Effects of an Invasive Bark Beetle Polygraphus proximus Blandf. Outbreak on Carbon Pool Dynamics in West Siberian Dark Coniferous Forests

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

 

Of course, assessing changes in the carbon stock in forest ecosystems during the impact of insects is important for calculating the processes of carbon sequestration in the biosphere. And in this regard, the task set in the paper is unconditional and important. The authors attempted to estimate the dynamics of carbon stocks in trees, woody debris, and in soil in four sample plots exposed to the influence of the bark beetle Polygraphus proximus Blandf. (Coleoptera: Curculionidae, Scolytinae). Observations on these sample plots were carried out from 2012 to 2023 and, according to the authors’ assumption, should have provided information about the patterns of dynamics of changes in the carbon stock in the forest ecosystem.

 

However, the presented results raise a number of questions.

IFirstly, all four sample plots are heterogeneous in composition and the proportion of Siberian fir in them

fluctuates almost twice - from 50 to 80%. The authors point out that the studied xylophagous species attacks only Siberian fir. And it is unclear whether the attractiveness of stands to pests varies depending on the composition of the forest stand. It would be possible to answer this question if the authors had repeated data on insect damage to stands with a similar species composition, but this data is not available. Further, it is unclear whether trees in different trial plots differed in tree attractiveness and resistance to pests. The authors did not assess the condition of the trees in the stands. With different attractiveness and resilience of trees, changes in carbon storage will vary.

 

It is clear that the intensity of tree attacks also depends on the local density of the pest population. However, these indicators are not given in the paper; it is unclear whether the studied sample plots are located within the same pest focus and whether the local densities of pest populations in the studied sample plots can be considered close, or whether these sample plots are located in areas that differ in pest population density. Thus, differences in the dynamics of stocks in different sample plots may depend on a whole complex of factors: the species composition of the stand, the physiological state of the trees, insect population density, plus variations in these characteristics for different stand with similar composition, which were also not assessed due to the uniqueness of each sample plot. And under these conditions, it is, in my opinion, incorrect to compare the data obtained for different sample plots and identify any general patterns.

In general, we can conclude that the presented work does not allow us to correctly assess the factors associated with the influence of insects on changes in the carbon stock in taiga forests. Any improvements to ten years of work and the introduction of additional data are obviously impossible for technical reasons.

Author Response

Thank you very much for your waiting. Many thanks to all the reviewers for their work and careful reading of the article, which pointed out weaknesses in the work and issues that we missed or did not describe clearly enough. We took into account all the reviewers’ comments and tried to answer them, and also made appropriate changes to the text, which undoubtedly had a positive effect on the accessibility of the described study and its results

Below is the answer to your questions:

Question 1 Firstly, all four sample plots are heterogeneous in composition and the proportion of Siberian fir in them fluctuates almost twice - from 50 to 80%.

Answer: Despite the difference in species composition in these stands, at least at the initial stages of monitoring, pathological death of only Siberian fir was observed, caused by its colonization by an alien pest

Question 2 The authors point out that the studied xylophagous species attacks only Siberian fir. And it is unclear whether the attractiveness of stands to pests varies depending on the composition of the forest stand. It would be possible to answer this question if the authors had repeated data on insect damage to stands with a similar species composition, but this data is not available.

Answer: The text cites a publication confirming this argument. We previously obtained this result based on the results of the analysis of more than four thousand trees on fifty sample plots with different participation of fir in the species composition (literary source Kerchev et al., 2022)

Question 3 Further, it is unclear whether trees in different trial plots differed in tree attractiveness and

resistance to pests.

Answer: As stated in the introduction, Siberian fir is a tree species that is vulnerable to the alien bark beetle and its symbiont fungi due to the lack of resistance mechanisms resulting from long-term coevolution

Question 4 The authors did not assess the condition of the trees in the stands. With different attractiveness and resilience of trees, changes in carbon storage will vary.

Answer: Perhaps the reviewer missed it, but the materials and methods describe the criteria for assessing the condition of trees, and a more detailed description of each category of trees is given in Appendix A.

Question 5 It is clear that the intensity of tree attacks also depends on the local density of the pest population. However, these indicators are not given in the paper; it is unclear whether the studied sample plots are located within the same pest focus and whether the local densities of pest populations in the studied sample plots can be considered close, or whether these sample plots are located in areas that differ in pest population density.

