Environmental Factors Driving the Transpiration of a Betula platyphylla Sukaczev Forest in a Semi-arid Region in North China during Different Hydrological Years

Round 1

Reviewer 1 Report

Observations

The manuscript is describing and discussing the daily transpiration responses in Betula forests related to environmental factors. It is valuable and interesting, but still needs multiple adjustments.

1. Title: I would think about the term regulation, maybe modification
2. Abstract: needs the method inclusions and the abbreviations only after the introduced terms. This observation about the abbreviations is valid for the whole text.
3. Through the whole manuscript the attention must be done to the scale of observation. If talking about transpiration, the scale must be defined (leaf, plant or stand), same as for photosynthesis and stomatal conductance.
4. The introduction is well done and sufficient but can include the references about papers that treated similar problems in other forests/species.
5. Also, can improve the construction, of all manuscript, shorter phrases, more direct. The differentiation between author’s actual work and everything previously published is generally made by using present for published and past for actual data. For that the phrases of Discussion must be direst, not counting the story about other authors.
6. The terms ‘normal’, ‘wet’… must be in ‘ ‘. Because they are relative and valid only for this paper.
7. The description about the messy data is very honest, but maybe it could be more direct and shorter,
8. I like the results, but maybe you needed some additional calculations, as RMSE and bias to understand the dispersion (Figure 5)? You must explain the letter significance in Figure 3.
9. Not necessary to put ‘.’ in measures.
10. Tables and figures must have the explanation text (i.e. Table 1 is practically included without the text in manuscript)
11. The Discussion is too extensive and written in only few paragraphs. Maybe you can focus and shorten it, finishing every paragraph with proper conclusion of that part of discussion. You made great Discussion, but it is too charged…
12. Conclusions are excellent. Still, take care about present and past.
13. Some detailed observations are included into the pdf of the 

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

This study focuses on the transpiration of Betula Platyphylla forest in a semi-arid environment in China. As the authors stated, drought severity is expected to increase so studies on the impact of droughts in trees at climate vulnerable regions are very important. Also, the authors have data from four hydrologically contrasting years which is very important as it allows to examine the effect of rainfall (and soil moisture) on transpiration. My major concern about this study is the poor description of some methodologies applied. More comments and suggestions are given below:

Introduction: The authors need to add more information on white birch and what did other studies (if any) found. Also, it would be nice to include the findings of other sap flow studies on forests with similar climate.

Line 43: Please rephrase the sentence. The “balance” cannot be depleted. Maybe use “water resources”, instead of “water balance”.

Lines 63-65: Sap flow is measured in 15-minute and hourly intervals too, so “from daily” is not valid.

Lines 124 – 128: How many DBH measurements were done in the forest?

Equation 1: This equation is physically not valid. According to this equation, any tree with DBH below 10cm will have zero and negative sap wood area, which is impossible. It would be better to test other equations too (power functions) and compare the results with literature. For example:

Eliades, M., Bruggeman, A., Djuma, H., Lubczynski, M., 2018. Tree Water Dynamics in a Semi-Arid, Pinus brutia Forest. Water 10, 1039. https://doi.org/10.3390/w10081039

Keyimu, M., Halik, Ü., Rouzi, A., 2017. Relating Water Use to Tree Vitality of Populus euphratica Oliv. in the Lower Tarim River, NW China. Water 9, 622. https://doi.org/10.3390/w9080622

Section 2.2: I think it would be better to follow a logic order in table 2 based on the calendar years, instead of the dry – wet years. I have the same consideration for the figures presented in the results section. It looks weird not to follow the time-series. Also, why are the years 2016, 2019 and 2020 missing? Instrumentation issues? Please explain the reasons of choosing these four specific years.

Lines 157 – 162: Please provide the manufacturer and country of origin, next to the instrument model in the parenthesis.

Equation 3: What is VWCm?

Lines 171 – 173: Can you provide some references for the definition of wilting point at 25% of the average field water holding capacity?

Lines 173 – 174: How did you measure the soil field water holding capacity?

Lines 178 – 180: Please rephrase this sentence. It is very difficult to read it. Check for syntax and grammar errors the entire manuscript.

Lines 193 – 194: Is there a natural colour difference between sapwood and heartwood in these species or did you apply an indication dye to see this difference?

