The Relationships Between Climate and Growth in Six Tree Species Align with Their Hydrological Niches

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper presents a small-scale, detailed study of tree-ring growth in the Mediterranean climate of central Spain. It analyzes the climate-growth relationships between tree species under varying soil moisture conditions (ranging from drier to wetter) across 300-800 m asl  over the past 50 years. The main finding highlights how slight changes in topography influence the relationship between hydroclimate and tree growth in six major tree species that make up the secondary forest of the Sierra de Gredos foothills.  All study sites are located within a mixed conifer–deciduous forest, where different species dominate depending on soil moisture /elevation, particularly in the low-elevation forest–woodland ecotone. This transitional vegetation zone is especially sensitive to environmental changes, and tree rings serve as valuable indicators of climate impacts on the ecosystem. 
The study aims to evaluate the impact of local and regional soil moisture conditions on the variability of tree-ring growth rates, using the Basal Area Increment (BAI) index, and to assess the influence of climate using tree-ring width indices. The analysis, discussion, and conclusions are primarily centered on these objectives. The study introduces a new 12-site tree-ring dataset on two parameters: tree-ring width indices and BAI index. Overall, the research appears suitable for the journal’s audience. However, a few key issues need to be addressed.

1) To analyze climate–growth relationships, the study employs two toolboxes—TreeClim and Climwin. TreeClim is applied to the first two principal components (PCA1 and PCA2) of the 12 chronologies, while Climwin is used on individual site chronologies to identify climate-sensitive seasonal windows related to temperature and precipitation. In all cases,  monthly resolved climate data is used. It appears that the authors tested the relationships using two approaches and obtained the same results (as indicated in lines 335–336). Pearson correlations (TreeClim) revealed consistent climate–growth relationships and similar seasonal windows in practically all tree species and sites.  No clear justification is provided for including both analytical methods, in the paper,  especially when the Climwin added complexity but yields no new insights.
Moreover, the Climwin results are not thoroughly analyzed, whereas the main emphasis is placed on the TreeClim outcomes. It would be more effective to select one toolbox or the other to assess the climatic impact on different tree species. If the authors  insist on using both, the rationale should be clearly stated in the Methods section. If the authors choose to retain the Climwin analysis, the results—specifically Figure 9 and Table 3—should be fully analyzed. In other words,  the implications of both analysis on the seasonal window shifts for the hydrological niche differentiation among species are lacking, yet should be explicitly discussed.

2) The second concern arises from the tested  linkage between tree growth and the streamflow of a small stream  (75 km² basin area). While both streamflow and soil moisture are valid components of the hydrological cycle, it is unclear how streamflow can meaningfully represent the hydrological niche of tree species. Streamflow may influence riparian tree growth, but only for trees growing directly within or adjacent to the floodplain. Direct casual relationship between the tree growth and streamflow does not exist. Rather, both tree growth and streamflow appear to respond independently to the same climate drivers—temperature and precipitation. Therefore, I would argue that gauged streamflow is not an appropriate proxy for the soil moisture gradient across the study sites. Including it in the analysis may lead to confusion, potentially misleading readers into thinking that species’ dependence on soil moisture is mediated through streamflow. To avoid this misinterpretation, it would be better to remove the streamflow correlation from the analysis altogether.

In the Discussion and Conclusion sections, there is no mention of the changes in wood production (as indicated by BAI analysis) among the tree species, nor is there a discussion of how these changes relate to their respective hydrological niches. This information should be included. Additionally, it should be clarified whether BAI patterns have changed differently across the moisture gradient over the 50-year analysis period.

Figures 
Nine figures is an excessive number, resulting in a cluttered presentation. Figure 3 could be removed, as it is not discussed in the text and does not reveal any notable patterns or features in the decadal or annual variability of the tree-ring indices used for the climate response functions. The correlation between the series is already provided in the form of correlation coefficients (Lines 266–269).

Additionally, Figure 8 is not justified and should be removed. It shows a correlation (r = 0.37) between a single chronology (Pine) and streamflow discharge  from a small watershed (basin area: 73 km²). See the main comment regarding the limited rand indirect relevance of streamflow discharge to tree growth in this context. 

