The sampling of heath vegetation

Extensive tracts of heath vegetation can be hard to find, fragmented now among improved lowland landscapes, and other stretches are difficult of access on the tops of sea-cliffs or remote mountain summits. But whether in such situations, or among the great expanses of heath that we have surveyed in the sub-montane zone of the north and west of Britain, we have not found this kind of vegetation awkward to sample. Again, though, in describing the variation encountered, we must distinguish between heath assemblages in the stricter sense and other sorts of plant community that can be found in intimate association with them on what are traditionally known as heaths or heathlands in the broader landscape sense. These were all sampled as part of our survey programme, but only the former are included in this section of the work. Here, then, heaths are taken to be vegetation types in which sub-shrubs play the most important structural role, albeit sometimes in a dwarfed or broken canopy, with such species as Calluna vulgaris and other ericoids, Vaccinium, Empetrum and Arctostaphylos spp., Loiseleuria procumbens, Ulex minor and U. gallii the usual dominants, alone or in various combinations. Thus, for the accounts of associated grasslands, moss and lichen vegetation, mires and scrub, in which such plants can be common but generally subordinate in their cover or at least accompanied by other prominent structural elements, readers will have to consult other sections of the work. Most confusing, perhaps, in this respect is the inclusion of much of what would generally be recognised as wet-heath vegetation among the mires. However, there are good floristic grounds for such a decision and, in this case as elsewhere, we have tried to remain sensitive to the close relationships between communities whose descriptions are, for one reason or another, widely separated in these volumes, and to their dependence upon the complex of environmental factors operative in the broader heathland scene where they can be found together. Some readers may also expect to find Ulex europaeus and Cytisus scoparius vegetation here, whereas we have thought it more sensible to include it among the scrubs, while Dryas octopetala communities figure with calcicolous grasslands. Once more, the contents pages and indices of the volumes should help locate particular vegetation types of interest.