The semi-natural woodlands of Britain are very diverse in their trees, shrubs and associated floras. The composition of these woodlands and their structure are determined by climate, soil composition and biotic influences; chiefly the direct and indirect impact of man through generations of woodland use and more recently by tree planting.
Ecologists and foresters have devised various ways of classifying UK woodlands.
National Vegetation Classification – No system is perfect as each woodland is unique – and some woods seem to be the exceptions to any rule! No man-made system can ever be superimposed flawlessly on a natural one. But for working purposes the woodlands part of the National Vegetation Classification (NVC) is the yardstick now.
The NVC provides a systematic description and classification of woodland and other vegetation types in Britain. Those are described in Rodwell (1991). It describes the major types of woodland. Each can be recognised by distinctive mixtures of trees and shrubs and has a characteristic associated flora of flowering plants and sometimes ferns, mosses, liverworts and lichens. Each is confined to a particular climatic zone and certain soil types and represents the kind of climax vegetation that could develop wherever such conditions occur if nature was allowed to take its full course.
The NVC recognises 18 classes of woodland, 5 of scrubland and 2 classes of edge habitat, each with between one and eight sub-classes. In all, the NVC recognises 74 units or types of woodland or scrub.
Semi-natural woods, are largely composed of trees and shrubs that are native to the site. They have developed from seedlings or stump re-growth through successive generations from the original trees in the wood which were self-sown. They can be split into:
- primary woods on sites that have always been wooded
- secondary woods which have colonised bare ground within historical times
Semi-natural woods, especially the oldest or “ancient” ones are the nearest we have to truly natural woodlands. They are very valuable wildlife habitats and an important part of our cultural heritage. The current area of ancient semi-natural woodland is approximately 300,000 ha.
Classification of Ancient Semi-Natural Woodlands – Though it would make foresters’ and ecologists’ lives much easier, there is no perfect way of classifying woodlands so they all fit neatly into a manmade pigeon-hole system. Each woodland is unique. However for the purpose of management, Britain’s ASNW are normally divided into eight main groupings. Those relate to the widely adopted National Vegetation Classification or NVC which looks at all types of natural vegetations in the UK.
Each of the eight types has a distinctive ecological and regional character, a different history of management and exploitation and distinct management requirements for the future. They are:
- Lowland Acid Beech and Oak Woods (NVC Types W15, W16)
- Lowland Beech-Ash Woods (NVC W12, W13 and W14)
- Lowland Mixed Broadleaved Woods (NVC W8(a-d), W10)
- Upland Mixed Ashwoods (NVC W8(e-g), W9)
- Upland Oakwoods (NVC 11, 17 (oak dominated))
- Upland Birchwoods (NVC W11, W17 (birch dominated) )
- Native Pinewoods (NVC W18, W19)
- Wet Woodlands (NVC W1 to W7)
This classification gives a working yardstick but there will always be exceptions that prove the rule such as woodlands which contain a mosaic of different types of trees which have been planted some time ago beyond their native range.
More: The Forestry Commission publishes a series of 8 Forest Practice Guides in the series “The Management of Semi-Natural Woodlands”. This series of booklets (2003) contains advice to help owners and managers to achieve best practice and ensure the woodlands’ future. See www.forestry.gov.uk/publications FC Bulletin 112. “Creating New Native Woodlands”. J.S. Rodwell & G.S. Patterson. 1994. HMSO. J.S. Rodwell (Ed.) “British Plant Communities” Vol. 1; “Woodlands Scrub”. 1991. Cambridge University Press.