Ecotones between plant communities have received considerable attention among ecologists in the context of fragmentation, climate change and the management of heterogeneous landscapes. However, the predictability of ecotone dynamics is low and the processes taking place within ecotones are still poorly understood. In this study we aimed to characterize the positional and structural dynamics of thirteen ecotones in an ecotone-rich steppe–wetland landscape of Hungary in relation to the inter-annual fluctuations of water regime and the gradients of elevation and of soil composition. According to our results, the ecotones between steppe and wetland communities were sharp and their positions coincided with those places in the landscape where the rate of change in elevation was the highest, confirming that microtopography is a major determinant of ecotone position. Soil boundaries were also detected, mostly downhill to the ecotones. Interestingly, the fluctuations of the water supply had no effect on the position of the ecotones but significantly influenced a structural ecotone parameter, the compositional contrast bridged by the ecotones. High water supply caused high contrast, while low supply went along with low contrast. We explain these changes by asymmetric sensitivities to edge effects. When the water supply was low, the wetland edges became similar to the steppe edges due to the decrease of wetland specialists and to the increase of steppe specialists, but steppe edges did not exhibit an opposite change in wet years, suggesting that steppe communities dominated over wetland communities. The asymmetry in the interaction between the two communities may have pushed the soil boundaries downhill to the ecotones but the currently steppe-like soil of wetland edges could also make wetland edges more sensitive to edge effects; thus, the cause-effect relationship is difficult to disentangle.