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Gaining an improved understanding of the strategies, traits and conditions that enable tree species to achieve dominance in forest ecosystems is important for predictions of community assembly and for the question how these species will respond to global change. A striking example of a species with strong dominance is Fagus sylvatica L. (European beech). In temperate European forests, the adoption of ‘close-to-nature silviculture’ and the cessation of forest management in forest reserves have allowed Fagus sylvatica to increase its share and have sparked new interest in the mechanisms of its dominance. An outstanding object to study its dominance is the largest remnant primary Fagus sylvatica forest, Uholka-Shyrokyi Luh in the Ukrainian Carpathians. The main objective of this thesis is to investigate the competitive advantages of Fagus sylvatica over Acer platanoides, A. pseudoplatanus and Ulmus glabra. To do so, traits of shade tolerance and associated competitive advantages were studied: i) the influence of species identity, tree age and biomass partitioning to leaves and shoots on leaf area ratio, absolute growth rate of tree biomass and storage pools in stem and root; ii) mortality rates and survival times of Fagus sylvatica and Acer spp.; and iii) the abundance of understory trees under canopy trees of Fagus sylvatica, Acer spp. and U. glabra as a proxy of replacement probability.

One individual per species, vitality class (low and high) and height class (eight classes: 0–10, 11–20, 21–35, 36–60, 61–90, 91–130, 131–200 and 201–500 cm) was randomly selected and harvested in each of the six plots. This resulted in a sample of 82, 80 and 89 living individuals of A. platanoides, A. pseudoplatanus and F. sylvatica, respectively. Additionally stems of dead Acer spp. and F. sylvatica trees that had died within the last three years (2015–2018) were randomly harvested, matching the height classes of the harvested living trees wherever possible. In total, 179 dead young trees (60 A. platanoides, 72 A. pseudoplatanus and 47 F. sylvatica) were collected. Variables: * species_code: a_pla - Acer platanoides, a_pse - Acer pseudoplatanus, f_syl - Fagus sylvatica * species: as above * dummy: 0 - living individual, 1 - dead individual * LAR_cm2_g: leaf area ratio or ratio of leaf area to total plant biomass, [cm2/g] * tree_age: in years * avg_ring_micron: average width of the last 5 rings in tree life excluding the last ring * dry_mass_g: aboveground and belowground biomass * DLI: direct light index (measured only under living individuals) * BLI: diffuse light index (measured only under living individuals) * GLI: global light index