Contrasting Drought Sensitivity in Silver Fir and Scots Pine Revealed Through Growth and Wood Density Data

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This manuscript fits the section reporting forest meteorology and climate change progress well. The authors investigated the growth sensitivity, wood density, and resilience to drought conditions of two species: silver fir (Abies alba) and Scots pine (Pinus sylvestris) over an extended period (from 1952 to 2020).  Several wood traits were determined, and their change over time discussed, including early wood density, latewood density, diameter at breast height, tree-ring width, basal area increment, resistance in wet sites, recovery in dry sites, and drought resilience indices. Particular attention was paid to four draft years, which were investigated in a 6-year timeframe (3 years before and 3 years after each draft year).
Instead of radiocarbon dating, which is considered the most accurate method for determining tree age, the authors used ring width measurements. Nonetheless, they took a careful approach, correcting missing rings, monitoring basal area increments, and performing statistics detrending and chronology computation of tree rings. The statistical evaluations are correct.
The study reiterates the vulnerability of silver fir and Scots pine to drought constraints, which occur, however, by different mechanisms. The authors suggest assessing the vulnerability of these species to climate change by considering multiple wood traits at various timescales. This data may alleviate the effects of water shortage under intensifying climate change conditions.
The authors’ work was conducted carefully. The manuscript has a good flow and will interest experts in the field.  
The observations and suggestions below are meant to improve the quality of the manuscript further.
1.    Please add a List of Abbreviations to assist the readers in following many notations.
2.    In Figure 2, please change the color of the yellow/orange data points and line for PE (Paco Ezpela), as they can barely be distinguished from the red data points and graph, corresponding to FA (Fago).
3.    In the discussion section, please add a table summarizing the study's main findings for both species. This would provide an easier overview than the present description in the text. 
Suggested style improvements:
On pages 6-9, there are many repetitions of a few terms, which various other terms can replace, without affecting the sentence's meaning.  Here is a short list of alternate terms. 
“Significant”: substantial, noteworthy, important, notable; (for correlations): clear, unequivocal, unambiguous 
“Consistently”: systematically, repeatedly, reliably, steadily, consistently, regularly
“Presented”: revealed, had, provided, given
“Revealed”: evidenced, indicated, documented, shown.

Comments on the Quality of English Language

The English style need slight improvements as suggested in the Comments to the Authors.

Author Response

Thank you for your careful and constructive feedback on our manuscript. We appreciate your suggestions, which have helped us improve clarity and readability. Below, we address each of your comments in detail:

1. Please add a List of Abbreviations to assist the readers in following many notations.

Response 1:

Thank you for this suggestion. We agree that a List of Abbreviations improves readability. Accordingly, we have added Table 1: List of Abbreviations in the M&M section) [see page 3, Line 109–110].

2. In Figure 2, please change the color of the yellow/orange data points and line for PE (Paco Ezpela), as they can barely be distinguished from the red data points and graph, corresponding to FA (Fago).

Response 2:

Thank you for this suggestion to the improvement of the figures. In the revised manuscript, Figure 2 now depicts clearly differentiated colors, with the caption updated accordingly [see page 6, line 232-236]. We have also applied the same color change in the Supplementary Materials [See Figure S1].

3. In the discussion section, please add a table summarizing the study's main findings for both species. This would provide an easier overview than the present description in the text.

Response 3:

We appreciate the intent behind this suggestion. After careful consideration, we have elected not to include an additional summary table. Our detailed narrative in Section 4 synthesizes the findings across growth, density and resilience axes without overloading the Discussion. We believe that introducing a summary table at this juncture would fragment the flow and duplicate information already concisely presented in the text and in Figures 3–6.

Suggested style improvements:

On pages 6-9, there are many repetitions of a few terms, which various other terms can replace, without affecting the sentence's meaning.  Here is a short list of alternate terms. “Significant”: substantial, noteworthy, important, notable; (for correlations): clear, unequivocal, unambiguous “Consistently”: systematically, repeatedly, reliably, steadily, consistently, regularly “Presented”: revealed, had, provided, given “Revealed”: evidenced, indicated, documented, shown.

We appreciate this suggestion. We change many terms to avoid repetitions of terms.

Thank you for helping us enhance the clarity and presentation of our work. We trust these revisions meet your expectations.

Reviewer 2 Report

Comments and Suggestions for Authors

Comments and Suggestions for Authors

Dear Authors, Your paper is very interesting. I have reviewed it and some corrections are needed:

Abstract: The abstract provides a comprehensive overview of species-specific drought responses in silver fir and Scots pine, emphasizing how integrating growth and wood density metrics enhances our understanding of forest resilience under increasing climate stress in mountain ecosystems.

