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The diversity relationship between tree and herb layer has often been investigated, but the results are contradictory. Moreover, few studies of deciduous European species have been conducted to date in natural or near-natural forests, while such studies in old-growth forest with considerable co-dominance of oak are missing.In one of the best preserved natural European beech-sessile oak forests (Runcu-Grosi Natural Reserve, Western Romania) we investigated whether there is a correlation between canopy-layer diversity and herb-layer diversity. Structural diversity, vegetation composition, ecological and functional traits were evaluated. Our results show that the herb-layer diversity is higher under canopy with greater tree-layer diversity, and the diversity of both layers depend on whether the overstorey is dominated by beech or sessile oak. Herb layers of plots with oak co-dominance showed higher indicator values for light and temperature, and a higher proportion of graminoides and shrub species. In contrast, herb-layer in beech plots is dominated by juvenile trees, mainly beech and competitive herb species. Oak plots are characterised by a generally more evenly distributed herb-layer composition. Species richness of herb-layer was higher under a diversely structured overstorey, which was mainly achieved when oak was present in the canopy, and correlated negatively with litter thickness, which was highest in beech plots. We conclude that the identity of the dominant canopy species is most important for herb layer species composition and diversity. Furthermore, the plots with oak occurrence in the overstorey even with weak proportion (around 20% of stand basal area) features a higher biodiversity of species in the understorey.

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The emergence of renewable energy infrastructures calls for a better understanding of their impact on biodiversity. The aim of the present study was to investigate in a mountain region the impact of a wind turbine on plant communities in their vicinity. A field survey was conducted in a wind farm situated in the Southern Romanian Carpathians, five years after the turbines were installed. We tested for the effects of the presence of the turbine and the distance to the turbine on plant species richness, on five plant ecological indicators and on the quality of the pastures. Overall, 33 plant species belonging to 16 families were recorded, and among them 21 were recorded in both the presence and the absence of wind turbine. The presence of a turbine did not affect the structure of the plant community, as the majority of the plots exhibited similar plant species richness and composition. Finally, the values of the ecological indicators and the pasture quality were not altered by the presence of the turbine. Such analyses could be extended over longer time periods so as to capture potential long-term effects and by integrating other environmental factors such as microclimatic conditions or soil properties.

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