Native Woodland Survey of Scotland has surveyed all native woods and near-native woods currently present on ancient woodland sites, as well as all other planted woods on ancient woodland sites (PAWS).
Ancient woodlands usually have a high value for natural and cultural heritage because of their long history of continuous woodland cover. Ancient and semi-natural woods (i.e. those where the current stands appear to be naturally regenerated rather than planted) are the woodland category that generally has the highest biodiversity value.
Ancient and semi-natural woodlands (ASNW)
NWSS provides current information on Ancient and semi-natural woodlands (ASNW) and so updates the information in the Ancient Woodland Inventory (Scotland). ASNW are often described as the most important single category of woods for nature conservation or biodiversity.
The NWSS data on semi-naturalness relates to current stand structure and composition. A wood scores highly for ‘semi-naturalness’ if it has a diverse structure and composition and an absence of indicators of planting such as cultivation, straight lines of trees or geometric shaped stand boundaries.
Woods like these are likely to have a higher biodiversity value than more uniform planted woods.
A high semi-naturalness value in NWSS also suggests that a wood has been largely or entirely naturally regenerated, but this cannot be said with certainty without documentary evidence. It is possible to create an irregular structure in a planted wood by management such as irregular thinnings, or by chance events (e.g. windthrow) and prolonged low intensity management.