Soil seed banks, habitat heterogeneity, and regeneration strategies in a Mediterranean coastal sand dune

Abstract

This study investigated the effects of microhabitat characteristics on soil seed bank structure, regeneration strategies, and plant composition in a Mediterranean coastal sand dune in Israel. Three different microhabitats were selected: (a) open patches between shrubs, (b) shrub understorey, and (c) open, disturbed patches in pedestrian trails. In each microhabitat two types of sampling plots were established: (a) seedling removal and (b) control (seedlings not removed). Emerging seedlings in each microhabitat were identified, counted, and removed every two weeks. In the controls, the vegetation was sampled only once at the peak of the herbaceous growing season. At the end of the growing season in plots where seedlings were removed, the upper soil was collected and sieved before seeds set. Viable non-germinated seeds were identified and counted. An estimation of persistent seed banks was obtained for each plot. Species composition, species richness, species diversity, and aboveground biomass by species were estimated. Germination fractions among species and plant functional groups were measured. Microhabitats differed in soil seed bank density, germination characteristics, above-ground biomass production, and species composition. The open patches between shrubs generally had the highest densities of seeds, seedlings, and mature individual herbaceous plants. Important density differences between total seedlings removed and mature vegetation may indicate strong plant mortality in all microhabitats. Annual and perennial grasses, composites, annual crucifers, and annual forbs produced transient seed banks, while legumes, umbelifers, and perennial forbs had persistent seed banks. Disturbance by public trampling in trails led to low seed and plant densities in this microhabitat. No effects of facilitation of shrubs on the annual vegetation were noted in shub understorey. Habitat heterogeneity had a strong impact on vegetation structure and regeneration strategies.