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Mistletoes have a global distribution and are the largest group of parasitic plants living within the canopies of woody plants. In European forests, Viscum album L. ssp. album (common mistletoe) is a common sight and, despite being considered a pest, can play beneficial roles in the ecosystem. However, mistletoe infections are becoming more severe and widespread throughout Europe, including recent reports of large‐scale host tree mortality events. These mortality events are hypothesized to be a result of increased water stresses from severe mistletoe infections in tandem with drought. In this study, we estimate an additional water loss from mistletoe‐infected forests that has not yet been described: interception, or the storage and evaporation of rainfall. Results from rainfall simulations on mistletoes sampled from Gostynin Forest District (central Poland) indicate mistletoes can store 0.16–1.32 mm of rainwater. Inputting this additional water storage capacity from mistletoes into a rainfall interception model suggests that, depending on the severity of the infection, mistletoes could reduce annual rainwater supply beneath the canopy by 2–11%. In forests experiencing water stress from mistletoe infection and climate change, the rainfall interception by mistletoes represents an additional water loss of a magnitude worthy of future investigation. [ABSTRACT FROM AUTHOR]

The canopy water storage capacity and wettability of the plant material are significantly dependent on the condition of the leaf surface. The aim of the present research was an analysis of the influence of infection with oak powdery mildew, seasonal changes occurring on leaves and factors related to location on the surface of leaves and their hydrological properties. This study performed a series of experiments connecting the direct spraying of tree branches with simulated rainfall under laboratory conditions; an analysis of the content of aromatic hydrocarbons in leaves with the use of the chromatograph; and measurements of the angles of adherence of raindrops to the leaf surface. Degree of wettability was determined and, additionally, photographs were taken with a scanning electron microscope. The experiments were performed on common oak (Quercus robur L.) both in the city and in the forest, on two dates: in May and September. All series of measurements were done on healthy leaves and on leaves covered with oak powdery mildew (Microsphaera alphitoides Griff. et Maubl.) to various degrees. Oak powdery mildew has the largest influence on the canopy water storage capacity and on hydrophobicity. In September, the leaves retained an average of 7.2 g/g more water than in May; and, in the leaves from the city, the canopy water storage capacity was 3.1 g/g higher. A decreasing angle of inclination of raindrops to leaves testified to growing wettability and increased the amount of water retained in tree crowns. An additional analysis of SEM photographs points to a dependency of the canopy water storage capacity on the condition of the surface of leaves. [ABSTRACT FROM AUTHOR]