the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 26 Jul 2023
Impacts and damages of the European multi-year drought and heat event 2018–2022 on forests, a review
Abstract. Drought and heat events are becoming more frequent in Europe due to human-induced climate change, affecting many aspects of human well-being and ecosystem functioning. However, the intensity of these drought and heat events is not spatially and temporally uniform. Understanding the spatial variability of drought impacts is important information for decision makers, supporting both planning and preparations to cope with the changing climatic conditions. Currently, data relating to the damage caused by extended drought episodes is scattered across languages and sources such as scientific publications, governmental reports and the media. In this review paper, we compiled data of damages caused by the drought and heat of 2018 until 2022 in forest ecosystems and relate it to large European data sets, providing support for decision making both on the regional and European levels. We partitioned data from 16 European countries to the following regions: Northern, Central, Alpine, and South. We focused on drought and heat damage to forests, and categorized them as (1) physiological (2) pest, and (3) fire damage. We were able to identify the following key trends: (1) Relative defoliation rates of broadleaves is higher than of conifers in every country with the exception of Czech Republic (2) the incidence of wood destroyed by insects is extremely high in Central Europe and Sweden (3) Although forest fires can be related to heat and drought, they are superimposed by other anthropogenic influences (4) In this period (2018–2022), forests in central Europe are particularly affected, while forests in the Northern and Alpine zones are less affected, and adaptations to heat and drought can still be observed in the Southern zone. (5) Although in several regions 2021 was an average year still high levels of damages were observed indicating strong legacy effects of 2018–2020. We note that the inventory should be continuously updated as new data appear.
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RC1: 'Comment on egusphere-2023-1463', Anonymous Referee #1, 01 Sep 2023
General comments
This paper covers a very important topic, and provides a thorough review of drought and heat events across four climate zones and 20 European countries. This is a monumental task given the inconsistencies in data availability and documentation and challenges associated with translation across at least 15 languages. The paper itself might benefit from additional tables or figures and less text to help facilitate comparisons across regions. Also a greater emphasis on how the results compare to a reference period (prior to 2018?) would help the readers better access how truly extraordinary (or not) the results are. The organization of the paper was generally good, but there were sections that were disconnected from previous sections. For example, the description of groundwater was very general and poorly linked with drought until the following page. Also, the section about dryland mechanisms was not well integrated into the paper and only discussed hydrophobicity. In fact, I’m not convinced this section is necessary (might flow better from future trends to policies without the section on hydrophobicity) but if the authors want to include it they should more comprehensively review the most important mechanisms that mitigate drought stress. The paper is generally well-written, with only minor typographical errors, which are documented below.
Specific comments
L79-80. The sentence could benefit from expanding upon “essential ecosystem services”.
L84. Explicitly state the level of political boundaries referred to in the data (i.e. country-level or county-level).
L98-100. Providing definitions for atmospheric processes mentioned would improve accessibility here. For example, “periods of blocking”, “positive North Atlantic Oscillation”, and “double jet stream configuration”.
F1. Comparison between two columns seems ill-suited, as the second column (Spring and Summer) includes data from the first column (Summer). It would be more apt to compare Spring and Summer. This figure should also be discussed further in the text.
L125. It would be good to include more information about how SPEI was calculated. What was the reference period and time scale?
T2. The data in this table seems like it would be better represented graphically (multiple line graph) as it is difficult to follow the trends in which country experienced the highest insect damage. List the full names of the countries since you have the space. Perhaps change the units to minimize zeros?
L418. These tree felling statistics come off as less impactful, given that the previous sentence indicates that the annual productivity is still over double the volume felled. Also, you don’t provide a reference level of felling so we can’t assess the % increase.
L426. How was “unfavorable condition” determined? Is this condition due to pests and disease or is it that the forest is in an unfavorable condition to resist pests and disease?
L530. This paragraph should connect these disturbances to drought, as drought is not mentioned in the paragraph. Providing context for prevailing rates of disturbance prior to the drought would also be helpful.
L531-536. In Germany you described the climate, but you didn’t do that in the other countries (see L516 where you just jump right to forests). It would be good to be consistent across countries.
