Wind tunnel tests inform Ammophila planting spacing for dune management

Coastal dunes are invaluable natural resources that bu er upland areas. Vegetation is key in dune development and stabilization. Dunes form with sufficient wind, sand source, and obstruction; plants are the ideal obstruction. Storms o en erode foredunes and coastal managers replant vegetation to re-establish the necessary obstruction for sand accretion and dune growth. We used a wind tunnel to examine the effect of planting density on bedform formation under constant 18.5 mph (8.25 m/s) winds for 30 min. We filled 1m x 1m x .3 m deep boxes with sand and then planted Ammophila breviligulata plugs in two densities commonly used in management, 12 inches (30.5 cm) and 18 inches (45.7 cm) on center. Sand was supplied by a downwind 1-inch sand bed to mimic backshore transport. We measured the morphology of each plant and used a 3D sensor to record the topography of the bedforms that formed in association with each plant. e bedforms did not vary in volume or basal area as a function of planting density, but biomass was a significant predictor of volume, with larger plants producing larger bedforms. We observed all accretionary bedforms in our low-density treatment, but both erosion and accretion in the high-density treatments potentially due to an inaccurate measure of pre-experiment base height or interactions among neighbors causing greater turbulent kinetic energy with tighter spacing. Bedform height, accretionary or erosive, did not vary by density, row, plant width, or biomass. The bedform shape, measured as the length to width ratio did vary by density; plants in the low-density treatment, despite being morphologically the same, produced bedforms with longer tails. These differences are likely a function of wind back ow and plant interaction interrupting ow, both of which are reduced with a lower planting density. The bedforms created at the onset of planting are thought to carry over through the life of the dune, such that understanding how density affects bedform shape should be considered when making management decisions.

海岸沙丘是无价的自然资源，它们对防止陆地侵蚀起着至关重要的作用。植被在沙丘的形成与稳定中占据着核心地位。沙丘的形成需要充足的风力、沙源以及障碍物，而植物正是理想的障碍物。风暴常常侵蚀前沿沙丘，沿海管理者通过重新种植植被来恢复必要的障碍物，以促进沙粒的沉积和沙丘的生长。本研究利用风洞实验，在恒定的18.5英里每小时（8.25米每秒）风速下，持续30分钟，考察了种植密度对床沙形态形成的影响。实验中，我们将1米 x 1米 x 0.3米深的盒子填满沙子，并在两种常用于管理的密度下种植了Ammophila breviligulata植物插穗，即中心间距为12英寸（30.5厘米）和18英寸（45.7厘米）。沙子由下风方向的1英寸沙床提供，以模拟沿岸沙粒的运输。我们测量了每株植物的生长形态，并使用3D传感器记录了与每株植物相关的床沙形态的地形。床沙形态的体积或基底面积并未随种植密度而变化，但生物量是体积的一个显著预测因子，较大的植物产生了更大的床沙形态。在我们的低密度处理中观察到了所有的沉积床沙形态，但在高密度处理中，由于实验前基线高度的测量不准确或相邻植物之间的相互作用导致更紧密的间距产生更大的湍流动能，可能出现了侵蚀和沉积。床沙形态的高度，无论是沉积的还是侵蚀的，均未随密度、行距、植物宽度或生物量而变化。床沙形态的形状，以长度与宽度的比例衡量，随密度而变化；在低密度处理中，尽管植物形态相同，但产生的床沙形态尾部更长。这些差异可能是由于风向回流和植物相互作用中断气流的结果，而这些都是随着种植密度的降低而减少的。据认为，在种植初期形成的床沙形态会在沙丘的生命周期中持续存在，因此，在制定管理决策时，应考虑密度对床沙形态的影响。