| A study on mistletoe on urban trees was conducted at the Austrian Research Centre for Forests. For this purpose, the tree registers of the cities of Vienna and Graz were evaluated. The aim of this study was to determine which mistletoe species occur, to determine the intensity of infection and to identify host species that are more susceptible to mistletoe parasitism. At the same time, the dependence of mistletoe occurrence on various factors was investigated. Data from the Austrian Forest Inventory served for assessing the potential of mistletoes to spread into surrounding forests.
It could be shown that the presence of mistletoe in the cities is closely related to the type of host tree, the location, the density of the trees, the age of the trees as well as tree height. In Vienna, new host trees not known in the literature were described for the first time. Host trees often showed marked adaptation of native tree species to mistletoe (i.e., less infections) and significant infestation in introduced trees. In some species, certain cultivars may be resistant or less susceptible to mistletoe. In terms of damage or disease to trees with mistletoe, bark damage occurred most frequently.
In the forests in the surroundings of Vienna, mainly pine mistletoe is present on auf Pinus sylvestris and P. nigra, as well as oak mistletoe. Mistletoes on hardwood also play a role, e.g. on poplars. Possibly, city trees can act as a source of “infections” for the surroundings, if compatible tree species and conditions (e.g. forest edges) are present. In this respect, rather pure beech forests, like in the Viennese Woods around Vienna, can act as a certain “barrier”.
The apparent spreading of mistletoes cannot be traced to a single factor; several factors are important and interacting. Determining the distribution of mistletoe and the underlying factors is of great importance for green space management in cities, especially in relation to climate change. A list of less susceptible or resistant tree species, hybrids and varieties is presented. Fruiting shrubs offering berries to birds in winter may “distract” them from spreading mistletoe seeds. Careful management of city trees is also a factor in minimizing future forest damage. |