Unlocking the potential of pollarded oaks: A 375&ndash;year hydroclimate reconstruction from northcentral Spain

Sanmiguel-Vallelado, Alba; Torbenson, Max C. A.; Esper, Jan; Sangüesa-Barreda, Gabriel; Prado-López, Carlos; Olano, José Miguel

doi:10.5194/egusphere-2025-4494

Preprints

https://doi.org/10.5194/egusphere-2025-4494

Preprints

13 Oct 2025

| 13 Oct 2025

Unlocking the potential of pollarded oaks: A 375–year hydroclimate reconstruction from northcentral Spain

Alba Sanmiguel-Vallelado, Max C. A. Torbenson, Jan Esper, Gabriel Sangüesa-Barreda, Carlos Prado-López, and José Miguel Olano

Abstract. Pollarded trees—traditionally pruned and maintained for centuries near rural settlements—represent an untapped resource for climate reconstruction in Mediterranean lowlands. In this study, we evaluate the potential of 102 pollarded deciduous oaks from two communal woodlands (dehesas) in northcentral Spain as proxies for past hydroclimatic variability. Using the correlation between latewood and November–June precipitation, we reconstruct regional precipitation variability from 1649 to 2023, achieving calibration/verification correlations of 0.71–0.83 against regional and large-scale instrumental datasets. The reconstruction reveals pronounced interannual to multidecadal variability, with precipitation ranging from 250 mm to 815 mm. The longest dry spell lasted 25 years (1818–1842), while the wettest sustained period extended over 29 years (1953–1981). We identify 14 extremely dry years (< 298 mm) and 24 extremely wet years (> 592 mm). Extreme droughts during the pre-instrumental period coincide with historical records, such as Catholic pro pluvia rogations—ceremonies traditionally held in response to agricultural drought—in 1683, 1698, 1734, 1737, 1738, 1775, 1868 and 1898. Our findings demonstrate that pollarded trees, when sampled from sites with asynchronous management, preserve robust climate signals and provide reliable high-resolution information on precipitation variability across Mediterranean dehesas.

Received: 12 Sep 2025 – Discussion started: 13 Oct 2025

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Journal article(s) based on this preprint

29 Jun 2026

Unlocking the potential of pollarded oaks: a 375-year hydroclimate reconstruction from northcentral Spain

Alba Sanmiguel-Vallelado, Max C. A. Torbenson, Jan Esper, Gabriel Sangüesa-Barreda, Carlos Prado-López, and José Miguel Olano

Biogeosciences, 23, 4287–4303, https://doi.org/10.5194/bg-23-4287-2026,https://doi.org/10.5194/bg-23-4287-2026, 2026

Short summary

Alba Sanmiguel-Vallelado, Max C. A. Torbenson, Jan Esper, Gabriel Sangüesa-Barreda, Carlos Prado-López, and José Miguel Olano

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-4494', Anonymous Referee #1, 30 Oct 2025
The authors present a new precipitation reconstruction for north-central Spain, notable for its innovative use of heavily managed oak trees. This study builds upon the group’s recent research, which analyzed growth patterns of pollarded oaks. The manuscript provides a strong demonstration of how reliable climatic signals can be extracted from such trees in very novel and robust approach.
My major concern relates to the effects of pollarding. It is still quite unexpected to observe such a small difference between the uncorrected and corrected RWI and LWI chronologies. As mentioned in the discussion, I agree with the authors that this is most likely due to the high replication and the asynchronicity of pollarding events among trees. However, this asynchronocity among events is not shown in the manuscript. I believe it would be valuable to include a figure showing how many trees were affected by pollarding over time.
Minor:
Line 54: “the upper part of the tree” I think that it would be better to say that part of the canopy is removed.

Figure 1. You have Quercus pyrenaica over the sea... is there any better map for this species?

Detrending: “smoothing splines with a 50% frequency cutoff set to two-thirds of the series length” I believe that this is a bit tricky detrending option since the stiffness of your spline changes from sample to sample and therefore one retain different climatic information (see Klesse 2021). I would suggest to redo the analyses while keeping a fixed frequency cutoff for the splines.

