Epsilon Archive for Student Projects

Abstract

European ash (Fraxinus excelsior) is a noble broadleaf of significant cultural and biological importance in Europe. In past years, its population has been in rapid decline due to an invasive fungal disease known as ash dieback, caused by the pathogen Hymenoscyphus fraxineus which causes necrosis and eventual death of the tree. The stability and existence of ash in the landscape of Europe are in danger. In this study, we inventoried 27 sites from an existing database of 1300 trees that show signs of resistance. The selection was based on the presence of at least one tree showing signs of resistance to the disease and their distribution in Sweden. Around each selected tree, we established eight circular sample plots of 2,78 m with centres located 8 and 20 meters away in the North, South, East and West directions. In each plot, we counted the number of naturally regenerated seedlings, higher than 25 cm, and categorized them into three size strata, six health classes (from No symptoms of disease to dead) and three stem forms. Later data about the site properties was extracted from online databases. The purpose of the study is to analyze the status of the understory seedlings and saplings of phenotypically tolerant ash trees, considering their potential for tolerance, as well as to grasp a better understanding of the joint effects of the disease and other environmental and site factors on ash natural regeneration. It was found that the natural regeneration surrounding ash trees selected for tolerance differed in health between sites. Correlation was found between ash dieback symptoms and stem form of the regeneration.The disease severity of the three size strata differed from each other, with trees higher than 4m exhibiting significantly worse health. In this study we have found that while the there is large potential in the natural regeneration, environmental and site factors may in complex ways affect the success and health of natural regeneration under the pressure of ash dieback.