Drought Sensitivity and Vulnerability of Rubber Plantation GPP—Insights from Flux Site-Based Simulation
, Lan Wu 2,* and Zhongyi Sun 1,2,*Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsIn this study, Zhang et al. aim to highlight and present the effects of drought on rubber plantations' GPP in tropical regions. In this direction, they use a model, that has been evaluated with eddy covariance measurements, and finally run simulations under different scenarios. The initial concept is interesting and of interest, however the study has serious flaws that make it, in my opinion, not appropriate for publication in the current form. The paper should be re-written and improved in every part of it.
Introduction
In the introduction, authors provide the bibliographical background, but they fail to define the objectives adequately. The reader has to guess. A better definition and presentation of the objectives of the study is necessary.
Methods
Methodology is very unclear and difficult to follow. The general impression is that there are many jumps from one topic to the next and then back, and this is something that doesn't create a logical flow. The model is very poorly presented, both in things concerning its parameterization, as well as the scenaria that was used for the simulations. The clearer and more precise description of the model is necessary and basic for the understanding of the next stages. Sensitivity and vulnerability are defined and described with the use of two indices, however no references are provided, neither any explanation or justification of their function and validity. This is something essential, as the results of the study as based on those indices.
Results
This section is really difficult to review, as the results are based in the objectives (that are not defined in the introduction) and the methodology (that is quite problematic, as described above). Results should be re-written along with the methodology.
Discussion
Following the above, unclear results cannot lead to clear discussion. However, this is not the only problem. The general impression after reading the manuscript is that the discussion is mainly a repetition of the introduction, reference to things that should had been putted in the introduction, unrelated topics and arbitrary statements. Along with the methodology and results impovement, discussion should be re-written as well. Authors should be focused to present an appropriate discussion of the results, not repetition of the introduction.
Some specific comments:
1. Lines 42-44: The provided reference is from 2012. Is it the latest IPCC review for sure?
2. Lines 88-96: According to this, the drought impacts on GPP of rubber plant have been extensively studied. What is the innovation and addition of the present study?
3. Lines 100-110: This part should be moved in the methods section. Last paragraph suits better in conclusions. Again, the objectives should be clearly defined.
4. Line 123: More information about the species composition is needed
5. Lines 127-129: Some better description of model parameterization is needed, maybe with some references as well. Additionally, soil moisture is absent. Why?
6. Lines 139-143: n my knowledge, ERA5 provides data either hourly or monthly, but not daily. What was the dataset that the authors used eventually? Did you use the calculator application for ERA5.
Additionally, more precision in definitions is needed. What is the meaning of "including variables such as". Variables should be well defined.
7. Lines 147-149: More information is needed about the methodology that was used, probably some references as well.
8. Line 150: What is the meaning of this title? It is already in the methodology section?
9. Line 159: What were those different scenarios? Some clarification is neseccary.
10. Line 172: This equation is somthing that the results are based on. What is this equation? Are there any references? Some explanation and better presentation is needed.
11. Line 180: See previous comment.
12. Line 204: Those are 100 years, not 1000.
13. Lines 212-212: Better explanation about the process is needed .
14. Line 231: What model did you use for the estimation of potential evapotransiration? Provide some details and some references.
15: Lines 240-244: Why did you chose these thresholds. Is this a standard modeling approach? They seem quite arbitrary. Some justification is needed.
16: Line 283: Does this mean that you adjusted 7599 parameters?
17. Fig3: What are the dots in the right diagram? Are they binned values? Please clarify. Additionally, the model performance does not look very promising, in my opinion, maybe you should consider about using a different model or different parameterization, or discuss uncertainties that arise from the poor model performance.
18. Lines 402-403: How do you justify this statement? Some justification is needed. I suggest to add an ombrothermic diagram to describe these relationships and define possibel xerothermic period.
19. Line 405: Please check the meaning of this sentence
20. Lines 414-423: Authors performed their simulations with the use of SPEI index. In this part, they discuss the SPI index, with no obvious reason. The study is not a comparative study of the two indices and this part of discussion is totally irrelevant.