L764-809. The description of groundwater and monitoring of groundwater is very long, compared to the very small section on how the drought affected groundwater (L793-798). Perhaps it could be shortened or the impacts expanded upon.
L822-835. This section starts with a discussion of groundwater, but I would think that seedling establishment is more influenced by surface/soil water and not groundwater. Maybe a section on surface moisture should precede this section on establishment.
L845-847. This paragraph about climate change effects on pests seems out of place when the above paragraph only discusses observations. It would be good to be consistent across the paragraphs in this section.
L884. I’m not convinced the survey is relevant. Just because people thought they should plant more trees, does not mean that the drought damage was clearly noticeable to visitors.
L1045-1089. The heading was about dryland mechanisms but they only discussed one: hydrophobicity. I’m not sure this section is needed, but if included, they should more comprehensively review the most important mechanisms that mitigate drought stress.
L1125-45. It might be better to describe the forest damage first and then discuss mitigation (i.e. switch the order of the first two paragraphs in the conclusion. Conclusions about the relative differences between regions might be helpful to include here
L1036. You suddenly switched from discussing soil temperature to albedo. Better transition?
L1067. Increasing bare patches reduces (not increases) connectivity of vegetation, but maybe you were referring to hydrologic connectivity. It would be good to clarify your statement.
Technical comments
L42. Which “large European data sets”? What variables are being considered? Climate vegetation?
L47. What do you mean by superimposed? Just driven by?
L49. Why do you say “can still be observed”? Why still? Is the Southern zone affected? That’s what you are describing in the other zones.
L51. This inventory or all inventories.
L65-67. Wording is a little vague. How long is this trend?
L73-74. This sentence seems out of place.
L77. I would say forest ecosystems, rather than these
L85. “The insight of” is awkward.
L86. Repace “assessing the” with “for the assessment of”
L88. It’s not clear why the context is needed only for the Southern region.
L93-94. State which European countries are not included in the research.
L119. Change “Britain/Scandinavia” to “Northern” to keep naming convention consistent.
Table 1. But earlier you said countries were assigned to one zone (L84).
L131-32. Include a citation here, as this longer-term drying trend is once again alluded to without reference.
L141. It’s not clear why it’s a “however”.
L159. This sentence makes a definitive statement based on results from a climate model. Replace “is going to” with “is projected to”.
L160. Seasons are not capitalized.
L166-67. Definitive language on our future climate emissions, even though there is great uncertainty surrounding projections. Replace “As soon as we” with “If we”.
L167. Should refer to the transition from the current state in future tense. Replace “is slowly” with “will slowly”.
L173. You should again address the uncertainty in the future climate system. Replace “once” with “if”.
L182. You wouldn’t start this sentence with despite as what you describe seems to be the logical conclusion. As it is difficult to reconcile… therefore there are few studies.
L194.Climate models project possible future climates, therefore there is inherent uncertainty. These models shouldn’t be used to “confirm” results. Replace “are confirmed in” with “match results from”.
L204. You didn’t tell us about Sweden first “as Sweden did”. Omit?
L211. “fires” not “Fires”
L221. What period of time are the climate models projecting more concentration ppt?
L235. What do you mean by “last place in Europe”? Do you mean sufficient water sources?
L240. Omit “shortage”
L245. Why is 2015 the reference period here?
L271. Than all the other countries?
L291. Alters rather than reflects?
L307. Change to “greater risk of embolism, which can cause…”
Figure 2. The colors in graphs b and c do not match, leading to possible misinterpretation.
L316. Need to define and expand on “moderate to severe defoliation”. Figure caption is difficult to interpret.
Figure 3. The legend should state that it’s only severe wildfires. Also, this figure should be included after the first time it is mentioned in the text, which is currently L514.
L357. But we can’t always limit disturbance damage, just be understanding it.
Figure 4. Replace “E” with “ESP'' to remain consistent in naming convention. Figure does not include a title, while the previous figure does. Similar to the previous figure, Figure 4 should be included after the first time it is mentioned in the text, which is currently L739. Does Figure 4 include tree cover loss from wildfires, wind and pests? It would be good to list the disturbances monitored.
