Ash trees: a world for lichen
Ash represents the whole world for many lichens and the invertebrate fauna which depends upon them
The bark of European Ash provides a uniquely hospitable sylvan niche for lichen in the UK context. The light dappled shade cast by the airy canopy of Ash alongside the relatively high pH (alkalinity) of its bark, which crucially buffers the atmospheric acidity of air pollution in urban areas, underpin its especial value for our native lichen flora. Indeed, the British Lichen Society cites 536 lichen species as associated with ash, comprising a remarkable 27.5% of the entire British lichen flora. Of this number, 220 are scheduled as Nationally Rare or Nationally Scarce.
Lichens do not in fact parasitize their tree hosts, but rather produce their own food by photosynthesis facilitated through a symbiotic and composite relationship between a fungi and algae or cyanobacteria. Many fascinating invertebrates, utilise lichens for shelter and food, with the caterpillar stage of a number of moth species dependent upon them for their survival. The beautiful Scarce Footman (Eilema complana), which has its UK stronghold in south east England, is just one of these lichen eating moth species. The adult Scarce Footman is recognisable through its metallic silver grey wings, bordered a lovely primrose yellow.
The images below underlines vividly the richness of lichen flora associated with Ash, even within the most urban of situations, with five species present on a small section of bark on a Kent street tree growing by the road in central Maidstone.
Present are: Common Orange Lichen (Xanthoria parietina), Rim Lichen (Lecanora chlarotera), Black Stone Flower (Parmotrema perlatum), Oakmoss (Evernia prunastri), Hoary Rosette Lichen (Physcia aipolia).
Text and Images supplied by Tony Harwood, Principal Resilience Officer for Kent County Council