Round 1

Reviewer 1 Report (New Reviewer)

Comments and Suggestions for Authors

Reviewer’s Report on a Research Paper Entitled

Adaptive Capacity of Scots Pine Trees to Meteorological Extremes in Highly Oligotrophic Soil in Hemi-boreal Forest

(Forests-4067203)

This study addresses a timely and important issue by examining how hemi-boreal forests respond to increasingly frequent and intense climatic extremes. Focusing on the Curonian Spit—a highly arid and environmentally fragile dune system—the authors provide valuable insights into tree-level adaptive responses under deplorable site conditions. The long-term dataset (2018–2024) strengthens the analysis and allows for a robust assessment of both immediate and lagged effects of climatic stressors on Scots pine ecophysiology.

The integration of sap flow density, stem volume increment, and water-use efficiency is a notable strength, as it offers a comprehensive view of tree functioning across dormant and vegetation periods. The finding that climatic factors may exert opposing effects depending on seasonal timing is particularly interesting and adds nuance to current understanding of tree–climate interactions. The emphasis on warmer winters and early-summer heatwaves as critical drivers of declining productivity is well supported by the results and aligns with emerging evidence from other hemiboreal regions.

However, the manuscript would benefit from clearer mechanistic explanations linking observed physiological responses to specific climatic drivers, especially regarding the lagged effects across seasons. A brief comparison with similar studies from other north-eastern European sites could also help contextualize the broader applicability of the findings. Additionally, explicit discussion of management or adaptation implications would strengthen the relevance of the study for forest sustainability planning. In addition, there are major and minor issues that need to be addressed carefully, and I recommend that the authors provide their version of the argument if they plan to submit a revised manuscript.   

 

Major Issues:

1. 
   a) At the outset, the study is conducted at a single, highly specialized location—the Curonian Spit—which represents an extreme and atypical hemi-boreal environment. While this strengthens insights into stress responses under harsh conditions, it limits the generalizability of the findings to broader Scots pine forests with more moderate soils and hydrological regimes.
2. b) Secondly, although the study highlights threats to forest sustainability, it provides limited guidance on how forest management practices (e.g., thinning, species mixing, or assisted migration) could mitigate the identified risks.

 

 

Minor Issues:

1. Page 1: Lines 42-44: The following sentence needs a reference: The WUE of Scots pine (Pinus sylvestris ), in particular, is 42 influenced by climatic variables such as temperature, precipitation, and vapor pressure 43 deficit (VPD), all of which interact to shape tree physiological processes.
2. Page 2: Line 70- Typo Error: ‘To meet the aim of the studies following objectives were drown’, may be drawn? And, the modified sentence looks as, ‘To meet the aim of the studies, the following objectives were drawn’.
3. Page 2: Line 89: This sentence, ‘Forest type: oligotrophic mineral soil site’, can be written as, ‘Forest type: Oligotrophic forest on mineral soil’.  
4. Page 4: Lines 159-160: Clarification is needed: ‘Predicted values were generated with the predict function in R’. The intention of the authors is ‘R software’ or something else?  
5. Please provide the geographic latitude and longitude of the Lithuanian Curonian Spit National Park at an appropriate place.
6. Page 3: Lines: 102-103: Provide units for ‘wind speed and direction, atmospheric pressure, precipitation, relative humidity, air temperature (mean, maximum, minimum), and solar radiation’.
7. It seems to me that Figure 2 has been copied from somewhere else and merely copied here. I suggest that the authors redraw it using appropriate software.
8. To the best of knowledge, no need to repeat ‘vapor pressure deficit (VPD)’, several times in the manuscript.
9. I did not understand why most of the equations were typed simply in MS Word version, which looks unprofessional to me. I, therefore, suggest that the authors use any authenticated software.

Comments for author File: Comments.pdf

Author Response

We have carefully studied all the reviewers' comments, taken them into account, and once again rewrote the article, hoping that it will now be suitable for publication in the journal Forests.

