and recreation on certain sites can lead to erosion. Habitat isolation 3.5 Habitat fragmentation of calcareous grassland areas results in poor recolonisation and loss of species from sites. Site size is linked to the 3 Buckinghamshire & Milton Keynes Biodiversity Action Plan Lowland Calcareous Grassland Habitat Action Plan economic viability of management. This has important implications for sustainable management. 4 Current action Legal status 4.1 Eighteen of Buckinghamshire’s key calcareous grasslands are protected as SSSIs. In addition some sites have been identified as Wildlife Sites which, although non-statutory, confers some protection from development and encourages positive management. Management, research and guidance 4.2 Traditionally these areas were grazed by sheep and occasionally cattle, producing a close-cropped sward. 4.3 The restoration of grazing on abandoned grassland and scrub management (rather than eradication) are priorities for the future management of calcareous grassland. 4.4 The Chilterns Chalk Managers Group provides a network for exchange of knowledge and resources throughout the Natural Area. 5 Objectives 5.1 It is important that Habitat Action Plan objectives and actions are considered in conjunction with those in Generic Issues (see Generic Issues). All Generic objectives and actions apply to each individual Habitat Action Plan. 5.2.1 The Calcareous Grassland HAP will contribute to the following UK BAP Targets T1 Maintain the current extent of Lowland Calcareous Grassland in the UK. (Target represents no loss of BAP habitat). T2 Maintain at least the current condition of Lowland Calcareous Grassland T3 Achieve favourable or recovering condition for 30,421ha of Lowland Calcareous Grassland by 2010 T4 Restore 399ha of Lowland Calcareous Grassland from semi- improved or neglected grassland, which no longer meets the priority habitat definition by 2010 T5 Re-establish 8,424ha of grassland of wildlife value from arable or improved grassland by 2010. 4 Buckinghamshire & Milton Keynes Biodiversity Action Plan Lowland Calcareous Grassland Habitat Action Plan T6 6,320 ha (75%) of re-established area to be adjacent to existing Lowland Calcareous Grassland or other semi- natural habitat by 2010. (Refer to T5) T7 4,200 ha (50%) of re-established area to contribute to resultant habitat patches of 2 ha or more of Lowland Calcareous Grassland by 2010. (Refer to T5) 6. Biodiversity Opportunity Areas Calcareous Grassland may be a priority habitat in the following Biodiversity Opportunity Areas • Ashridge & Ivinghoe • Central Chilterns Chalk Rivers • Chess Valley • Chiltern Escarpment • Gomm Valley • Hambleden and Wormsley Valleys • Medmenham • Ouse Valley • Radnage Valley • South Bucks Heaths & Parklands • South Western Commons • Upper Hughenden Valley • Wendover Woods 5 Buckinghamshire & Milton Keynes