Changing patterns The influence of stress on vegetation patterns in a salt marsh

Abstract

Biotic and abiotic stress can both be present on salt marshes. Factors as sea level rise and anthropogenic land use may increase stress and thereby influence ecosystems. Many researches involve the consequences of abiotic stress on ecosystems, but little is known about the effects of biotic stress or a combination of the two stress types on ecosystems. The aim of this study was to increase the knowledge about the effects of biotic and abiotic stress on salt marshes. Vegetation patterns are present in salt marshes and patterns are known to shift under influence of stress. Species are the basic elements of plant communities and their interactions influence the formation of vegetation patterns. The effects of biotic and abiotic stress on species growth, species interactions and patch sizes were tested in this research. Grazing history was used as a measure for biotic stress and salinity as a measure of abiotic stress. Juncus maritimus is a species that forms vegetation patches in salt marshes at Schiermonnikoog. It was found that Juncus cover was not affected by biotic stress, but was negatively influenced by abiotic stress. Species interactions were influenced by a combination of biotic and abiotic stress. Facilitation increased with biotic stress at low abiotic stress, but did not change with biotic stress at high abiotic stress. Patch sizes were influenced by biotic stress. Large patches were more abundant on salt marshes with medium and high biotic stress than on salt marshes with low biotic stress. Abiotic stress also influenced patch sizes, but no trend could be discovered. These results imply that presence of one stress type or both stress types largely influence the plant community in salt marshes.