Questioning the reliability of “ancient” woodland indicators: Resilience to interruptions and persistence following deforestation

Indicator species can provide invaluable insights into environmental conditions but robust empirical testing of their effectiveness is essential. Ancient woodland indicators (AWIs) are plant species considered indicative of sites that have been continuously wooded for a long period by virtue of poor dispersal ability and intolerance of non-woodland habitats. Many countries now utilise AWI species lists to classify ancient woodlands. Here we use a metastudy approach to test resilience of AWIs to interruptions and persistence following deforestation − and thus the robustness of using AWI lists − using a novel approach. We compare current AWI assemblage with woodland history based on pollen evidence at nine sites across the UK with a robustly-dated and spatially-precise palynological profile. Sites were split into: (1) proven continuous woodland; (2) previously interrupted woodland; and (3) previously but not currently wooded. Vegetation history was >1000years at most sites. Assessment of ancientness using AWIs agreed with palynologically-proven ancient woodland at two sites, including a species-poor woodland of previously-uncertain age. However, four interrupted woodland sites and three clear-felled sites supported extensive AWI floristic communities. This suggests AWIs are resilient to interruptions, possibly by remaining in the seed bank longer than expected, and persistent following deforestation. Persistence might be due to other species (e.g. heathland plants) acting as pseudo-canopy or because some AWIs are more tolerant of non-woodland locations than previously thought. We conclude that use of floristic AWIs alone in defining ancient woodland should be reviewed, especially where status links to planning policy and conservation prioritisation. We suggest species on AWI lists be reviewed under expert and local guidance and a system of weighting species based on their strict or strong affinity solely with ancient woodland be developed. The use of multi-taxa indicators is recommended to allow stakeholders globally to make informed decisions about ancient woodland status.