Epsilon Archive for Student Projects

Abstract

Fraxinus excelsior has great ecological, cultural and a somewhat economical importance in Sweden despite its
low abundance. The future of common ash is however seriously threatened by the ascomycete fungus Hymenoscyphus
fraxineus rapidly spreading across Europe and currently affecting ash throughout Sweden. To evaluate this affect inventories of ash stands were conducted during the summer of 2014 in the counties of Jönköping and Östergötland. Plot inventory (which incorporated all species in plots) was performed in stands of forest setting while in a second inventory that included avenues, pasture land and one seed stand, all ash were inventoried.
The inventories contained assessments of health (i.e. visible crown damage), height and crown class and measurements of diameter at breast height. The results showed that the majority of ash in this area were highly susceptible to ash dieback and will probably die within a few years time; the seriously affected ash with more than
65 % visible crown dieback was 82 % in the plot inventory (60 % dead/almost dead) and 64 % in the avenues, pasture land and seed stand (23 % dead/almost dead). The results also showed that a small proportion of ash were seemingly more resistant ash (crown dieback less than 35 %); only 2 % (2.6 % if healthier ash found outside plots were included) in the entire plot inventory and 12 % in the avenues, pasture land and seed stand. The small and scattered distribution of these more resistant ash trees strongly points to a future probable risk of genetic diversity loss due to genetic drift and inbreeding. Relationships among different size classes and higher or lower susceptibility were explored in the data from the plot inventory (random sample) but no clear trends were found. A significantly higher proportion of healthier Ulmus glabra trees were found compared to common ash in the surveyed sites. This is inconsistent with the fact that elm is ranked as being more threatened to Dutch elm disease compared to ash to ash decline on the Red list of endangered species. The results from the sites herein were instead indicating a vast deterioration of the ash population and that, if these results are representative for the situation in Sweden, the current ranking of ash on the Red list should be revised. An additional aim of this survey was to locate more resistant ash trees that could be used as potential candidates for breeding. Of the 69 relatively resistant ash trees found in this survey 25 have been selected for scion collection and will, with others, be tested further. The summarized results from these inventories strongly points to the necessity of a breeding program to secure the future of ash and preserve enough genotypic variation for this tree species to cope with this aggressive invasive pathogen, as well as future challenges.