Tables
Table 3 related to Climwin calculations  is not well organized (for example, no marked significance) or analyzed in the text. See the main comment on the Climwin analysis. 

The paper lacks balance in its structure. The analysis is relatively brief in the Results section, while it is disproportionately occupied by three large tables and nine figures. See the specific comments regarding the content and necessity of all these tables and figures.

Methods spans over 4 pages, which is disproportionally long. It should be shorten with removal of information that duplicates across subsections,  has little relevance to the analysis (e.g. how the diameter of largest trees were measured, L176-178, which is metadata for a database, etc)  and some trivial description in the  methodology  on tr chronology calculation. 

Reference list 
it is unbalanced. The list is overloaded with unnecessary  and subject-replicated papers. It is not clear or hard justify why the authors chose to include them in such number.  The citation list should be revised, with certain references either removed, reconsidered, or more clearly justified within the text. This may involve rewording or clarifying statements to better support their inclusion. As it stands, the reference list may be perceived as containing excessive self-citation.

For example, in Methods, section 2.4, the authors cite dplR package with three citations 35-37  (Bunn 2010, Bunn et al 2025 and RCore Team).  This software package could be properly  cited  with one paper -Bunn et al.  2025, not three papers (!). 
Another example from Introduction, L95-96:   Authors cite 4 of their tree-ring papers to say that "Pinus pinaster Ait. (Pinaceae) is a shade-intolerant, fast-growing, isohydric and drought-tolerant conifer found at low to mid elevations on acidic soils [13-16]."  I doubt the necessity and relevance of these citations to this statement.  

Other minor remarks
L. 58: not proper choice of the word, replace "capitalize " with another verb  "Here, we capitalized on a tree-ring network built in a topographically complex area...". 

L60-63: Inaccurate and overstated sentence. Revise the second task related to show "different traits and strategies to tolerate drought stress".  The results are not analyzed or discussed through these angles. 

L65-67: Revise the specific objective ii. The impact of streamflow on the tree growth is irrelevant to the study.

L83-85. Inaccurate statement. Revise this sentence about the studied vegetation area, since your sites are not going above 800 m asl. This looks like a description of the Serra de Gredos vegetation.  

Line 95: "Therefore, they have dendrochronological potential. " Not clear on which sense?  Revise the writing. 

Lines 212, 218, 389-391 and 418: The authors repeatedly use the term "humidity" throughout the text, including in the conclusion. However, they do not analyze actual humidity measurements. Instead, their analysis is based on soil moisture, inferred as a function of temperature and precipitation. Moreover, the hydrological niche concept specifically refers to soil moisture, not  humidity. This terminology needs to be corrected consistently throughout the manuscript to avoid confusion and improve accuracy.

L194-195: The formula and its description are not accurate. 
the authors use tree-ring width series to calculate BAI.  So the formula should include not the radius of tree but the tree-ring widths. Adjust the formula for the ring width series.
Also define the π . 

Line 204 and Line 209: "Lastly" 
 
Conclusions
This section does not fully address all the objectives outlined in the Introduction. The Conclusion should include a sentence summarizing how "variability at regional to local scales impacts" tree-ring growth, as this was one of the stated objectives of the study.

L 421: please remove "river flow", see the scope of the study and relevant comment above. 

 

Author Response

Comments and Suggestions for Authors

This paper presents a small-scale, detailed study of tree-ring growth in the Mediterranean climate of central Spain. It analyzes the climate-growth relationships between tree species under varying soil moisture conditions (ranging from drier to wetter) across 300-800 m asl  over the past 50 years. The main finding highlights how slight changes in topography influence the relationship between hydroclimate and tree growth in six major tree species that make up the secondary forest of the Sierra de Gredos foothills.  All study sites are located within a mixed conifer–deciduous forest, where different species dominate depending on soil moisture /elevation, particularly in the low-elevation forest–woodland ecotone. This transitional vegetation zone is especially sensitive to environmental changes, and tree rings serve as valuable indicators of climate impacts on the ecosystem. 

