Caspian remnant coastal dunes: how do natural and anthropogenic factors impact on plant diversity and vegetation?

Abstract

This vegetation–environmental relation study is the first large-scale survey along 34 cross-shore transects in 650 km-coastal dune remnants of the south Caspian Sea, Iran. The five vegetation zones dedicated here seem to be driven by both zonal (climate, distance to the sea and pH) and azonal (salinity) factors. To assess conservation status, different attributes of H dune diversity index, endemicity index (EI) and Naturalness (N) were estimated based on endemic, alien and total species contributions per plot. Contrary to H dune index, EI followed a decreasing pattern across the coast–inland gradient, whereas N shows a unimodal pattern of distribution with the highest value at the mobile dune zone. Two main gradients of salinity and alkalinity shaping floristic composition are more prominent than climate, distance to the sea and the anthropogenic factors particularly when a full range of coastal habitats are considered. Human-related factors only partially explain the variability of the vegetation data and negatively affect naturalness and endemicity indices, even though their impact on community composition is aggravated in the western parts of the Caspian coasts. Both N and EI indices can be suggested as bioindicators for proper conservation strategies to preserve the last fragments of sand dunes of the Caspian Sea.