Figure 2. I do not think that the points on the maps regarding the pro pluvia events are necessary here. I would add them in figure 1.

Lines 89: there are some typos there.

Line 387: historical asynchrony: this is what is missing a bit here. Maybe the authors have already published about it somewhere else but since it is one of the main reasons that your reconstruction is kind of robust, this needs to be also be shown here.
Citation: https://doi.org/10.5194/egusphere-2025-4494-RC1
- AC1: 'Reply on RC1', Alba Sanmiguel-Vallelado, 09 Jan 2026
  
  We would like to thank Reviewer 1 for their thoughtful and constructive feedback. We have carefully considered all of the reviewer’s comments and have made the necessary revisions to the manuscript. In particular, we have addressed the concern regarding the effects of pollarding and provided additional information on the asynchrony of pollarding events across trees, as suggested. Furthermore, we have made several adjustments to improve the clarity and precision of the text and figures. A detailed point-by-point response to the minor comments is provided in the attached document. We hope that the revised version meets the reviewer’s expectations and contributes to the clarity and robustness of the study.
  
  Citation: https://doi.org/10.5194/egusphere-2025-4494-AC1
EC1:
'Comment on egusphere-2025-4494', Ny Riavo G. Voarintsoa, 19 Dec 2025

Dear authors,
While waiting on the second reviewer to post their reviews, I encourage you to already respond to Reviewer 1. Thank you!

Citation: https://doi.org/10.5194/egusphere-2025-4494-EC1
- RC2:
  'Reply on EC1', Anonymous Referee #2, 09 Apr 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4494/egusphere-2025-4494-RC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-4494-RC2
  - AC2: 'Reply on RC2', Alba Sanmiguel-Vallelado, 22 Apr 2026
    
    We thank Reviewer 2 for the constructive evaluation of our manuscript. We have carefully considered all comments and revised the manuscript accordingly. In particular, we have strengthened the justification of key methodological decisions, clarified the treatment of extremes and the bias-correction procedure, and incorporated additional analyses and supplementary material to improve the transparency and robustness of the study. We have also revised the text, tables, and figures to improve clarity and precision. A detailed point-by-point response to all comments is provided attached.
    
    Citation: https://doi.org/10.5194/egusphere-2025-4494-AC2

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2025-4494', Anonymous Referee #1, 30 Oct 2025
The authors present a new precipitation reconstruction for north-central Spain, notable for its innovative use of heavily managed oak trees. This study builds upon the group’s recent research, which analyzed growth patterns of pollarded oaks. The manuscript provides a strong demonstration of how reliable climatic signals can be extracted from such trees in very novel and robust approach.
My major concern relates to the effects of pollarding. It is still quite unexpected to observe such a small difference between the uncorrected and corrected RWI and LWI chronologies. As mentioned in the discussion, I agree with the authors that this is most likely due to the high replication and the asynchronicity of pollarding events among trees. However, this asynchronocity among events is not shown in the manuscript. I believe it would be valuable to include a figure showing how many trees were affected by pollarding over time.
Minor:
Line 54: “the upper part of the tree” I think that it would be better to say that part of the canopy is removed.

Figure 1. You have Quercus pyrenaica over the sea... is there any better map for this species?

Detrending: “smoothing splines with a 50% frequency cutoff set to two-thirds of the series length” I believe that this is a bit tricky detrending option since the stiffness of your spline changes from sample to sample and therefore one retain different climatic information (see Klesse 2021). I would suggest to redo the analyses while keeping a fixed frequency cutoff for the splines.

Figure 2. I do not think that the points on the maps regarding the pro pluvia events are necessary here. I would add them in figure 1.

Lines 89: there are some typos there.

Line 387: historical asynchrony: this is what is missing a bit here. Maybe the authors have already published about it somewhere else but since it is one of the main reasons that your reconstruction is kind of robust, this needs to be also be shown here.
Citation: https://doi.org/10.5194/egusphere-2025-4494-RC1
- AC1: 'Reply on RC1', Alba Sanmiguel-Vallelado, 09 Jan 2026
  
  We would like to thank Reviewer 1 for their thoughtful and constructive feedback. We have carefully considered all of the reviewer’s comments and have made the necessary revisions to the manuscript. In particular, we have addressed the concern regarding the effects of pollarding and provided additional information on the asynchrony of pollarding events across trees, as suggested. Furthermore, we have made several adjustments to improve the clarity and precision of the text and figures. A detailed point-by-point response to the minor comments is provided in the attached document. We hope that the revised version meets the reviewer’s expectations and contributes to the clarity and robustness of the study.
  
