Area: 72.2 hectares.
Boundary amended by deletion and extension. Merthen Wood lies within the Cornwall Area of Outstanding Natural Beauty. This is a Nature Conservation Review Site.
Description and Reasons for Notification:
Merthen Wood extends for nearly 2 kilometres along the northern shore of the Helford River, occupying the peninsula between the main river and Polwheveral Creek. It lies equidistant between Gweek in the west and Helford to the east.
The steep south facing woodland extends down to the low cliffs at the river’s edge, which terminate at Groyne Point to the west. Three stream valleys dissect Merthen Wood descending steeply to short creeks.
Soils are deep, well-drained and mostly acidic. The underlying shaley Gramscatho Beds of Devonian age are only exposed along the shoreline.
Merthen Wood is an ancient wood dating back to at least the medieval period. Its special importance is that it is a rare example of a woodland comprising of an almost pure, natural population of sessile oak Quercus petraea. It is one of the largest remaining oakwoods in Cornwall and historical records indicate that it has been coppiced for centuries.
The major standtype is sessile oak coppice, which is wind-pruned and stunted to a height of 10-12 metres. The understorey is locally dense and dominated by holly Ilex aquifolium or hazel Corylus avellana. Species of particular note include wild service Sorbus torminalis, a species which is very local in Cornwall, alder buckthorn Frangula alnus a species uncommon to Cornwall, the locally rather rare skullcap Scutellaria galericulata and the soft shield fern Polystichum setiferum which is rare in West Cornwall.
The ground flora on the upper slopes is dominated by dense brambles Rubus fruticosus agg. or by bluebell Hyacinthoides non-scripta in more open areas.
The lower slopes support a more heathy flora with bilberry Vaccinium myrtillus, heather Calluna vulgaris and some bell heather Erica cinerea, with wild madder Rubia peregrina, which is mainly confined to coastal locations in south and west Britain, common cow-wheat Melampyrum pratense and moss species.
Parts of the woodland, mainly along stream valleys have a high forest structure. These are dominated by sessile oak Quercus petraea, sycamore Acer pseudoplatanus and beech Fagus sylvatica with an understorey of holly Ilex aquifolium and hazel Corylus avellana.
Along the middle valley is a small strip of alder carr, with a ground flora of hemlock water dropwort Oenanthe crocata, opposite-leaved golden saxifrage Chrysosplenium oppositifolium and lady fern Athyrium felix-femina.
Additional species of note include bastard balm Melittis melissophyllum which is nationally uncommon and goldilocks Ranunculus auricomus which is rare in Cornwall.
Moss species of interest occurring in Merthen Wood are the nationally rare Fissidens curnowii and the oceanic species Hookeria lucens.
Merthen Wood supports an interesting invertebrate fauna, with the largest known British population of the rare weevil Anchonidium unguiculare, a species whose British distribution is restricted to woodlands on the Helford River. The local weevil species Acalles roboris, A. ptinoides and Caenopsis waltoni also occur. The wood is the only known location in West Cornwall for an ancient woodland indicator species of slug – Limax cineroniger. Also present here is the ant species, Stenamma westwoodi and the holly blue butterfly Celastrina argiolus.