The impact of ash dieback on veteran trees in southwestern Sweden




Ash dieback (Hymenoscyphus fraxineus) is a fungal disease which affects ash throughout Sweden.  Monitoring to study of the impact of ash dieback on veteran trees was undertaken in southwest Sweden in 2009, 2011, 2013, 2015, and 2020. The study found that 94.5% of the ash trees observed were affected by ash dieback disease in 2020 compared with 62% in 2009.  70 of the studied ash trees have died (21%) since the monitoring began. In 2009 there was no relationship between girth and ash dieback, but in 2020 the correlation between girth and the impact of ash dieback was statistically significant. In 2020, also for the first time during monitoring, the ash trees in the shade were significantly more affected by ash dieback, compared with trees standing in the open. This difference was not detected in 2013 or 2015. The effect of ash dieback on pollarded trees has varied between the years studied, but in 2020 there is no longer any significant difference between the pollarded and the non-pollarded ash trees.  There was however a significant difference in the mortality rates between the groups of trees, with ash trees pollarded in more recent times having the highest mortality. Therefore, the recommendation in relation to veteran trees with ash dieback is that all pruning on veteran ash trees should be avoided. Pollarding should only be done on ash pollards that are in a regular cutting cycle and are not showing any symptoms of ash dieback.  If possible, clear around old ash trees if they are in shaded conditions. Given that there are relatively few studies on the impact of ash dieback on veteran ash trees, the results of this study should also be relevant outside of Sweden and for the management of ash trees in non-woodland situations. Key words: Ash dieback, pollards, veteran trees, Hymenoscyphus fraxineus, ash

Author Biographies

Vikki Bengtsson, Pro Natura, Sweden

Vikki Bengtsson is an ecologist and has worked professionally with nature conservation since 1992. Up until 2003, she worked in England and now works primarily in Sweden. Vikki has worked throughout her career with issues relating to practical management and restoration of ancient trees and wood pastures. She also trains arborists, landscape architects, site managers and planners in the care and management of ancient trees across Europe.

Anna Stenström, County Administrative Board of Västra Götaland, Sweden

Anna Stenström has a PhD in plant ecology. Anna works in the Nature Conservation Department at the County Administrative Board of Västra Götaland in western Sweden. Anna is responsible for implementation of the Action Plan for Veteran Trees in the County of Västra Götaland, which includes surveying, restoration and monitoring activities. She is a member of the Species Information Centre’s committee responsible for the Red Data Book for vascular plants.

C. Philip Wheater, Manchester Metropolitan University, UK

Phil Wheater is Professor Emeritus in Environmental and Geographical Sciences at Manchester Metropolitan University. He has been researching and teaching in the fields of countryside management, human impacts on the environment, and the conservation of both habitats and species for over 35 years. He also has a strong interest in ecological field techniques.

Karin Sandberg, County Administrative Board of Västmanland, Sweden

Karin Sandberg is an ecologist and has worked with nature conservation since 2004. Since 2006 she is working at the County administrative board in Västmanland county and since 2011 she has been the national coordinator for the Action plan for veteran trees. In addition to working with practical nature conservation, Karin produces information material and lectures on management of ancient trees.



How to Cite

Bengtsson, V., Stenström, A., Wheater, C. P. ., & Sandberg, K. (2021). The impact of ash dieback on veteran trees in southwestern Sweden. Baltic Forestry, 27(1).



Phytopathology and Mycology