Ash trees are medium to large trees of the genus Fraxinus of the family Oleaceae (Olive-tree like). The family contains between 45 and 65 species. Some of them are evergreen, but most are deciduous. They grow in most parts of the world. The seeds are commonly known as keys in English. They are a type of fruit known as a samara. Most of the ash species have light-green, oval shaped, pinnate leaves. The central stem of the compound leaf has 9 – 13 leaflets (small leaves) in pairs, with one at the tip. There are no stalks to the side leaflets. The leaflets are pointed and toothed, with hairs on the lower surface. The leaves appear relatively late in spring, and are amongst the first to be shed in autumn.
The buds are black, sooty or velvety in appearance and are sometimes compared to a Bishop’s Mitre in shape.
The emerald ash borer (Agrilus planipennis) is a wood-boring beetle. It was accidentally introduced to North America from Asia by solid wood packing material in the late 1980s. It has killed tens of millions of trees in 15 states in the United States and adjacent Ontario in Canada. Research is being done with three Asian wasps which are natural predators of the beetle biological control.
The European ash, Fraxinus excelsior, has been affected by the fungus which causes "ash dieback". The disease has infected about 90% of Denmark's ash trees. In October 2012 ash dieback was found in mature woodland in Suffolk. In 2016, the ash tree was reported as in danger of extinction in Europe.
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- "The Problem". Don't move firewood. Retrieved 14 October 2011.
- Kowalski T. 2006. Chalara fraxinea sp. nov. associated with dieback of ash (Fraxinus excelsior) in Poland. Forest Pathology 36(4), 264-270
- E. Halmschlager & T. Kirisits (2008). "First report of the ash dieback pathogen Chalara fraxinea on Fraxinus excelsior in Austria". University of Natural Resources and Applied Life Sciences. Archived from the original on 29 September 2009. Retrieved 10 February 2010.
- N. Ogris, T. Hauptman & D. Jurc 2009. "Chalara fraxinea causing common ash dieback newly reported in Slovenia". Slovenian Forestry Institute. Archived from the original on 9 November 2009. Retrieved 10 February 2010.
- "'Ash dieback' fungus Chalara fraxinea in UK countryside". BBC. 25 October 2012. Retrieved 25 October 2012.
- BBC News 'Ash dieback' fungus, Chalara fraxinea found in UK countryside. Retrieved 25 October 2012.
- Marshall, Claire 2016. "Ash tree set for extinction in Europe". BBC.