Calcareous Grassland

Roselle Chapman - Community Ecologist

Oxfordshire has some of the rarest and finest grasslands in the country. Species-rich grasslands are not only biodiverse but are an intrinsic part of our natural and cultural heritage. The county covers an area of 259800 ha, of which the key grassland habitats include floodplain grazing marsh (4502.94 ha), hay meadows (1220.28 ha), limestone and chalk grasslands (778 ha) and acid grasslands (48.17ha).

Calcareous grassland meadows have dominated the chalk hills of Southern England for many centuries, and were widespread until the 1940s, covering many of the steeper slopes in the Chilterns, the North and South Downs, Salisbury Plain and the Lincolnshire and Yorkshire Wolds. They are now a relatively rare habitat with less than 41,000 ha remaining in the lowlands.

Oxfordshire’s calcareous grassland meadows support nationally important rare plants, including the bulk of the UK populations of downy woundwort Stachys germanica, meadow clary Salvia pratensis, early gentian Gentianella anglica and Chiltern gentian Gentianella germanica. They are also important sites for invertebrates, particularly for butterflies, whose short life cycles result in quick responses to subtle habitat or climatic changes. Two of Oxfordshire’s rarest butterfly species, the Adonis blue Polyommatus bellargus and silver-spotted skipper Hesperia comma, are chalk-grassland specialists, as is one of the UK’s most threatened butterflies, the Duke of Burgundy Hamearis lucina. All three of these species can still be seen in small numbers in the county, and Upper Thames Butterfly Conservation are working with landowners to maintain and enhance areas of good habitat for them, for example at Aston Upthorpe Downs in south Oxfordshire.

Although this habitat has been shown to be relatively robust to the direct threats posed by short term climate change, other non-climate change drivers such as nutrient enrichment from atmospheric nitrogen deposition, under or over-grazing and cultivation represent greater threats. Some airfields, both used and disused, support areas of calcareous grassland which are now under threat of loss and fragmentation from housing developments.

Sites that have avoided agricultural intensification are often situated on steep slopes with rocky outcrops and thin soils, making them unsuitable for modern machinery. As a result, they tend to be managed as extensive grazing pasture and are at risk from abandonment leading to successional changes, including encroachment by rank grasses, competitive plant species, scrub, when grazing is reduced or ceases altogether. While Juniper must be maintained and encouraged to spread, strategic cutting and grazing of areas of scrub and grassland is vital in order to arrest succession, thereby maintaining a patchwork of habitats and woody plants at various stages of growth. For example, hawthorn provides the best habitat for insects and birds during the early and mid-stages of growth, and less so as it ages further.

Swyncombe Downs SSSI (46.4 ha) is an exquisite part of the Chilterns Escarpment North Conservation Target Area (CTA), renowned for its chalk grassland, scrub and bird communities. The beech woodland at the eastern end of the Downs, demonstratesthe later phases of ecological succession, and provides a valuable interface with adjacent scrub and grassland communities. The grassland includes some exceptionally species-rich grassland, comparable with the best examples in the country. A variety of aspects, gradient and soil depth give rise to a variety of features of high value for invertebrates including very short areas, areas with a mosaic of short and slightly longer sward, and areas with a sheltered glade type structure. The site is outstanding for its butterflies and moths. During the 1980s the site suffered from lack of grazing which resulted insignificant habitat degradation. Over the last 20 years the current landowner has worked tirelessly to restore the quality of the habitats. SSSIs are designated to protect small islands of remnant high quality habitat and landowners are legally obliged to manage them appropriately. Where real gains start to be made is where landowners stop cultivating adjacent parcels of land and bring them into conservation management. The Swyncombe Estate has done just this with 32.5ha of arable land which,over time with careful grazing management and natural regeneration has developed into good quality, species rich, semi-improved grassland with herb-dominated swards. Additionally, the last 10 years has seen the reversion of 14.8ha from arable to grassland through flower meadow creation by contiguous landowners. With award winning examples of arable reversion through meadow creation taking place in near-by Greenfield and Christmas Common in the Chilterns Dipslope and Plateau CTA, significant progress in calcareous grassland enhancement, restoration and creation will contribute to the future of this precious habitat and dependant biodiversity

Meanwhile Plantlife have been working hard with landowners in the Blewbury to Streatley Downs CTA to secure the future of the iconic Juniper shrub within Oxfordshire’s chalk grassland landscape. For many years it has been failing to regenerate naturally and is predicted to go extinct within 30-50 years’ time without intervention, taking with them over 100 specialist invertebrates and fungi that depend on them. Although Juniper is the focus for this project, the work will be benefiting chalk grassland conservation overall. Plantlife have found that creating scrapes of bare chalk for Juniper seeds to germinate on, adjacent to existing species rich grassland, benefits many precious chalk grassland wildflowers, which thrive in the absence of competition from vigorous grass, and it shouldn’t be long before these associated chalkland species are supporting other wildlife too. Read more about Plantlife’s Juniper work.

If you would like to take part in flower-rich chalk grassland management, the Aston Rowant National Nature Reserve Volunteer Group meets every Monday from 9am to 4pm. Site maintenance tasks, led by experienced site managers and local experts, include scrub clearance, path maintenance, fencing, species protection, interpretation, and some livestock husbandry. Members of the group can do tasks according to their ability and can gain skills for career development or personal achievement as well as enjoying the social side of volunteering. Aston Rowant National Nature Reserve sits on the north-western scarp of the Chiltern Hills, within the Chilterns Area of Outstanding Natural Beauty. To find out more about volunteering opportunities contact Mick Venters on email at michael.venters@naturalengland.org.uk or by calling 01844 351833.