the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 25 Sep 2024
Biomechanical parameters of marram grass (Calamagrostis arenaria) 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's modulus of the vegetation, with higher values observed in winter, crucial for understanding dune erosion processes, and increased flexibility and density in summer, which are important for dune accretion. The findings emphasize 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 study also highlights the differentiation among plant parts, 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, allowing for a simplified representation 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 the application of these findings 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.
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Status: open (until 24 Dec 2024)
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RC1: 'Comment on egusphere-2024-2688', Anonymous Referee #1, 29 Nov 2024
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Overall, I think this is extremely valuable study on differences in dune grass traits to inform modeling. However, I think the current framing of the study narrows the audience of the paper more than is needed. Some careful reframing of the introduction and discussion would make the paper more interesting to readers who are not intimately familiar with dune models. For example, I think the discussion could elaborate on how the findings alter our understanding of dune resistance and recovery. Additionally, can these findings inform modeling in dunes with different grass species or other coastal ecosystems?
I found the introduction overly lengthy. I have some specific suggestions below, but I generally think the readability of this section could be improved if extra details were removed. This paper is likely written for someone familiar with sand dunes, and certainly someone familiar with coastal vegetation, so think about what background is common knowledge to the reader. Briefly, you want to convey that dune vegetation traits modulate sediment dynamics, and that some traits are not well understood while others vary with season, mechanical stressors, and soil properties. Some of these main points are currently buried because there’s so much info in the intro. Also, there is no mention of different grass components and how these are important, but differences between plant parts (sprouts, leaves, stems) are a key part of the study that could use introducing.
Minor Comments
-Line 32: “Short term changes” to what?
-Paragraph 2: The first half of this paragraph feels very drawn out, especially to a reader knowledgeable about dunes or Nbs. I think distilling to the key points would be valuable, especially since vegetation and models are not mentioned until the 2nd half of the paragraph
Paragraph beginning line 66: This has a lot of good info summarizing what has been done, but it is challenging to read with all the parentheticals and citations. Could it be summarized or presented in a supplementary table? Most readers will not need all this info I don’t think
Intro generally: Why are dune models important and what are current models missing? Addressing this will explain why this paper is so valuable
Paragraph beginning 182: Are these conditions representative of other sites dominated by marram grass? In other words, do you expect that the properties measured in this study will apply to marram grass elsewhere?
Methods: Great distilling of methods and use of supplementary information.
Line 252: the name of the universal testing machine did not proof correctly
Line 260: define Young’s modulus.
Line 273: elaborate on why these specific metrics are important. What does a different EI mean for dune growth, for instance. It may be helpful to mention this earlier in the bending test section.
Line 278: I support grouping into summer and winter seasons, but in Fig. 2 and 3 the terms spring and autumn are used, which does not match this grouping
Fig 4: mention in caption that no flowering was observed in winter so it doesn’t look like a bar is missing from the graph
Section beginning Line 230: Present these results in the order they appear in Fig 5 or re-order fig. 5 to match the presentation of results here. Going from sprouts to leaves to stems felt odd when the figure was sprouts, stems, leaves. Same for the stiffness figure
Fig 5: Explain why there are no winter stems in the caption
Figures 8-13: I’m wondering if the figures with the same metric can be combined. For instance, can Fig. 8 and 9 be combines with the Dune Ridge site shown in darker colors than the Cusp Dune site? This will facilitate better comparisons between the sites and eliminate the need for Fig. 14
All data figures: You can absolutely disagree with this, but I think it may be beneficial to remove some of the extreme values from the graphs. This would allow you to keep the scales consistent and zoom in on the majority of the data. For example, in Figure 11, it’s hard to see how the data differs because the plots are so small. I think you can say “Seven extreme values from Brown Leaves fell outside the scale of this figure and were excluded to enable better visualization.”
Discussion: Generally somewhat repetitive of the results section. I’d recommend removing some areas that only restate the results and instead focusing on the implications of these findings. What does this finding mean for dune evolution or dune modeling? What critical factors were learned here and how do these findings improve our understanding of dune systems?
Section 4.5: I think these considerations could be summarized in a single paragraph, this section is very detailed for a general reader
Conclusions: Can the conclusions highlight concrete guidance rather than a summary of the results? For example, how should models be adjusted to account for seasonal variation. Should managers collect data on plant parts in order to accurately model these dynamics?
Citation: https://doi.org/10.5194/egusphere-2024-2688-RC1
Data sets
Geometric and mechanical properties dataset of marram grass (Calamagrostis arenaria, formerly Ammophila arenaria) across dune habitats on Spiekeroog Island (December 2021 - December 2022) : Exploring seasonal and site-specific variability in marram grass' geometric and mechanical traits through field investigations and bending tests V. Kosmalla, K. Keimer, L. Ahrenbeck, B. Mehrtens, O. Lojtek, D. Schürenkamp, and N. Goseberg https://doi.org/10.24355/dbbs.084-202404230724-0
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