21: Lines 426-432: This is mainly a repetition of the introduction
22: Lines 461-462: Again, no comparative information is provided, only the authors' statement.
23: Lines 476-485: This suits better in the introduction, rather than discussion.
Comments on the Quality of English Language
English should be improved in the manuscript, but this is not its main problem.
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for AuthorsThis manuscript presents an interesting analysis of drought functional responses of a tropical rubber plantation in China relaying on the plausible responses of the GPP ecosystem parameter as the main proxy for function. Authors argument on the use an ecosystem process model (SEIB-DGVM) to gauge the drought response of their example ecosystem. Overall, some response scenarios to drought are shown and I believe are appealing to grow interest on the reader about the potential responses of the rubber plantation to distinct drought characteristics. The manuscript can be read from start to end in proper language (although some misuse of punctuation needs to be resolved in some paragraphs).
The introduction is long, in the sense that many details on climate change and many fine details of the ecosystem region are mentioned that later in the discussion are not utilized.
Instead, some background on the SEIB-DGVM model would be of value so the readers can get an idea of the strengths and weakens of the model as it is adapted to the rubber plantation.
Please revise the definition and implications of the GPP parameter, I do not believe that it “represents” the carbon sequestration capacity of an ecosystem, remember that it is simply an expression of photosynthesis at the ecosystem level, please read:
https://doi.org/10.1007/s10021-005-0105-7)
More importantly, the introduction lacks a clear Objective or a fundamental Hypothesis to be tested which makes the reading difficult and dissuasive.
The materials and methods section have two fundamental flaws. 1) being GPP such an important parameter for the fundamental discussion of this paper (i.e. model calibration), the authors should offer a lot more details on how the eddy covariance and micrometeorological measurements where conducted (instrumentation details, spatial and time integration and representation, uncertainties…), this is very important because GPP it is no measured directly with eddy covariance but rather modelled using micrometeorological variables, so again, detail for the potential sources of uncertainties is important. Similarly, 2) the paper lacks criteria to understand the mechanics of the SEIB-DGVM to get at the GPP parameter. With the information offered in the paper, I leaned about the basic structure, diversity and perhaps phenology of the rubber plantation, but sadly I did not see any physiological criteria on the mechanics of the model, while I believe it is fundamental to understand the potential of expressing GPP. I commend authors to try on providing key mechanistic detail on this in order to justify why eddy covariance estimates of GPP are the solution to calibrate the model (I am no questioning figure 3, I simply think that transparency on the robustness on the measurements and the model is needed).
The results section is sufficient and graphical material is attractive, but as mentioned above the fundamentals behind the results need clarification.
In the discussion, the impacts of the different drought characteristics are well emphasized based on the results offered. I however believe that some argumentation on how is that these drought characteristics mechanistically affect GPP. For example, what triggers leaf shading and to what extent the photosynthetic capacity is reduced? What is the physiological condition of the vegetation during the peak rainy season that allows for a low drought impact. Section 4.1 is interesting and offers insights on the ecosystem limits for desiccation, but better context is needed to separate the temperature and drying effects. How does the model treat stomatal behavior and general gas exchange characteristics as a function of temperature, radiation or vapor pressure deficit? do the authors know anything about thresholds for water limitations of this system?. Fianally, little is discussed on the “carbon sequestration potential” as invoked early in the paper…
Some other minor comments and edits.
Line 100. Can the author provide one or two fundamental citations regarding the model?
Line 102 delete recognition.
Line 128-129. Please organize how the soil temperature measurements were conducted. Can the authors justify why soil temperatures a 300cm depth are needed, since at such depths the soil temperature is rather invariant, this is important since figure 1 suggest that it is an input parameter in the model.
Line 143. Please indicate “2m maximun (or minimum) air temperature”, why is Specific capitalized?
Line 147. Should it be period instead of comma?
Line 237. How was the model configured to simulate GPP?
Line 293 delete period.
Line 403. Delete “too”.
Line 405. Please revise sentence construction.
Line 448. SPEI1?
Line 451-452. Reads awkward, what if not shown?
