Springtime Bark-Splitting of Acer pseudoplatanus in Germany

Round 1

Reviewer 1 Report

Ms. Ref. No.: Forests-572208

Title: Spring-time bark splitting of Acer pseudoplatanus

The manuscript entitled “Spring-time bark splitting of Acer pseudoplatanus” by Schulze ED et al. (Ref: Forests-572208) is an interesting document on abnormal bark damage (cracking and splitting) on Acer pseudoplatanus possibly caused by drastic and abrupt changes in spring temperature, in a temperate climate region of Germany. The main hypotheses of the authors for this bark damage is a “late-frost damage near cambial zone, which had initiated growth before the frost event”. For me, the most important finding of the manuscript is that authors reported that not only the cumulative changes of temperature and precipitation but also drastic and abrupt changes on these climate variables should be responsible for different patterns of frost resistance of the distinct woody tissues: it seems that cambium and cortex are capable of developing a limited freezing tolerance while xylem is freezing sensitive. This can decisively affect the wood quality and quantity.

This paper on this subject is clearly appropriate for Forests and should result on interesting insights on Acer pseudoplatanus forest management, under the future scenarios of climate change with an increasing trend of fluctuations of daily temperature in the spring months.

I will outline some points (the most important points) that should be addressed.

I find important the location of the study on the title and on the introduction Keywords are missing Most of the literature is not accessible as is not in English or/ and is not is paper but book chapters. Also, the reference list is incomplete, e.g. Schweingruber et al., 2017 ( this is key reference that it is missing) In the introduction please had a state-of-the-art related to the main hypotheses “As main hypotheses we consider late-frost damage near the cambial zone, which had initiated growth before the frost event, as cause for this phenomenon. Desiccation of the active layer of growth at the time when xylem flow and bleeding started but the phloem was still dormant, could have interacted with the late-frost event.” The reader must understand why this hypothesis is formulated and appear? I would like to have the information of frost days in the study period, between 1 of March and 30 of April in the year 2018. The climate characterization is somewhat incomplete and should be more well presented. I would like to have more concise information on the incidence of the phenomenon. Some sentences are anecdotal and no spatial data were collected or eventually presented, at tree, stand or landscape level in the paper: ”The damage occurred mainly on the south facing side of the stem, starting at the base of the tree” (WHY?). “Also, the damage was more pronounced in open stands and for trees that were selected and pruned as future high-quality trees (WHY?). In young stands, up to 100% of Acer trees of that dimension were damaged (WHY?).” Moreover, none of these “facts” were directly addressed and explained by the authors. In the introduction it is missing a figure with a stem-cross section of an Acer pseudoplatanus for the presentation of the location of the woody tissues related to the study. Also, it will be interesting to know something about the patterns and fluctuations of cambial activity of this tree species along the different months of the year to accept (or understand) the main hypotheses of the authors. The main findings should be more explored: the differences in frost sensitivity in the woody tissues (not completely discussed) and the difference between trees related to trees age (or dbh size), or between stands ( stand density or stan canopy cover) not fully addressed. All in all this is an interesting paper for publication but need to be improved to be more clear. We need more sound data, more statistical analysis or instead we need more anatomical evidences at tree level and a more interesting and rich discussion.

 

Some detailed points are related to:

In the “The Climate in spring 2018” section

Lines 42: Fig 1? (instead of Fig 2)

Table 1 : this information can be placed in the Figure 1…

I find important to have the geographic coordinates of the meteorological stations and a map with the study area.

Lines 47-52: This information should be supported by a (new) table  

In the “The damage” section

It will be interesting to have the length and the width of the cracks per DBH class e.g. < 5 cm; 5-10 cm; 10-15 cm; > 15 cm.

In the “Anatomical evidence” section

Line 72: Schweingruber et al., 2017. This is a key reference that it is missing from the References

Line 71- 73. This is probably because the authors should have a schematic cross-section of a Acer pseudoplatanus. The innerbark should be better characterized in a scheme of a stem cross-section  

Line 73-74: Very imprecise terms related to anatomical tissues… What is “bark active”?

