Aeolian dynamics in relation to vegetation in a blowout complex in the Meijendel dunes, The Netherlands

Changes in surface elevation in a former blowout in the coastal dunes of Meijendel, The Netherlands, have been monitored almost weekly during one year at 48 erosion pin sites, distributed over 12 units. The units are characterized by specific geomorphological processes. The changes in elevation are caused by wind, slope wash and mass movements. At almost each pin, periods of erosion alternate with periods of accumulation in a random way. Erosion and accumulation sequences are relatively long in areas dominated by aeolian activity, but even here they are randomly distributed. It is the balance between the effects of periods of erosion and periods of accumulation which determines the formation of blowouts or dunes. Units with the highest degree of erosion or accumulation at the end of the year of monitoring also show the highest fluctuations in elevation during that year. In the accumulation units there is even a significant positive correlation between surface lowering by erosion and surface rise by accumulation. Plant species in the blowout are divided into four groups on the basis of responses to aeolian dynamics: (1) Sedum acre is the only species associated with deflation; it might be suitable for blowout stabilization; (2) Ammophila arenaria, Festuca rubra and Ononis repens are associated with aeolian accumulation and can be used for the stabilization of accumulation sites; (3) Erodium cicutarium, Koeleria macrantha and Corynephorus canescens, occurring at lower aeolian activity; (4) Tortula ruralis var. ruraliformis and Galium verum are found where slope wash and mass movements (Galium) are active. In the relationship between aeolian dynamics and vegetation, the former appears to be the independent variable: there is no consistent relationship between accumulation and vegetation cover. This means that the formation of blowouts and adjacent dunes is not controlled by vegetation with its present cover.