 

Third part of the positive evaluation of the manuscript: (I) the manuscript would benefit from clearer mechanistic explanations linking observed physiological responses to specific climatic drivers, especially regarding the lagged effects across seasons. (II) A brief comparison with similar studies from other north-eastern European sites could also help contextualize the broader applicability of the findings. (III) Additionally, explicit discussion of management or adaptation implications would strengthen the relevance of the study for forest sustainability planning. In addition, there are major and minor issues that need to be addressed carefully, and I recommend that the authors provide their version of the argument if they plan to submit a revised manuscript.

(I) the manuscript would benefit from clearer mechanistic explanations linking observed physiological responses to specific climatic drivers, especially regarding the lagged effects across seasons.

Response to I part:

Lagged effects of meteorological conditions across seasons represent a major challenge in the integrated evaluation of environmental drivers of tree ecophysiological responses. To address this complexity, dendrochronological approaches are widely used to identify both direct and delayed relationships between climate and tree functioning. Following this established framework, we applied a mathematical approach that explicitly compares the significance of direct (current-season) and indirect (lagged) effects of the same meteorological variables on the investigated physiological processes.

Tree growth, particularly in coniferous species, reflects climatic conditions integrated over multiple years because needles persist for several years (approximately 3 years in pine and 7–9 years in spruce). Consequently, observed physiological responses cannot be attributed solely to current-season climate but rather to cumulative and lagged meteorological influences. We believe that our analytical approach adequately captures these mechanisms and meets the main objectives of the study in a reliable and scientifically sound manner. In addition, we further elaborate on these mechanistic linkages and lagged effects in the Discussion section.

 

(II) A brief comparison with similar studies from other north-eastern European sites could also help contextualize the broader applicability of the findings.

Response to II part:

The primary aim of this study was not to generalize the findings across north-eastern Europe, but rather to assess the resistance and resilience of Scots pine under exceptionally unfavorable growing conditions, specifically under the pressure of extreme heat and drought. Our objective was to approach potential threshold conditions for pine growth, beyond which targeted silvicultural measures may be required to ensure survival or reduce mortality.

Contrary to our expectations, the results did not provide clear evidence that extreme meteorological conditions reduced the sustainability of pine trees growing under extremely poor site conditions. Because the study focuses on highly specific and extreme environmental settings, direct comparison with broader regional studies is inherently challenging and may be of limited applicability. Nevertheless, the findings contribute valuable insight into pine performance under near-threshold conditions, which may inform assessments of forest resilience under future climate extremes.

Additionally, explicit discussion of management or adaptation implications would strengthen the relevance of the study for forest sustainability planning.

Response to III part:

Management and adaptation implications were addressed in the Discussion section of the manuscript. To further strengthen this aspect, we emphasize that adaptive forest management practices—such as appropriate thinning of pine stands and the development of mixed-species coniferous stands—can enhance overall stand sustainability, as well as resistance and resilience to unfavorable biotic and abiotic factors. These measures may be particularly important under increasing pressure from climatic extremes, even though the pine trees in this study demonstrated exceptional resistance and resilience, with a high adaptive capacity to survive unfavorable environmental conditions without the implementation of such measures.

In addition, there are major and minor issues that need to be addressed carefully, and I recommend that the authors provide their version of the argument if they plan to submit a revised manuscript.

Major Issues:

1. At the outset, the study is conducted at a single, highly specialized location—the Curonian Spit—which represents an extreme and atypical hemi-boreal environment. While this strengthens insights into stress responses under harsh conditions, it limits the generalizability of the findings to broader Scots pine forests with more moderate soils and hydrological regimes.

Response: We acknowledge that the study was conducted at a single, highly specific site—the Curonian Spit—which represents an extreme and atypical hemi-boreal environment and therefore limits direct generalization to Scots pine forests growing under more moderate soil and hydrological conditions. However, this site was intentionally selected to examine pine responses under exceptionally unfavorable environmental conditions, where stress effects are expected to be most pronounced. Under typical site conditions, Scots pine rarely faces severe survival constraints, as it is among the most climatically adaptive tree species in boreal and hemi-boreal forests. By focusing on near-threshold environments, our approach provides valuable insight into the limits of pine resistance and resilience under current and future climatic extremes.

