Woodlands and wooded areas can be classified by various criteria, as outlined below.
Age
Ancient woodlands
Ancient woodland is land that has had continuous woodland cover since at least 1600 AD, and is categorised into two types. Ancient Semi-Natural Woodlands are sites that have retained their native tree and shrub cover, and have not been altered by planting. The woodland may have been managed by coppicing or felling, and allowed to regenerate naturally. Ancient Replanted Woodland is woodland where the original native tree cover has been felled and replaced by planting, usually with conifers, and usually during the 20th century.
The year 1600 was chosen because there was little planting of woodlands before that date, and maps are available from about that time which can be linked to evidence on the ground. In Scotland, ancient woods are those which were present before 1750, when the first national survey was made. Woods can still be ancient even if they have been felled many times, as the trees grow up again from the same genetic stock. Ancient replanted woodlands can be partly restored by removing the introduced species, and allowing the native cover to re-establish. Continuity of ancient woodland is broken by alternative land use such as agriculture or urban development.
Some ancient woodlands are remnants of the primary or prehistoric woods, while others are secondary woodlands which have grown up on ground cleared at some time in the centuries before 1600.
The Ancient Woodland Inventory for England lists over 22,000 ancient woodland sites. The Inventory is being constantly updated as new details become available. Ancient woodland is identified using presence or absence of woods from old maps, information about the wood’s name, shape, internal boundaries, location relative to other features, ground survey, and aerial photography. The Inventory is managed by English Nature. For further details see Guidelines for Identifying Ancient Woodland (English Nature, 1999), or visit the English Nature website. Similar information is being compiled for Wales and Scotland by their respective nature conservation agencies, who should be contacted for further details. In Scotland, the Caledonian Pinewood Inventory of native Scots pine woodland has been compiled.
Recent
Recent woodlands are those that have grown up since 1600, on previously unwooded sites. They may be planted, or naturally regenerated trees.
Primary
These are woodlands which have existed continuously since the original wildwoods developed. It is difficult to prove that a woodland is primary. All primary woods are ancient.
Secondary
These are woodlands which have grown up on land which was cleared at some time in the past for agriculture or some other purpose. All recent woodlands are secondary.
Apart from the difficulty of identifying the age and origin of woodlands, the classification blurs at the edges of woodlands. The expanding margins of ancient woodland onto unaltered soils can be classified as ancient. Woodland which has grown up or been planted on altered soils next to ancient woodland is classified as secondary.
Why ancient semi-natural woodlands are valuable
- They include all primary woods, which are the lineal descendents of the wildwood, with wildlife communities and soils unaltered by clearance or cultivation.
- Their wildlife communities are usually richer than those of recent woods, which tend to be dominated by fast growing species, or have elements of the habitat which they replaced.
- They contain a high proportion of the populations of rare and valuable woodland species.
- They may contain natural features such as springs and streams, and microtopographical features formed under periglacial conditions.
- Rides and glades within ancient woodlands may contain rare communities of plants, invertebrates and other organisms.
- Most ancient woodlands have been managed, and some have detailed historical records associated with them.
- Some ancient woodlands contain earthworks which predate them, and which are of archaeological value.
In the uplands, the difference between ancient and recent woodlands is less marked.
- Upland woods are typified by pine, birch and oak which regenerate in open areas, so woodland cover tends to be mobile over time, and is less strongly associated with particular sites.
- Upland woods are more open, and there is less microclimatic difference between the interior of the wood and the land around, so a specialised woodland flora and fauna does not usually develop.
- Most upland woods are severely modified by grazing, and tend to merge into moorlands.
- There are few historical records.
Species
The National Vegetation Classification (NVC) describes 19 major types of woodland plant communities. Each has a distinctive mixture of trees and shrubs, with a characteristic associated flora of flowering plants, and for most types, ferns, mosses, liverworts and lichens. Each type is limited to a particular climatic zone and soil type, and represents the kind of climax vegetation which could develop wherever such conditions occur, if succession was allowed to occur. Succession has been highly modified by man in most woodlands in Britain, but they still preserve much natural diversity.
The 19 woodland types are listed here, with further details here.
The full details of the 19 woodland types and their distribution are given in British Plant Communities Volume 1: Woodlands and Scrub (CUP, 1998) and summarised in Summary of National Vegetation Classification woodland descriptions (JNCC, 1994). For details on using the NVC for designing new native woodlands, see Creating New Native Woodlands (Forestry Commission, 1994).
System of management
Woodlands can also be classified by how they have been managed. The effect of management is most obvious in the structure of the woodland and the form of growth of the trees within it, but past management may also have affected the species mix, either by intentionally or unintentionally favouring particular species over others, or by planting.
All woodlands in Britain have been affected by man’s activities. It’s essential to understand how a woodland was managed in the past before making decisions for future management. Most new native woodlands will also need to be managed in order to become attractive habitats for amenity and wildlife.
Few woodlands have been managed continuously under the same system. Those coppices and wood pastures that have had continuity of management over centuries are amongst the most ecologically and historically valuable woodlands in Britain. The management of most woodlands has lapsed at various times, or the management system has changed from one type to another.
Coppice
This describes the regular cropping of deciduous trees by cutting growth down to the stump or stool. Rotations of 5-30 years are used, depending on the species and the end use. The cut material is used for fuel, fencing, greenwood crafts and many other uses. Hazel, a multi-stemmed shrub, is the most common coppice species, and declines as it becomes shaded by other trees. Alder, oak, lime, hornbeam and sweet chestnut were widely coppiced in the past for various purposes. Where coppicing is abandoned, these species tend to grow up into a form of high forest. Coppice (except hazel) can be converted to high forest by singling, which involves cutting all the stems but one, which is left to grow on to form a single-stemmed tree. For further details see Chapter 9 – Coppicing.
Coppice with standards
This two-storey system developed to provide a coppice crop and a timber crop from the same piece of woodland. The coppice or underwood was cut at frequent intervals, and the timber trees, normally oak, were allowed to grow into standards and were felled at intervals of 80-100 years. The number of standards was regulated so that they did not outshade the coppice growth. Coppice and coppice with standards were the most widespread method of woodland management in lowland mixed woods from at least the early Middle Ages until the 20th century.
Wood-pasture
Wood-pastures probably developed as a consequence of domestic animals being grazed in woodlands, which over time favoured grasses rather than trees. The Domesday Book (1086) recognised wood-pastures as a different category from coppice woodlands, and the rights to graze animals, cut timber, cut pollards, collect fruit and other rights of the system were strictly regulated. Some regeneration of trees took place naturally in thorny scrub, and other trees were pollarded, so that new growth occurred out of reach of grazing animals. Many wood-pastures were enclosed as deer parks or landscape parks, of which some still survive. Where grazing in wood-pastures lapses, seedling trees and shrubs survive and develop, and open grassy areas decline, until the area is mainly wooded. Amongst the more recent trees, the presence of wide-spreading mature or veteran trees, whose form indicates that they developed in the open conditions of wood-pasture, are a clue to the previous management system.
High forest
In a high forest system, the trees are allowed to grow to their mature height, creating a closed canopy. The trees may be of even age, as in a plantation, or of mixed ages. Historically, this system was little used in Britain. Many oak plantations of the 19th century were left unmanaged and have grown up into densely-stocked high forest. Conifer plantations are managed as high forest. Selection of species, brashing or pruning, removal of underwood species and other management may take place.
