Biomechanical parameters of marram grass ( <i>Calamagrostis arenaria</i> ) for advanced modeling of dune vegetation

Abstract. This study investigates the biomechanical properties of marram grass (Calamagrostis arenaria, formerly Ammophila arenaria) over a 12-month period on the island of Spiekeroog, Germany, to enhance the modeling of coastal dune dynamics. The research reveals significant seasonal variations in the stiffness and Young modulus of the vegetation, with higher values observed in winter, indicating increased mechanical resistance important for dune stability during storm events. In summer, increased flexibility and density are prominent, enhancing dune accretion. To account for these dynamics, the study emphasizes the importance of incorporating seasonally adjusted parameters into models, particularly accounting for the increased horizontal density, the presence of flower stems in summer, and the longer leaf lengths in winter. The differentiation among plant parts is highlighted, with flower stems providing the highest structural support due to their greater stiffness, while leaves contribute more to flexibility and dynamic responses. Interestingly, the minimal differences between green and brown leaves suggest that these can be treated similarly in modeling efforts, simplifying parameterization without compromising accuracy. Additionally, the study found no consistent evidence that wind exposure significantly affects the biomechanical properties of marram grass, suggesting that wind influence may not need to be factored into biomechanical models. The results also demonstrate that the biomechanical properties of marram grass are broadly transferable between fixed and dynamic dune systems, supporting their applicability across various coastal environments. The key outcome of this research is the detailed compilation of the biomechanical traits of marram grass's aboveground vegetation, reflecting the seasonal dynamics found in dune processes, which will serve as a valuable resource for future modeling efforts of dune vegetation and their surrogates.