Ancient woodland indicators
Ancient woodland indicators (AWIs) are species that are usually more common in ancient woodland than in more recent sites. They are most commonly vascular plants, although they have been identified in other plant and animal groups (e.g. lichens, invertebrates). The presence of such species in a woodland may sometimes be used as supportive evidence that the site is ancient. However, no plant species should be used as the only indicator of ancient woodland, and the degree of association of a species with ancient woodland may vary across the country. A number of lists of AWIs have been produced by various authors, typically separated into geographical areas.
Many AWIs thrive in conditions provided in the late seral stages of forest development and rely upon the stability provided by long term woodland continuity. The characteristics of AWI plants include poor dispersal ability, short-lived seed banks, poor ability to compete with more generalist species in sunlight, an adaptation to deep shade and low nutrients, and reliance upon vegetative propagation via rhizomes, stolons or suckers.
As a result, AWIs are often reluctant to colonise secondary woodland even when the secondary wood is on an ancient woodland site, and they have also been shown to have difficulty persisting in fragmented habitats. Consequently, some rarer AWIs such as orchids are in steep decline and may only survive as small relic populations on ancient woodland sites.
Examples of AWI plants include:
- Wood anemone
- Yellow archangel
- Wild strawberry
- Herb paris
- Wood spurge
- Wood forget me not
Many AWIs are ‘saproxylic’ (species that depend upon dead or dying wood for some stage of their life cycle) and include: invertebrates such as Black hairstreak butterfly; hole-nesting birds such as woodpeckers, pied flycatchers and redstarts; and lower plants such as epiphytic lichens.