Due to the wide variety of differing habitats and geology in Cumbria, the county has several diverse types of grassland habitat, each of which support their specialised butterfly fauna. In all cases the amount of grazing is critical to maintaining biodiversity of a site. Threats to our grassland sites primarily arise due to incorrect grazing pressure and Agricultural ‘improvement’ the consequences of which are shown below:
Grazing: Undergrazing results in a dominance of coarse grasses and scrub encroachment resulting in shade, a rank sward dominated by coarse grasses and loss of floral diversity. Long term overgrazing results in a close cropped sward totally lacking in butterfly interest.
Agricultural improvement: A combination of undersoil drains, reseeding with Rye grass and application of fertilisers are the typical treatments applied in order to enhance the productivity of a grassland. When this is carried out the biodiversity of the site will be reduced close to zero.
Whilst the county is predominantly made up of acidic rocks, the south of Cumbria is formed from carboniferous limestone that supports a rich and varied flora on the calcareous grassland and limestone pavement found, especially, on the north side of Morecambe Bay. The soils here tend to be thin, dry and nutrient poor thus supporting a wide variety of alkaline tolerant flowers and fine grasses including many important larval foodplants.
This type of grassland is very important for butterflies in Cumbria, especially so where Bracken forms a mosaic within the grassland. Species present include habitat specialists such as Northern Brown Argus, Pearl Bordered Fritillary, High Brown Fritillary and Duke of Burgundy as well as a large number of habitat generalists. Many good sites can be visited in the Kendal area and around the north shore of Morecambe bay such as Whitbarrow Scar, Latterbarrow and Hutton Roof Crags, with Smardale Gill near Kirby Stephen also being another good site.
The best examples of this habitat are in west Cumbria and the Solway plain. It is often found as marginal or abandoned pasture because of the very wet ground conditions, low pH and poor nutrient value of the plants growing there.
Threats to the habitat are destruction due to agricultural improvement, drainage and loss of floral diversity due to under or overgrazing. This is a nationally rare habitat and supports important populations of butterflies, in particular the Marsh Fritillary and habitat generalists such as the Ringlet, Orange Tip, and Small Pearl Bordered Fritillary. Good sites are Ennerdale Longmoor common and Finglandrigg NNR.
Coastal Dunes and Heaths
The fine coastal dunes and heaths of Cumbria are a relatively unknown habitat and are found all along the west coast from Walney Island in the south to Silloth in the north.
Interestingly, some sites such as North Walney and Sandscale Haws are alkaline whereas others such as Drigg dunes is acidic enough to support a rich dune heath flora including Heathers and in the wetter dune slacks Cross Leaved Heath. The thin sandy soils are constantly moved by the wind providing patches of bare soil ideal basking locations for species like the Grayling and Wall Brown. Other species found in abundance on coastal grassland and dune heath are the Dark Green Fritillary, Small Heath, Gatekeeper and Common Blue.