The Situation and Perspectives of European Ash (Fraxinus excelsior) in Ukraine: Focus on Eastern Border

The health condition of European ash (Fraxinus excelsior) stands in Ukraine has become worse since 2006. An alien invasive pathogenic fungus Hymenoscyphus fraxineus was firstly identified in 2011 in the eastern part of the country and subsequently, its presence had been confirmed in the western and central parts. The aims of our research were to evaluate the forest health of ash trees and identify the main causes of ash decline in different regions of Ukraine with emphasis on ash dieback and its association with collar rots. Results showed that since 2013 the number of trees with ash dieback symptoms has been gradually increasing, reaching up to 92 % in 2018. Total mortality due to ash dieback was up to 9 % in 2018. Disease intensity remains high in the north and central Ukraine comparing with the east. Branch dieback, collar rots, epicormic shoots and bacterial disease of ash were more often in the eastern region, some symptoms were observed simultaneously. Ash bark beetle galleries, as well as foliage browsing insects, were found mostly in weakened and/or dying trees. It was indicated that collar rots significantly increase the mortality of ash trees. Armillaria spp. fungi were found to be frequently associated with ash dieback on living stems and fallen trees in 2017, causing high rates of mortality in the northern and central regions. For further ash conservation and breeding programs, resistant trees in severely damaged regions should be selected to preserve genetic diversity in ash populations.