Relative contribution of ancient woodland indicator and non‐indicator species to herb layer distinctiveness in ancient semi‐natural, ancient replanted, and recent woodland

Abstract

AbstractQuestionsThe floristic distinctiveness of ancient woodland relative to recent woodland is commonly measured by Ancient Woodland Indicator (AWI) species richness. However, focussing on a pre‐defined subset of species means that wider community‐level differences may be overlooked. Can ancient semi‐natural, ancient replanted, and recent woodland herb layer communities be distinguished by alpha, beta, and gamma diversity? How are any differences partitioned across AWI and non‐AWI species communities?LocationCotswolds, southwest UK.MethodsTo quantify AWI and non‐AWI responses to stand history in ancient semi‐natural, ancient replanted, and recent woodland, we conducted floristic surveys of 45 sites. Using a modelling approach, we tested the relative and additive contribution of alpha‐scale AWI and non‐AWI species richness to woodland distinctiveness. Ordination was applied to analyse beta species composition distinctiveness, and multilevel pattern analysis was used to examine which species were significant contributors to gamma‐scale richness differences.ResultsAWI species richness models significantly distinguished ancient semi‐natural woodland from both ancient replanted and recent woodland at the alpha scale. For the classification of ancient semi‐natural woodland and recent woodland, the hierarchical inclusion of non‐AWI alpha richness resulted in a superior and more significant model. AWI gamma richness was numerically similar for all three woodland categories, whereas non‐AWI was more varied. AWI and non‐AWI species composition showed significant beta diversity differences among all woodland types, with six species being significant drivers of differences.ConclusionsOur results have revealed previously undetected complexity in the contributions of AWI and non‐AWI species to floristic distinctiveness of ancient woodland. In addition to traditional AWI species, the non‐AWI assemblage also exhibited a sensitivity to habitat continuity that: (a) adds weight to the argument that ancient woodland is floristically distinct from recent woodland; and (b) provides a useful measure of success for ancient replanted woodland restoration.