Limited seed retention during winter inhibits vegetation establishment in spring, affecting lateral marsh expansion capacity

• Published in: Ecology and evolution 2019-12, Vol.9 (23), p.13294-13308
• Main Authors: Regteren, Marin, Colosimo, Irene, Vries, Pepijn, Puijenbroek, Marinka Elisabeth Barbara, Freij, Victor Sebastiaan, Baptist, Martin Josephus, Elschot, Kelly
• Format: Article
• Language: English
• Subjects: Adaptation; Animal behavior; Aquatic plants; Aster tripolium; Availability; Biodiversity; Boundary conditions; Carbon sequestration; Climate change; Coastal zone management; Coasts; Dispersal; Ecosystem assessment; Ecosystem services; Elevation; Environmental changes; Environmental protection; Expansion; Geomorphology; lateral expansion; Original Research; Retention; Salicornia spp; salt marsh; Salt marshes; sediment dynamics; Sedimentation & deposition; Sediments; seed bank; Seed banks; Seed dispersal; seed viability; Seeds; Soil dynamics; Soil erosion; Spartina anglica; Spring (season); Surface layers; Transition zone; Vegetation; Vegetation establishment; Viability; Weather; Winter; Winter storms
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.5781

Coastal systems worldwide deliver vital ecosystem services, such as biodiversity, carbon sequestration, and coastal protection. Effectivity of these ecosystem services increases when vegetation is present. Understanding the mechanisms behind vegetation establishment in bio‐geomorphic systems is necessary to understand their ability to recover after erosive events and potential adaptations to climate change. In this study, we examined how seed availability affects vegetation establishment in the salt marsh–intertidal flat transition zone: the area with capacity for lateral marsh expansion. This requires vegetation establishment; therefore, seed availability is essential. In a 6‐month field experiment, we simulated a before and after winter seed dispersal at two locations, the salt‐marsh vegetation edge and the intertidal flat, and studied seed retention, the seed bank, and the seed viability of three pioneer marsh species: Salicornia procumbens, Aster tripolium, and Spartina anglica. During winter storm conditions, all supplied seeds eroded away with the sediment surface layer. After winter, supplied seeds from all three species were retained, mostly at the surface while 9% was bioturbated downwards. In the natural seed bank, A. tripolium and S. anglica were practically absent while S. procumbens occurred more frequently. The viability of S. procumbens seeds was highest at the surface, between 80% and 90%. The viability quickly decreased with depth, although viable S. procumbens seeds occurred up to 15 cm depth. Only when seeds were supplied after winter, many S. procumbens and some S. anglica individuals did establish successfully in the transition zone. Viable seed availability formed a vegetation establishment threshold, even with a local seed source. Our results suggest that, although boundary conditions such as elevation, inundation, and weather conditions were appropriate for vegetation establishment in spring, the soil surface in winter can be so dynamic that it limits lateral marsh expansion. These insights can be used for designing effective nature‐based coastal protection. Germinated seedlings of Salicornia procumbens in the transition zone; a first step of lateral salt‐marsh expansion. Seeds were retained at the salt‐marsh edge and tidal flat when dispersed after winter in March, but not when dispersed before winter in December. Salicornia procumbens was the only pioneer present in the natural seed bank with viable seeds at depth. Early dispersal