1. Secondly, although the study highlights threats to forest sustainability, it provides limited guidance on how forest management practices (e.g., thinning, species mixing, or assisted migration) could mitigate the identified risks.

Response: We agree that the present study provides limited guidance on specific forest management practices (e.g., thinning, species mixing, or assisted migration) to mitigate the identified risks. However, our results indicate that exceptional or intensive forestry interventions are not required for Scots pine to survive extreme environmental conditions at the studied site. Instead, conventional forest management practices appear sufficient to ensure the sustainable development of pine forests under such stress.

As noted in the Discussion section, standard silvicultural measures—particularly thinning aimed at maintaining lower stand density and promoting trees with larger structural parameters—can enhance stand sustainability by increasing resistance and resilience to climatic stress. These findings suggest that adaptive capacity in Scots pine is already high under extreme site conditions, and that well-established management practices remain appropriate under current and near-future climatic extremes.

Minor Issues:

1. Page 1: Lines 42-44: The following sentence needs a reference: The WUE of Scots pine (Pinus sylvestris ), in particular, is 42 influenced by climatic variables such as temperature, precipitation, and vapor pressure 43 deficit (VPD), all of which interact to shape tree physiological processes.

Response: We have done it.

1. Page 2: Line 70- Typo Error: ‘To meet the aim of the studies following objectives were drown’, may be drawn? And, the modified sentence looks as, ‘To meet the aim of the studies, the following objectives were drawn’.

Response: We have done it.

1. Page 2: Line 89: This sentence, ‘Forest type: oligotrophic mineral soil site’, can be written as, ‘Forest type: Oligotrophic forest on mineral soil’.  

Response: We have done it.

 

1. Page 4: Lines 159-160: Clarification is needed: ‘Predicted values were generated with the predict function in R’. The intention of the authors is ‘R software’ or something else?  

Response: We have done it.

1. Please provide the geographic latitude and longitude of the Lithuanian Curonian Spit National Park at an appropriate place.

Response: We have done it in Fig. 1.

1. Page 3: Lines: 102-103: Provide units for ‘wind speed and direction, atmospheric pressure, precipitation, relative humidity, air temperature (mean, maximum, minimum), and solar radiation’.

Response: We have done it.

1. It seems to me that Figure 2 has been copied from somewhere else and merely copied here. I suggest that the authors redraw it using appropriate software.

Response: We have done it.

1. To the best of knowledge, no need to repeat ‘vapor pressure deficit (VPD)’, several times in the manuscript.

Response: We have done it. Only a few instances remain, where its use is necessary for clarity in the main text, as well as in figure and table captions.

1. I did not understand why most of the equations were typed simply in MS Word version, which looks unprofessional to me. I, therefore, suggest that the authors use any authenticated software.

Response: We have done it. All complex equations have now been typeset using appropriate equation-editing software. For simple – one line formula it is no difference which method is applied.

 

Thank go to the Reviewer 1, which gave final positive evaluation of the manuscript.

Reviewer 2 Report (New Reviewer)

Comments and Suggestions for Authors

The authors report on a study of high precision measurements of stem diameter fluctuations and sap flow of ten pine trees from four plots on the poor soils (coastal sand dunes) of the Curonian spit over seven years. The dataset is very solid (eco-physiological assessments on multiple trees during a long time) and allows for a reliable discussion on stem increment, transpiration and water use efficiency. The study species is Pinus sylvestris (Scotch pine) that has an exceptionally wide geographic distribution and shows a strong tolerance to diverse environmental stressors. Understanding the dynamics of water use efficiency in Scots pine is indeed important, giving the changing climate. The study area is characterized by very dry soil conditions, making the experimental setup suitable to study the consequences of drought on tree growth and transpiration. Scots pine seems to be able to maintain growth performance and adjust water use efficiency, even under challenging conditions. Warm winters had a significant positive effect on stem increment at the beginning of the growing season, but this effect was weaker in mid-season and was especially weak toward the end of growing season. Moisture deficits combined with heat waves—particularly in June—reduced stem increment and increased sap flow and raised the water content in the wood. Higher trees showed a higher water-use efficiency.

