How Can Active and Stabilized Coastal Dunes Coexist under the Same Climate Conditions?

Coastal dunes, found in all latitudes from polar to tropical climates, are one of the most degraded ecosystems due to excessive exploitation of the coasts and beaches. Some of them are partly or fully vegetated while others are active with little or no vegetation. The percentage of vegetation cover on coastal sand dunes has environmental and ecological importance because it can turn dunes from stable to active or vice versa. For that reason earth scientists try to predict the effect of the anticipated climate change on the mobility and stability of coastal sand dunes. There are many sites along the coasts where stabilized and active dunes coexist. We provide several examples for the coexistence of active and fixed sand dunes under similar climatic conditions.

The axiom saying more rain brings about more vegetation while less rain means less vegetation doesn't always work for coastal sand dunes. The moisture balance (balance between precipitation (P) and potential evapotranspiration (PE)) is not the factor that determines whether vegetation can grow on coastal sand dunes. A model is developed for coastal dune vegetation cover that includes wind power, precipitation rate and anthropogenic effects. Hysteretic behavior of dune mobility is predicted by the model with respect to wind power and with respect to changing precipitation and human pressure parameters. Our model predicts when active and fixed dunes can exist together in the same place and where only stable or active dunes subsist.