The Impact of Herbivory and Competition on Flowering and Survival during Saltmarsh Succession

Abstract: For succession, the establishment and turnover of plants, in terms of generative spreading and renewal, is of crucial importance. Especially the success of seedling establishment into the existing vegetation might be of prime importance for the further development of plant species composition. Flowering, on the other hand, is the necessary first step towards generative output and later seed set. In a chronosequential gradient of a saltmarsh succession, we investigated the performance of transplants of three common species under different conditions: Artemisia maritima, Atriplex portulacoides and Plantago maritima were transplanted as seedlings and mature plants into plots in early-, mid-, and late-successional stages (15, 30 and 40 years) on the Dutch island of Schiermonnikoog. Natural herbivory (by hares and geese) and neighbourhood competition were excluded in a factorial design. Flowering and survival rates of the three species were generally greatly reduced under natural conditions, compared to competition- and herbivory-free plots. The survival rates of Artemisia maritima and Plantago maritima reflect their position as early-successional species: early in succession, both show their highest survival and abundance. For late-dominant Atriplex portulacoides a different explanation has to be invoked for the medium-high survival and low abundance: probably winter grazing by hares and the importance of a high nitrogen supply rate, rather than flowering and survival, determine its low abundance in the early and mid-phase of this saltmarsh succession. Some long-term impacts of herbivores affecting flowering and survival are discussed.