Lowland Calcareous Grassland
Lowland calcareous grasslands are found on thin base-rich soils derived from underlying limestone rocks at altitudes below 250 m. They are characterized by a variety of lime-loving plant species such as thyme Thymus praecox, quaking grass Briza media, salad burnet Sanguisorba minor and hoary plantain Plantago media.
Calcareous grasslands support an exceptionally rich diversity of plants, including some rare species that are restricted entirely to lime-rich soils. The habitat is also important for many birds and for invertebrates, such as the northern brown argus butterfly Aricia artaxerxes.
The total amount of lowland calcareous grassland within the UK has been estimated at 33 000 - 41 000 ha. The majority of this is chalk grassland, found predominantly in the lowlands of southern England. Lowland calcareous grassland suffered significant losses during the last century. For example, there was a 20% loss in English chalk grassland sites between 1966 and 1980.
Within the Region, calcareous grasslands are mainly found on the Carboniferous limestone which runs north-east from the North Pennines towards the Northumberland coast, on the Magnesian Limestone of County Durham, and in association with the Whin Sill where they often form a mosaic with areas of acid grasslands.
The Magnesian Limestone grasslands found in the lowlands of County Durham and Tyne and Wear are of particular national interest. Magnesian Limestone grassland is unique to Britain. It is one of the UK’s scarcest and most restricted habitat types, of which the North East Region is the stronghold; only 279 ha are represented in the national SSSI series and two thirds of this lies within County Durham and Tyne and Wear. These grasslands are characterised by the presence of blue moor-grass Seslaria albicans and small scabious Scabiosa columbaria.
Lowland calcareous grasslands in the Region have a highly fragmented distribution, due to variation in overlying drift deposits and past losses to agricultural improvement. The most important sites are designated as SSSIs.
- Neglect and absence of grazing can lead to scrub encroachment or bracken invasion and a loss of grassland areas.
- Overgrazing can cause soil erosion and lead to a loss of species-richness and structural diversity within the grassland.
- Agricultural intensification in the form of fertilizer use, herbicide application,ploughing and re-seeding has historically been a major source of losses of grassland sites and may still potentially be damaging and destroying some grasslands.
- The in-filling of abandoned limestone quarries (eg, by use as landfill sites) where calcareous grasslands have become established is a threat in some localities.
- Quarrying may still be a threat in some areas.
- Acidification and nitrogen enrichment caused by atmospheric deposition may have a deleterious effect on calcareous grasslands, but potential impacts have not been fully assessed.
Opportunities for protection and enhancement
- The MAGical Meadows Project, run by the Durham Biodiversity Partnership, aims to protect, enhance and create Magnesian Limestone grasslans within County Durham and Tyne and Wear
- Payments for the sympathetic management of lowland calcareous grasslands are available under the Environmental Stewardship Scheme. Natural England makes payments through its Wildlife Enhancement Scheme for the management of the majority of Magnesian Limestone grassland SSSIs in the Region.
- Restorartion of aggregates sites can provide an opportunity to create new Magnesain Limestone grasslands.
- The Magnesian Limestone grasslands of Thrislington and Cassop Vale are managed as NNRs by Natural England. A number of other lowland calcareous grassland sites are managed as nature reserves by other conservation bodies, eg the Durham Wildlife Trust reserve at Bishop Middleham Quarry.