Line 75-77: “After an un-known time, most likely after 1 year, the cambial cell division resulted again in the formation of functional sieve and xylem elements which lead to the formation of new round stems attached to the bark.” How authors know this? It is not clear in the presented results. In cork oak this time it will depend on the crack width and length and on the tree conditions, but one year is definitively not enough…

The section of “Colonization by Fungi and Insects” can be addressed in a paragraph. The colonization was a consequence of bark splitting and should be reported more extensively in my opinion.

Discussion

Line 111-113: “The event of spring bark-splitting of Acer indicates, that climate change may not only mean a  rise in temperatures or a change in precipitation, but also an increase in the variation of spring time temperatures” It is missing some discussion and reference to other works

Line 115-116 “This may not only important for Acer but also for other deciduous broadleaved tree species, where we observed similar bark damage (mainly oak and ash)” It is missing some discussion and reference to other works

Line 126-130: ”Temperatures in March of 2018 following a warm winter activated xylem flow, and this period was followed by a cold spill with temperatures below -10°C. The damage occurred regionally at a wide scale covering North Bavaria and southern Thuringia (500 x 500 km), as we know from inquiries by several forest managers, but no systematic investigation about the regional extent of the observation was made.” This sentence is not for the discussion section. Perhaps for the introduction or for a Materials and methods sections and in the later before the climate

Line 131-132: “Based on the anatomical evidence, the damage occurred in the expanding xylem cells, and not in the cambium” I find this finding very interesting because shows a different pattern of frost resistance of the distinct woody tissues: it seems that cambium and cortex are capable of developing a limited freezing tolerance while xylem is freezing sensitive…Is that correct? This should be compared to other tree species, e.g. oak species.

Author Response

Open Review

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
( ) English language and style are fine/minor spell check required
(x) I don't feel qualified to judge about the English language and style

 

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	( )	( )	(x)	( )
Is the research design appropriate?	( )	( )	(x)	( )
Are the methods adequately described?	( )	( )	(x)	( )
Are the results clearly presented?	( )	( )	(x)	( )
Are the conclusions supported by the results?	( )	( )	(x)	( )

Comments and Suggestions for Authors

Ms. Ref. No.: Forests-572208

Title: Spring-time bark splitting of Acer pseudoplatanus

The manuscript entitled “Spring-time bark splitting of Acer pseudoplatanus” by Schulze ED et al. (Ref: Forests-572208) is an interesting document on abnormal bark damage (cracking and splitting) on Acer pseudoplatanus possibly caused by drastic and abrupt changes in spring temperature, in a temperate climate region of Germany.

We extended the title in order to make sure that this refers to Germany

The main hypotheses of the authors for this bark damage is a “late-frost damage near cambial zone, which had initiated growth before the frost event”. For me, the most important finding of the manuscript is that authors reported that not only the cumulative changes of temperature and precipitation but also drastic and abrupt changes on these climate variables should be responsible for different patterns of frost resistance of the distinct woody tissues: it seems that cambium and cortex are capable of developing a limited freezing tolerance while xylem is freezing sensitive. This can decisively affect the wood quality and quantity.

Thanks for this concise summary. We extended the abstract to make the main result clearer

This paper on this subject is clearly appropriate for Forests and should result on interesting insights on Acer pseudoplatanus forest management, under the future scenarios of climate change with an increasing trend of fluctuations of daily temperature in the spring months.

Thanks for this summary

I will outline some points (the most important points) that should be addressed.

Before commenting the remarks by Referee 1 we like to emphasize the comment by referee 2: This is an observational study with à posterior analyses and interpretations. It will be very difficult to explore this observation experimentally.  Nevertheless, we think that novel observations are important for future research. We also think that the observation of this manuscript has consequences for forest management. Our intention was also to writing a short communication, and not a long paper.

I find important the location of the study on the title and on the introduction Keywords are missing

Sorry, we missed the keywords and added them in the revision

Most of the literature is not accessible as is not in English or/ and is not is paper but book chapters.

 

We apologize, but this is the literature we could find on Acer. The genus has rarely been studied

Also, the reference list is incomplete, e.g. Schweingruber et al., 2017 ( this is key reference that it is missing)

The 2017 is a typo. We added the relevant reference.

In the introduction please had a state-of-the-art related to the main hypotheses “As main hypotheses we consider late-frost damage near the cambial zone, which had initiated growth before the frost event, as cause for this phenomenon. Desiccation of the active layer of growth at the time when xylem flow and bleeding started but the phloem was still dormant, could have interacted with the late-frost event.” The reader must understand why this hypothesis is formulated and appear?

