Ash dieback
The first occurrence of this aggressive fungal disease in Sweden was confirmed in 2001, and since then the disease has spread throughout the entire Swedish distribution range of ash.
As recently as 2006, it was confirmed that ash dieback is caused by a newly described fungus, Chalara fraxinea. The fungus attacks leaves and young shoots, growing into the stem where it forms cankers. Infected trees eventually die. As far as is known, the fungal spores are windborne, which makes control and eradication difficult.
Ash dieback affects all known Fraxinus species of all ages, regardless of whether they are planted or naturally regenerated. In Lithuania, 60–80% of ash stands are now infected. We must assume that ash dieback in Sweden may become just as extensive as in Lithuania. A drastic decline in ash populations would lead to major losses in biodiversity, and valuable forests would be lost.
Significant ecological and cultural values associated with ash (Fraxinus excelsior) are also found in older, large trees in the agricultural landscape as well as in protected areas. Our survey was conducted in 2009 and 2010. More than 50% of ashes with a diameter greater than 10 cm at breast height showed substantial crown thinning. Approximately 30% of the ashes were severely damaged or dead. The extent of the damage differed only marginally between 2009 and 2010.