Major comments

• Change title to avoid reference to the Darwinian concept of “adaptation” and to make it more precise: e.g. “Scotch pine growing on nutrient-poor soils maintain a high WUE in the changing climate of the hemi-boreal forests
• All figures and tables need to be self-explaining through extended legends.

Abstract

• Many statements are too general. Refer to the precise scientific results of the paper.

Introduction

• Make clear that you are working on the level of the individual trees
• The selection of eco-physiological measurements needs to be justified.

Material and Methods

• Give more details on the particular site conditions. Is there substantial influence from the sea to be expected? Strong winds? Mist, condensation on the needles?
• More details needed on the dendrometer and sap flow measurements. What is the allometry to transfer diameter measurements into volumes? Give the formula. What is the formula to transfer sap flow measurements to transpiration values?
• How did you distinguish between swelling and growth?

Results

• There are many figures and tables. To emphasize the main message of the paper, you might transfer some of the graphical elements to a supporting material section.
• The chapter on linear mixed models could also go to supporting material. This will make the structure of the paper more clear.
• There is a very strong focus on mean values and general (linear) trends. This contrasts somehow with the eco-physiological angle ; you may select some of the extreme weather conditions (could be justified, given your ecophysiological angle)
• Next to the mean values and trends, you can make a selection of particular cases (diurnal pattern on rainy days and after prolonged drought) that are worth reporting and discussing. See for instance that a typical stem shrinkage just before the start of the growing season is absent in 2024.
• Give also an overview of the pattern of shrinkage.
• Introduce the phenomenon of negative transpiration (downward sapflow?)
• How did you define the “vegetation” period, the dormant season, the peak period ?

Discussion:

• Refer to stable isotope (C13) measurements on tree rings
• Discuss the model function of a study on the Curonian spit. To what extent the results are representative, for what type of forests?
• Don’t discuss the methods (mixed effect models)
• Add references to water use efficiency studies through stable carbon isotopes

Author Response

Major comments

• Change title to avoid reference to the Darwinian concept of “adaptation” and to make it more precise: e.g. “Scotch pine growing on nutrient-poor soils maintain a high WUE in the changing climate of the hemi-boreal forests

Response: We respectfully disagree that the use of the term adaptation is inappropriate in the context of this study. The primary focus of the manuscript is the assessment of adaptive capacity of Scots pine growing under exceptionally poor site conditions, where meteorological parameters have changed most markedly in recent years. The physiological and growth responses observed under such extreme environmental conditions reflect the species’ ability to cope with and adjust to sustained climatic stress, which we consider a valid representation of adaptive processes at the individual and stand level.

Furthermore, the selection of the manuscript title is the responsibility of the authors and should accurately reflect the scientific scope and objectives of the study. We therefore consider the current title to be appropriate and consistent with the content and intent of the manuscript.

• All figures and tables need to be self-explaining through extended legends.

Response: We have revised the manuscript to improve table formatting and enhance the clarity of figure legends. In particular, Figure 2 has been updated. Previous reviewers indicated that the figures, after the last round of improvements, were acceptable. To ensure that all figures meet the current reviewer’s expectations, we would appreciate specific guidance on any figures that are considered unclear or insufficiently self-explanatory.

Many of the figures were prepared using Excel, which is widely accepted for producing figures in scientific publications. We have ensured that all figures are clear, legible, and informative in their current format.

Please indicate which figure is not acceptable in the presented format.

Abstract

• Many statements are too general. Refer to the precise scientific results of the paper.

Response: We have revised the abstract to ensure it is fully based on the specific results obtained in the study. General statements have been replaced or supported with precise scientific findings, so that the abstract accurately reflects the key outcomes and conclusions of the research.

Introduction

• Make clear that you are working on the level of the individual trees

Response: We have done it.

 

• The selection of eco-physiological measurements needs to be justified.

Response: We have done it in in the relevant section. 

Material and Methods

• Give more details on the particular site conditions. Is there substantial influence from the sea to be expected? Strong winds? Mist, condensation on the needles?