  Citation: https://doi.org/10.5194/egusphere-2025-4494-AC1
EC1:
'Comment on egusphere-2025-4494', Ny Riavo G. Voarintsoa, 19 Dec 2025

Dear authors,
While waiting on the second reviewer to post their reviews, I encourage you to already respond to Reviewer 1. Thank you!

Citation: https://doi.org/10.5194/egusphere-2025-4494-EC1
- RC2:
  'Reply on EC1', Anonymous Referee #2, 09 Apr 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2025/egusphere-2025-4494/egusphere-2025-4494-RC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2025-4494-RC2
  - AC2: 'Reply on RC2', Alba Sanmiguel-Vallelado, 22 Apr 2026
    
    We thank Reviewer 2 for the constructive evaluation of our manuscript. We have carefully considered all comments and revised the manuscript accordingly. In particular, we have strengthened the justification of key methodological decisions, clarified the treatment of extremes and the bias-correction procedure, and incorporated additional analyses and supplementary material to improve the transparency and robustness of the study. We have also revised the text, tables, and figures to improve clarity and precision. A detailed point-by-point response to all comments is provided attached.
    
    Citation: https://doi.org/10.5194/egusphere-2025-4494-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Reconsider after major revisions (05 May 2026) by Ny Riavo G. Voarintsoa

Dear authors,

Thank you for providing responses to the review. Both reviewers made constructive feedback.
While I notice that the authors responded to the minor comments of R1, I acknowledge that they have not responded to the major points which I copied below:
"My major concern relates to the effects of pollarding. It is still quite unexpected to observe such a small difference between the uncorrected and corrected RWI and LWI chronologies. As mentioned in the discussion, I agree with the authors that this is most likely due to the high replication and the asynchronicity of pollarding events among trees. However, this asynchronocity among events is not shown in the manuscript. I believe it would be valuable to include a figure showing how many trees were affected by pollarding over time."
Also, it is hard to evaluate whether the authors truly addressed the comments of Reviewer 1. For example, the update made to Figure 1 is not shown.

Responses to the comment about Detrending is not well-substantiated, and responses are based on belief is not a strong rationale for why the cut-off was set.
Keeping the chronology as is, because the authors feel comfortable is not a scientific approach. I would advise the authors to be more careful in writing their response statement.

Responses to the comments by Reviewer 2 is more detailed, and I thank the author for being diligent in their responses.

With this said, my decision is "major revisions". Please consider the comments above, very carefully and please indicate clearly in the revisions (with marked changes) where the edits were made. When your revised manuscript is received, I have it reviewed again.

Lastly, please make sure that data used in the manuscript are cited if not original from this work, or had obtained permission to reuse from the original researchers.

Best wishes,
Voary

Hide

AR by Alba Sanmiguel-Vallelado on behalf of the Authors (13 May 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (13 May 2026) by Ny Riavo G. Voarintsoa

RR by Anonymous Referee #2 (04 Jun 2026)

