Catalogus

Our findings show that (1) the dominant and most successful colonization strategy of S. maritimus is clonal expansion from the marsh edge, with average rates of more than 1 m per year at the study sites. Wave exposure might influence the speed of this type of expansion as the expansion rate at the sheltered site was almost twice that of the exposed site. Moreover, the expansion rate was predictable at the sheltered site as it appeared to be linked to elevation at the marsh edge, and therefore related to inundation time. In contrast, at the more exposed site wave exposure appears to overrule any other limiting factors. (2) We detected that S. maritimus can follow both a stress-tolerance and a stress-avoidance strategy. The strategy depends on life stage (with flexible stress-avoiding seedlings and stiffer stress-tolerating shoots) and exposure (with flexible and shorter stress-avoiding shoots at more exposed sites and stiffer and taller stress-tolerating shoots at more sheltered sites). In our flume experiments, we found that these respective life-stage related strategies were successful for wind-generated waves while they failed under artificial long waves potentially caused by passing ships. (3) Our results further showed that important wave attenuation occurred over the first 12 m of the marsh and that relative wave attenuation was more important at the exposed site compared to the sheltered site. Although survival chances of transplants were generally better at the sheltered site, survival was equal within both marshes, emphasizing the relevance of wave sheltering capacities of marsh vegetation.