Ontogenetic structure of populations of forest-forming species of the Left-Bank Polissya of Ukraine

The results of study of the population ontogenetic structure of the main forest-forming species (Pinus sylvestris, Quercus robur, Acer platanoides, Betula pendula, Populus tremula) of the Left Bank Polissia of Ukraine are presented. The study covered plant communities, which are the most common and typical in the region. They are represented by four formations of forest vegetation, viz. Pineta sylvestris, Querceta roboris, Betuleta pendulae, Populeta tremulae, and belonged to 24 syntaxes in the rank of association groups and up to 42 syn-taxons in the rank of associations. The study was based on the use of geobotanical and population-ontogenetic approaches and methods. It was established that in the forests of the region, the most part of main forest-forming species populations have left-sided ontogenetic spectrum. Invasive populations are the predominant category. Only in the populations of the species involved in the formation of the second and especially the first tier of stands reveals the centred and bimodal spectra. In these species, the frequency of normal population occurrence increased, but their proportion was within 6.7–13.6%. No regressive populations were found in the main forest-forming species of the region. It was fixed that the ontogenetic spectra of the most of populations of the studied species were incomplete due to the absence of plants of some ontogenetic states. It was noted that the individual extinction of the young generation before they reached the generative ontogenetic state, was the clear evidence of significant disturbance in the region forests of the generation variability in forest-forming species. The limited representation of windfall microsite complexes in the composition of the forest plant communities of the Left-Bank Polissia of Ukraine as well as gaps enough in size to ensure successful undergrowth development and formation of a continuous flow of generations is one of the consequences of long-term man-made impact on these forests. Keywords: forest phytocoenosis, forest-forming tree species, population analysis, population structure, ontogenetic spectrum, Polissia of Ukraine