Ancient semi-natural woodland ASNW

Ancient semi-natural woodland (ASNW) is mentioned in the National Planning Policy Framework (NPPF) as an example of an ancient woodland but without definition. It is also listed within the Biodiversity Gain Requirements (Irreplaceable Habitat) Regulations 2024 under its schedule of irreplaceable habitats.

The Woodland Trust defines Ancient semi-natural woods (ASNW) as being "woods that have developed naturally. Most have been used by humans – often managed for timber and other industries over the centuries – but they have had woodland cover for over 400 years."

Essentially these are areas that have been continuously wooded for at least 400 years (since 1600 AD in the UK) composed of primarily native trees and shrubs, arising from natural regeneration or coppice rather than plantation. These, are often mentioned alongside plantations on ancient woodland sites (PAWS) as in the NPPF, and generally considered as being irreplaceable, high-biodiversity habitats.

The Wildlife and Countryside Link describe ASNWs thus "Ancient woodlands comprise native flora and fauna. The flora includes the native trees themselves, which have often regenerated through natural processes or woodland management techniques such as coppicing. Around half of Britain's ancient woods are ASNW."

The Policy paper; Keepers of time: ancient and native woodland and trees policy in England published by the UK government 27 May, 2022 describes ASNW's as "Ancient woodland of mostly native tree species, usually derived from coppice or natural regeneration. ASNW often include old-growth characteristics such as ancient and veteran trees and large diameter standing and fallen deadwood. They are dynamic ecosystems that can include many other habitat types such as species rich grassland, heathland, wetland and freshwater systems."

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