L363. Replace “2.2” with “3.2”. You might want to recheck the numbering of your section headings throughout.
L367. Expand on historic forest damage directly coming from drought.
L377. I’m not sure if it’s a steady increase if it omits 2019.
L389. Comparison between volume harvested and total area confusing as metrics are different. Especially confusing as the unit for volume (m^3) looks very similar to m^2.
L393. Replace “thus over than” with “thus over”
L427. Ash should not be capitalized. Accordingly should start a new sentence.
L421. Forest Research should be capitalized. August should be too.
L435. Omit harsh to avoid sensationalizing. Replace with large?
L436-37. Provide further context. Is 15-30,000 ha burned in a year a lot? What is the historic average?
L438. Punctuation issue. 1.323 instead of 1,323. If you prefer to use the European decimal notation, keep this consistent throughout the paper as you change between the two.
L445. What about the other 88%? Is it grassland?
L448. Add from, as in “suffers from”
L477. Replace “2.3” with “3.3”
L478. Remove “has”
L486. Entire hectares? A hectare isn’t that big.
L504. Why is there a parenthesis before 2018?
L504. It was what?
L505. I think you need another and before “a decrease”
L509. The Krotoszyn Plateau could use a reference.
L513. Was this the only factor behind the relatively good situation in Poland compared to geographic neighbors? If so, you should provide evidence.
L524. Change to “Damaged wood infected almost exclusively with…” for clarity.
L525. Add “the fire” as a new sentence, rather than using “it”.
L553. “Caused in the periods of heat” is awkward. Perhaps “had an outbreak during a period of heat…”.
L574. I don’t think it’s necessary to remind us that Austria and Switzerland are also described in the alpine section. You told us this at the beginning. It would also be helpful to provide criteria about how you assigned the zones.
L579. Replace “for tree” with “of tree”
L582. Replace “for the” with about
L583. I think you just need to tell us “but the results have not been published”.
L585. Put Flanders in parentheses instead to improve readability?
L587. Remove “deciduous” as you then specify the inclusion of Norway spruce which is coniferous.
L591. I think you could just add the definition of vitality in the next sentence “ of trends in vitality (e.g. loss of needles..”)
L603 I would add “burned” after 659 ha.
L607. Do you mean elevation?
L623. Evolved is not the best word to use here. Perhaps increased is sufficient.
L625. Replace “an increased defoliation” with higher defoliation rates.
L629. In instead of with would be better.
L637. I’m not sure why you used the word balance.
L640. Replace wood with damage to be more specific
L651. The years 2018 and 2022 seem out of place in that sentence.
L659. Replace colon with semicolon
L660. Which disease? Citation?
L670 The phrasing “2022 it is around” is awkward.
L674 Too many modifiers. Rephrase to “in a week, consuming mainly broadleaved forests”...
L676. Omit situation. Just say Fires
L689. Damage, not damages
L697. I think you could combine this with the previous sentence- “increase in defoliation, forest mortality and leaf discoloration”...
L710. I don’t think it’s necessary to remind us that Italy is also described in the alpine section. You told us this at the beginning.
L812. Might be better to say “demographic processes” rather than just demography.
L817. I would remove the term “long lasting” as I would argue that most of these examples are of short term legacies from drought.
L855-857. The sentence about “an additional factor” seems out of place. Omit? Or improve the transition to this section on how easily forests can be attributed to climate change. It’s been done by John T. Abatzoglou in the U.S. if you need a citation or want to discuss this topic more.
L860. Replace “literally no” with “very little” as there is a reduction from 7.8 to 7.6 to 6.0.
L878. You could omit “for example”
L882. remove “also”
L897. Replacing the phrase “Fort the forest damage…” would improve readability.
L920. Add a reference for the statement about massive damage? Maybe you mean extensive rather than massive, as well.
L922. The roots don’t have enough what?
L927. Add “the” main tree species
L939. You shift from discussing increases in diversity and say that means less conifers, even though those things are not necessarily relate. Either omit the “less conifers” or add an explanation.
L951. Because should be lower-case
L953. I think wildfires should replace the word systems
L968. Situation, not situatione
L975. Decay might not be the best word to use here. Decrease might be best.
