The Bialowieza Primeval Forest (BF) is one of the well-known forests in Central Europe. The most common tree species in BF was Norway spruce (Picea abies (L.) H. Karst), comprising 26%. However, a mass dieback of spruce has occurred during recent years. The spruce dieback in Bialowieza Forest is directly caused by the spruce bark beetle. However, the mass appearance of this pest can be a consequence of global warming and drought. Changes in air temperature were presented and drought indices were calculated as follows: standardized precipitation index, Palmer drought severity index, climatic water balance and soil water storage deficit. The warming of the climate of Bialowieza from 1950 to 2015 is comparable to that observed throughout central Europe. The temperature increased by 1.27 °C. The occurrence of drought from 1950 to 1966 and from 1985 to 2015 had a similar frequency. From 1963 to 1966, the volume of removed deadwood from the managed part of Bialowieza Forest was 27 thousand m³ but from 2012 to 2016, the volume was more than one million m³.

Drought in the forest is not only a prolonged state of water shortage, but also an occasion where interactions between plants and fungi are affected. Water efficiency accelerates a range of pathologies in interactions between organisms, influencing the ecosystems and their interacting biological components. This study focuses on the role of mycorrhizal and endophyte fungi in alleviating the effects of soil water shortage, and on the impact of their altered activity during drought on the health of trees. The issues presented here show the fundamental role of the mycorrhizal mycelium and the mechanism of water transport to the plant in the course of other phenomena (withering, pathogenesis, endophytes biology) that occur in trees under influence of drought, with particular attention on managed coniferous stands. Conclusions resulting from published information on this topic emphasize the negative impact of soil moisture deficiency on the ectomycorrhizal fungi functioning and, in contrast, on the promotion of the growth of some endophytes, pathogens and hemi-parasitic mistletoes (Viscumspp.).

One effect of global warming is the increasing risk of drought. The shortage of water in the soil has a direct impact on crop plants. It can therefore be expected that drought stress will negatively affect forests. The aim of this study was to determine the length of the drought in the forests of Poland in 2015. Calculations were carried out using data from 21 meteorological stations for the conditions prevailing in the reference stand, which was determined to be a middle-aged pine stand growing on poor sandy soils classified as Dystric Arenosol. Drought was treated as the state when the soil water available to plants is depleted up to a depth of one meter. Daily changes in soil water storage were measured on the basis of the balance of water inflow-outflow. Climatic water balance was also determined. The calculations of the soil water storage deficit for the conditions of the reference forest ecosystem showed that in 2015 drought soil occurred in almost all of the forests of Poland. Wielkopolska was affected by the earliest-starting and longest-lasting drought. To a lesser extent, however, it extended throughout all of central Poland, from the west to the eastern border of the country. This is where one could expect to see the negative effects of the lack of water available to trees, which can be manifested as a smaller increase in growth, a decrease in health status, and – in particularly unfavorable conditions – dying trees. The climatic water balance showed that the annual water deficit in Wielkopolska exceeded 100 mm.