Common ash, also known as European ash, is one of more than 45 species in the genus, with the greatest diversity in North America and Asia. It is a deciduous broadleaved tree with a widespread natural distribution from Ireland, in the west, to continental Russia (almost to the River Volga), in the east. It reaches to 64° N in Norway and to the northern parts of Italy, Spain and Greece in the Mediterranean, and as far south as 37° N in Iran. It will survive on a wide variety of soil types, but good growth is generally limited to fertile, alkaline, soils.
Ash features in a range of ways in European culture: the rhyme, Oak before Ash, in for a splash, ash before Oak, in for a soak, which notes the pattern of spring leaf flushing is also found in German and Norwegian. In Norse mythology, Yggdrasil was the hollow ash tree from which the first man, Ask ('Ash') emerged. Throughout its distribution its wood is widely used, its flexibility giving it particular value in tool handles and sports equipment. In Ireland there is high demand for ash trees to make 'hurleys' used in the Gaelic sport of hurling. Ash leaves have been used as fodder and the unripe ash keys (fruit) in cooking as alternatives to capers.
Ash is wind pollinated with the flowers opening before leaf flush in spring. With a range of flower types: male, female and hermaphrodite, some trees are entirely male, others female and others hermaphrodite, with mixtures of male and hermaphrodite or female and hermaphrodite flowers on the same tree. Some trees will even change sex from one year to the next, with hermaphrodite trees becoming more female or male.
Common ash has proven particularly susceptible to dieback caused by the fungus Hymenoscyphus fraxineus, with more than 60% of trees dying in parts of Europe, since its spread west from first observation in Poland in 1992. Its detection in Britain in 2012 resulted in a media frenzy and the start of intensive projects to sequence the ash genome and to find trees with resistance or low susceptibility to the fungus. On the horizon is another threat, the emerald ash borer which has been observed close to Moscow and already caused large scale damage to Fraxinus species in the USA. Key to the future of Fraxinus excelsior will be its high levels of genetic diversity.
Fraxigen 2005. Ash species in Europe: biological characteristics and practical guidelines for sustainable use. University of Oxford.