We formulated this explanation because we observe that cambial cells re-initiated growth. We are grateful to the referee to have formulated the observation into a hypothesis, and we included a sentence at the end of the introduction

I would like to have the information of frost days in the study period, between 1 of March and 30 of April in the year 2018. The climate characterization is somewhat incomplete and should be more well presented.

Thanks for this comment. The climate description was indeed very short. We extended the description of the climate record, even though the information is visualized by the green line in Fig. 1

I would like to have more concise information on the incidence of the phenomenon.

We are sorry to say, but this is all we have. The event was unpredicted. The best record was the observation by the forest engineer as cited in the introduction, who witnessed the event.

Some sentences are anecdotal and no spatial data were collected or eventually presented, at tree, stand or landscape level in the paper:

We regret to say, but a regional study was not conducted. The spatial extent remains anecdotally, because it is based on discussions with forest neighbors after the event had passed. All we know, the observation is independent of the habitat conditions.

”The damage occurred mainly on the south facing side of the stem, starting at the base of the tree” (WHY?). “Also, the damage was more pronounced in open stands and for trees that were selected and pruned as future high-quality trees (WHY?). In young stands, up to 100% of Acer trees of that dimension were damaged (WHY?).

We can discuss these reasons, but we have no data. Clearly sun exposed parts get warmer and thus initiate growth earlier than non-sun-exposed parts of a stem, but this was not measured, because the event occurred unexpectedly. We wanted to make sure that the observation is documented as short as possible in a short communication.

” Moreover, none of these “facts” were directly addressed and explained by the authors. In the introduction it is missing a figure with a stem-cross section of an Acer pseudoplatanus for the presentation of the location of the woody tissues related to the study.

We think that a cross section of stems has been published so often in wood anatomy and in general text books, that a new figure would be a repeat. After all, this paper is addressed to forest-majors who should know this.

Also, it will be interesting to know something about the patterns and fluctuations of cambial activity of this tree species along the different months of the year to accept (or understand) the main hypotheses of the authors.

We regret, but this information is not available. We tried to find growth data from that year, asking cooperating research groups. No chance: Acer was not measured. We also think that the steel bands, normally used to study growth, do not distinguish between swelling of tissues and cambial activity. To study growth activity from repeated sampling would be a study by itself, and it could not be planned ahead, because we could not foresee the weather pattern. Only an experimental set up might be able to give this information. However, this would be a complicated study of its own in the future.  

The main findings should be more explored: the differences in frost sensitivity in the woody tissues (not completely discussed) and the difference between trees related to trees age (or dbh size), or between stands ( stand density or stan canopy cover) not fully addressed.

We did the correlation of damage and DBH, but the result is trivial: Small trees have smaller cracks. The axes are not independent. We think, that all we know, and all we can document, is being said. It would be possible to extend the discussion, but this would be not based on data.

All in all this is an interesting paper for publication but need to be improved to be more clear.

We hope that the revision is more clear. We regret that for an á posteriori observation it is not possible to take process related data

We need more sound data, more statistical analysis or instead we need more anatomical evidences at tree level and a more interesting and rich discussion.

Thanks for this comment, but more process data could only be generated by an experiment, which would be a major and complicated study for the future.

Some detailed points are related to:

In the “The Climate in spring 2018” section

Lines 42: Fig 1? (instead of Fig 2)

No, this refers to Fig 2 which is presented and discussed later. We extended the reference to this Figure

Table 1 : this information can be placed in the Figure 1…

We prefer to leave Table 1 with the climate section

I find important to have the geographic coordinates of the meteorological stations and a map with the study area.

We have added the coordinates in the introduction.  We do not think that a short communication warrants a map of the study area

Lines 47-52: This information should be supported by a (new) table

Sorry to say, but all information is embedded in the text. A Table would be a repeat, and it would not save space  

In the “The damage” section

It will be interesting to have the length and the width of the cracks per DBH class e.g. < 5 cm; 5-10 cm; 10-15 cm; > 15 cm.

We did these correlations, and introduced a sentence, but x- and y-axes are not independent. Small trees have smaller damage.

