Determining ancient woodland indicator plants for practical use: A new approach developed in northwest Germany

Ancient woodlands that have been in continuous existence for hundreds of years have a floristic composition which greatly differs from younger afforestations. The occurrence of certain associated vascular plant species, termed ancient woodland indicator plants, can be used to recognise the continuity of woodland cover. Ancient woodland habitats frequently contain a typical and rich forest biodiversity and can often be regarded as biodiversity hotspots. To pinpoint these habitats for nature conservation, there is a need to compile ancient woodland indicator lists with a widespread validity. In this study, we introduce a new methodical approach that enables the compilation of such lists from the readily available resources of plant species monitoring programs, archive records, and land cover data. Using northwest Germany as a model region, we have developed an ecologically grounded list of 67 ancient woodland indicator plants for this area. In this context, we consider the ancient woodland indicator plants as a subset of the larger group of ancient woodland plants. The widely applicable ancient woodland indicator plants list presented here may be a useful tool for future forest nature conservation. Potential applications include: (a) the identification of ancient woodlands in areas where historical maps are lacking, (b) the identification of biodiversity hotspots of ancient woodland indicator plants, and (c) locating ancient semi-natural woodlands. Finally, we highlight the importance of effective conservation management, which should seek to promote the typical plant diversity of ancient semi-natural woodlands. In doing so, conservation management should promote the preservation of remaining ancient deciduous woodlands and inhibit the conversion of ancient woodlands to coniferous or mixed forests. Additionally, conservation management should strengthen the connections between recent and ancient woodlands through habitat corridors. Furthermore, careful forest management of deciduous ancient woodland sites with high typical woodland plant diversity has to be ensured to avoid soil damage.