Suggestions for revision or reasons for rejection

The revised manuscript is substantially improved. The authors have addressed the central concern raised in the previous round regarding the effect of pollarding on the climate signal. In particular, the new supplementary figure showing the temporal distribution of pollarding events supports the authors’ interpretation that management effects were largely diluted at the stand level because events were highly asynchronous among trees. Before publication, however, I recommend minor revisions, mostly related to clarity, reproducibility, and consistency.
Main comments
1. The detrending sensitivity analysis should be included in the manuscript or Supplement.
The response to the editor presents a useful comparison of different detrending approaches, including the reviewer-suggested alternative. This is exactly the type of evidence needed to justify the selected method. However, the analysis currently appears only in the response document. Because detrending choice was a major review concern, the comparison should be added to the Supplement, with the acronyms defined clearly, including Fixed-50, ADC/ADCS, PT, and non-PT. The authors should also state briefly in the Methods or Supplement that the correlations with FIC and CRU are not significantly different among detrending choices, preferably reporting the Fisher z-test result or a concise summary.
2. Please clarify the reconstruction workflow and bias correction.
The revised manuscript now includes a cross-dataset calibration-validation framework using FIC for calibration and CRU for validation, followed by final calibration over the full FIC period and quantile mapping. This is a reasonable approach, but the order of operations could be explained more transparently. In particular, the authors should distinguish between:
(1) the raw regression reconstruction used to assess model skill,
(2) the quantile-mapped reconstruction used to improve the distribution and identify extremes, and
(3) the independent validation against CRU.
The current text sometimes gives the impression that these steps overlap. I recommend adding a short workflow paragraph or schematic explanation in Sect. 2.4.3. Please also specify exactly which period was used to train the quantile mapping correction and whether the correction was applied unchanged to the full 1649-2023 reconstruction.
3. The detrending-method sentence needs revision.
The Methods currently state that age-related growth trends were removed using “cubic smoothing splines with a 50% frequency cutoff set to two-thirds of the series length.” This is difficult to parse, I think. Please rewrite this sentence so the detrending choice is unambiguous. For example, state whether each individual series was detrended using a cubic smoothing spline with a 50% frequency-response cutoff at two-thirds of the individual series length, and whether this was applied identically to RW, EW, and LW.
4. Ameliorate the data and code availability statement.
The current statements, “Code will be made available upon request” and “Data will be made available upon request,” are not ideal for reproducibility. Copernicus requires a data availability statement explaining how the underlying research data can be accessed, and recommends depositing data and related metadata in FAIR-aligned repositories with persistent identifiers. Copernicus also encourages software, algorithms, and model code to be deposited in FAIR-aligned repositories and cited with a DOI where possible.
At minimum, the authors should provide repository links or accession information for the tree-ring chronology, reconstructed precipitation series, and scripts needed to reproduce the main analyses and figures. If FIC data cannot be redistributed, the access conditions should be stated clearly.

Minor comments and editorial corrections
The new pollarding asynchrony figure is helpful. In the main text, please specify that the reported percentages are calculated relative to the number of trees available in the chronology in each year.
Please check figure captions for final wording. Figure 5 should clearly distinguish raw reconstruction, bias-corrected reconstruction, instrumental FIC/CRU data, calibration period, validation period, and prediction intervals.
Please clarify whether “extreme” dry and wet years are defined by the ±1.5 SD criterion, the 5th/95th percentiles, SPI categories, or by agreement among all three. The revised manuscript now uses all three approaches, which is good, but the wording should avoid implying that there is a single definition unless one is selected as primary.

Hide

ED: Publish subject to minor revisions (review by editor) (05 Jun 2026) by Ny Riavo G. Voarintsoa

Dear authors,
Thank you for revising your manuscript. After sending it to reviewers, they found your revision to be satisfactory, pending minor revisions. I agree with the reviewer's evaluation.

Copied below are the comments for your information. Please makes sure to provide link to data if they are available somewhere.

