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Previous studies found that pedunculate oak, one of the most widespread and abundant species in European deciduous forests, regenerates in open habitats and forest edges, but not in closed forest interiors. However, these observations usually come from the core areas of the biome, and much less is known about such processes at its arid boundary, where limiting factors may be different. In a full factorial field experiment, we tested the effects of different habitats (grassland, forest edge, forest interior) and increased growing season precipitation on the early regeneration of pedunculate oak in a forest-steppe ecosystem in Central Hungary, at the arid boundary of temperate deciduous forests. In the grassland habitat, seedling emergence was very low, and no seedlings survived by the fourth year. In contrast, seedling emergence was high and similar at forest edges and forest interiors, and was not affected by water addition. Most seedlings survived until the fourth year, with no difference between forest edge and forest interior habitats in numbers, and only minor or transient differences in size. The lack of oak regeneration in the grassland differs from previous reports on successful oak regeneration in open habitats, and may be related to a shift from light limitation to other limiting factors, such as moisture or microclimatic extremes, when moving away from the core of the deciduous forest biome towards its arid boundary. The similar number and performance of seedlings in forest edges and forest interiors may also be related to the decreasing importance of light limitation. [ABSTRACT FROM AUTHOR]

Climate change and disturbance are two major factors affecting the establishment of invasive species, yet few studies to date have assessed the individual and interactive effects of these two factors in a common setting. Disturbance has often been found to facilitate the establishment of invading species, while climate change may affect them positively or negatively through altering abiotic conditions, or indirectly by modifying species interactions. In a full-factorial field experiment in a semiarid temperate grassland in Central Hungary, we studied the effects of drought (40% rain exclusion throughout the year) and soil disturbance on the emergence, survival and aboveground biomass of four invasive plant species that represent different life forms and that are of concern in the region and at a broader scale. We added seeds of Ambrosia artemisiifolia (annual forb), Cenchrus incertus (annual grass), Asclepias syriaca (perennial forb) and Ailanthus altissima (deciduous tree) in drought and non-drought plots with and without soil disturbance. Ailanthus germinated poorly irrespective of treatments. Disturbance facilitated while drought suppressed seedling emergence in the other three species. Ambrosia was more sensitive to disturbance, while Cenchrus was more responsive to drought. Asclepias achieved substantial emergence in disturbed non-drought plots only, as drought strongly suppressed its emergence even in the presence of disturbance. Seedling survival and late-season aboveground biomass of Ambrosia and Cenchrus were positively affected by disturbance but were unaffected by drought, while no Asclepias seedling survived until late summer. Our results highlight that both drought and disturbance may considerably impact the establishment of invasive plants, with potential interactive effects, but responses may greatly differ among species and life stages. Overall, our findings in this study suggest that although drought may negatively affect seedling establishment, a drier climate may not suppress or eliminate invasive species if soil disturbance is present. They also highlight the importance of including disturbance in studies assessing the potential effects of climate change on plant invasions. [ABSTRACT FROM AUTHOR]