In the “Anatomical evidence” section

Line 72: Schweingruber et al., 2017. This is a key reference that it is missing from the References

We corrected this reference. The earliest observation is in Schweingruber, 2007. We added more precise information, especially Schweingruber et al., 2012 with Fig. 5.6. We are sorry that all this information is published in books on wood anatomy

Line 71- 73. This is probably because the authors should have a schematic cross-section of a Acer pseudoplatanus. The innerbark should be better characterized in a scheme of a stem cross-section  

Schemes of cross sections have been published repeatedly. This paper should be a short communication. We refer to Fig 5.6 in Schweingruber et al., 2012.

Line 73-74: Very imprecise terms related to anatomical tissues… What is “bark active”?

We meant to say “where the bark remained alive”, but, “active” implies also that living cells divide. We changed the wording.

Line 75-77: “After an un-known time, most likely after 1 year, the cambial cell division resulted again in the formation of functional sieve and xylem elements which lead to the formation of new round stems attached to the bark.” How authors know this?

The study was made one year after the damage. We reworded this sentence.

It is not clear in the presented results. In cork oak this time it will depend on the crack width and length and on the tree conditions, but one year is definitively not enough…

We did not say that the crack was healed. In fact, in the abstract and discussion we say that the crack may never heal. We only say that the healing process was started by new tissue (Line 75, 2 cm per year)

The section of “Colonization by Fungi and Insects” can be addressed in a paragraph. The colonization was a consequence of bark splitting and should be reported more extensively in my opinion.

Thanks for the comment. This section is important to us, because it shows the interaction of biological and physical damage. However, we do not have trees with damage and no splitting of the bark as control. We add a comment.

Discussion

Line 111-113: “The event of spring bark-splitting of Acer indicates, that climate change may not only mean a  rise in temperatures or a change in precipitation, but also an increase in the variation of spring time temperatures” It is missing some discussion and reference to other works

We would be happy to know a publication on the variability in spring temperatures over the past 40 years. We could not find such reference. Maybe the referee could share his knowledge about this observation.

Line 115-116 “This may not only important for Acer but also for other deciduous broadleaved tree species, where we observed similar bark damage (mainly oak and ash)” It is missing some discussion and reference to other works

In line 132 we refer to oak and ash. However, the “frost-ribs” in these species have been interpreted as damage by winter temperatures and xylem-cracking in radial direction, not by late frost damage and damage by expanding xylem cells in tangential direction. We add some explaining text.

Line 126-130: ”Temperatures in March of 2018 following a warm winter activated xylem flow, and this period was followed by a cold spill with temperatures below -10°C. The damage occurred regionally at a wide scale covering North Bavaria and southern Thuringia (500 x 500 km), as we know from inquiries by several forest managers, but no systematic investigation about the regional extent of the observation was made.” This sentence is not for the discussion section. Perhaps for the introduction or for a Materials and methods sections and in the later before the climate

Thanks for the suggestion. However, since we did not make a systematic regional survey, we like to maintain this information in the discussion.

Line 131-132: “Based on the anatomical evidence, the damage occurred in the expanding xylem cells, and not in the cambium” I find this finding very interesting because shows a different pattern of frost resistance of the distinct woody tissues: it seems that cambium and cortex are capable of developing a limited freezing tolerance while xylem is freezing sensitive…Is that correct? This should be compared to other tree species, e.g. oak species.

Thanks for the comment. Indeed this is the main finding, and we are ashamed that this did not come across. We added a sentence, even though we feel it is a repeat.

 

Submission Date

29 July 2019

Date of this review

19 Aug 2019 17:47:00

 

 

Open Review

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
(x) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

 

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	( )	(x)	( )	( )
Is the research design appropriate?	( )	( )	( )	(x)
Are the methods adequately described?	( )	( )	( )	(x)
Are the results clearly presented?	(x)	( )	( )	( )
Are the conclusions supported by the results?	(x)	( )	( )	( )

Comments and Suggestions for Authors

The authors report an interesting phenomenon of bark splitting related to weather conditions and subsequent observations regarding response of the injured trees to the injury.  This work is primarily observational and is most suitable as a note or short communication.

Thanks for this comment. We wished to write a short communication. It may have become a short paper. However, the length increased with dealing with so many aspects of this damage.

