There are few if any plants that only inhabit such sites, they point out in the journal Forest Ecology & Management. Instead, using the "highly fragmented" woodlands of north-west Germany as a model, they developed what they called "an ecologically grounded list" of 67 plants that they claim are "widely applicable" in indicating continuous woodland cover.
These can be used to identify ancient woodlands in areas where historical maps are lacking or in small sites such as hedgerows, can identify biodiversity hotspots, so strengthen the case for careful management and against changes in woodland use, and can over time spread into adjacent recent woodlands, say the researchers.
Lists of ancient woodland indicator plants already exist for UK regions, they acknowledge, but argue that "for the application of ancient woodland indicator lists - such as by nature conservation authorities or woodland surveyors - it is more convenient to cover larger areas at the supra-regional greater landscape level to achieve enhanced validity and comparability".
Moreover, their indicator species list was compiled "using consistent and repeatable statistical methods" including a requirement that 75 per cent occurrences of a candidate species should be included in documented ancient woodland.