Impact of microhabitats on the heterogeneity of seedling emergence in a Mediterranean coastal sand dunes community

Abstract

Seedling emergence and establishment was monitored in 3 microhabitats during growing seasons in a Mediterranean coastal sand dune community in Poleg Stream Nature Reserve, Israel. Seedling emergence varied temporally among the 3 microhabitats, with a delay in the timing of seedling emergence in shrub understoreys due to lower soil average temperatures and lower irradiance. In contrast, seedling emergence on trails was advanced because of more intense irradiance and higher soil temperatures on their more exposed soil surfaces. Microhabitats showed significant differences in individual densities, species diversity, and species richness of total seedlings (P < 0.0001). Open areas generally possessed significantly greater total seedling densities, species diversity, and species richness compared to shrub understoreys and trails. Twelve key species and 5 functional groups showed significant microhabitat preferences. Seedling patterns indicated that emergence responses could account for observed patterns of variation in the 5 functional groups and dominant species populations. In this semi-arid ecosystem, negative interactions between the shrub canopy species (white weeping broom) and its understorey occurred for seedling establishment because of lower seed densities in the seed bank, a larger amount of litter on the soil surface, and the dense woody canopy. On the trails, trampling decreased plant diversity and discouraged the establishment of most functional groups and key species except annual grasses and 'Polycarpon succulentum' and 'Cutandia philistaea'. The variability in seedling response patterns for the different microhabitats will assist in understanding the patchy regeneration strategies of this coastal sand dune community and provide a basis for vegetation management.