Section 2.4.1: Are the selected power and multiplier values in equation 4 applicable for these tree species and environment? How did you define the “zero” sap flow? This is a crucial step in order acquire accurate sap flow rates and it is missing from the methodology.

Section 2.5: Did you use a specific software to apply the multiplication functions?

Figure 2:  Please see my comment above for the calendar years. Looking at q) and x) I can see that trees are transpiring even at 0 REW. Is this due to sensor accuracy errors or can this be explained by bedrock water uptake by the tree roots? Bedrock water uptake is common in semi-arid areas due to insufficient water supply from the soil.

Eliades, M., Bruggeman, A., Lubczynski, M.W., Christou, A., Camera, C., Djuma, H., 2018. The water balance components of Mediterranean pine trees on a steep mountain slope during two hydrologically contrasting years. J. Hydrol. 562, 712–724. https://doi.org/10.1016/j.jhydrol.2018.05.048

Also, in 2017 there are two high rainfall events (>50 mm / day) but strangely I don’t see any increase in the transpiration of young trees in the following days (2u). How is this possible?

Section 3.4: Can you also show the model results for the years 2018 and 2015? What is the bias between model and observed values?

Discussion and conclusion sections: I will add some comments/suggestions on these comments after the revisions.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

This is an average type of manuscript, investigating a topic that is very old in science. Investigating how much water certain plants consume daily and what is the effect produced by the variation of intra-annual and inter-annual precipitation, especially in trees that only depend on the precipitation. The only contribution that can be considered "new" is the elaboration of a multiplicative statistical model (not so new idea) with which it is possible to predict the consumption of water by the tree species studied. In addition to the wealth of data it contains. This manuscript it is more or less well written, but despite following the journal format, it is not well structured and there are many points that need to be paid close attention to.

Main concerns

Why not Penman-Monteith model?

Missing a section deeply describing all statistical analyses, including envelope curves, sample sizes.

The equation 8 arises from the search to model the responses of stomatal conductance as a function of environmental factors such as Rn, T, VPD, WP (water potential) instead of REW, etc. It was Paul G. Jarvis who first proposed it in 1976. However, this initial formulation lacked the contribution of each environmental variable that can restrict or enhance stomatal performance, which is now updated. However, this model presented in this manuscript suffers from the contribution of each factor (Rn, VPD, REW). The final transpiration model would be T = T_MAX[t˘ (Rn) t˘ (VPD) t˘ (REW)] where t˘(Rn), t˘(VPD), g(˘ VPD) and t˘ (REW) are the boundary-line functions and are weighted by the effect of each environmental variable taking a proportionality k from 0 to 1; these values change according to the studied species. And if it does, the authors do not explain in great detail how they obtained it, and this is crucial in the application of the model.

Proper credit needs to be given to the authors who initiated this formulation. Authors need to consult the literature on the multiplicative model around the world.

Lines 53-54: However, in discussion or conclusions there is nothing about. What next?

Lines 80-82: What about evaporation from the soil surface. Sometimes this component is important in the water balance.

Line 128: How many trees, small and large, were measured per sample?    

Line 159: : 2 m from the soil surface? within the cover of the trees? I am afraid that measurements were not valid for this study... the same for the other sensors. This sensors should be above the tree stand.

Line 198: equation 4: what is 0.714? where or what does it come from? Same for equation 5.

It does not agree with the initial statement of the problem that drought affects the performance of trees. Although it is true that in dry years transpiration is reduced (this was to be expected), the answer would be: how does this drought affect the trees? and not in terms of transpiration.

Lines 273-283: What statistical analyzes were performed to detect differences between the variables?

Fig. 4: The upper boundary line for T vs Rn appears be more linear than quadratic.  There are many doubts about the adjustment of the points to the upper boundary lines. The only apparently clear fit is T vs REW and probably it is a hyperbolic function not an exponential.  This method needs to be rigorously justified. What about this model T = k(VPD/(ra+rs))?

Equation 9: Whay not RMSE?

Line 253 Please show it in a supplemental apendix the obtention of these factors: 23, 0.43 and 0.32.

Minor concerns

In the title, Line 3: It is customary to write the species with lower case so Platyphylla must be platyphilla and if the authority is added it is better.