Answer: Thanks to your comment, we drew attention to the difficulty of understanding the spatial arrangement of sites. When making changes, we provided a map of the location of the areas. They belong to the same focus and are located at a distance from each other at a distance that is orders of magnitude smaller than the maximum range of the dispersal flight of the beetle, while their different disturbances are due to the diffuse expansion of the focus in time and space, which was formed in the area with the greatest participation of fir SP 1-12

Question 6 Thus, differences in the dynamics of stocks in different sample plots may depend on a whole complex of factors: the species composition of the stand, the physiological state of the trees, insect population density, plus variations in these characteristics for different stand with similar composition, which were also not assessed due to the uniqueness of each sample plot. And under these conditions, it is, in my opinion, incorrect to compare the data obtained for different sample plots and identify any general patterns. In general, we can conclude that the presented work does not allow us to correctly assess the factors associated with the influence of insects on changes in the carbon stock in taiga forests. Any improvements to ten years of work and the introduction of additional data are obviously impossible for technical reasons.

Answer: The article was aimed primarily at assessing the dynamics of qualitative and quantitative transitions of carbon reservoirs between living (preserving sequestration potential) and dead (gradually released as a result of heterotrophic decomposition) plant matter and soil in stands that died in a rather limited time period as a result of the action of an alien pest. The activity of the pest is comparable to, say, a fire, but at the same time it has completely different dynamics and little predictable consequences in the ecosystems under study, and observations were carried out in areas subject to damage with some delay, including due to the different proportion of fir between areas.

Reviewer 2 Report

Comments and Suggestions for Authors

The study investigates the effects of the invasive bark beetle Polygraphus proximus Blandf. outbreak on carbon pool dynamics in West Siberian dark coniferous forests. The author monitored the carbon pool dynamics on four plots with various degrees of damage. However, the article has several serious flaws. Here are my main comments, which I hope will be helpful to the author.

First, there was no replicate. The author just described the results for each single plot, and there was no statistical analysis. The comparisons along the time or among the different damage degrees were incredibility.

Second, is there any plot with no damage or weak damage? The no damage or weak damage plot can be used as a control.

Third, the paper investigates carbon pool change, but the introduction mainly introduced the invasive of the bark beetle and has little information about carbon processes. Simplify the information about beetle invasive, and review how would carbon processes change under beetle invasive and how the degrees of damage regulate the change.

Forth, the method for carbon content determination in wood and soil samples could be simplified.

Fifth, there was many results and analysis about carbon content with different degree of decomposition (debris). But the variation of debris carbon content seems useless, the paper mainly focused on carbon stock in debris.

 

Line 14, “monitoring of carbon fluxes” the paper didn’t detect carbon flux

Line 209, correlation analysis was used, but I didn’t find any association results about correlation analysis.

Table 1 and 2, what does 8F, 1SP, 1S, 7S`````` mean? I cannot follow these tables.

Figure 2, what does deposited carbon mean? Which part carbon belongs to deposited carbon?

 

Author Response

Thank you very much for your waiting. Many thanks to all the reviewers for their work and careful reading of the article, which pointed out weaknesses in the work and issues that we missed or did not describe clearly enough. We took into account all the reviewers’ comments and tried to answer them, and also made appropriate changes to the text, which undoubtedly had a positive effect on the accessibility of the described study and its results

Below is the answer to your questions:

First, there was no replicate. The author just described the results for each single plot, and there was no statistical analysis. The comparisons along the time or among the different damage degrees were incredibility.Second, is there any plot with no damage or weak damage? The no damage or weak damage plot can be used as a control.

Answer: Answer for 1 and 2 questions: Since at the time of the start of observations all the fir forests in the region were damaged to a greater or lesser extent, one trial plot was established in the Larinsky reserve in the least damaged part, which in our case was used as a control. It was there that the changes in the state of the forest stand were monitored. In addition, when tracking the dynamics of the state of the forest stand, the inventory data of the reserve's plantings, obtained five years before the date of pest penetration established by the dendrochronology method, were taken into account as a starting point.

Third, the paper investigates carbon pool change, but the introduction mainly introduced the invasive of the bark beetle and has little information about carbon processes. Simplify the information about beetle invasive, and review how would carbon processes change under beetle invasive and how the degrees of damage regulate the change.

Answer: Considering that not all readers are familiar with the problem of P. proximus invasion, which is the key reason for the drying out of fir forests in Russia, the aspects presented in the introduction are important for understanding the reasons for the transformation of plantings damaged by it. At the same time, we also tried to reveal in more detail the problem of the relationship between these processes and the dynamics of carbon pools

Forth, the method for carbon content determination in wood and soil samples could be simplified.