Line 459. Natural rubber “trees”.
Line 473. Rubber “trees”.
Line 491. Drought scenarioS
Line 497. Drought scenarioS
Line 504. Please replace damage by effect
Line 507. Please delete “most pronounced”.
Line 508-512. I suggest removing these lines as this is not a conclusion from this work.
Comments on the Quality of English LanguageOnly minor issues with punctuation were detected.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsDear Editor,
Thank you for allowing me to review the manuscript entitled "Drought Sensitivity and Vulnerability of Rubber Plantation GPP – Insights from Flux Site-Based Simulating."
I have read the manuscript thoroughly and I think the manuscript is well written and relevant to Land. Unfortunately, at this stage, the manuscript needs substantial improvement – several things are not clear to me.
Major Issues
(1) Only one figure shows observational data and most of the manuscript is about modelling results. Therefore, as it is, it is an unbalanced manuscript. You need to write more about modelling (see 3 and 4 below, for e.g.).
(2) In line 210, you changed the source of the meteorological forcing to compare it with site observation GPP. What are the implications of this on GPP? Isn’t SEIB-DGVM sensitive to meteorological data?
(3) You calibrated the SEIB-DGVM model. Isn’t it worth writing the values of key parameters that you’ve obtained that we know impact/control GPP?
(4) There are a few studies (and are latest) that modelled carbon fluxes of rubber (e.g. GPP, NEE) like you did such as Ali et al. (2022), Kumagai et al. (2013) and Yang et al. (2019). All these studies should be brought in the introduction and discussion sections and compared with your model results (where possible).
(5) The meteorological and rubber flux data that you have used and studied in this study should be made publicly available. Many rubber studies from Southeast Asia have presented and shared their meteorological and eddy covariance flux data (e.g. Giambelluca et al. 2016; Wang et al. 2022).
Minor Issue
(1) Please check your reference list. Some references have been repeated there.
After the above issues are resolved, I think the manuscript will be clearer and then it could be useful or informative.
References
Ali AA, Fan Y, Corre MD, Kotowska MM, Preuss-Hassler E, Cahyo AN, Moyano FE, Stiegler C, Röll A, Meijide A and others 2022. Implementing a New Rubber Plant Functional Type in the Community Land Model (CLM5) Improves Accuracy of Carbon and Water Flux Estimation. Land.
Giambelluca TW, Mudd RG, Liu W, Ziegler AD, Kobayashi N, Kumagai To, Miyazawa Y, Lim TK, Huang M, Fox J and others 2016. Evapotranspiration of rubber (Hevea brasiliensis) cultivated at two plantation sites in Southeast Asia. Water Resources Research 52(2): 660-679.
Kumagai To, Mudd RG, Miyazawa Y, Liu W, Giambelluca TW, Kobayashi N, Lim TK, Jomura M, Matsumoto K, Huang M and others 2013. Simulation of canopy CO2/H2O fluxes for a rubber (Hevea brasiliensis) plantation in central Cambodia: The effect of the regular spacing of planted trees. Ecological Modelling 265: 124-135.
Wang X, Blanken PD, Kasemsap P, Petchprayoon P, Thaler P, Nouvellon Y, Gay F, Chidthaisong A, Sanwangsri M, Chayawat C and others 2022. Carbon and Water Cycling in Two Rubber Plantations and a Natural Forest in Mainland Southeast Asia. Journal of Geophysical Research: Biogeosciences 127(5): e2022JG006840.
Yang X, Blagodatsky S, Marohn C, Liu H, Golbon R, Xu J, Cadisch G 2019. Climbing the mountain fast but smart: Modelling rubber tree growth and latex yield under climate change. Forest Ecology and Management 439: 55-69.
Comments on the Quality of English LanguageGenerally, the manuscript is written well. However, I think some proof reading and checks might be useful.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsAuthors appropriately respond to review comments and the manuscript is now in good condition to be published
Reviewer 3 Report
Comments and Suggestions for AuthorsThe authors have now responded to my comments satisfactorily. Therefore, I do not see any potential issues from my side.
