Large old trees occupy the same space for centuries, modifying the local environment by forming litter and releasing chemicals, which affect many generations of young trees. As a result, the spatial arrangement of tree groupings around old trees reflects the effects of complex past interactions between trees, as well as between trees, other organisms and the environment.
In our work, in the strict protection area of the Białowieża National Park, we measured the distance to the central tree of 605 trees grouped around 114 monumental central trees (55 oaks Quercus robur, 22 lindens Tilia cordata, 21 maples Acer platanoides, 20 spruces Picea abies and 26 hornbeams Carpinus betulus). We also measured trunk diameters of all trees. We revealed that the species of the central tree significantly affected the mingling index, the mean distance between trees and the species composition of neighbouring trees. Large trees are most often surrounded by trees of other species, but lindens were most often surrounded by young trees of their own species. Young lindens were also often found around old hornbeams. The surrounding of old lime trees with their own regeneration is probably due to the fact that they usually produce a large number of offshoots from the base of the tree or from roots up to five metres from the parent trunk, which develop over time into young trees closely surrounding the parent tree. In the case of hornbeam, the deep shade produced by its crown not only hinders the development of more light-demanding species in the neighbourhood, but also translates into the greatest distance in which neighbouring trees grow in relation to the central tree among the trees studied. In contrast to lime and hornbeam, nearly 100% of the central trees of oak and maple were surrounded by trees of other species. This is on the one hand the result of the generally low regeneration success of these species, most likely due to foraging selectivity of ungulates. On the other hand, it is probably the result of the more open crown of these trees and therefore less shading of the forest floor at their trunk. In effect, the neighbouring trees grew around the monumental oaks, lindens and maples significantly closer than around the old hornbeams. As expected, the average distance between the monumental tree and neighbouring trees increased with increasing tree trunk thickness, which is the result of large crowns of trees with thick trunks that produce deep shade.
Our study confirmed the very important role played by old large trees in shaping the spatial structure of the forest, which was also demonstrated in previous publications. However, we also showed that not only the size of the trees, but also their species identity plays an important role in this process.
The paper, published in the journal Forests, was prepared by the BSG team (Olga Cholewińska, Bogdan Jaroszewicz, Barbara Kusińska), in collaboration with Andrzej Keczyński from the Białowieża National Park. The publication uses materials collected by Barbara Kusińska for her Bachelor’s thesis. The entire work is available (Open Access) at the following link: https://www.mdpi.com/1999-4907/12/9/1162/pdf.