the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 29 Apr 2026
Simulation of long-term peat accumulation dynamics & vulnerability: Insights from a Pole Forest and Palm Swamp in Amazonia
Abstract. Peruvian peatlands represent one of the largest reservoirs of carbon in Amazonia. This heterogeneous landscape exhibits several types of ecosystems, including pole forest (PF), palm swamp (PS), open peatlands (OP), and seasonal flooding forest (SFF). We apply the HPMTrop_EcoTy model, a novel development that represents ecological succession via bespoke parametrisations of ecohydrological mechanisms, to gain insights into long-term peat accumulation dynamics across these ecosystems and to assess their vulnerability to carbon gain and loss. Model results suggest that carbon accumulation rates in Amazonian peatlands are similar to or greater than those reported for the Congo Basin and Southeast Asia. Peat and carbon accumulation in Amazonia are particularly sensitive to local-scale changes, especially those driven by ecosystem succession. Amazonian peatlands appear less sensitive to precipitation changes, likely due to the extremely high rainfall across the Peruvian Amazon. However, reducing rainfall to levels similar to those of the present-day Congo Basin (45 % reduction) produces an exponential decline in peat and carbon accumulation, suggesting a critical tipping point. Sensitivity analysis shows that PF, the most carbon-dense ecosystem, is the most sensitive, likely because it is rain-fed and therefore more vulnerable to ecohydrological changes, whereas SFF, the least carbon-dense, is the least sensitive. Considering the exceptionally high precipitation in the region, peatland formation appears mainly controlled by local processes such as river migration, which drives vegetation succession linked to peatland development.
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- RC1: 'Comment on egusphere-2026-2272', Anonymous Referee #1, 22 May 2026 reply
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RC2: 'Comment on egusphere-2026-2272', Anonymous Referee #2, 15 Aug 2026
reply
First, I apologize for the delay in providing this review, as August is a common vacation period.
This manuscript uses a relatively simple one-dimensional model to simulate long-term peat and carbon accumulation at two peatland sites in the Peruvian Amazon. This is an important research topic, as our understanding of the long-term development of tropical peatlands—and peatlands more generally—remains limited. I find the research question valuable and clearly defined. Although the model is relatively simple, it appears broadly capable of reproducing long-term peat accumulation at the two sites. Nevertheless, its simplicity introduces several assumptions and uncertainties that require clarification.
I hope the following comments will help improve the manuscript.
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Use of abbreviations. The frequent use of abbreviations somewhat disrupts readability. Examples include pole forest (PF), palm swamp (PS), open peatland (OP), seasonally flooded forest (SFF), and ecosystem type (EcoTy). Because these are not commonly used abbreviations and the full terms are relatively short, I often had to return to earlier sections to recall their meanings. I suggest reducing the number of abbreviations, particularly “EcoTy”.
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Precipitation tipping point. How likely is a precipitation reduction of 30–45% at these particular sites under future climate and land-use scenarios? If such a reduction is unlikely, I suggest presenting the result primarily as precipitation sensitivity rather than as evidence of a tipping point. The use of “tipping point” may require stronger evidence than a sharp response among several prescribed precipitation scenarios.
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Constant evapotranspiration. The assumption of constant evapotranspiration at 100 mm month⁻¹ seems highly simplified, particularly because the simulated water table depends directly on this value. Are evapotranspiration data available from the palaeoclimate simulation? Alternatively, could evapotranspiration be reconstructed using temperature, precipitation, or another simple method? At minimum, the uncertainty introduced by this assumption should be discussed or evaluated through sensitivity analysis.
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NPP–water-table relationship. The empirical relationship between NPP and water-table position is an important component of the model. Can this relationship be evaluated against independent observations or through cross-validation? The manuscript should provide information about the amount of data used, goodness of fit, and uncertainty in the fitted relationship. Could past temperature variability also have affected NPP? Although temperature may not be a major present-day limitation on tropical peatland productivity, the authors should discuss whether temperature changes over the last approximately 6000 years may be relevant.
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Peat depth versus peat height. Around L203, please clearly explain the difference between “peat depth” and “peat height”. Figures 2 and 3 appear to show similar temporal patterns, with the main visual difference being the direction of the y-axis. Please clarify their physical meanings, how the model calculates each variable, and why both need to be presented.
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Human influence. Around L312, were these peatlands affected by human activities during their developmental histories? If anthropogenic disturbance, burning, vegetation modification, or hydrological alteration is plausible, its omission should be acknowledged as a source of uncertainty.
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Sign convention in Figure 5. Net ecosystem carbon uptake is often presented as negative, whereas carbon loss to the atmosphere is positive. Figure 5 appears to use the opposite convention. Please either adopt the more common convention or clearly state the sign convention in the axis label and caption.
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Causes of ecosystem transitions. Section 4.4 would benefit from a clearer explanation of why the ecosystem types changed over time. Were these transitions related to precipitation, river dynamics, local hydrology, autogenic succession, or a combination of these processes? If precipitation is considered a possible driver, showing the reconstructed precipitation history together with the prescribed ecosystem transitions would help readers understand their relationship.
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Figure B1. Please add a clearly labelled scale for water-table position, apparently on the right-hand y-axis. The units, sign convention, and reference level should also be specified.
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L4. Typo in “parameterisations”.
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River migration. River migration is not explicitly represented in the model. Therefore, the conclusion that it controls peatland development should be moderated or better supported.
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Model transferability. Please discuss whether the calibrated model and its parameters can be applied to other peatland sites, or whether substantial site-specific calibration would be required.