L979. You already stated that your results were in accordance with Gazol in L973. Omit this sentence?
L987. Replace interpretation with interpreting.
L1111. The sentence is very repetitive with L1004. Omit or alter the sentence.
L1017. You could use a better transition after conditions. Semicolon or add “and therefore”.
L1033. It’s not clear what you mean by your statement “not a robust feature”.
L1091. Replace sticking with another word. Complex?
L115. Maybe rename to Issues of Data availability. I thought it was a statement about where your data will be made available (i.e. github).
Citation: https://doi.org/10.5194/egusphere-2023-1463-RC1 -
EC1: 'Reply on RC1/RC2', Andreas Hense, 07 Dec 2023
Having read the manuscript and the two reviewers comments it is clear that the manuscript need major changes. I would suggest to the author team to concentrate upon the central problems issued by both RC1&RC2: (a) the reorganisation/streamlining of the manuscript including the introduction (or at least a clarification) of a "take-home-message", a strengthening of the connections between the subchapter on hydrology and the remaining parts and (b) the introduction of some sort of a reference in time to allow an evidence based estimation of the reported levels of forest damages. If these points can be successfully implemented the manuscript would indeed constitute a nice review on the desired topic. Also, please consider the extensive list of specific comments by RC1 although some of those may become obsolete after revision acc. to (a) and (b). After submission of the revised manuscript RC1/RC2 will be asked to rereview the text.
Citation: https://doi.org/10.5194/egusphere-2023-1463-EC1 -
AC2: 'Reply on RC1', Florian Knutzen, 25 Jan 2024
Dear Reviewers,
thank you for the opportunity to improve our manuscript based on your thorough review. We appreciate your valuable feedback and acknowledge the need for major revisions. We will focus on addressing the central issues highlighted by both Reviewer 1 and Reviewer 2, specifically:
(a) Reorganizing and streamlining the manuscript, with particular attention to enhancing the introduction by incorporating a clear "take-home message." We will work on strengthening the connections between the subchapter on hydrology and other relevant sections.
(b) Introducing a reference in time to facilitate an evidence-based estimation of the reported levels of forest damages. After an initial assessment based on recent climate history and data availability, we decided to choose a reference period from 2010 to 2014 to compare it with the period 2018-2022. We chose this period because we have relatively good data availability here. In addition, these five years are largely free of strong climate extremes. So we think it is quite good to contrast this period with the abnormally dry and hot period 2018 to 2022.
We understand the importance of these points in improving the overall quality and coherence of the manuscript. Additionally, we will carefully consider the specific comments provided by Reviewer 1, even though some may be addressed through the proposed revisions in (a) and (b).
We are committed to making these necessary changes to enhance the manuscript, and are grateful for the opportunity to submit a revised version for your consideration. We appreciate your guidance and look forward to the opportunity to improve the manuscript based on your insightful suggestions.
A few direct comments to RC1: We appreciate your thoughtful and constructive feedback on our manuscript. Your acknowledgment of the importance of the topic and recognition of the challenges involved in conducting a review across diverse climate zones and countries is encouraging. We take note of your suggestions and agree that additional tables or figures, along with concise text, can enhance the clarity and comparability of our findings across regions. Regarding the organization of the paper, we will work on improving the flow and coherence, particularly in sections where disconnections were noted. We will reassess the relevance of the section on dryland mechanisms and groundwater, ensuring it integrates seamlessly into the broader narrative. If retained, we will expand the review of mechanisms mitigating drought stress. Thank you for highlighting the overall quality of the writing, and we will address the minor typographical errors as indicated in your comments. We are committed to refining the manuscript based on your suggestions.
Thank you for your valuable insights, and the opportunity to resubmit an improved version of our manuscript.
Sincerely yours
Florian Knutzen and coauthors
Citation: https://doi.org/10.5194/egusphere-2023-1463-AC2
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EC1: 'Reply on RC1/RC2', Andreas Hense, 07 Dec 2023
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RC2: 'Comment on egusphere-2023-1463', Anonymous Referee #2, 23 Nov 2023
In this paper, Knutzen and colleagues present an in-depth assessment of the damages of the recent drought and heat events on European forests. They divided Europe into four regions with different climate backgrounds to account for regional specificities. This paper undoubtedly contains a lot of information, and I commend the authors for their thorough search across various information media. However, this strength of the paper is also one of its strongest weaknesses. The information remains raw and unprocessed, and many sections of the paper read like a succession of somehow related facts. As they advance with this manuscript, I strongly recommend the authors digest and sort through the information and try to see what key messages might emerge from their compilation.
