Area: 135.5 hectares.
Previously known as Rosenannon Bog. Site boundary amended by extension.
Description and Reasons for Notification:
Rosenannon Downs lie 5 kilometres to the northeast of St. Columb Major on an exposed southeast facing slope. A small stream flows southwards across the east side of the Downs widening into Rosenannon Bog. The bedrock, formed by the Lower Devonian Staddon Grits, is overlain on the valley floor, by alluvial deposits and locally by accumulations of head and valley gravel. The soils developed on the slopes are peaty ferric stagnopodzols whilst those on the valley floor and at the south-east corner of the Downs are poorly drained raw oligoamorphous peat soils. These acidic, nutrient-poor conditions support a variety of heathland types and have a rich flora and fauna.
The dry heath is dominated by heather Calluna vulgaris with frequent western gorse Ulex gallii and bell heather Erica cinerea, forming a mosaic with purple moor-grass Molinia caerulea and bristle bent Agrostis curtisii. Associated species include lousewort Pedicularis sylvatica, saw-wort Serratula tinctoria, and heath milkwort Polygala serpyllifolia. Locally, there are good populations of heath spotted-orchid Dactylorhiza maculata and deer grass Trichophorum cespitosum, a plant of restricted occurrence on Cornish heathland.
Cross-leaved heath Erica tetralix and purple moor-grass dominate the wet heath with abundant bog myrtle Myrica gale. Black bog-rush Schoenus nigricans flourishes in the wet, more base-rich areas. Wet hollows support the bog mosses Sphagnum spp. along with large populations of the insectivorous round-leaved sundew Drosera rotundifolia.
The valley-bog is enclosed by a fringe of broad-leaved woodland consisting largely of willows Salix spp., and sessile oak Quercus petraea. The wood is notable for its large stands of royal fern Osmunda regalis, a plant of decreasing occurrence nationally.
The valley bog has remained largely undisturbed for a long period, and supports a rich flora. Amongst the purple moor-grass and cross-leaved heath there is abundant bog asphodel Narthecium ossifragum, common cottongrass Eriophorum angustifolium, white beak-sedge Rhynchospora alba, pale butterwort Pinguicula lusitanica, bog pimpernel Anagallis tenella, royal fern and lesser skullcap Scutellaria minor. Of particular note is the presence of wavy St. John’s-wort Hypericum undulatum, a plant of very limited distribution in Britain.
Rosenannon Bog and Downs provide important feeding and nesting habitat for a number of heathland birds. Snipe Gallinago gallinago, curlew Numenius arquata, and meadow pipit Anthus pratensis breed here; as has the stonechat Saxicola torquata, a species which has declined nationally in recent years. Both hen harrier Circus cyaneus and Montagu’s harrier C. pygargus have been recorded.