Area: 56.9 hectares.
Description and Reasons for Notification:
Warmwell Heath represents one of the most westerly blocks of Dorset heathland and has a long history of isolation which is of interest for the study of habitat fragmentation and the resulting faunal and floral richness. The heathland lies over the acidic Bagshot Beds and Plateau Gravels of the Poole Basin, with alluvial deposits and peat predominant within the adjacent river valley. The area supports a range of heathland habitats from dry heath to bog. Associated with the heathland are peripheral areas of woodland, carr and swamp vegetation.
The dry heath of the higher slopes is dominated by ling Calluna vulgaris with bell heather Erica cinerea, dwarf gorse Ulex minor and typical heathland lichens, especially Cladonia portentosa. common gorse Ulex europaeus and bracken Pteridium aquilinum form locally dense stands. The vegetation rapidly grades from dry to humid heath, with cross-leaved heath Erica tetralix, which dominates the lower slopes. The eastern section of the heath is interspersed with fairly dense patches of Scots pine Pinus sylvestris, birch Betula spp. and pedunculate oak Quercus robur.
The lower lying areas are dominated by wet heath and bog communities in which purple moor grass Molinia caerulea is abundant along with varying amounts of the cross-leaved heath. The rare marsh gentian Gentiana pneumonanthe and petty whin Genista anglica, which is infrequent in Dorset, are also present on the wet heath. Associated with these wetter areas are several species of bog moss Sphagnum spp. including the rare S. pulchrum as well as the very local marsh clubmoss Lycopodiella inundata. Other species frequent within the bog communities are common cottongrass Eriophorum angustifolium, bog asphodel Narthecium ossifragum, round-leaved sundew Drosera rotundifolia and bog-myrtle Myrica gale.
The Tadnoll Brook, a tributary of the River Frome, rises as a chalk spring 3 kilometres to the west, and within its valley vegetation communities have developed which are influenced by both the base-rich river water and the acidic lateral flow from heathland. The area comprises a mosaic of alder Alnus glutinosa and willow Salix spp. carr, interspersed with more open fen vegetation. The mixed fen vegetation close to the river banks includes species such as meadowsweet Filipendula ulmaria, common valerian Valeriana officinalis, marsh-marigold Caltha palustris, common comfrey Symphytum officinale, and wild angelica Angelica sylvestris. Beyond this are areas of tall fen dominated by lesser pond-sedge Carex acutiformis and reed canary-grass Phalaris arundinacea. The carr is fringed by tall tussocks of greater tussock-sedge Carex paniculata which particularly follow the line of former ditches. Within the carr itself are patches of tussocky purple moor-grass and bog mosses, these reflecting the acidic influence on the area. A tussock-form of common sedge Carex nigra also occurs locally.
Although Warmwell Heath is further west and separated from the main blocks of Purbeck heathland the rare and protected smooth snake Coronella austriaca is known to occur on this site. The dragonfly fauna is rich and includes the uncommon small red damselfly Ceriagrion tenellum.