The effect of herbivory and competition on survival and growth of Elymus athericus seedlings

1. At Schiermonnikoog, a Dutch island in the Waddensea, a vegetation succession gradient can be observed from east to west and it features a natural productivity gradient. 2. Elymus athericus (a perennial grass) is a dominant species in the oldest stages of salt marsh succession on the island Schiermonnikoog, The Netherlands. It is present in low abundance at the youngest stages, but only when herbivores (especially hares) are absent. 3. Brown hare, Brent geese and Barnacle geese forage most on salt marshes with intermediate plant standing crop. 4. In the present study the effect of herbivory and competition on Elymus at four different stages of the salt marsh were examined. Elymus seedlings were transplanted in a full factorial design (control, no herbivores and/or no neighbours) A no-geese treatment was added to distinguish the effects of hares and geese. 5. Survival of Ely,nus is lowest at the youngest site, where environmental conditions are very severe (wind, seawater, low nutrient concentration). 6. Overall shoot biomass production increases with ageing of the salt marsh, very likely caused by the increasing amount of nitrogen as the salt marsh gets older. 7. Competition enormously reduces the amount of biomass produced, the maximal shoot length and the number of ramets of Elyrnus significantly. The older the salt marsh, the larger this reduction is, because competition for light increases with salt marsh-age. Plant survival is almost not influenced by competition. 8. Herbivory plays no important role on plant performance; plant biomass, number of ramets and plant height are hardly influenced by this factor. Only at the youngest salt marsh herbivores cause a large reduction in biomass. Herbivory has a small negative effect on plant survival, significant for two sites. 9. It seems there's a window of opportunity for Elymus to establish, which is present at the youngest salt marsh. During this period, herbivores prevent permanent establishment of seedlings. As succession proceeds other plant species hinder (further) establishment and compete with young Elymus plants, which may be enhanced by herbivore grazing forming a denser low vegetation.