Environmental Factors Influencing Coastal Vegetation Pattern: New Insights from the Mediterranean Basin

Coastal dune ecosystems show strongly dynamic interactions between abiotic and biotic factors. The relationship between plant communities and environmental factors has been previously studied in oceanic dune systems, but few studies have been conducted along Mediterranean coasts. In this study we analyze the relative contribution of environmental factors associated with two of the main drivers of vegetation zonation: soil and wind. We chose two representative coastal dune systems in the western Mediterranean Basin subject to low levels of human disturbance. Within 54 plots we recorded floristic and environmental data. Vegetation zonation and relationships with environmental variables were investigated through unconstrained and constrained ordinations, correlation, and variance partitioning. Environmental factors shift along the gradient from coastal to inland dunes, concomitantly with the pattern of community types from annual beach communities to shrub-covered fixed dunes. This general gradient is similar both in the Mediterranean and in the oceanic coastal ecosystems, with the same factors that show similar trends along the dune profile. However, our results highlight some peculiarities of the Mediterranean dune systems in relation to the amount of variation explained by environmental factors. While most studies conducted in oceanic ecosystems find that wind-related parameters may control the vegetation zonation, in our study areas we observed a minor importance of the wind-related variables when compared to soil properties. In particular, organic matter and grain-size variability were found to be closely correlated with the distribution of plant communities along the gradient.