EN
Competition is an evolutionary mechanism which exerts a selection pressure on living organisms. Forest trees compete for light, water and nutrients, especially at a young age. It was observed that the Quercus petraea and Padus serotina natural regenerations occupied the same site growing under the canopy of Scots pine (Pinus silvestris L.). To simulate the competition between young sessile oaks and black cherries found in forest, a controlled experiment was conducted using one-year-old seedlings of both species. There were eight treatments of different competition intensity. The treatments were established varying the number of potted seedlings and adding fresh cherry leaves to the substrate to enhance allelopathic effects. It was hypothesized that black cherry would reduce the height growth and diameter at root collar of sessile oak seedlings and this inhibitory effect would be magnified by an increasing number of cherry seedlings and/or fresh leaves. Black cherry as an invasive, fast-growing species was presumed to win the growth competition with oak. However, the differences in growth parameters would not only depend on genetic differences between the species, but also on the number of competing seedlings in pots and an allelopathic effect of cherry leaves. During the whole vegetative season, each two weeks, the growth parameters of seedlings (height, height increment and diameter at root collar) were measured. The results did not support the hypothesis that cherry had an inhibitory effect on oak growth, at least after one vegetative season. Contrary, a presence of cherry seedlings enhanced the oak height increment (F = 8.6, P <0.001) which might be due to either the strong interspecific competition for light or, less plausibly, positive allelopathic effect, or an interaction of both. Our results indicated a negative auto-allelopathic effect of cherry seedlings and/or fresh cherry leaves on height of cherry seedlings (F = 47.7, P <0.001). This invader showed a continuous and steep height increment within the whole vegetative season, whereas oak seedlings grew rapidly only in July. When compared the mean initial heights in April with those after the bud set in September, cherry was four fold and oak only two fold higher. A very intensive height increment gives black cherry an advantage over sessile oak at a young age which can disturb the spontaneous conversion of pine stands into a mixed pine-oak forest with a greater share of oak and other native deciduous tree species.