The role of beach and sand dune vegetation in mediating wave run up erosion
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2019 Coastal dunes are often the first and only line of physical defense for communities subjected to damaging storms and waves. Planting vegetation on them has been proposed as one way to increase their protective capacity, but it is unknown how dune plant architecture reduces erosion. We conducted wave flume and field experiments to address this question and found that dune plants primarily reduced erosion by attenuating wave swash and run up bores with their stems and leaves, while their roots initially enhanced erosion through uprooting. After excavation, the roots also attenuated waves and reduced erosion. We then sampled the biophysical attributes of a broad distribution of plants, and found that herbaceous non-Graminoid (non-grass) species that inhabited the lowest latitudes and most seaward zones had the most efficient structures for erosion reduction. Our results suggest that there is a fundamental tradeoff in the ability of dune plant species to respond to hydrodynamic versus Aeolian processes, based on the relative allocation of aboveground versus belowground biomass. Through the combination of flume experiments, field survey, and meta-analysis, our findings show that vegetation provides on average 1.6 factor of safety over bare sand across a wide range of latitudes in the northern hemisphere - translating into a reduction of wave run up erosion by approximately 40% for dunes.
