1 Despite much debate about their importance, only a few field studies have evaluated the intensity of competition and herbivory.
2 Artemisia maritima, Atriplex portulacoides and Plantago maritima, three plant species which are common in European temperate salt marshes, were transplanted into different successional stages (15, 30 and 45 years old) of a temperate salt marsh. Biomass of each transplant was measured as the response variable to treatments that manipulated competition and the level of herbivory.
3 All species were shown to be negatively influenced by both competition and herbivory, with competition being in general of greater importance than herbivory. No change could be detected during succession in the intensity of either competition or herbivory. Their combined impact, however, increased over succession for Atriplex, although no trend was observed for the other two species.
4 Both biomass and allocation patterns reflected further adaptations of these salt-tolerant species to environmental stress and biotic interactions present in the salt marsh. Plantago, which is the best adapted to salinity, was shown to be markedly affected by competition and herbivory. Atriplex showed less response to herbivory and little response to competition, to which it is well adapted. The grazing-deterrent Artemisia was influenced by herbivory only as a seedling.