Castle Down (Tresco)

Also within

Cornwall County Isles Of Scilly Scenic Area

Condition (Natural England)

Climate exposure

This is about exposure to a nationwide pressure this habitat type carries — not a verdict on this site's own management.

Habitats

Bracken scrub

Geology & landscape

Geological Feature: Cave / Cavern, Erratic, Raised Beach, Rock Outcrop · Rock Type: Granite

Landscape processes: Coastal, Glacial, Karst, Volcanic / Igneous

Birds & fish recorded

Birds

Description

Area, 58.1 hectares 143.6 ac Description Castle Down is an exposed headland on the north side of the island of Tresco on the northern margins of the Isles of Scilly archipelago. Hercynian granite underlies the site forming a low windswept plateau only 35 metres above sea level. This extreme maritime exposure and the thin podzolic soils have resulted in the development of an extensive area of ‘waved’ maritime heathland with a particularly important lichen flora. Glacial outwash gravels with abundant erratic pebbles outcrop over much of the northern part of the plateau and are particularly well exposed along the western shore between Cromwell’s Castle and Gimble Point. Of additional interest is Piper’s Hole, a small cave in raised beach deposits in the cliffs on the north east coast of the island. ‘Waved’ maritime heathland covers much of the central part of the site. Here the vegetation is dominated by distinctive low, prostrate ridges of heather Calluna vulgaris together with some bell heather Erica cinerea and western gorse Ulex gallii. There are few other plant species within this wind pruned habitat but tormentil Potentilla erecta, common bird’s foot trefoil Lotus corniculatus, heath bedstraw Galium saxatile and English stonecrop Sedum anglicum also occur. Thrift Armeria maritima and buck’s horn plantain Plantago coronopus are more common along the coastal edge. The more sheltered depressions with deeper soils on the margins of the plateau have bracken Pteridium aquilinum, bramble Rubus fruticosus and honeysuckle Lonicera periclymenum merging into the heathland. Castle Down is also of particular importance for its lichen flora, exhibiting a range of rare oceanic heathland species including the only known European record of Heterodermia propagulifera together with H. leucomelos and H. obscurata. These Heterodermia communities are now very rare and comparable sites, outside Scilly, only occur in Brittany and Channel Islands. The 45 species of lichen recorded also include Lobaria pulmonaria growing on Calluna vulgaris and a number of Cladonia species dominating the shallow soils and open pans on the central heathland. In addition the short lichen rich heathland on the Downs supports an important breeding colony of common tern Sterna hirundo. Site Notified to the Secretary of State on 10 December 1986.

Species mentioned

Insects to look out for

These moths, butterflies and beetles are known to feed on plants recorded at this site, and carry a notable UK conservation status — but a host-plant being present doesn't mean the insect has actually been recorded here. Treat this as "worth watching for," not a confirmed sighting.

Host-plant data: Cook et al. (2025), Traits data for the butterflies and macro-moths of Great Britain and Ireland, 2024, UK Centre for Ecology & Hydrology / Butterfly Conservation; and Padovani et al. (2020), Database of Insects and their Food Plants (DBIF), UK Centre for Ecology & Hydrology (both Open Government Licence). Contains data supplied by UK Centre for Ecology & Hydrology.

Plant communities