Line 27: Suk which is the authority should be written non-italics as Suk

Line 77: “…are the two main parts, it is better to write components instead of parts.

Line 85: Just typical or dominant?

Line 90: What Rn, VPD and REW stand for?

Line 104: Public dat? Why noy include the annual accumulated precipitation?

Line 105: Please add maxima and minima temperature.

Line 109: Please add authority in every species.

Line 116: Please add a detail description of the studied species. 

Fig. 1: Please Increase the resolution of the figure and include a better tower figure. From what level were the Rn measurements taken?

Line 134: Equation 1 it is better to use parenthesis, since × is a vector product and not a scalar.

Line 147: wetter is more humid than wet, so change that.

Line 150: What do you mean with water year, instead of use humid or wet season, or just year with no water.

Lines 257-263: This paragraph is not understable.

Line 271: (361mm) but in line 104, 375mm is written

Line 272: Please tell how these percentages were obtained.

Lines 273-274: Hard to believe between the driest and the wettest year. Include the statistical parameters.

Fig 3. Why not include precipitation? Statistical values? Figure legend needs more explanation.

Fig 4. I do not agree with that upper lines!!! Also, they are not relationships because they are upper lines.

What if numbers were written instead of letters in figure 2?

Equation 15 needs a better explanation

Lines 357- 359: It is not believable. Once again, it is very necessary to describe this method which is somewhat confusing,

Line 361: Really?

Line 375: What is this? Do you know how much water is invested in photosynthesis? Not too much! Almost nothing!!!

Line 399: Also leaf and air temperature have a direct effect on T. Since your calculated VPD is just with air temperature.

Line 417: Reference number?

Line 486: What about stand evaporation? This variable also affect the soil water content!

Line 599: Why in capital letters?

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors improved the manuscript, but it still needs lot of work.

Title - I gave one proposition how not to use effects, impacts... but to be directly connected to your results.

Abstract - take care about the verbs and times.

Introduction - some parts of Discussion could be included in Introduction (in a very reduced form).

M&M - Please, all method details must be included here, not in Results.

Results - Please, do not repeat the similar statements, or phrases. Organize your figures with alphabet end always define where the reader must read.

Discussion - the worst part of the manuscript. Not mature. Compare your results with other results of other scientists. Not describe extensively the work of others, but please, compare their work and results to your data and results. Every paragraph must conclude something.

Detailed observations are done in 'pdf' file.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

The authors have addressed my comments and suggestions and the manuscript has been significantly improved. I recommend this manuscript for publication in Forests. 

Author Response

Thank you for your comments and suggestions, which are very helpful to my manuscript.

Reviewer 3 Report

This paper has been greatly improved, however, there are still some concerns about it with some confusing passages mainly in material and methods section.

The manuscript presents many approximations and one of them is to ignore the direct evaporation from the soil and the location of the instruments such as the net radiometer that should be installed above the treetops, and do not discuss anything about it in the discussion section. Fuerthermore, in the analyzes of envelope functions, the air or leaf temperature is not taken into account. Remember that temperature is the way in which the amount of heat that a body can have is measured. Therefore the air or leaf temperature should have been taken into account. No matter what VPD is introduced since vpd is the ability of the air or the atmosphere to absorb water vapor and not the heat delivered to the leaf. The authors claim that transpiration only depends to a large extent on Rn and VPD, but they have not used other environmental variables to affirm this relationship.

Lines 243 - 247. Difficult to follow.

Lines 248 - 250. You must use all the data. All Rn vs all Tt and so on, it is no clear why data were selected.

Lines 261-265. This possibly biases the envelope function, and the data is selected without having to do with the envelope. This method is confusing. What are the statistical parameters of the envelope functions? In addition, this not the way to select the envelope function.

I do not understand all the 2.7 section. The contribution of every environmental variable is on the envelope functions according to the values of every variable is giving at any time.

Figure 3. What is the value of N? How did you perform the ANOVA with just two trees?

Figure 4. What are the statistical parameters of the envelope functions?

Figure 5. What do you mean with odd days?

Conclusions section is not complete, what about stand transpiration?

Bibliography not exahustive 

Author Response

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Author Response File: Author Response.docx