the ecologist Oliver Rackham in his 1980 book Ancient Woodland, its History, Vegetation and Uses in England, which he wrote following his earlier research on Hayley Wood in Cambridgeshire. The definition of ancient woodland includes two sub-types: Ancient semi-natural woodland (ASNW) and Planted ancient woodland site (PAWS). 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. Planted ancient woodland (PAWS) is an ancient woodland site where the native species have been partially or wholly replaced with a non locally native species (usually but not always conifers). These woodlands typically have a plantation structure, with even aged crops of one or two species planted for commercial purposes. Many of these ancient woodlands were converted to conifer plantations following war-time fellings. PAWS sites, whilst not being of such high ecological value as ASNW, typically contain remnants of semi-natural species where shading has been less intense, and restoration of more semi-natural structures through gradual thinning is often possible. Since the recognition of the ecological and historical values of ancient woodland, PAWS restoration has been a priority amongst many woodland owners and governmental and non-governmental agencies, and has been supported by various grant schemes. Some restored PAWS sites are now practically indistinguishable from ASNW. There is no formal method for reclassifying restored PAWS as ASNW, although some woodland managers now use the acronym RPAWS (Restored planted ancient woodland) for a restored site. Species which are particularly characteristic of ancient woodland sites are called ancient woodland indicator species, such as bluebells, ramsons, wood anemone, yellow archangel and primrose for example, 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 plants of known woodland sites and analysing patterns of occurrence to determine which species were most indicative of sites from before