Introduction: The introduction describes the increasing threat of drought to temperate and Mediterranean forests and presents wood density and growth traits as key indicators of hydraulic strategies and vulnerability of trees, especially conifers. The objectives of the study are defined and the importance of the study in the context of silver fir population decline is emphasized.

Materials and Methods
Line 141–150 – The criteria used to classify trees as dead or declining are not described (e.g., visual crown assessment, degree of defoliation, presence of disease symptoms, dead top, etc.).
Line 168–170 – The reasons for using an alternative method for detrending of EWD and LWD should be explained in more detail.

Results
Line 259–265 – Significance levels for correlations should be reported.
Line 273–288 – The climate sensitivity analysis is presented in a condensed form. There is no detailed description of which specific months and variables (Tmax, Tmin, P-PET) have the strongest influence on density and growth.

Discussion
Line 328–338 – The comment about the difficulties in obtaining data from dead wood is justified, but it limits the reliability of the conclusions. This should be more clearly emphasized in the conclusions.
Line 372–373 – The term "other physiological mechanisms" should be elaborated.

Conclusions
Line 465–476 – The conclusion should more explicitly state that the data from dead trees are limited, which may affect the interpretation of resistance based on EWD and LWD. Currently, this is only briefly mentioned.

Supplementary
Figure S8 – The figure appears cluttered and difficult to read.
Additionally, it would be helpful to include individual chronologies for the measured traits, and to display the sample size (number of trees) on the same graph.

 

Author Response

Thank you for your insightful comments. We have addressed each point below; all changes are highlighted in red in the revised manuscript.

Materials and Methods

Line 141–150 – The criteria used to classify trees as dead or declining are not described (e.g., visual crown assessment, degree of defoliation, presence of disease symptoms, dead top, etc.).

Response 1:

We agree that this clarification is needed. We have added: “… based on visual crown defoliation. Non-declining trees exhibited less than 50 % crown defoliation, whereas declining or recently dead trees showed 50 % or greater defoliation (including completely defoliated crowns)” [See page 4, Line 146–149].

Line 168–170 – The reasons for using an alternative method for detrending of EWD and LWD should be explained in more detail.

Response 2:

We have expanded the Methods on page 5 to clarify that TRW, EWD and LWD all used the same detrending method, differing only in the spline window (30 years for TRW and two-thirds series length for density). We also removed the incorrect subtraction‐based indexing mention and noted that ratio detrending was used to the variance and maintain consistency with TRWi series [See page 5, Line 173–179].

Results

Line 259–265 – Significance levels for correlations should be reported.

Response 3:

Exact p-values have now been added to the Pearson correlations. [See page 8, Line 266–269].

 

Line 273–288 – The climate sensitivity analysis is presented in a condensed form. There is no detailed description of which specific months and variables (Tmax, Tmin, P-PET) have the strongest influence on density and growth.

Response 4:

We have change and improve the paragraph explaining the Results to describe the strongest monthly drivers. [See pages 8 and 9, Line 278–298].

Discussion

Line 328–338 – The comment about the difficulties in obtaining data from dead wood is justified, but it limits the reliability of the conclusions. This should be more clearly emphasized in the conclusions.

Response 5:

We have further highlighted this limitation in the Conclusions section [See page 13, Line 490–495]

Line 372–373 – The term "other physiological mechanisms" should be elaborated.

Response 6:

In the Discussion, section 4.1. Growth and wood density we expand and discussed the “other physiological mechanism” [See page 12, Line 373–387].

Conclusions

Line 465–476 – The conclusion should more explicitly state that the data from dead trees are limited, which may affect the interpretation of resistance based on EWD and LWD. Currently, this is only briefly mentioned.

Response 7:

As mentioned above (see Response 5), we have strengthened this statement in the final paragraph of the Conclusions [See page 13, Line 490–495].

 

Supplementary

Figure S8 – The figure appears cluttered and difficult to read.

Response 8:

We have replaced Figure S8 with a simplified correlation matrix highlighting only the four key site–trait correlations for each population and added significance boxes to help the reader, see Supplementary Figure S20, of the new Supplementary Materials.

Additionally, it would be helpful to include individual chronologies for the measured traits, and to display the sample size (number of trees) on the same graph.

Response 9:

We now show all individual TRWi, EWDi and LWDi chronologies in Supplementary Figure S2 (12 panels, one per site × trait) on pages S2–S3, and each panel caption includes “n = XX cores” as sample size.