Answer:  In the description of the methods used for analyzing carbon content in wood and soil, unnecessary details were removed as suggested by the reviewer

Fifth, there was many results and analysis about carbon content with different degree of decomposition (debris). But the variation of debris carbon content seems useless, the paper mainly focused on carbon stock in debris.

Answer: The importance of analyzing the carbon content in debris is due to the fact that the primary result of an outbreak of a stem pest is the death of living trees - that is, the loss of their ability to fix carbon dioxide from the atmosphere (a quantitative indicator of this ability is the supply of living woody phytomass). In our study, we were interested in how much woody mortmass formed as a result of the fall of dead trees after a bark beetle outbreak retains carbon during heterotrophic decomposition and how this will be reflected in the soil

 Line 14, “monitoring of carbon fluxes” the paper didn’t detect carbon flux

Answer: “carbon fluxes” replaced by “carbon pool dynamics”

Line 209, correlation analysis was used, but I didn’t find any association results about correlation analysis.

Answer: Lines 359-361 Correlation was used in debris density, decomposition rate and carbon content analysis

Table 1 and 2, what does 8F, 1SP, 1S, 7S`````` mean? I cannot follow these tables.

Answer: There is a note for these two tables that describes what each letter in the abbreviation means.

Figure 2, what does deposited carbon mean? Which part carbon belongs to deposited carbon?

Answer: “deposited carbon” changed on “stored carbon”, stored in forms of organic compounds of wooden tissue

Reviewer 3 Report

Comments and Suggestions for Authors

An initial question I have from reviewing this paper is, why did you not include a survey plot in an area without any evidence of P. proximus invasion/outbreak? This would provide a nice comparison to highlight the damage directly associated with the invasive P. proximus. I noticed in table 2 you present stand characteristics from before the invasion. Where did these data come from? Why was this not mentioned in the methods? This provides a starting point and the "control" like point of comparison I mention.

Please better document when statistical tests and their results are actually being presented. Most of the comparisons it isn't clear if you performed a specific test or are speaking on general differences. 

I think this paper needs to be revisited with a tighter focus on what you really measured and what you have observed. I feel like the focus is a spread a little bit too thinly.

Overall, I am recommending reconsideration following major revisions.

I have several specific comments in the attached pdf file.

 

Comments for author File: Comments.pdf

Comments on the Quality of English Language

The English does require a bit of work for both clarity and readability. Throughout the paper there are instances where the translation is too wordy and statements can and should be made more directly. In several additional cases the syntax is a little out of order, e.g. "The alien species bark beetle..." should be "The alien bark beetle species...". I suggest the authors work with a translation editor to clean up these issues. 

Author Response

Thank you very much for your waiting. Many thanks to all the reviewers for their work and careful reading of the article, which pointed out weaknesses in the work and issues that we missed or did not describe clearly enough. We took into account all the reviewers’ comments and tried to answer them, and also made appropriate changes to the text, which undoubtedly had a positive effect on the accessibility of the described study and its results

Below is the answer to your questions:

An initial question I have from reviewing this paper is, why did you not include a survey plot in an area without any evidence of P. proximus invasion/outbreak? This would provide a nice comparison to highlight the damage directly associated with the invasive P. proximus.

Answer: Since at the time of the start of observations all the fir forests in the region were damaged to a greater or lesser extent, one trial plot was established in the Larinsky reserve in the least damaged part, which in our case was used as a control. It was there that the changes in the state of the forest stand were monitored.

 I noticed in table 2 you present stand characteristics from before the invasion. Where did these data come from? Why was this not mentioned in the methods? This provides a starting point and the "control" like point of comparison I mention.

Answer: In addition, when tracking the dynamics of the state of the forest stand, the inventory data of the reserve's plantings, obtained five years before the date of pest penetration established by the dendrochronology method, were taken into account as a starting point. Thanks for the suggestion to highlight this in materials and methods

 

Please better document when statistical tests and their results are actually being presented. Most of the comparisons it isn't clear if you performed a specific test or are speaking on general differences. 