Overall, I consider this modelling framework useful as an exploratory and hypothesis-generating tool. However, the manuscript should more clearly distinguish between model calibration and independent validation, and between processes represented explicitly by the model and interpretations inferred from external evidence. With these clarifications and more cautious interpretation of the tipping-point and river-migration results, the study could make a useful contribution to understanding long-term tropical peatland development.
Citation: https://doi.org/10.5194/egusphere-2026-2272-RC2 -
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Major comments
This is an interesting site-specific modelling study investigating peat development in two Peruvian peatlands. Research on tropical peatlands is critically underrepresented. Therefore, more modelling studies on tropical peatlands are urgently needed. The model is validated against peat presence/depth over time using a single peat core from each site. I am particularly concerned about the lack of validation data. At this stage, it is not possible to say whether the model can reproduce peatland accumulation dynamics. The depth and presence of peat at a particular time point is a great first step to validating the model. However, the depth and presence of peat is not indicative of carbon accumulation rates or carbon storage. The manuscript refers to in situ NPP measurements from other studies. Can this be used to validate the model in the present day? WTD (estimated from precipitation) is the primary driver of NPP in the model. Can this be validated against present day site data? I encourage the authors to validate at least one other model output.
In terms of the structure and readability of the manuscript, much more can be done to improve the flow and readability. There are only five figures in the main text, despite an extensive supplementary material and appendix. The number of figures and tables is relatively low for a manuscript of this length. Many details are omitted from the main text, including a comprehensive description of relevant model processes and I think including more figures and tables in the main text would help clarify several details. It remains unclear which parameters were changed. This is a very exciting study and a wonderful application of the model. With a bit more work, this paper can become a very useful contribution.
Small comments:
L18. Peatland formation is the result of a very slow process spanning thousands of years, during which the material from dead vegetation accumulates a process regulated by climatic and hydrological conditions.
L22. I assume you mean unique or endemic? Can you give an example?
L25. Remove ‘their history and’.
L37. Important how? Carbon-rich? Biodiversity? Oldest?
L40. Here or in the methods? Could you explain how/why these sites have developed to be a pole forest and a palm swap?
L43- L48. Net primary production? How was this measured? Can this be used as validation data in this study?
L67. Large? Do you mean tall? How tall? How thin? What are the dominant aboveground species? What are the dominant peat-forming species?
L70. What is a permanent vegetation plot?
L71. What method was used to collect the core?
L72. Re Åkesson et al. data? Do you use this? Why is it referenced?
L73 – L76. What time periods does ‘initial formation’, ‘middle to later stage’, and ‘most recent stage’ span? What were the drivers of these transitions?
When giving the length of the ‘peat core’, was this the length of the core or the peat section? Did both cores include basal peat? It’s unclear.
L83. Again, pollen, DBD, LOI etc. Are you analysing this data? Why is it referenced?
L85. Again, what were the drivers of the transitions? What is the dominant vegetation today? And the dominant peat forming vegetation?
L95. Here an elsewhere. I don’t see the need to abbreviate ecosystem, palm swamp, and pole forest. It reduces the readability of the manuscript.
L98. Are you calling the new parameterisations, a new model? Is it not just a new application of an existing model? Was any model code changed? If only new parameters, I wouldn’t change the name of the model.
Table 2. Where does this information come from? You’ve derived this from the sampled cores? Does the information become model input? Or validation data?
Figure A1. Simulation results should be in the results section.
Figure 1. Please change labels, core VEN-O2 and NYO-03 to site names. Can you show a photo of the core for both sites? Perhaps this figure can be sperated into two: First figure: The two Maps. The second figure: photo of each site (are these photos of these specific sites or ecosystem type in general. Specific site would be preferable), Photo of each core, radiocarbon dates of each core. It would be good to perhaps use dots in the figure so it is clear, at what ages, the samples were taken .
L105. Can you include equations in SI?
L116. Where can I find the codedataavailability or Table HPMTrop_EcoTy_Parameters.xlsx? I looked throughout the manuscript but could not find it.
Table 1. How does the pollen record vs the peat core agree/disagree? Are the dates radiocarbon dates? How were the ecosystem types determined? Using pollen or peat core visual analysis? Figure A3 and A4 are useful to show you developed the ecosystem types and transitions. It would be great if these were included in the main manuscript alongside the core photos.
L140. Precipitation product was compared to meteorological station data and bias corrected. Can you show this in a figure?
L152. Was this WTD assumption validated against in situ site observations? This is critical to determine whether the simulated changes in NPP and peat accumulation are related to representative changes in WTD.
L155. Please include the equations for NPP, litter, peat depth, peat height, and carbon storage here in the main text. These equations are critical for interpreting the results of this study.
L200. Peat height relative to what?
Fig 4. Core/observed data should be in black. Please then use a solid line for the base simulation with shading to indicate ±25%. Which parameters were changed? Why does some figures have a grid and others not? Please be consistent. Why does the shaded grey patch span across all time period but the caption reads that it represents the Holocene hiatus? Shouldn’t this be vertical? Can you also include lines or discuss over which time periods you expect, based on literature, the Holocene hiatus at these sites?
Discussion: Perhaps, I missed it but a limitation of this study seems to be the reliance of pollen analysis to infer vegetation presence. Pollen records only capture pollen producing plants. Can the authors discuss to what extent non-pollen producing plants likely to have been present at these sites?
Table A1. It's a bit unclear but it seems that these are model input parameters. Without presenting model equations, it's difficult to understand how these parameters are relevant to the study or used by the model. Please provide model equations in the methods of the main text.