Articles | Volume 22, issue 18
https://doi.org/10.5194/bg-22-4903-2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.European tree cover during the Holocene reconstructed from pollen records
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- Final revised paper (published on 24 Sep 2025)
- Supplement to the final revised paper
- Preprint (discussion started on 27 May 2024)
- Supplement to the preprint
Interactive discussion
Status: closed
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
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RC1: 'Comment on egusphere-2024-1523', Thomas Giesecke, 07 Jun 2024
- AC1: 'Reply on RC1', Luke Sweeney, 05 Jul 2024
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CC1: 'Comment on egusphere-2024-1523', Marie-Jose Gaillard, 10 Jul 2024
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AC3: 'Reply on CC1', Luke Sweeney, 24 Jul 2024
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CC2: 'Reply on AC3', Marie-Jose Gaillard, 03 Aug 2024
- AC4: 'Reply on CC2', Luke Sweeney, 07 Aug 2024
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CC2: 'Reply on AC3', Marie-Jose Gaillard, 03 Aug 2024
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AC3: 'Reply on CC1', Luke Sweeney, 24 Jul 2024
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RC2: 'Comment on egusphere-2024-1523', Anonymous Referee #2, 18 Jul 2024
- AC2: 'Reply on RC2', Luke Sweeney, 23 Jul 2024
Peer review completion
AR: Author's response | RR: Referee report | ED: Editor decision | EF: Editorial file upload
ED: Reconsider after major revisions (11 Aug 2024) by Petr Kuneš

AR by Luke Sweeney on behalf of the Authors (23 Dec 2024)
Author's response
Author's tracked changes
Manuscript
ED: Referee Nomination & Report Request started (13 Jan 2025) by Petr Kuneš
RR by Thomas Giesecke (20 Jan 2025)

ED: Reconsider after major revisions (21 Jan 2025) by Petr Kuneš

AR by Luke Sweeney on behalf of the Authors (25 Apr 2025)
Author's response
Author's tracked changes
Manuscript
ED: Referee Nomination & Report Request started (13 May 2025) by Petr Kuneš
RR by Thomas Giesecke (05 Jun 2025)

ED: Publish subject to minor revisions (review by editor) (06 Jun 2025) by Petr Kuneš

AR by Luke Sweeney on behalf of the Authors (16 Jun 2025)
Author's response
Author's tracked changes
Manuscript
ED: Publish as is (23 Jun 2025) by Petr Kuneš