Thank you for your careful attention to the comments.
-----------
The revised manuscript is substantially improved. The authors have addressed the central concern raised in the previous round regarding the effect of pollarding on the climate signal. In particular, the new supplementary figure showing the temporal distribution of pollarding events supports the authors’ interpretation that management effects were largely diluted at the stand level because events were highly asynchronous among trees. Before publication, however, I recommend minor revisions, mostly related to clarity, reproducibility, and consistency.
Main comments
1. The detrending sensitivity analysis should be included in the manuscript or Supplement.
The response to the editor presents a useful comparison of different detrending approaches, including the reviewer-suggested alternative. This is exactly the type of evidence needed to justify the selected method. However, the analysis currently appears only in the response document. Because detrending choice was a major review concern, the comparison should be added to the Supplement, with the acronyms defined clearly, including Fixed-50, ADC/ADCS, PT, and non-PT. The authors should also state briefly in the Methods or Supplement that the correlations with FIC and CRU are not significantly different among detrending choices, preferably reporting the Fisher z-test result or a concise summary.
2. Please clarify the reconstruction workflow and bias correction.
The revised manuscript now includes a cross-dataset calibration-validation framework using FIC for calibration and CRU for validation, followed by final calibration over the full FIC period and quantile mapping. This is a reasonable approach, but the order of operations could be explained more transparently. In particular, the authors should distinguish between:
(1) the raw regression reconstruction used to assess model skill,
(2) the quantile-mapped reconstruction used to improve the distribution and identify extremes, and
(3) the independent validation against CRU.
The current text sometimes gives the impression that these steps overlap. I recommend adding a short workflow paragraph or schematic explanation in Sect. 2.4.3. Please also specify exactly which period was used to train the quantile mapping correction and whether the correction was applied unchanged to the full 1649-2023 reconstruction.
3. The detrending-method sentence needs revision.
The Methods currently state that age-related growth trends were removed using “cubic smoothing splines with a 50% frequency cutoff set to two-thirds of the series length.” This is difficult to parse, I think. Please rewrite this sentence so the detrending choice is unambiguous. For example, state whether each individual series was detrended using a cubic smoothing spline with a 50% frequency-response cutoff at two-thirds of the individual series length, and whether this was applied identically to RW, EW, and LW.
4. Ameliorate the data and code availability statement.
The current statements, “Code will be made available upon request” and “Data will be made available upon request,” are not ideal for reproducibility. Copernicus requires a data availability statement explaining how the underlying research data can be accessed, and recommends depositing data and related metadata in FAIR-aligned repositories with persistent identifiers. Copernicus also encourages software, algorithms, and model code to be deposited in FAIR-aligned repositories and cited with a DOI where possible.
At minimum, the authors should provide repository links or accession information for the tree-ring chronology, reconstructed precipitation series, and scripts needed to reproduce the main analyses and figures. If FIC data cannot be redistributed, the access conditions should be stated clearly.

Minor comments and editorial corrections
The new pollarding asynchrony figure is helpful. In the main text, please specify that the reported percentages are calculated relative to the number of trees available in the chronology in each year.
Please check figure captions for final wording. Figure 5 should clearly distinguish raw reconstruction, bias-corrected reconstruction, instrumental FIC/CRU data, calibration period, validation period, and prediction intervals.
Please clarify whether “extreme” dry and wet years are defined by the ±1.5 SD criterion, the 5th/95th percentiles, SPI categories, or by agreement among all three. The revised manuscript now uses all three approaches, which is good, but the wording should avoid implying that there is a single definition unless one is selected as primary.

Hide

AR by Alba Sanmiguel-Vallelado on behalf of the Authors (09 Jun 2026) Author's response Author's tracked changes Manuscript

ED: Publish as is (11 Jun 2026) by Ny Riavo G. Voarintsoa

AR by Alba Sanmiguel-Vallelado on behalf of the Authors (12 Jun 2026)

Journal article(s) based on this preprint

29 Jun 2026

Unlocking the potential of pollarded oaks: a 375-year hydroclimate reconstruction from northcentral Spain

Alba Sanmiguel-Vallelado, Max C. A. Torbenson, Jan Esper, Gabriel Sangüesa-Barreda, Carlos Prado-López, and José Miguel Olano

Biogeosciences, 23, 4287–4303, https://doi.org/10.5194/bg-23-4287-2026,https://doi.org/10.5194/bg-23-4287-2026, 2026

Short summary

Alba Sanmiguel-Vallelado, Max C. A. Torbenson, Jan Esper, Gabriel Sangüesa-Barreda, Carlos Prado-López, and José Miguel Olano

Supplement

https://doi.org/10.5194/egusphere-2025-4494-supplement

Alba Sanmiguel-Vallelado, Max C. A. Torbenson, Jan Esper, Gabriel Sangüesa-Barreda, Carlos Prado-López, and José Miguel Olano

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We studied centuries-old, traditionally pollarded oak trees in Spanish open woodlands to see if they record past rainfall. By analyzing tree rings from 102 trees, we reconstructed 375 years of precipitation. The trees captured long wet and dry periods, including extreme droughts in historical records, providing reliable, high-resolution climate information for the previously overlooked Mediterranean lowlands.


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