Ash tree (Fraxinus excelsior) growing in limestone pavement

Ash tree (Fraxinus excelsior) growing in limestone pavement. This tree is a local landmark near Malham, Yorkshire Dales, UK. The Ash is under threat from ash dieback. Hymenoscyphus fraxineus is an Ascomycete fungus that causes ash dieback, a chronic fungal disease of ash trees in Europe characterised by leaf loss and crown dieback in infected trees. The fungus was first scientifically described in 2006 under the name Chalara fraxinea. It is now widespread in Europe, with up to 85 per cent mortality rates recorded in plantations and 69 per cent in woodlands. It is closely related to a native fungus Hymenoscyphus albidus, which is harmless to European ash trees. The limestone pavement in which it grows is a deeply fissured formation called clints (the tabular blocks) and grikes (the deep fissures) so typical of glaciated karst landscapes., by MARTYN F. CHILLMAID/SCIENCE PHOTO LIBRARY