Survey of Hymenoscyphus fraxineus in a central European urban area and exploration of its possible environmental drivers

摘要

There are relatively few studies surveying how meteorological and qualitative characteristics of tree sites in urban areas influence Hymenoscyphus fraxineus (T. Kowalski) Baral et al. ( Chalara fraxinea T. Kowalski, = Hymenoscyphus pseudoalbidus Queloz et al.) or infection by that. Based on the significance of ash trees in urban areas and the frequent use of ash species and their varieties, it becomes increasingly important to identify factors that drive the pathogen. The aim of this study was to identify the effects of both meteorological parameters and tree characteristics on the severity of the disease in the city of Leipzig, Germany. We assessed 401 ash trees along streets and in green spaces distributed across Leipzig. The assessment included scoring the level of damage by H. fraxineus, visually estimating the degree of soil sealing under a tree's crown, measuring tree height, the height of crown base and the diameter at breast height, determining sex, year of planting and species variety, as well as recording qualitative characteristics (e.g. secondary pathogens, feeding marks). Mean relative air humidity, mean annual temperature and a combined index of meteorological conditions were used as meteorological parameters. In addition, we sampled tissue of 45 ash trees for the purpose of genetically verifying the occurrence of H. fraxineus. We analysed the effects of all variables on ash dieback by using linear mixed effect models. Results show an extensive damage by H. fraxineus in the whole city area with 70% of trees being infected. Mean relative air humidity and the index of meteorological conditions show a significant positive influence on the severity of ash dieback, whereas year of planting has a negative effect. Trees with feeding marks at the trunk tend to be more damaged by the fungus. Moreover, we found a significant difference in susceptibility between F. excelsior and its variety 'Atlas'. Both meteorological conditions and the susceptibility of species and their varieties should be taken into account when planting ash trees in urban areas.