Another area for improvement is that there is no point of comparison for the presented data. This synthesis would greatly benefit from having a reference against which most numbers from 2018-2022 could be compared. I couldn’t help but wonder if the changes were slightly worse, way worse, or extremely worse. The reader needs a baseline to understand better how worse things got during those extreme years.
The structure of the paper could be refined as well. The information is only sometimes connected, making it difficult for a global picture to emerge. Some information is also repeated several times, like to which group each country belongs. It is said once at the beginning, and that’s sufficient. What are the take-home messages for each region? For Europe? What results are specific to the study region, and what results are not? Some of these details are in the paper but must be more clearly visible. In theory, Section 5 should take all the previous elements together. In practice, it introduces many new elements whose added value often needs to be clarified. The conclusions of the paper are unclear.
Finally, the English needs to be improved. In particular, the punctuation could be more accurate because it is currently misleading in some places.
Overall, I support this manuscript, and it should become a significant contribution. However, it needs some serious remodelling and streamlining to become publishable. Improved structure and simplified language will also contribute to taking the paper to the expected level of a review paper.
Citation: https://doi.org/10.5194/egusphere-2023-1463-RC2 -
EC2: 'Reply on RC1& RC2', Andreas Hense, 07 Dec 2023
see ec1 comment
Citation: https://doi.org/10.5194/egusphere-2023-1463-EC2 -
AC1: 'Reply on RC2', Florian Knutzen, 25 Jan 2024
Dear Reviewers,
thank you for the opportunity to improve our manuscript based on your thorough review. We appreciate your valuable feedback and acknowledge the need for major revisions. We will focus on addressing the central issues highlighted by both Reviewer 1 and Reviewer 2, specifically:
(a) Reorganizing and streamlining the manuscript, with particular attention to enhancing the introduction by incorporating a clear "take-home message." We will work on strengthening the connections between the subchapter on hydrology and other relevant sections.
(b) Introducing a reference in time to facilitate an evidence-based estimation of the reported levels of forest damages. After an initial assessment based on recent climate history and data availability, we decided to choose a reference period from 2010 to 2014 to compare it with the period 2018-2022. We chose this period because we have relatively good data availability here. In addition, these five years are largely free of strong climate extremes. So we think it is quite good to contrast this period with the abnormally dry and hot period 2018 to 2022.
We understand the importance of these points in improving the overall quality and coherence of the manuscript. Additionally, we will carefully consider the specific comments provided by Reviewer 1, even though some may be addressed through the proposed revisions in (a) and (b).
We are committed to making these necessary changes to enhance the manuscript, and are grateful for the opportunity to submit a revised version for your consideration. We appreciate your guidance and look forward to the opportunity to improve the manuscript based on your insightful suggestions.
Some comments directly to RC2:
We sincerely appreciate your thorough review and constructive feedback on our manuscript. Your acknowledgment of the extensive assessment of drought and heat impacts on European forests is encouraging. We acknowledge your observations regarding the raw presentation of information and the need for careful digestion and organization. We will work diligently to refine the paper, ensuring a more cohesive structure that highlights key messages and eliminates unnecessary repetitions. The recommendation to enhance the paper's structure, particularly in Section 5, aligns with our commitment to providing a more integrated and streamlined narrative. We will ensure that take-home messages for each region and Europe are clearly articulated. We appreciate your keen eye on language improvement, and we will meticulously address punctuation issues to enhance clarity.
Thank you for your valuable insights, and the opportunity to resubmit an improved version of our manuscript.
Sincerely yours
Florian Knutzen and coauthors
Citation: https://doi.org/10.5194/egusphere-2023-1463-AC1
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EC2: 'Reply on RC1& RC2', Andreas Hense, 07 Dec 2023
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