Area: 42.5 hectares.
Description and Reasons for Notification:
Crowhill Valley lies on the upper reaches of the River Fal between Grampound and St Stephen. The site is of importance for its woodland complex. The valley sides carry ancient broadleaved woodland dominated by sessile oak Quercus petraea. The wet flood plain supports an extensive area of carr woodland, predominantly of willow Salix spp and alder Alnus glutinosa, with a very rich ground flora. Very few comparably large areas of sump al
der woodland are known from south-west England.
The valley at Crowhill runs north-south and cuts at right angles across the junction between Upper Devonian rocks of Grampound Grit and the older Meadfoot Beds. Well-drained steep valley sides fall from an altitude of 100 m to a narrow waterlogged flood plain at 35 m. The soils of the valley floor are alluvial stagnogleys while those of the slopes are well-drained silty loams.
The main watercourses of the site are the river Fal itself and a mill race which runs, parallel with the Fal, from a stream-fed pool at the foot of Carnwinnick Wood. Between the race and the river the valley floor is criss-crossed with old man-made drains as well as innumerable small natural streams and rivulets which meander between these. A series of small pools are probably a remnant of tin-streaming operations.
The valley side oak woodlands are of ancient origins and a variety of past management techniques has resulted in a wide range of structure and ground flora. Large areas are dominated by bilberry Vaccinium myrtillus and great woodrush Luzula sylvatica with a good associated bryophyte ground flora as well as woodland herbs including wood sorrel Oxalis acetosella, wood sage Teucrium scorodonia, wood anemone Anemone nemoralis and bluebell Hyacinthoides non-scripta. Of particular note is the presence of the local grass wood millett Milium effusum. The woody understorey is typically dominated by holly Ilex aquifolium, with rowan Sorbus aucuparia and hazel Corylus avellana. There is a rich epiphyte flora with honeysuckle Lonicera periclymenum, ivy Hedera helix and polypody Polypodium vulgare.
The wet valley bottom, extending to nearly 20 hectares, is dominated by a closed canopy of willow mainly Salix cinerea with alder. Higher drier islands within this have some self-seeded oak, holly and blackcurrant Ribes nigrum. The water table fluctuates and in periods of high rainfall much of the woodland is inundated. Hemlock water dropwort Oenanthe crocata forms extensive stands which are interspersed with areas of mixed tall herbs including meadowsweet Filipendula ulmaria, common valerian Valeriana officinalis, yellow loosestrife Lysimachia vulgaris, water figwort Scrophularia aquatica, marsh speedwell Veronica acutellata and ferns, notably royal fern Osmunda regalis. Prostrate herbs include marsh violet Viola palustris, yellow pimpernel Lysimachia nemorum and the rare Cornish moneywort Sibthorpia europaea.
Scattered pools within the carr support a rich flora with Sphagnum moss species, marsh cinquefoil Potentilla palustris, broad-leaved pondweed Potamogeton natans and common water plantain Alisma plantago-aquatica.
The site is of local importance for lichens. The species list includes seven ancient woodland indicator species and there is a record of the nationally rare Parmelia endochlora.