In Europe only some small isolated patches of forests with a high degree of naturalness still exist. These are forests, whose structure, composition and function has been shaped by natural dynamics without substantial anthropogenic influence over the long period. In this respect, Białowieża Forest is a unique location in Europe, with continuous forest cover for close to 12,000 years. The palynological, archaeological and historical data document only a weak anthropogenic fingerprint compared to other European lowland forests in Holocene history. Due to long-lasting protection, a large portion of the forest is still composed of stands originating from the pre-silvicultural period. Moreover, the stands of Białowieża Forest converted by silvicultural activities during the 20th century have the potential to recover owing to patches of stands with high naturalness, scattered throughout the forest. As conflict over management of the forest has recurred regularly for close to century, there is a need to summarize our knowledge on the forest history and natural assets, to help making scientifically informed decisions over its future. Expansion of a non-intervention approach to the Polish part of the forest is suggested to increase the stability of the entire ecosystem and enhance the chances for its successful adaptation to changing environmental conditions. This will increase the importance of Białowieża Forest as an open-door laboratory for biology, ecology, and forestry.

Many studies show the significant impact of direct and indirect human activity on the functioning of terrestrial ecosystems, including forests. The increase in the number of invasive species, changes caused by climate change, or eutrophication of habitats resulting from air pollution can irrevocably affect biodiversity, species composition, or species interactions. Many of these effects cannot be seen in commercial forests due to the significant impact of direct human use of the forest and the high degree of transformation of forest ecosystems. In this work, we ask: how have forest communities changed over the past 70 years? What was the reason for these changes? To answer the above questions, we conducted research on repeated observations in the core area of the Białowieża National Park, which is characterized by one of the highest degrees of naturalness in Europe, where ecological processes have occurred without direct human intervention since the last glaciation. Studies have shown directional changes in species composition and biotic homogenization of three forest communities. Directional changes were found to be associated with both eutrophication of habitats as well as with changes in humidity and temperature. However, the observed changes in species composition were opposite to the hypotheses based on the observed global change. In contrast, changes in the species composition of the stand and the ability to shade and buffer the temperature and humidity under the canopy caused changes in the species composition of forest communities. In the mixed deciduous forest, homogenization occurred along with the simultaneous change of species composition of forest communities. This was caused by an increase in fertility caused by increased nitrogen deposition and changes in environmental conditions prevailing under the canopy of trees, which, however, were caused by changes in the species composition of the stand.

The distribution of large ungulates in space is in large extent driven by the availability of forage, which in temperate forests depends on light availability, and associated plant diversity and cover. We hypothesized that the increased number of GPS fixes of European bison (Bison bonasus L.) in usually avoided spruce forests was an effect of higher plant species richness and cover of the forest floor, which developed owing to increased light availability enhanced by spruce mortality. We carried out 80 forest floor plant surveys combined with tree measurement on plots chosen according to the number of GPS locations of GPS‐collared European bison. The mean plant species richness per plot was higher on intensively visited plots (IV) than rarely visited (RV) plots (30 ± 5.75 (SD) versus. 26 ± 6.19 (SD)). The frequency of 34 plant species was higher on IV plots, and they were mainly herbaceous species (32 species), while a significant part of 13 species with higher frequency on RV plots was woody plants (5 species). The species richness of forbs was higher on IV plots, while other functional groups of plants did not differ. Tree stem density on the IV plots was lower than on the RV plots (17.94 ± 6.73 (SD) versus 22.9 ± 7.67 (SD)), and the mean value of Ellenberg's ecological indicator for light availability for all forest floor plant species was higher on IV plots. European bison visiting mature spruce forests was driven by higher forest floor plant cover and species richness, and high share and species richness of forbs. The two latter features may be translated into higher quality and diversity of forage. In spite of morphological characteristics suggesting that European bison is a species of mixed (mosaic) habitats, it seems to be well adapted to thrive in diverse forests.

Large trees are keystone structures for the functioning and maintenance of the biological diversity of wooded landscapes. Thus, we need a better understanding of large-tree–other-tree interactions and their effects on the diversity and spatial structure of the surrounding trees. We studied these interactions in the core of the Białowieża Primeval Forest—Europe’s best-preserved temperate forest ecosystem, characterized by high abundance of ancient trees. We measured diameter and bark thickness of the monumental trees of Acer platanoides L., Carpinus betulus L., Picea abies L. H. Karst, Quercus robur L., and Tilia cordata Mill., as well as the diameter and distance to the monumental tree of five nearest neighbor trees. The effects of the monumental tree on arrangements of the surrounding trees were studied with the help of linear models. We revealed that the species identity of a large tree had, in the case of C. betulus and T. cordata, a significant impact on the diversity of adjacent tree groupings, their distance to the central tree, and frequency of the neighboring trees. The distance between the neighbor and the large trees increased with the increasing diameter of the central tree. Our findings reinforce the call for the protection of large old trees, regardless of their species and where they grow from the geographical or ecosystem point of view.