Box 13 An example of the UK National Vegetation Classification NVC Wistmans Wood Dartmoor Devon

Wistman's Wood, owned by the Duchy of Cornwall, has been managed since 1961 under a nature reserve agreement with what is now Natural England, the Government conservation body. This long narrow 3.5 ha wood is divided into the North, Middle and South Woods, all situated in the valley of the West Dart river. Its vegetation in general conforms to W17, an upland Oak-Birch-Dicranum moss woodland (Quercuspetraea-Betulapubescens-Dicranum majus woodland, subcommunity Isothecium myosuroides-Diplophyllum albicans), a grouping in which non-vascular plants are particularly important. The wood is dominated by pedunculate oak Quercus robur, with occasional rowan, holly, hawthorn, hazel and willow (Salix aurita, S. cinerea). Note that the pedunculate oak is not the oak from which the community takes its name - the sessile oak Q. petraea. This shows the robustness of taking into account all the vegetation; a community which otherwise looks like any other W17 woodland is not misclassified by one main species being 'wrong'.

Cattle and sheep have free access to this high altitude wood in an area of high rainfall; species sensitive to grazing such as bilberry, ivy and polypody sometimes occur with the lichens and mosses growing on tree branches. The granite boulders on which the wood has arisen are largely covered with lichens, especially Parmelia saxatilis, P. laevigata, Sphaerophorus globosus and various species of Usnea, and patches of moss in which Dicranum scoparium, Hypnum cupressiforme (s.l ), Isothecium myosuroides, Plagiothecium undulatum and Rhytidiadelphus loreus are frequent. Acid grassland with wavy hair-grass, common bent, sheep's fescue, creeping soft-grass, heath-bedstraw, tormentil and sorrel, develops where soil has accumulated. Woodland clearance in this area of Devon was extensive by the Iron Age and largely complete by the thirteenth century.

Wistman's Wood is surrounded by Bronze and Iron Age hut circles and has been influenced by humans and their grazing animals for thousands of years. An excellent summary of this wood is provided by Mountford et al. (2001); Wistman's Wood also provides an example of forest change in Section 9.4.1. Fragments of similar high altitude Dartmoor oakwood occur at Black Tor Copse and Higher Piles Copse.

ground (or from the map if human disturbance is great) and for foresters conveys information on what trees will grow in a particular area. However, given the size of New England (almost exactly half the area of the British Isles), the classification is rather coarse with the consequence that each zone contains much variation. For conservation (where the complete range of habitats is of interest) and for resource management (where small differences in vegetation may be important), something with a finer scale and which preferably includes all the other habitats, not just forests, is needed.

Types Classification Ecology
Figure 1.14 Natural forest zones of New England as compiled by the Society of American Foresters in 1955. (From Westveld et al., 1956. Journal of Forestry, 54.)

At the state level, a number of finer resolution schemes have been produced, based on a variety of criteria but predominantly the current vegetation, both woody and herbaceous. So, for example, in Massachusetts 105 vegetation types, not including aquatic habitats, have been identified by Swain and Kearsley (2000) compared with the four zones of Westveld in the same area. Although attempts are made to cross-reference (crosswalk) classifications between nearby states, each state typically uses its own names for communities, compounded by geographical differences in species distributions, making it difficult to determine if communities in two states are really equivalent. It is clear from this that some sort of national classification would assist effective communication, but given the size of the USA and the huge number of habitats, it is a tremendous undertaking (and much like the current attempt to create an integrated classification across Europe). Country-wide classification schemes for forest types have been in place for decades but something with a wider inclusion of habitats is needed. A number of schemes are in progress aiming to produce hierarchical classifications so that forests and woodlands at the continent scale can be subdivided repeatedly down to individual habitat types so everyone will be happy! These schemes include:

* The US National Vegetation Classification (USNVC) which is part of the International Vegetation Classification (IVC), a continent-wide scheme (see: www.esa.org/vegweb). These schemes are based primarily on current vegetation (physiognomic at coarser levels - what the vegetation looks like - and floristic at finer levels - what species are there).

* The Ecological Systems Classification (ESC) put forward by NatureServe which takes the finest levels of the IVC (plant communities) and builds them into progressively bigger systems based on similarity of ecological processes, substrates and/ or environmental gradients (see: www.natureserve.org).

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