Answer: Thank you very much, in the materials and methods we emphasized in the analysis of what data statistical methods were used

 

Answer: Edits highlighted by the reviewer are made The English language was corrected by shevchuk-editing.com

Reviewer 4 Report

Comments and Suggestions for Authors

Reviewer

 

Journal: Forests

Manuscript ID: forests-2823909

Type of manuscript: Article

Title: Effects of the invasive bark beetle Polygraphus proximus Blandf. outbreak on carbon pool dynamics in West Siberian dark coniferous forests

Authors: Ivan Andreevich Kerchev *, Elvina Mikhailovna Bisirova, Nikita Anatol`evich A. Smirnov, Igor Gennad`evich Grachev, Artem Nikolaevich Nikiforov, Daria Andreevna Kalashnikova

Abstract: The authors studied the alien species bark beetle Polygraphus proximus Blandf. of Far Eastern origin, which has caused Siberian-fir dieback in vast areas within several regions of Russia. The authors mentioned that rapid spread of the pest and its outbreaks raise the issue of preserving the most important functions, including carbon sequestration, by the damaged forests. In this study, monitoring of carbon fluxes was carried out during 2012–2023 on four sample plots showing various degrees of damage in the southern taiga zone of Western Siberia in the Larinsky Landscape Reserve. The authors discovered that the dynamics of the forest stands’ vitality were reflected in a rapid decline of the number of viable trees and an increase in amounts of deadwood, debris, and soil, resulting in a transformation of the natural biological carbon cycle in the native dark coniferous ecosystems.

 

Positive aspects:

·         The ecological studies on forest ecosystems are very precious, especially if we consider national parks or any other protected areas.

·         The information presented in the manuscript is new, original, complex and modern (focusing on one of the most important ecosystem function- carbon flow).

·         The manuscript is sustained by a suitable and diverse literature, strongly connected with the proposed research area.

·         The manuscript is well structured.

·         The manuscript presents an ecological study on long term (2012-2023), which is more and more rare our days, is a special research area (a protected area from Siberian region).

·         The objective of the study is clear defined.

·         The methodology is detailed described, scientific argued, modern, adequately for the proposed research area (detailed description of studied areas; Evaluation of dynamics of the woody phytomass pool; debris stock assessment and soil analysis).

·         Results and discussion are detailed presented (the authors making a comparison with data from North America and Canada).

·         The figures and tables are proper, reflecting the obtained results.

·         The proposed research subject is proper for Forest Journal.

 

Minor Comments:

·         Keywords (line 20): arrange them in alphabetic order.

·         Study area (line 78). Please, insert the geographical coordinates, the maximum altitude. Where the four study plots were situated from geographical point of view? I strongly recommend inserting a map or a scheme with the investigated plots.

·         Debris stock assessment (line 150). There is the same reference as those below, 29?

·         Soil analysis (line 159). Please, insert the references for the soil analysis methodology (including subchapter 2.6). I saw only one reference (no 30). It is available for whole chapter?

·         Table 3 (Line 351). Please, insert on insert in the material and methodology chapter, the criteria (and references) for decomposition degree!

·         Conclusions (line 470). I strongly recommend highlighting the practical importance of this study, focused on protection method of forest or implications on management plans of protected area.

·         References: Please, check if the all references were found in the manuscript and vice versa. Please, follow the instruction for the authors for references.

·         Appendix 1 (line 527). Please insert the VII category (even if they are fallen trees).

·         Appendix B (line 532). On averages values, please insert the standard error!

 

ALL these comments were inserting in the manuscript!

 

 

Comments for author File: Comments.pdf

Author Response

Thank you very much for your waiting. Many thanks to all the reviewers for their work and careful reading of the article, which pointed out weaknesses in the work and issues that we missed or did not describe clearly enough. We took into account all the reviewers’ comments and tried to answer them, and also made appropriate changes to the text, which undoubtedly had a positive effect on the accessibility of the described study and its results

Below is the answer to your questions and corrections:

Keywords (line 20): arrange them in alphabetic order.

Answer: keywords are arranged

• Study area (line 78). Please, insert the geographical coordinates, the maximum altitude. Where the four study plots were situated from geographical point of view? I strongly recommend inserting a map or a scheme with the investigated plots.

Thank you very much for the indicated disadvantage, we took a map with materials and methods.

• Debris stock assessment (line 150). There is the same reference as those below, 29? ·Soil analysis (line 159). Please, insert the references for the soil analysis methodology (including subchapter 2.6). I saw only one reference (no 30). It is available for whole chapter?

For these two subsections of the description of materials and methods, a revision of the citation of methods was carried out and they were replenished

• Table 3 (Line 351). Please, insert on insert in the material and methodology chapter, the criteria (and references) for decomposition degree!

We have added a list of criteria for assigning residues to one or another stage of decomposition

         Conclusions (line 470). I strongly recommend highlighting the practical importance of this study, focused on protection method of forest or implications on management plans of protected area.

Practical significance added to conclusions

• References: Please, check if the all references were found in the manuscript and vice versa. Please, follow the instruction for the authors for references.

Checked

• Appendix 1 (line 527). Please insert the VII category (even if they are fallen trees).

