The fungal pathogen Chalara fraxinea is killing ash trees (Fraxinus excelsior) throughout Europe. Also potentially under threat is the large diversity of lichens that these ash trees support.
Using data from the UK National Biodiversity Network (www.nbn.org.uk), we obtained British Lichen Society data housed in the NBN Gateway, demonstrating that 536 lichen species (corresponding to some 30% of UK lichens) occur on ash. Of these, 84 are categorized as under threat in Britain using International Union for Conservation of Nature standards.
For at least six of these threatened species, more than half of the records in the database are for specimens found on ash trees. This includes Fuscopannaria ignobilis, a lichen that receives the highest UK legislative protection status under Schedule 8 of the 1981 Wildlife and Countryside Act, and Wadeana dendrographa, for which the United Kingdom has international conservation responsibility.
Ash, along with non-native tree species such as sycamore (Acer pseudoplatanus), provided an alternative host for lichens affected by the catastrophic decline of elm trees during the 1970s. If the UK ash population succumbs to dieback, the rescue effect for lichens is a consideration that should influence landscape management of non-native trees.
Article reproduced by kind permission of Christopher J. Ellis, Brian J. Coppins, Peter M. Hollingsworth Royal Botanic Garden Edinburgh, UK. Article originally appeared in Nature.
Image copyright British Lichen Society – Boundary Ash Dorset with Wadeana dendrographa