Ancient Woodland - Characteristics

Characteristics

The definition of ancient woodland includes several sub-types. Ancient semi-natural woodland (ASNW) is composed of native tree species that have not obviously been planted; features of ancient woodland often survive in many of these woods as well, including characteristic wildlife and structures of archaeological interest.

Species which are particularly characteristic of ancient woodland sites are called ancient woodland indicator (AWI) species, representing a type of ecological indicator. The term tends to be applied more usefully to desiccation-sensitive plant species, and particularly lichens and bryophytes, than to animals, as they are slower to colonise planted woodlands, and are thus viewed as more reliable indicators of ancient woodland sites. Sequences of pollen analysis are also indicators of forest continuity.

Lists of ancient woodland indicator species among vascular plants were developed by the Nature Conservancy Council (now Natural England) for each region of England, each list containing the hundred most reliable indicators for that region. The methodology involved studying the flora of known woodland sites and analysing patterns of occurrence to determine which species were most indicative of sites from before 1600. Although ancient woodland indicator species can and do occur in post-1600 woodlands, and also in non-woodland sites such as hedgerows, it is uncommon for a site which is not ancient woodland to host a double-figure AWI species total.