 

The study aims to evaluate the impact of local and regional soil moisture conditions on the variability of tree-ring growth rates, using the Basal Area Increment (BAI) index, and to assess the influence of climate using tree-ring width indices. The analysis, discussion, and conclusions are primarily centered on these objectives. The study introduces a new 12-site tree-ring dataset on two parameters: tree-ring width indices and BAI index. Overall, the research appears suitable for the journal’s audience. However, a few key issues need to be addressed.

 

• We thank you for your positive comments. We have revised the manuscript addressing the issues you commented and enhancing the quality of English.

 

1) To analyze climate–growth relationships, the study employs two toolboxes—TreeClim and Climwin. TreeClim is applied to the first two principal components (PCA1 and PCA2) of the 12 chronologies, while Climwin is used on individual site chronologies to identify climate-sensitive seasonal windows related to temperature and precipitation. In all cases, monthly resolved climate data is used. It appears that the authors tested the relationships using two approaches and obtained the same results (as indicated in lines 335–336). Pearson correlations (TreeClim) revealed consistent climate–growth relationships and similar seasonal windows in practically all tree species and sites.  No clear justification is provided for including both analytical methods, in the paper, especially when the Climwin added complexity but yields no new insights.

 

Moreover, the Climwin results are not thoroughly analyzed, whereas the main emphasis is placed on the TreeClim outcomes. It would be more effective to select one toolbox or the other to assess the climatic impact on different tree species. If the authors insist on using both, the rationale should be clearly stated in the Methods section. If the authors choose to retain the Climwin analysis, the results—specifically Figure 9 and Table 3—should be fully analyzed. In other words,  the implications of both analysis on the seasonal window shifts for the hydrological niche differentiation among species are lacking, yet should be explicitly discussed.

 

• We used both approaches because climwin analyses are robustly tested based on Information Theory and allow defining the temporal window, whereas correlations do not precisely provide a temporal window. We justified the use of climwin when introducing it in the methods and discussed the related results.

 

2) The second concern arises from the tested linkage between tree growth and the streamflow of a small stream  75 km² basin area). While both streamflow and soil moisture are valid components of the hydrological cycle, it is unclear how streamflow can meaningfully represent the hydrological niche of tree species. Streamflow may influence riparian tree growth, but only for trees growing directly within or adjacent to the floodplain. Direct casual relationship between the tree growth and streamflow does not exist. Rather, both tree growth and streamflow appear to respond independently to the same climate drivers—temperature and precipitation. Therefore, I would argue that gauged streamflow is not an appropriate proxy for the soil moisture gradient across the study sites. Including it in the analysis may lead to confusion, potentially misleading readers into thinking that species’ dependence on soil moisture is mediated through streamflow. To avoid this misinterpretation, it would be better to remove the streamflow correlation from the analysis altogether.

 

• We agree and have removed the analyses involving streamflow as you suggested.

 

In the Discussion and Conclusion sections, there is no mention of the changes in wood production (as indicated by BAI analysis) among the tree species, nor is there a discussion of how these changes relate to their respective hydrological niches. This information should be included. Additionally, it should be clarified whether BAI patterns have changed differently across the moisture gradient over the 50-year analysis period.

 

• We agree and have includes this information in the revised Discussion and Conclusions. Note, however, that this was not the main focus of our study.

 

Figures Nine figures is an excessive number, resulting in a cluttered presentation. Figure 3 could be removed, as it is not discussed in the text and does not reveal any notable patterns or features in the decadal or annual variability of the tree-ring indices used for the climate response functions. The correlation between the series is already provided in the form of correlation coefficients (Lines 266–269).

 

Additionally, Figure 8 is not justified and should be removed. It shows a correlation (r = 0.37) between a single chronology (Pine) and streamflow discharge  from a small watershed (basin area: 73 km²). See the main comment regarding the limited rand indirect relevance of streamflow discharge to tree growth in this context. 

 

 

• After the revision, only 7 figures are kept. We prefer keeping the figure 3 to show the year-to-year growth variability of the study sites and species. The figure 8 was removed as suggested.

 

Tables

Table 3 related to Climwin calculations is not well organized (for example, no marked significance) or analyzed in the text. See the main comment on the Climwin analysis. 

 

• We better organized and described Table 3 in the revised ms.

 

The paper lacks balance in its structure. The analysis is relatively brief in the Results section, while it is disproportionately occupied by three large tables and nine figures. See the specific comments regarding the content and necessity of all these tables and figures.

