plants Article Ecological and Landscape Factors Affecting the Spread of European Mistletoe (Viscum album L.) in Urban Areas (A Case Study of the Kaliningrad City, Russia) Liubov Skrypnik 1,* , Pavel Maslennikov 1 , Pavel Feduraev 1 , Artem Pungin 1 and Nikolay Belov 2 1 Institute of Living Systems, Immanuel Kant Baltic Federal University, Universitetskaya str., 2, Kaliningrad 236040, Russia;
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[email protected]; Tel.: +74012533707 Received: 1 March 2020; Accepted: 19 March 2020; Published: 23 March 2020 Abstract: Green spaces are very important for an urban environment. Trees in cities develop under more stressful conditions and are, therefore, more susceptible to parasite including mistletoe infestation. The aim of this study was to investigate the ecological, microclimatic, and landscape factors causing the spread of European mistletoe (Viscum album L.) in urban conditions. The most numerous hosts of mistletoe were Tilia cordata (24.4%), Acer platanoides (22.7%), and Populus nigra (16.7%). On average, there were more than 10 mistletoe bushes per tree. The mass mistletoe infestations (more than 50 bushes per the tree) were detected for Populus berolinensis, Populus nigra, × and Acer saccharinum. The largest number of infected trees was detected in the green zone (city parks), historical housing estates, and green zone along water bodies. Based on the results of principal component analysis (PCA), the main factors causing the spread of mistletoe on the urban territories are trees’ age and relative air humidity.