Response: We agree that detailed information on site-specific conditions is important. While we would have liked to provide more information on microclimatic influences such as sea proximity, strong winds, and condensation on needles, space constraints required the removal of several figures from the manuscript.

Wind speed was initially included as a predictor variable, but it was removed from the final analysis due to its negligible effect on the studied ecophysiological processes. Other factors, such as mist and needle condensation, were not directly measured at the site, and their short-term and highly variable nature makes it difficult to assess their impact reliably within the scope of this study.

• More details needed on the dendrometer and sap flow measurements. What is the allometry to transfer diameter measurements into volumes? Give the formula. What is the formula to transfer sap flow measurements to transpiration values?

Response: For the estimation of stem volume increment, we applied a standard silvicultural formula based on tree diameter recalculated to basal area, tree height, and a stem form index. This approach is widely used in forestry science, and we believe that the formula is sufficiently standard that explicit presentation in the manuscript is unnecessary.

Sap flow measurements were converted to transpiration values using specialized software rather than a single formula. Specifically, measured temperature differences were processed to calculate sap flux density, and total tree water use was determined using the International Sap Flow Tool software (for HFD and HRM data) [22], which is calibrated for Scots pine sapwood properties. Detailed information on this procedure is provided in the Methods section.

• How did you distinguish between swelling and growth?

Response: In this study, it was not necessary to explicitly separate swelling/shrinking from growth processes, as these phenomena are most relevant on hourly or diurnal timescales. To minimize their influence on measured stem circumference changes, we focused on periods during the growing season when actual radial growth occurs. Swelling and shrinking predominantly occur in late autumn and early spring. By selecting measurement intervals within the active growing season, we effectively eliminated the influence of these short-term fluctuations on the calculated annual stem increment.

Results

• There are many figures and tables. To emphasize the main message of the paper, you might transfer some of the graphical elements to a supporting material section.

Response: We have already removed several figures from the manuscript to improve clarity and focus. We are willing to consider further adjustments if the reviewer identifies additional figures that could be moved to the supplementary material or deleted. Regarding the tables, we believe that all of them are essential for presenting the results comprehensively and have therefore retained them in the main manuscript.

• The chapter on linear mixed models could also go to supporting material. This will make the structure of the paper more clear.

Response: We are very disappointed by the reviewers’ view of this section of the manuscript. The linear mixed models’ chapter was a key reason why our manuscript was not accepted for publication in the previous review, resulting in the loss of the opportunity to publish the manuscript free of charge. Now, the suggestion is to move this entire section to the supplementary material as if it were non-essential, and that the manuscript would be clearer without it. We find this suggestion very unfortunate and disagree with it. It is very sad to give such suggestion.

• There is a very strong focus on mean values and general (linear) trends. This contrasts somehow with the eco-physiological angle ; you may select some of the extreme weather conditions (could be justified, given your ecophysiological angle)
• Next to the mean values and trends, you can make a selection of particular cases (diurnal pattern on rainy days and after prolonged drought) that are worth reporting and discussing. See for instance that a typical stem shrinkage just before the start of the growing season is absent in 2024.

Response: The objectives of the present study were addressed using monthly, seasonal, and annual data. Investigating variation in pine tree ecophysiological responses on hourly or diurnal scales represents a separate research question, which we have already addressed in earlier publications cited in the manuscript. Integrating all temporal scales into a single manuscript would be an extremely complex task, requiring detailed investigation beyond the scope of the current study. We plan to address these finer-scale dynamics in forthcoming publications that are currently under preparation.

• Give also an overview of the pattern of shrinkage.

Response: The detection of true stem increment is achieved by accounting for swelling in late autumn and shrinking in early spring, which allows us to isolate actual growth. Additionally, manual stem dendrometers, which are less sensitive to short-term circumference fluctuations, provide reliable measurements of real growth. While these processes can have direct effects on stem ring formation, their influence is primarily driven by meteorological conditions. At the monthly or annual scale used in this study, we consider these effects to be negligible for the analysis of pine tree increment. Figure 7 effectively illustrates this pattern and supports our interpretation.

• Introduce the phenomenon of negative transpiration (downward sapflow?)