Lines 28-34: this type of damage is not especially unusual in Acer and certain other tree species in ornamental tree nurseries after harsh winters.

Thanks for the comment. In Line 163 we cite Lucas, 1887, which seemed to have been one of the earliest reports of this type of damage. We also cite orchards and fruit trees. We added ornamentals.

Line 31: should be Fig. 1 not 2.

No, we refer to the color Fig 2, which comes later. We clarify this reference

Line 138: Xylosandrus germanus not Xyleborus germanus.  We often see the same thing in nurseries on trees with split bark. Ambrosia beetles appear attracted to these wound sites.

Sorry for taking an old name

 

Submission Date

29 July 2019

Date of this review

23 Sep 2019 20:44:44

 

Reviewer 2 Report

The authors report an interesting phenomenon of bark splitting related to weather conditions and subsequent observations regarding response of the injured trees to the injury.  This work is primarily observational and is most suitable as a note or short communication.

Lines 28-34: this type of damage is not especially unusual in Acer and certain other tree species in ornamental tree nurseries after harsh winters.

Line 31: should be Fig. 1 not 2.

Line 138: Xylosandrus germanus not Xyleborus germanus.  We often see the same thing in nurseries on trees with split bark. Ambrosia beetles appear attracted to these wound sites.

Author Response

Open Review

(x) I would not like to sign my review report
( ) I would like to sign my review report

English language and style

( ) Extensive editing of English language and style required
( ) Moderate English changes required
(x) English language and style are fine/minor spell check required
( ) I don't feel qualified to judge about the English language and style

 

	Yes	Can be improved	Must be improved	Not applicable
Does the introduction provide sufficient background and include all relevant references?	( )	(x)	( )	( )
Is the research design appropriate?	( )	( )	( )	(x)
Are the methods adequately described?	( )	( )	( )	(x)
Are the results clearly presented?	(x)	( )	( )	( )
Are the conclusions supported by the results?	(x)	( )	( )	( )

Comments and Suggestions for Authors

The authors report an interesting phenomenon of bark splitting related to weather conditions and subsequent observations regarding response of the injured trees to the injury.  This work is primarily observational and is most suitable as a note or short communication.

Thanks for this comment. We wished to write a short communication. It may have become a short paper. However, the length increased with dealing with so many aspects of this damage.

Lines 28-34: this type of damage is not especially unusual in Acer and certain other tree species in ornamental tree nurseries after harsh winters.

Thanks for the comment. In Line 163 we cite Lucas, 1887, which seemed to have been one of the earliest reports of this type of damage. We also cite orchards and fruit trees. We added ornamentals.

Line 31: should be Fig. 1 not 2.

No, we refer to the color Fig 2, which comes later. We clarify this reference

Line 138: Xylosandrus germanus not Xyleborus germanus.  We often see the same thing in nurseries on trees with split bark. Ambrosia beetles appear attracted to these wound sites.

Sorry for taking an old name

 

Submission Date

29 July 2019

Date of this review

23 Sep 2019 20:44:44

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Forests: Spring-Time Bark Splitting of Acer pseudoplatanus

By Schulze et al.

The authors report an interesting phenomenon of bark splitting related to weather conditions and subsequent observations regarding response of the injured trees to the injury. This report, while primarily observational, is interesting and should have value to foresters.

Line 37: delete “like to”.

Line 43: what you describe is weather because it occurred during a single season. Climatic conditions are related to long periods of time.

Line 52: delete xylem between No and bleeding.

Line 163: delete hormonal before balance.

Line 192: frost-scar-like not “frost-scare-like”.

Author Response

The authors report an interesting phenomenon of bark splitting related to weather conditions and subsequent observations regarding response of the injured trees to the injury. This report, while primarily observational, is interesting and should have value to foresters.

I thank the referee for pointing out these mistakes in the text

Line 37: delete “like to”.

Has been changed

Line 43: what you describe is weather because it occurred during a single season. Climatic conditions are related to long periods of time.

Has been changed

Line 52: delete xylem between No and bleeding

Has been changed.

Line 163: delete hormonal before balance.

Has been changed

Line 192: frost-scar-like not “frost-scare-like”.

I had to laugh that I made this typo. Has been changed. Thanks for pointing this out.

Author Response File: Author Response.docx