The study was carried out at 6 plots in the city of Kharkiv, Ukraine. Following the field surveys, the place of the White Mistletoe in biotic communities of artificial tree stands was highlighted, in particular, the host tree species with which the mistletoe is closely associated. Interactions between the White Mistletoe and its tree host were studied at the level of a whole tree, as well as its different parts, e.g. trunk, branches, leaves. It was found that the mistletoe infestation can deteriorate the tree health state down one degree (applying the A. D. Maslov’s scale for assessing tree health). From studying interactions of the White Mistletoe with the model host tree species, the Silver Maple, I’ve found that the mistletoe infestation caused almost twofold increase in radial wood increment comparing to the control (non-infested trees of the same age in the same growing conditions of an urban park). In another model host tree species, the Cottonwood, I’ve found that both diameters and strength of infested branches behind the mistletoe’s fixation point decrease remarkably (by 9 % and 28 % in average respectively) with the mistletoe shrub’s growth comparing to non-infested branches at the same trees. Moreover, the mistletoe causes decrease in leaf biomass growth (by 24 % in average) at this host tree species.
I’ve found that the White Mistletoe is gradually colonizing new neighbourhoods in the studied urban area north-eastward, in general.
The data on the number and age structure of the mistletoe populations obtained from survey plots served as an input to the model of the White Mistletoe’s population dynamics. This scenario-based model enables both hind casting and forecasting of the species dynamics that, in turn, can be used as a tool for defining urgent actions to manage mistletoe’s populations in urban areas in a sustainable way.
Interactions between the White Mistletoe and its primary dispersal vector – birds – were investigated following a case of the Bohemian Waxwing that is a major disperser of mistletoe’s seeds in the studied area. Following analysis of almost
30-year long time series of Waxwing’s winter invasions to the north-east Ukraine I’ve concluded that ornithochory cannot be viewed as a single vector of mistletoe’s dispersal but anemo-hydrochory should be considered as an additional powerful driver of the mistletoe patch dynamics.
For an integrated study of ecological factors favouring the mistletoe’s expansion in urban areas, its functional relations with tree stands were scaled down to three levels: a single tree, a woody patch, and a landscape. From the correlation and the Principal Components (PC) analyses I got known that mistletoe infestation risk to a single tree from the susceptible species set is increasing at increase of a crown diameter in both cross-perpendicular directions. Negative impact of the White Mistletoe on a single tree is also manifested by increased peripheral crown’s dieback and defoliation, as well as general deterioration of the tree health status.
The density of the White Mistletoe on the surveyed plots is positively correlated with the tree species richness. However, at the woody patch level, no correlation was found between the mistletoe’s density and tree species diversity (measured with the Shannon’s and Berger-Parker’s diversity indexes). Negative correlation was found between the White Mistletoe’s density and the finite growth rate of its populations that is an illustration of the Ch. Allee’s principle.
At the landscape level, multiple correlation and PC analyses revealed factors that positively influenced the mistletoe’s expansion. These included urban road and street density, building density, mean distance between trees in a stand, and prevailing tree age. Thus, the White Mistletoe can be regarded as valuable indicator of an overall anthropogenic transformation of landscapes.
The study resulted in methodological backgrounds for local ecological monitoring of urban forest in cities and municipalities of Ukraine, as a measure to provide for achieving the urban sustainable development goals.