 

Methods spans over 4 pages, which is disproportionally long. It should be shorten with removal of information that duplicates across subsections,  has little relevance to the analysis (e.g. how the diameter of largest trees were measured, L176-178, which is metadata for a database, etc)  and some trivial description in the  methodology  on tr chronology calculation. 

 

• We respectfully disagree. The description of field sampling and tree-ring chronology calculation are critical parts of Material and Methods. Moreover, the journal does not impose a limitation of words.

 

Reference list it is unbalanced. The list is overloaded with unnecessary  and subject-replicated papers. It is not clear or hard justify why the authors chose to include them in such number.  The citation list should be revised, with certain references either removed, reconsidered, or more clearly justified within the text. This may involve rewording or clarifying statements to better support their inclusion. As it stands, the reference list may be perceived as containing excessive self-citation.

 

For example, in Methods, section 2.4, the authors cite dplR package with three citations 35-37  (Bunn 2010, Bunn et al 2025 and RCore Team).  This software package could be properly  cited  with one paper -Bunn et al.  2025, not three papers (!). 

 

Another example from Introduction, L95-96:   Authors cite 4 of their tree-ring papers to say that "Pinus pinaster Ait. (Pinaceae) is a shade-intolerant, fast-growing, isohydric and drought-tolerant conifer found at low to mid elevations on acidic soils [13-16]."  I doubt the necessity and relevance of these citations to this statement.  

 

• We respectfully disagree. First, dplR proper citation requires citing the 3 papers as indicated by the authors (see https://cran.r-project.org/web/packages/dplR/citation.html). Second, the 4 references regarding pinaster are necessary and appropriate and only 2 of them correspond to the authors. Again, the journal does not impose a limitation of references. We re worded statements to support the inclusion of some references.

 

 

Other minor remarks

1. 58: not proper choice of the word, replace "capitalize " with another verb  "Here, we capitalized on a tree-ring network built in a topographically complex area...". 

 

• We changed the verb.

 

L60-63: Inaccurate and overstated sentence. Revise the second task related to show "different traits and strategies to tolerate drought stress".  The results are not analyzed or discussed through these angles. 

 

• We rephrased the sentence.

 

L65-67: Revise the specific objective ii. The impact of streamflow on the tree growth is irrelevant to the study.

 

• We revised the objective (ii).

 

L83-85. Inaccurate statement. Revise this sentence about the studied vegetation area, since your sites are not going above 800 m asl. This looks like a description of the Serra de Gredos vegetation.  

 

• We rephrased the sentence.

 

Line 95: "Therefore, they have dendrochronological potential. " Not clear on which sense?  Revise the writing. 

 

• We removed the sentence.

 

Lines 212, 218, 389-391 and 418: The authors repeatedly use the term "humidity" throughout the text, including in the conclusion. However, they do not analyze actual humidity measurements. Instead, their analysis is based on soil moisture, inferred as a function of temperature and precipitation. Moreover, the hydrological niche concept specifically refers to soil moisture, not humidity. This terminology needs to be corrected consistently throughout the manuscript to avoid confusion and improve accuracy.

 

• We replaced the term “humidity” by “soil moisture”.

 

L194-195: The formula and its description are not accurate. 

the authors use tree-ring width series to calculate BAI.  So the formula should include not the radius of tree but the tree-ring widths. Adjust the formula for the ring width series.

 

Also define the π . 

 

• We disagree. The BAI formula shown in the ms is widely presented and used in many tree-ring papers. The BAI is calculated with the cumulative sum of tree-ring widths (radii length); so, including the tree-ring widths in the formula would make it unnecessarily complex. Nevertheless, we explained how the radii lengths were obtained. “p” is the pi number, i.e. the perimeter divided by the diameter.

 

 

Line 204 and Line 209: "Lastly" 

 

• We rephrased it.

 

Conclusions

This section does not fully address all the objectives outlined in the Introduction. The Conclusion should include a sentence summarizing how "variability at regional to local scales impacts" tree-ring growth, as this was one of the stated objectives of the study.

L 421: please remove "river flow", see the scope of the study and relevant comment above. 