Thank you again for your constructive feedback, which has greatly improved the clarity and rigor of our manuscript.

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript about the drought sensitivity of two tree species (Silver Fir and Scots Pine), inferred from tree ring width and wood density, is one of the studies on a significant topic of tree resilience to climate change, specifically drought. In general, the manuscript is written in good language, and appropriate methods for data acquisition, tree-ring data and wood density measurement treatment are used. The manuscript could be of interest to a wider audience. The main limitation of this study is a rather low number of sites analysed (only three sites), and not all parameters are obtained for all sites. This limitation should be clearly stated in the abstract and in the conclusion to show that the generalisation of the obtained results is limited.

Methods

Line 159 – replace “IDE Rstudio” with the “R” as the version number and reference corresponds to “R”

Lines 192-201 – additional information is needed regarding the ring width, EWD and LWD – what values were used in the analysis, measurement for each year or mean value per tree. If measurements for each year are used, then ANOVA or the Kruskal-Wallis test is not suitable, as those models do not account for interconnected multiple measurements per tree. Instead, the linear mixed effects or generalised linear mixed effects models should be used, setting the tree ID as the random factor.

Line 214 – the package “broom” does not implement linear regression models in R; it just helps to use those models in a tidy way.

Results

Figure 2 – use more distinctive colours for site FA and PE.

Lines 259-264 – please add exact p-values in the brackets after the correlation coefficients.

Figure 6 and Table S3 – The R² value for FA AA variable EWD (RC vs Rs) is 0.001, but this relationship is shown as statistically significant. Is this really a case because there is no other situation where such a small relationship is considered significant?

 

Additional comments

Line 118 – add “fir” after the “silver”

 

Author Response

Thank you for your insightful comments. We have addressed each point below; all changes are highlighted in red in the revised manuscript.

Methods

Line 159 – replace “IDE Rstudio” with the “R” as the version number and reference corresponds to “R”

Response 1:

Corrected on page 7, line 164: “using the dplR package in R (version 4.1.1)” [See page 5, Line 164].

Lines 192-201 – additional information is needed regarding the ring width, EWD and LWD – what values were used in the analysis, measurement for each year or mean value per tree. If measurements for each year are used, then ANOVA or the Kruskal-Wallis test is not suitable, as those models do not account for interconnected multiple measurements per tree. Instead, the linear mixed effects or generalised linear mixed effects models should be used, setting the tree ID as the random factor.

Response 2:

We clarified that all ANOVA/Kruskal–Wallis tests were performed on mean values per tree, thereby satisfying independence assumptions and validating one-way ANOVA or Kruskal–Wallis testing [See page 6, Line 204–205].

Line 214 – the package “broom” does not implement linear regression models in R; it just helps to use those models in a tidy way.

Response 3:

Thank you for your comment, your correction is much appreciated. The statistical analyses were conducted using the base R package and broom was used for tidying model outputs, we have simplified the Methods to cite only R. The revised sentence now reads “Analyses were performed in R (version 4.1.1)” [See page 13, Line 223].

Results

Figure 2 – use more distinctive colours for site FA and PE.

Response 4:

Thank you for this suggestion to the improvement of the figures. In the revised manuscript, Figure 2 now depicts clearly differentiated colors, with the caption updated accordingly [see page 6, Line 232-236]. We have also applied the same color change in the Supplementary Materials to Figure S2.

Lines 259-264 – please add exact p-values in the brackets after the correlation coefficients.

Response 5:

Exact p-values have now been added to the Pearson correlations. [See page 8, Line 266–269].

Figure 6 and Table S3 – The R² value for FA AA variable EWD (RC vs Rs) is 0.001, but this relationship is shown as statistically significant. Is this really a case because there is no other situation where such a small relationship is considered significant?

Response 6:

Thanks for pointing it out, we have re-checked the regression and made proper corrections on the Rc vs Rs regression analysis Figure [See page 10, Line 331-337] and updated Table S3 accordingly. Note that this reinforces the results (predominance of Rt over Rs), so the results paragraph has been adjusted. The BAI results have also been adjusted so that their presentation style matches the density and is as enjoyable to read as possible.

Additional comments

Line 118 – add “fir” after the “silver”

Response 7:

Corrected to “silver fir” in the title on page 1, line 2. [See page 3, Line 113]

Thank you again for your thorough review and helpful insights. We believe these revisions have strengthened the manuscript and clarified all points you raised. We appreciate your time and consideration of our work.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have implemented the changes suggested by reviewers, and the manuscript can be accepted in its current form.

Author Response

Thanks for your comments and useful review.