AR by Luke Sweeney on behalf of the Authors (03 Jul 2025)
Manuscript
There is a need for assessing past forest cover change from pollen regionally and the REVEALS model requiring knowledge on pollen productivity may not be the method of choice where that information is lacking or incomplete. Thus it is useful to explore other avenues and the manuscript by Sweeney et al. does that. It also adds interesting comparisons between the European estimates produced applying the REVEALS model and the modern analogue technique. While I welcome the attempt of applying a regression, I have my doubts on the choice of predictor variables. The authors should demonstrate how % needle leave and the Shannon index improve a regression model for overall tree cover. I can see how elevation improves the model in the current situation but have my doubt that this variable will improve past reconstructions. Instead using information on over and underrepresented pollen could perhaps make this a real winner. It is also not clear to me in which way this regression model improves upon the modern analogue technique requiring the same input information and seemingly yielding a similar performance. The manuscript is not explaining how the proposed regression model reduces the bias of simply using arboreal percentage, which may be dominated by pine and birch versus elm and lime.
My second concern with the manuscript is the lack of appropriate recognition and citation of databases and initiatives that collected and curated the pollen data used here. Most of the modern and downcore pollen data used here was initially made available by the EPD/Neotoma or PANGAEA with a cc by 4 license requiring attribution and citation of this initial data release. Please see the recent discussion of the manuscript by Schild et al. (https://essd.copernicus.org/preprints/essd-2023-486/#discussion).
Specific comments
L. 57: The LRA includes local reconstructions (LOVE) which has not been applied on the European scale. Only the REVEALS model was used.
L. 58: You should cite Zanon et al. (2018) already here.
L. 63: The main focus was on reconstructing the proportion of open versus forest land cover.
L. 65: As an introductory overview this is almost too detailed while it is lacking studies to work as a good review of all that has come before: e.g. Pirzamanbein et al. (2014, Ecological Complexity), Roberts et al. (2018) Scientific Reports 8:716. Some of these appear in the discussion, but it would be good to mention them here already.
L. 80: Fall speeds are not the major issue as they can be estimated based on pollen size.
L. 86: Since you mention PFTs you may want to include Davis et al. (2015) here already not only in the discussion.
L. 115: The SPECIAL Modern Pollen Dataset (Villegas-Diaz and Harrison, 2022) compiles samples from other data sources including Neotoma and PANGAEA which also have a CC-BY-4.0 license, hence you need to cite or acknowledge the original data source not just the data compilation.
L. 116: SMPDS needs to be introduced. It is not clear from the above that this refers to the surface sample data.
L. 119: Particularly where core tops were used thus assumption is daring.
L. 122: Give a brief motivation not just a reference.
L. 122-124: Here you are referring to surface samples, core tops or Holocene records?
L. 126: So you include small bogs but exclude large bogs? I cannot find this constraint discussed in Githumbi et al. (2022).
L. 135: It would be useful to mention what is included in shrub pollen: Are you including dwarf shrubs like Calluna or rather taller perennial woody plants like Corylus and Juniperus?
L. 139: How did you deal with situations where alien tree plantations make up most forest cover: e.g. Eucalyptus. Also plantations of Pseudotsuga (0.83 million ha in Europe) may be a potential problem.
L. 140: Large proportions of Cyperaceae and Polypodiales are limited to bogs, excluding them would reduce the biases from including bog samples.
L. 145: It would be good if you mentioned here the range of resulting source areas considered.
L. 153: What do you mean by “non-natural vegetation” here?
L. 154: How many from bogs?
L. 156: The same problem of attribution applies to the SPECIAL-EPD. Please cite and acknowledge the EPD. See https://www.neotomadb.org/data/data-use-and-embargo-policy
L. 167ff: I like the idea, but am skeptical about the predictors used. Rather than using % needleleaf, it would have been better to classify the pollen types according to high mid and low pollen producing plants. Needleleaf trees include the high pollen producing Pines and low producing Larix (or Pseudotsuga). I am not sure elevation is a good predictor when thinking about the past as vegetation belts moved up and down the mountains during the Holocene. I would perhaps rather limit the inclusion of modern and fossil sites to below 500 m. I don’t understand the need of including the Shannon Index, particularly I don’t understand the provided motivation.
L. 233ff: We know that % tree pollen is a strong predictor of forest cover without any transformation so it would be useful to compare the model performance to the performance of a simple regression model of % tree and shrub pollen (depending on what is in the shrubs) versus forest cover.
L. 233: The negative correlation between %needleleaf and tree cover is interesting and unexpected. Could that be due to frequent Pine pollen in generally open areas. Picea pollen should however correlate with high tree cover.
L. 258: The overestimation of tree cover in northern Scandinavia is interesting and expected as pollen productivity is lower. This is also the case for higher elevations, which is why elevation is a good covariable for the present, but this relationship may not hold true in the past where temperature changes resulted in changing pollen productivities in the mountains.
L. 330: The difference in tree cover between the reconstructions for the last 1000 years and the early Holocene is intriguing. As Zanon et al (2018) and Serge et al (2023) use completely different methodologies, but show the same trend, my initial response would be to trust them more, even if the absolute modern cover is off for both. Here it would be interesting to explore the reasons for the deviations of the current study. Could one reason be the separation of shrub pollen from tree pollen?
L. 341: Please see the recent manuscript by Schild et al. (https://essd.copernicus.org/preprints/essd-2023-486/#discussion ) who argue that the REVEALS method underestimates the forest cover. If that would be true then your new method would perform worse as it scores below the REVEALS estimates. If you argue that forest cover was generally lower then it would be useful to find supporting evidence and make that a point of discussion.
L. 421: The main deforestation of Northwestern Europe took place during the Bronze Age and Medieval period leading to an all-time low around 1800 (see e.g. Bradshaw and Sykes 2014 Ecosystem Dynamics, Wiley).