Ecological and Landscape Factors Affecting the Spread of European Mistletoe (Viscum album L.) in Urban Areas (A Case Study of the Kaliningrad City, Russia)

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. The factors reflecting environmental pollution (the content of heavy metals in the soil and the concentration of nitrogen dioxide in the air) did not statistically affect the mistletoe distribution in the study area. However, this result may be due to the heterogeneity of other parameters in the studied areas. Therefore, additional research is required to more accurately interpret the data on the relationship between environmental pollutions and distribution of mistletoe infestation of trees in urban areas.

The future of Viscum album L. in Europe will be shaped by temperature and host availability

“…An increase in the abundance of mistletoe is associated with planting of parks or parkways with suitable hosts and good light conditions for single or loosely planted trees; it may also be important to note that the urban area has many locations conducive to birds that may spread mistletoe 64 , 65 . Thus, the conditions for growth and spreading in urban conditions are very good, especially since mistletoe is very resistant to air pollution 66 , 67 . Viscum album subsp.…”

Changes in Antioxidative Compounds and Enzymes in Small-Leaved Linden (Tilia cordata Mill.) in Response to Mistletoe (Viscum album L.) Infestation

“…This tree species was selected as it is more susceptible to European mistletoe infestation ( Viscum album L. subsp. Album ) in Kaliningrad [ 8 ]. The trees under study were located on a test plot of approximately 250 m × 250 m, situated in the territory of Kaliningrad (54°44′56″ N, 20°30′55″ E).…”

“…Previous studies [ 8 ] showed that in the territory of Kaliningrad, the trees of the small-leaved linden ( Tilia cordata Mill.) are more susceptible to mistletoe infestation compared to other urban trees.…”

Drought in the forest breaks plant–fungi interactions

“…abietis on fir (Plagnat 1950;Zuber 2004;Szmidla et al 2019). This hemiparasite is indicated in Poland by crown thinning and death of Scots pine trees during drought, most often in older stands The intense occurrence of mistletoe also limits the activity of mycorrhizal roots by a shortening carbohydrates supply from dying tree crowns, worsening its water balance and accelerating drought symptoms (Barbu 2010;Szmidla et al 2019;Billigly et al 2018;Skrypnik et al 2020). Gehring and Whitham (1991) found a significant impact of Juniperus mistletoe (Phoradendron juniperinum Engelm.)…”