Response: It is effect of temperature below 0 degree and it is not significant data analyzing tree reaction to stress. Sap flow is measured as difference between upper and lover temperature of the installed needles in xylem. When air temperature is below 0, this data is quite usual and not important for the annual investigation.

• How did you define the “vegetation” period, the dormant season, the peak period ?

Response: we define the “vegetation” period, the dormant season, the peak period based on intensity of the considered response variables, data of which are presented figures 7, 10, 12.

Discussion:

• Refer to stable isotope (C13) measurements on tree rings

Response: It is not the task of the presented study.

• Discuss the model function of a study on the Curonian spit. To what extent the results are representative, for what type of forests?

Response: the answer is prepared replying to the comments of the first reviewers. Forest type is described in the second section of the manuscript.

• Don’t discuss the methods (mixed effect models)

Response: there was the key point why the manuscript was rejected from the previous presentation.

• Add references to water use efficiency studies through stable carbon isotopes

Response: It is not the tasks of the presented studies.

The main response to the reviewers 2 comments: notwithstanding this that reviewer at the beginning of evaluation of the manuscript quite well evaluated our presented study, but afterwards all comments were addressed not to the maim tasks of the study. We tried to evaluate the adaptive capacity of pine trees under exceptional growing condition at monthly and annual scales to the aim to detect threshold in them, exceeded which pine increment dropped up to the minimal with big probability to die. In the present study we did not detect such condition and it is not our fault. Finally, it seems that the reviewer did not review the manuscript but examined the authors. This should not be done during article evaluation procedures, especially in high-level scientific journals.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is already the third time this manuscript has been sent for review. In the previous two rounds, the main concern was the statistical models that were inappropriate for the hierarchical data structure. In this version, the authors have implemented linear mixed effects models (LMM) to account for data structure. But this is done not by replacing the original models (regression and ANOVA) but as an additional analysis. There is no need to have two types of models for the same data. LMM should be used as a replacement for the regression models and ANOVA, and not as a tool to re-check the data. Using just one type of model will also reduce the necessity to repeat result explanations as it is written now – the same main texts are written for regression models and then for the LMM.

The reviewer still believes that existing statistical models are not appropriate and should be replaced with LMM.

When using the LMM, the authors should also consider whether the site ID is the only random factor. If multiple observations from the same tree are present, then the random factor structure should include nested structures (trees within sites).

Additional comments:

Results section 3.7: Part of the information could be presented as a table with the main model and model statistics, so there is no need to write all the information as text.

Figure 6 – move the x-axis text (dates) to the bottom of the plot so they do not overwrite the actual data. The same principle applies to Figures 7, 9, 12, and 14.

Author Response

Comment: The reviewer still believes that existing statistical models are not appropriate and should be replaced with LMM.

Response: 

we have reconstructed the analyses using linear mixed-effects models (LMMs) for annual data on tree stem volume increment, sap flow density, and water-use efficiency. This approach allows us to account for random variability among subplots and trees, thereby improving the robustness and reliability of the statistical results. All corresponding sections in the Methods and Results have been updated accordingly.

Comment: When using the LMM, the authors should also consider whether the site ID is the only random factor. If multiple observations from the same tree are present, then the random factor structure should include nested structures (trees within sites).

Response: We tested alternative random-effect structures, including a nested model with tree ID within site ID ((1 | Site/Tree)), to account for potential tree-level autocorrelation. However, model comparison using AIC indicated no improvement in model fit, and the variance component for tree ID was negligible. Therefore, we retained site ID as the single random factor to maintain model parsimony and avoid overparameterization.

Comment: 

Results section 3.7: Part of the information could be presented as a table with the main model and model statistics, so there is no need to write all the information as text.

Response: It is done

Comment: 

Figure 6 – move the x-axis text (dates) to the bottom of the plot so they do not overwrite the actual data.

Response: 

In Figure 6, the elements identified as “x-axis text” are actually the figure legend, which has been placed in the middle of the plot to avoid overlapping with the data lines.

Comment: 

The same principle applies to Figures 7, 9, 12, and 14.

