Vegetation and sedimentation on coastal foredunes

On a timescale of years to decades, vegetated foredunes may show various modes of morphological development. Vegetation is one of the factors that determine the sedimentation pattern and thus morphology on the foredune. In turn, the vegetation pattern may be controlled by the sedimentation pattern. Although these effects have been quantified for short timescales, there is relatively little information on the interaction between vegetation and sedimentation for timescales of over a year. For the island of Ameland, the Netherlands, elevation measurements and aerial photographs between 2002 and 2012 were used to derive changes in elevation and vegetation patterns on a year-to-year basis. This was done for a range of stable to accreting foredunes. Sedimentation increases from the beach to a maximum halfway up the seaward slope of the foredune, and then decreases again when going landward. This trend is further modified by the vegetationʹs spatial pattern. On a timescale of years, there is no correlation between the density of vegetation cover and the amount of accretion. However, by accounting for the gradual depletion of the sand load over the foredune, a relationship can be defined between vegetation cover and its trapping efficiency. Foredune vegetation spreads mainly by lateral expansion of existing patches. No strong effect was found of the sedimentation balance on the expansion of vegetation. It is suggested that other growth-limiting factors are of similar importance, masking any possible dependency of vegetation growth on sand accretion.