Temporal change in plant communities and its relationship to soil salinity and microtopography on the Caspian Sea coast

The gradual drying up of saltwater bodies creates habitats that are characterised by changing environmental conditions and might be available only for a subset of plants from the local flora. Using two terrestrial areas with different ages on the Caspian Coast as a chronosequence, we investigated factors including microtopography, ground water level and soil salinity that drive plant community succession after the retreat of the sea. Vegetation of the two key sites appearing after the retreat of the Caspian Sea about 365 and 1412 years ago were compared in terms of both evolutionary and ecological traits of plants. Both edaphic conditions and vegetation differed between the two sites with harsher edaphic conditions and more xerophytes on the elder site. Species that grew only in the ‘early’ site were dispersed across the phylogenetic tree, but their loss on the 'late' site was not random. Species that grew only on the 'late' site were phylogenetically clustered. On the level of microtopography, elevated spots were more densely populated in the ‘early’ site than lowered spots, but on the 'late' site the situation was opposite. The main edaphic factors that drive the difference in vegetation composition between the two sites are likely salinity and moisture. During environmental changes, different plant traits are important to survive and to appear in the community de novo. Microtopography is important for forming plant communities, and its role changes with time.