Area: 85.64 hectares.
New site. Within West Dorset Area of Outstanding Natural Beauty. Part is Dorset Trust for Nature Conservation Reserve.
Description and Reasons for Notification:
Comprising a series of remote West Dorset valleys of striking landscape, Mapperton and Poorton Vales has diverse nature conservation interest. Streams have cut steep-sided valleys, the floors of which are occupied by wet woodland, fen or marshy grassland. These wet valley bottoms provide outstanding habitat for invertebrates and support a rich fauna including many rare and nationally scarce species. Some of the valley slopes have been relatively little modified by agricultural improvement and retain floristically interesting grassland of several types which are now of restricted distribution both nationally and in Dorset.
The Bridport and Yeovil sands which dominate the geology of the area support unimproved acidic grassland of the sheep’s fescue Festuca ovina – common bent Agrostis capillaris – heath bedstraw Galium saxatile community type. The short grazed turf, while naturally species-poor, includes the herbs tormentil Potentilla erecta, heath speedwell Veronica officinalis and common dog-violet Viola riviniana. It has a well developed bryophyte (mosses and liverworts) component. Anthills are a conspicuous feature and provide a different habitat for mosses as well as other plants such as sheep’s sorrel Rumex acetosella and early hair grass Aira praecox.
In places, localised outcrops of Inferior Oolitic limestone have a calcareous influence on the grassland, reflected by the presence of the sheep’s fescue Festuca ovina – meadow oat grass Avenula pratensis community type. A range of small herbs occurs including wild thyme Thymus polytrichus, mouse-ear hawkweed Hieracium pilosella, salad burnet Sanguisorba minor and bird’s-foot-trefoil Lotus corniculatus, together with lady’s bedstraw Galium verum and small scabious Scabiosa columbaria.
Fuller’s Earth clay mantles the gentler slopes to the north where species-rich neutral grassland of the crested dog’s-tail Cynosurus cristatus – common knapweed Centaurea nigra community type occurs. This community has an attractive diversity of flowering plants such as devil’s-bit scabious Succisa pratensis, betony Stachys officinalis, ox-eye daisy Leucanthemum vulgare, pignut Conopodium majus and the nationally scarce corky-fruited water dropwort Oenanthe pimpinelloides.
The woodland of the valley bottoms is predominantly a mixture of unmanaged hazel Corylus avellana and alder Alnus glutinosa coppice under an ash Fraxinus excelsior and pedunculate oak Quercus robur canopy, with grey willow Salix cinerea and alder carr in wetter places. Aspen Populus tremula and holly Ilex aquifolium occur locally. Characteristic herbs are wood sorrel Oxalis acetosella, ramsons Allium ursinum, bluebell Endymion non-scriptus, wood spurge Euphorbia amygdaloides and yellow archangel Lamiastrum galeobdolon. Particularly associated with the alder carr is tussock sedge Carex paniculata and the local alternate-leaved golden-saxifrage Chrysosplenium alternifolium.
Interspersed amongst the woodland and carr are several small wet meadows and areas of ungrazed fen in which rushes Juncus spp., great horsetail Equisetum telmateia and tall herbs such as meadowsweet Filipendula ulmaria, wild angelica Angelica sylvestris and yellow Iris Iris pseudacorus are prominent. Frequent associates include marsh orchid Dactylorhiza praetermissa, marsh valerian Valeriana dioica, fen bedstraw Galium uliginosum and marsh marigold Caltha palustris.
The broad range of closely juxtaposed habitats in these valleys has resulted in a rich invertebrate fauna whose interest centres mainly on the fen, seepages, stream margins and carr woodland. Diptera (true flies) are particularly well represented with four Red Data Book* and 20 nationally scarce species. The cranefly Scleroprocta pentagonalis, the snail-killing fly Antichaeta brevipennis, the soldier fly Oxycera analis and the robber fly Dioctria cothurnata are all Red Data Book species restricted to wet woodland or shaded fen. The carr also supports at least six nationally scarce craneflies. Most of the other scarce flies are found in open or shaded fen or seepages and include three semi-aquatic soldier flies Oxycera pardalina, Stratiomys potamida and Vanoyia tenuicornis, and the snail-killing fly Colobaea distincta. Trampled stream margins are the habitat of the dung fly Themira gracilis, a species previously recorded mainly from northern Britain.
At least seven further nationally scarce invertebrates are known from this site, of which six are beetles. Two species of leaf beetle, Cassida murraea and Chrysolina menthastri, are associated with marshy areas, while dead wood supports the longhorn beetle Judolia cerambyciformis and soldier beetle Malthodes guttifer as well as the fly Oedalea tibialis. The weevil Cneorhinus plumbeus and the wolf spider Pardosa agrestis are associated with dry grassland.
* The Red Data Book is a listing of rare and threatened insects.