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.

We investigated the occurrence and pathogenicity of Beauveria spp. (Hypocreales: Cordycipitaceae) in forest soils in Poland, in outbreak areas of cockchafers (Coleoptera: Scarabaeidae): Melolontha melolontha L. and M. hippocastani F. We also examined the occurrence of Beauveria in relation to soil pH. Beauveria spp. isolates were characterised at species and genotype levels using ITS and microsatellite markers. Beauveria spp., which were detected at over 80% of sites, were sensitive to pH, preferring neutral or alkaline soils. This suggests that the acidity of forest soils in Poland can affect their efficacy as biological control agents (BCAs). B. brongniartii (Sacc.) Petch as a pathogen of cockchafers occurred at 41% of sites, but often at densities below the threshold values for infection, and it infected only 1.3% of cockchafer grubs. Our results suggest that B. brongniartii genotype isolated from cockchafers in forest soils can potentially expand the pool of BCAs in this environment.

Aims: The aim of the project was to determine the vertical variability of soil under the influence of deadwood (DWD) in a temperate forest ecosystem. Methods: The laboratory analyses included soil layers of 0–5 cm, 5–10 cm, 10–20 cm and 20–40 cm, which were taken directly under the deadwood, as well as the forest litter layer and deadwood fragments. The control samples were taken 30 m away. Results: The decomposition processes of deadwood are associated with a 55% increase in soil organic carbon (SOC) deposition to a depth of -40 cm and a 36% increase in total nitrogen (N) content compared to soils without deadwood. DWD significantly increases exchangeable cations, especially at a depth of -5 cm to -20 cm. Deadwood contains slightly more hydrogen (H⁺⁾ and aluminum ions (Al³⁺) than forest litter, but soil acidification is related to pedogenic processes rather than decomposition of deadwood in hyperacid forest soils. The soil surface under deadwood with a high degree of decomposition is characterised by a lower bulk density (BD) value than the soil where only forest litter was present. Conclusions: Our studies suggest that the physicochemical properties of forest soils change under the influence of deadwood such that the deeper layers beneath the logs take on propertie8s that make them similar to the shallower layers without deadwood. To summarise, leaving deadwood in the forest has a positive effect on soil fertility by enriching the soil with nutrients (Ca²⁺, K⁺, Na⁺, less Mg²⁺) and improving its physical properties.

The response of an ash-alder swamp forest to water damming was studied in the Łutownia stream running in Białowieża Forest. The Łutownia stream with artificial dam existing from 2001 for small water retention purposes was the test object. The first observation of vegetation was done in 2004, when small retention construction started to influence surrounding forest, but beavers had not built their dam yet. After one year of experiments (2005) the beaver dam was constructed close to man-made dam and its influence was most significant for further studies. So, the first observation refers to the status of ash-alder swamp forest before beaver damming. Water table level was measured from the beginning of 2004. The main goal of presented studies was to determine changes of terrestrial vegetation and its habitat after increasing of the water level in the stream. One square metre plots in a frame 5 x 5m were localized in a transect close to the stream upstream and downstream artificial dam. Within 104 such plots ground vegetation (growing up to 0.5 m above ground) was described using Braun-Blanquet scale of abundance. The vegetation studies were conducted twice in 2004 and repeated in 2007. The list of species and their abundance were determined twice: in spring and in summer. Changes of species richness and coverage by species characteristic for floodplain and swamp forest site were evaluated. Ecological indices of soil moisture and fertility determined as the means weighed by percent cover by plant species were calculated for two periods of observation. Calculated indicator values showed that water retention increased the number of swamp forest species by 8 times, but the area of swamp habitat increased 16 times compared with 2004. The mean number of species per sample plot was the same before and after water damming by beavers. The plant association (ash-alder riparian forest) changed its floristic composition to swampier variant. Obtained results showed real impact of beavers’ activity on ground vegetation and its habitat in ashalder swamp forest. Observed increased number of swamp species close to the beaver dam is positive from ecological point of view. Presented results indicate also, that species richness is strongly controlled by beaver damming. The population dynamics of beavers could also potentially affect species richness by altering the age distribution of beaver dams and abandoned ponds across the river valley landscape. Generally, this point of view could have adverse social effects because beavers’ activity brings losses to forestry and agriculture. Therefore, we should try to find a balance between economy and wildlife management. Monitoring of the beaver sites should be continued to evaluate ecological consequences and to find best solution of these problems.

Carpinus betulus (CB) is becoming increasingly important in the forests of Central Europe and is significantly increasing its proportion in various habitat types. We have analysed how the increase in CB affects soil properties. The study was conducted in the Białowieża Forest (BF). We monitored the changes in CB cover between 1962 and 2013 on 56 permanent plots and collected samples of the litter sub-horizons and the content of the underlying A horizons for laboratory analyses in 2014. During the study period, there was a significant increase in CB cover in the second tree layer by an average of 17.4 % (±1.8) and in the shrub layer by 3.8 % (±1.0), as well as an increase in species diversity from 41 % in the past to 59 % currently. The C/N ratio of the Oi sub-horizon was 32.0 (±0.9), and NH₄+ compounds predominated over NO₃-, with all nitrogen forms most closely associated with the C/N ratio. In the Oea sub-horizon, the C/N ratio was 23.4 (±0.4), and the sum of mineralised nitrogen reached 8%, with a clear predominance of NO₃-. The characteristic most strongly associated with the increase in CB coverage was the NO₃- content in the Oea sub-horizon. The MID analysis confirmed that the change in CB cover was not only significant, but also ecologically important. We suggest that there is a feedback loop in which the generally observed climate changes lead to trees occupying new habitats that supply the forest floor with high quality litter, which in turn affects the soil and promotes the persistence of changes in the species composition of the forest.

Raised bogs dominated by the vegetation association Ledo-Sphagnetum magellanici Sukopp 1959 em. Neuhäusl 1969 are a valuable and ecologically important plant community that occurs in Central Europe. They develop in impervious depressions with precipitation as the only water source, and are particularly sensitive to drainage, climate change, eutrophication and overgrowing by trees and shrubs. The high pressure of threat justifies taking protective measures. This research focused on the effects of the removal of birch from two bogs, which were dominated by two birch species (Betula pubescens, B. pendula) and also included stands of Scots pine (Pinus sylvestris); the bogs are located in northeastern Poland and showed signs of drying. The trees were removed in early spring 2008. To capture the response to tree cutting, vegetation monitoring was performed for 7 years. The results were compared to pre-cutting environmental conditions (precipitation, temperature, air transpiration). At the first site, which was drained at the beginning of the twentieth century, the ground water level initially decreased; then, from 2010 onwards, the level stabilised and exhibited a negative correlation with the average annual air temperature. While the second site exhibited no significant differences in the ground water table, a correlation with the average annual rainfall was found. At both sites, there was an increase in the coverage of species appropriate for raised bogs, Oxycocco-Sphagnatea Br.-Bl. et R. Tx. 1943, whereas only the second site had significant coverage of these species. These actions improved the habitat conditions and initiated the process of raised bog restoration at that site because Oxycocco-Sphagnatea species cover and frequency increased.