Category VII was introduced only to display the dynamics of the transition of dead wood into the category of debris. The corresponding reference to the literary source for describing the classes of xylolysis is given in materials and methods·       

  Appendix B (line 532). On averages values, please insert the standard error!

Standard errors added to the table Appendix B

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I looked at the new edition of the article and recommend it for publication

Author Response

Thank you very much, we are glad that you were satisfied with our answers and the changes made

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript has been improved with the additional information provided. But I still have several comments.

1.     My initial question about the replicates kept unclear, I don’t know how the author carried out the “Friedman ANOVA” analysis.

Although the author replied that “one trial plot was established in the Larinsky reserve in the least damaged part, which in our case was used as a control”, but there was no introductions and results about the control.

2.     The four plots (sp1-12, 2-12, 3-12, 4-12) seemed to represent the degradation degree of the forest stand, such as severe degradation, medium degradation, and or weak degradation. But in line 279 it was described as a chronological order, and in line 489 and line 507, it seemed combined with degradation degree and chronological order. I was confused by these descriptions. More strangely, it noted as I, Ⅱ, Ⅲ in the caption of figure 6 in line 507/8. Please introduce this information about plots at the material and method part, and keep the information consistently along the text.

Why emphasized degradation degree or chronological order in the soil part (3.4), but not on other parts (such as 3.2 and 3.3).

3.     Some paragraphs in the introduction and conclusion were too short, please combined some of them together.

4.     It’s better to give a figure of total carbon stock (including wood phytomass, wood mortmass, soil carbon```) along the time. The dynamics of total carbon pool will be interesting.

 

Figure 5 and 6, please tell the readers which year is the first year/beginning of the study, and which year is the final year/end of the study.

Line 129 “the degree of decomposition of forest stands” what does this phrase mean? Does it mean the degree of degradation of forest stands?

Also for line 480 “with the growing decomposition degree of forest stands” what does this phrase mean?

Author Response

The manuscript has been improved with the additional information provided. But I still have several comments.

1. My initial question about the replicates kept unclear, I don’t know how the author carried out the “Friedman ANOVA” analysis.

 

Although the author replied that “one trial plot was established in the Larinsky reserve in the least damaged part, which in our case was used as a control”, but there was no introductions and results about the control.

Answer: This two moments clarified in the text.

2. The four plots (sp1-12, 2-12, 3-12, 4-12) seemed to represent the degradation degree of the forest stand, such as severe degradation, medium degradation, and or weak degradation. But in line 279 it was described as a chronological order, and in line 489 and line 507, it seemed combined with degradation degree and chronological order. I was confused by these descriptions. More strangely, it noted as I, Ⅱ, Ⅲin the caption of figure 6 in line 507/8. Please introduce this information about plots at the material and method part, and keep the information consistently along the text.

Why emphasized degradation degree or chronological order in the soil part (3.4), but not on other parts (such as 3.2 and 3.3).

Answer: Considering that the idea of ​​using chronological orders was used only for the soil part, we abandoned it and the corresponding amendments were made to the text.

3. Some paragraphs in the introduction and conclusion were too short, please combined some of them together.

Answer: Relevant paragraphs have been merged

4. It’s better to give a figure of total carbon stock (including wood phytomass, wood mortmass, soil carbon```) along the time. The dynamics of total carbon pool will be interesting.

Answer: Unfortunately, as was reasonably explained in the soil research methodology, the third site was excluded from the analysis due to soil turbidity, and without it a complete picture of the four sites would not be possible.

Figure 5 and 6, please tell the readers which year is the first year/beginning of the study, and which year is the final year/end of the study.

Modified according to reviewer's suggestion

Line 129 “the degree of decomposition of forest stands” what does this phrase mean? Does it mean the degree of degradation of forest stands?

Answer: “Decomposition” changed on “degradation”.

Also for line 480 “with the growing decomposition degree of forest stands” what does this phrase mean?

Answer: “Decomposition” changed on “degradation”.

Reviewer 3 Report

Comments and Suggestions for Authors

I believe the information here is sound and this is interesting work. The manuscript has been improved with the additional information provided, particularly in the methods section. I am; however, concerned that the English was not improved from version 1 to version 2. This manuscript still requires extensive editing/review for correct English. I have difficulty understanding what you mean to say in parts, likely due to mistranslations. I recommend that the authors work directly with someone for whom English is their primary language to help clean-up this manuscript. 

Comments on the Quality of English Language

Per above, the English needs significant work to improve the readability and comprehensibility of this work.

Author Response

Additional clarifications were made in the text and inaccuracies that could make it difficult to understand were eliminated