Response: We have done it

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Congratulations on the work you have carried out and, above all, on the choice of topic, which is highly relevant to the current needs of the forest science community.

That said, I have attached a PDF file containing some detailed comments. I believe your manuscript presents an impressive level of detail across all analyzed parameters. However, this depth does not fully align with the initial hypothesis. Specifically, while the study is both interesting and well-executed, the assumptions made are not supported by a sample size sufficient to validate the results. At present, this represents a significant limitation, which I hope you will be able to address.

Additionally, I would like to offer a structural suggestion: the results section is very well detailed, and I recommend integrating the discussion directly within it, creating a unified "Results and Discussion" section. I believe this would improve the overall readability and coherence of the manuscript, although the final decision naturally remains yours.

Comments for author File: Comments.pdf

Author Response

Comment: 

At present, sample size represents a significant limitation, which I hope you will be able to address.

Response: 

We appreciate the reviewer’s valuable comment and acknowledge that the limited sample size constrains the scope of inference. Addressing this limitation would require additional long-term data collected under specific climatic conditions, particularly deep droughts in June–July combined with warm winters. However, such extreme events are difficult to predict and have not occurred again in the Curonian Spit National Park since our observation period.

We believe that the seven-year monitoring period provided sufficient temporal coverage to meet the main objectives of this study and capture the key climatic–ecophysiological relationships. Increasing the sample size by analyzing data at the level of individual trees did not improve the reliability of causal relationships, but only increased the statistical weight of dendrometric parameters.

Comment: 

Suggestion: the results section is very well detailed, and I recommend integrating the discussion directly within it:

Response: 

We thank the reviewer for this thoughtful suggestion. However, integrating the Discussion directly into the detailed Results section would make the section excessively long and difficult to follow. We believe that keeping the Results and Discussion separate ensures greater clarity and readability, allowing readers to distinguish between data presentation and interpretation. For this reason, we retained the traditional structure of separate sections while ensuring that key findings are clearly linked to their interpretation in the Discussion.

 

Response to the rest comments: All other comments and suggestions from the reviewers have been carefully considered and fully implemented in the revised manuscript.

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This is already the fourth round for this manuscript to be sent for review. The authors in the response letter write that they have restructured the manuscript regarding the LMM, and that this has been done. But, they have not taken into account the main comment that was present in all previous reviews -  there is no need to use the multiple linear regression, and instead use linear mixed effects models for all data. The authors also do not provide reasoning why they still ignore this recommendation. 

Next, the authors write that they have made changes to figures 6, 7, 9, 12, and 14. But if you look at the manuscript, all those figures still have the same problem (for some of them, the numbering has been changed)—the x-axis texts are located in the middle of the plot, and so the bars or lines go under or through those names. The axis labeling should be placed on the bottom of the plot so it does not interfere with the bars/lines.

Author Response

Comment: This is already the fourth round for this manuscript to be sent for review. The authors in the response letter write that they have restructured the manuscript regarding the LMM, and that this has been done. But, they have not taken into account the main comment that was present in all previous reviews -  there is no need to use the multiple linear regression, and instead use linear mixed effects models for all data. The authors also do not provide reasoning why they still ignore this recommendation. 

Comment: When using the LMM, the authors should also consider whether the site ID is the only random factor. If multiple observations from the same tree are present, then the random factor structure should include nested structures (trees within sites).

Comment: Results section 3.7: Part of the information could be presented as a table with the main model and model statistics, so there is no need to write all the information as text.

Response: It is done based on 10 monitored pine trees represented 4 subplots. In this revised version, we now analyze all relevant datasets exclusively using linear mixed-effects models, following the recommendation provided in previous review rounds. The random-effects structure has been updated to reflect the hierarchical nature of the data: individual trees are nested within sites (TREE_N within SITE_N), and “Year” is included as an additional random factor where interannual variability is relevant (Section 2.5). Furthermore, the statistical outputs of the LMMs are now summarized in Tables 3 and 4, which reduces the amount of descriptive text previously included in Section 3.7.

