This study describes plant species diversity in well preserved dry coastal dune systems along the southern Baltic coast. Variations in diversity and in distributional character of plant species and plant communities throughout the study areas result mainly because of the interplay between plant succession, exposure, disturbance and resource availability. Environmental indicator values, used to describe dynamics in dune habitats, show a decline of light and temperature with increased distance to the sea, accompanied by higher soil moisture due to accumulation of organic matter. Species richness and species diversity showed a humped-shaped curve along a coast-to-inland gradient. The highest species richness of vascular plants and cryptogamic species were found in plant communities of grey dunes at intermediate levels of environmental and disturbance gradients, which confirms the intermediate disturbance theory.