Yarnbury Castle - Ecology

Ecology

Yarnbury Castle is located in an area of unimproved grassland on the upper chalk north of the Wylye Valley, and on the edge of Salisbury Plain, which is the largest remaining area of calcareous grassland in north-west Europe. The local area supports a rich and diverse grassland flora, which led to it being declared a biological Site of Special Scientific Interest in 1951. Designated as Yarnbury Castle SSSI, the site encompasses a total of 9.1 hectares (22 acres).

The SSSI designation for the site arises due to interest in the biodiversity and species present upon the earthworks of the fort themselves, with the inner and surrounding parts of the site being of improved agricultural grassland of little interest. The earthworks support a rich chalk grassland flora, including for several rare species. There are 16 species of grass and sedge recorded; with upright brome Bromus erectus, sheep's fescue Festuca ovina, quaking grass Briza media, crested hair-grass Koeleria cristata, and dwarf sedge Carex humilis. Various herb species include for dwarf thistle Cirsium acaule, chalk milkwort Polygala calcarea, horseshoe vetch Hippocrepis comosa, common thyme Thymus praecox, squinancywort Asperula cynanchica and common rock-rose Helianthemum nummularium.

Rarer national species include for field fleawort Senecio integrifolius, bastard-toadflax Thesium humifusum, and burnt orchid Orchis usulata, Fragrant orchid Gymnadenia conopsea, and other orchids.

The site was previously populated with scattered juniper Juniperus communis bushes, but these are now removed and the current grazing regime ensures that they do not return. There are some invertebrates recorded, including for marsh fritillary Eurodryas aurinia and small heath Coenonympha pamphilus butterflys, and a number of downland birds are present including for the skylark, corn bunting and grey partridge.