 

• We rewrote the Conclusions as you suggested. We also removed any reference to “river flow”.

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The manuscript with the title “The relationships between climate and growth in six tree species align with their hydrological niches” deals with the influence of growth and the hydrological niches. The manuscript is well structured. Yet, there is some missing information in the methods and discussion that should be addressed (see comments). Thus, major changes are recommended.

 

Comments

1) Lines 77-82 – reference should be added.

2) Lines 104-107, 114-116 – the species shade tolerance should be included.

3) Figure 1 – please consider improving the quality of the figure. Also, it is not easy to read the site code.

4) Lines 168-175 – how many trees were sampled per species and per site?

5) Lines 176-178 – at which height were the cores taken?

6) Line 185 – the text is not clear. The measurements were made in two cores taken perpendicularly in each tree?

7) Figures 2, 3 – legend for Prunus lusitanica is missing.

8) Figure 6 – this figure is hard to read because it is too small and the colours have low contrast. Please consider improving it.

9) Line 321 – The authors include a variable, RWI, that was not defined in the methods. Please consider including it in methods.

10) Figure 9 – please consider improving the quality of the figure. Also, the right sided figures are difficult to distinguish the different tones of grey.

11) Discussion – the authors pointed out through the text some of the limitations of the study. Yet, they were not addressed in the discussion. It is suggested that a paragraph should be included at the end of the discussion pointing out the limitations regarding the tree age and regime, along with suggestions to overcome these limitations in future studies.

Author Response

Comments and Suggestions for Authors

The manuscript with the title “The relationships between climate and growth in six tree species align with their hydrological niches” deals with the influence of growth and the hydrological niches. The manuscript is well structured. Yet, there is some missing information in the methods and discussion that should be addressed (see comments). Thus, major changes are recommended.

 

• We thank you for your positive comments. We have revised the manuscript to provide the missing information you pointed out.

 

Comments

• Lines 77-82 – reference should be added.

 

• done

 

• Lines 104-107, 114-116 – the species shade tolerance should be included.

 

• done

 

• Figure 1 – please consider improving the quality of the figure. Also, it is not easy to read the site code.

 

• We added bigger labels for sites’ codes and improved the figure.

 

• Lines 168-175 – how many trees were sampled per species and per site?

 

• This info is shown in Table 2.

 

• Lines 176-178 – at which height were the cores taken?

 

• At 1.3 m. We indicated it in the revised ms.

 

• Line 185 – the text is not clear. The measurements were made in two cores taken perpendicularly in each tree?

 

• Yes, we measured two cores per tree. We rephrased the sentence.

 

• Figures 2, 3 – legend for Prunuslusitanica is missing.

 

• It is not missing because they are the same sites and symbols as those used for Quercus pyrenaica.

 

• Figure 6 – this figure is hard to read because it is too small and the colours have low contrast. Please consider improving it.

 

• We improved it by making it larger, but kept the same colors to be consistent with Fig. 7.

 

• Line 321 – The authors include a variable, RWI, that was not defined in the methods. Please consider including it in methods.

 

• We mentioned it in the revised methods.

 

• Figure 9 – please consider improving the quality of the figure. Also, the right sided figures are difficult to distinguish the different tones of grey.

 

• We removed the figure to shorten the article given that its information was not so important and it was already provided in Table 3.

 

11) Discussion – the authors pointed out through the text some of the limitations of the study. Yet, they were not addressed in the discussion. It is suggested that a paragraph should be included at the end of the discussion pointing out the limitations regarding the tree age and regime, along with suggestions to overcome these limitations in future studies.

 

• We added the suggested paragraph on the study limitations.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Although the responses are brief and the author  disagree in some cases, the suggestions and comments are satisfactory.  The corrections have improved the manuscript overall, particularly its presentation. 

 

Author Response

Thanks a lot for your editorial concerns.

Reviewer 2 Report

Comments and Suggestions for Authors

The majority of the reviewer's comments were addressed and the manuscript was improved in the second version. One point that could be improved would be including a reference to Table 2 in the text (lines 154-164), where the number of samples referred. It is considered that the manuscript can be accepted for publication.

Author Response

Thank you, we included the reference to Table 2 and checked again the English usage.