Comment: Next, the authors write that they have made changes to figures 6, 7, 9, 12, and 14. But if you look at the manuscript, all those figures still have the same problem (for some of them, the numbering has been changed)—the x-axis texts are located in the middle of the plot, and so the bars or lines go under or through those names. The axis labeling should be placed on the bottom of the plot so it does not interfere with the bars/lines.

 Figure 6 – move the x-axis text (dates) to the bottom of the plot so they do not overwrite the actual data. The same principle applies to Figures 7, 9, 12, and 14.

Response: The x-axis labels in Figures 6, 7, 9, 12, and 14 have now been moved from the center of the graph so that they no longer overlap the data. During the revision, we encountered limitations in the plotting library where the x-axis text was limited to the minimum Y values, but these issues have now been resolved by moving the X-axis to the maximum Y-axis values. All affected figures have been updated accordingly in the revised manuscript.

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors,

Thank you for implementing some of the modifications I suggested. However, I remain convinced that your study presents limitations that are too significant to support the conclusions you have drawn.

Moreover, I regret to say that I do not fully understand the statement in your response:
"We appreciate the reviewer’s valuable comment and acknowledge that the limited sample size constrains the scope of inference. Addressing this limitation would require additional long-term data collected under specific climatic conditions, particularly deep droughts in June–July combined with warm winters. However, such extreme events are difficult to predict and have not occurred again in the Curonian Spit National Park since our observation period."

In your manuscript, you explicitly state that no significant climatic differences have occurred in the past 15 years. This appears to contradict the rationale provided in your response.

I hope you will consider presenting the work in a different form or supplementing it with additional data to enhance its scientific relevance.

Author Response

Comment: Thank you for implementing some of the modifications I suggested. However, I remain convinced that your study presents limitations that are too significant to support the conclusions you have drawn.

Response: To address these concerns, we have recalculated all models using tree-level data only. This resulted in a final dataset consisting of 10 monitored trees across 4 sub-sites, yielding 70 observations over the investigation period. We believe this restructuring substantially reduces the methodological limitations identified by the reviewer and strengthens the reliability of the presented conclusions.

Comment: Moreover, I regret to say that I do not fully understand the statement in your response:
"We appreciate the reviewer’s valuable comment and acknowledge that the limited sample size constrains the scope of inference. Addressing this limitation would require additional long-term data collected under specific climatic conditions, particularly deep droughts in June–July combined with warm winters. However, such extreme events are difficult to predict and have not occurred again in the Curonian Spit National Park since our observation period."

We appreciate the opportunity to clarify this point. Due to the limited occurrence of extreme climatic conditions during the study period, we were not able to test our full hypothesis that warm winters increase the sensitivity of Scots pine to subsequent summer droughts and heat waves. In our dataset, warm winters were followed only by relatively cold and humid growing seasons, which allowed us to analyze tree responses under those conditions but not under the combined warm-winter and summer-drought scenario central to the hypothesis. This represents the main limitation of our study, and only future observations under naturally occurring extreme events will allow this hypothesis to be fully evaluated.

Comment: In your manuscript, you explicitly state that no significant climatic differences have occurred in the past 15 years. This appears to contradict the rationale provided in your response.

Response: there is some misunderstanding. The statement that no significant climatic differences occurred in the past 15 years refers specifically to the absence of the particular combination of events required to fully test our hypothesis—namely, a warm winter followed by an extremely hot and dry summer.

However, this does not mean that climatic trends were absent. On the contrary, we detected significant long-term trends in both temperature and precipitation, which form the basis of the study. What has been missing is the specific sequence of extreme events (warm winter → summer drought/heat wave) needed to evaluate the hypothesized interaction. Therefore, there is no contradiction: climatic trends exist, but the key climatic pattern relevant to the hypothesis did not occur during the study period. Therefore we changed the main hypothesis.

Comment: I hope you will consider presenting the work in a different form or supplementing it with additional data to enhance its scientific relevance.

Response: With the available dataset, we have revised the manuscript as comprehensively as possible and believe that the current version now represents the strongest and most transparent presentation of the study. We fully agree that additional long-term data would further enhance the scientific relevance of this work, and we intend to continue data collection to support future extensions of the study.