Reversible Impacts of a Cold Spell on Forest Cover, Tree Growth and Carbohydrates in Mediterranean Pine and Oak Forests

Round 1

Reviewer 1 Report

Currently, investigations that would monitor climate change are very important. They can help predict the consequences of these changes on living organisms. Without a doubt, the present study is a very high-level study, and the results presented by the authors are relevant. Of course, in terms of its content, the paper fits into the scope of Forests journal. The results have both fundamental and practical significance. Materials and Methods are described in detail and match the aims completely.

But in my opinion, there are some points that should be improved.

 

 

Major points

1.      I think that Introduction Section and Discussion Section are not enough referenced according to Conclusion made. Reasoning about the role of sugars and their diagnostic function in the process under study should be better described from the standpoint of existing research. You should emphasize why sugar content is important in this study. It is necessary to describe why exactly the leaf apparatus and sapwood were considered in terms of sink-source interactions.

2.      It is necessary to add more specifics to the method for determining sugars, namely: what purity of the substance was used, how calibration graphs were built, which spectrophotometer was used, how many technical replicates were done.

3.      Was the raw data tested for normality?

 

 

 

Minor points

1.      English language editing

Line 53 – economic loses   literal error

Line 107 – climate should be replaced to the climate

Line 113 – dry should be replaced to a dry

Line 146 – so as can be missed

Line 194 – in should be replaced to on

Line 253 – were should be replaced to was

Line 301 – where should be replaced to were

Line 314 – in situ should be written in Italics

Line 335 –comma is missed

Line 350 –comma is missed

Line 353 –opens should be replaced to opened

 

 

 

2.      Figures

Figure 3     0.0 is not correct. You should change the format.

 

Figure 5     The same point as in Figure 3.

Author Response

Comments and Suggestions for Authors

Currently, investigations that would monitor climate change are very important. They can help predict the consequences of these changes on living organisms. Without a doubt, the present study is a very high-level study, and the results presented by the authors are relevant. Of course, in terms of its content, the paper fits into the scope of Forests journal. The results have both fundamental and practical significance. Materials and Methods are described in detail and match the aims completely.

• We thank the reviewer for her/his positive comments on the ms.

But in my opinion, there are some points that should be improved.

 

Major points

1. I think that Introduction Section and Discussion Section are not enough referenced according to Conclusion made. Reasoning about the role of sugars and their diagnostic function in the process under study should be better described from the standpoint of existing research. You should emphasize why sugar content is important in this study. It is necessary to describe why exactly the leaf apparatus and sapwood were considered in terms of sink-source interactions.

• We added some references to the potential role played by sapwood sugars as C reserves or osmolytes in the revised Introduction and Discussion.

2. It is necessary to add more specifics to the method for determining sugars, namely: what purity of the substance was used, how calibration graphs were built, which spectrophotometer was used, how many technical replicates were done.

 

• We added more details to the NSC analyses methods.

 

3. Was the raw data tested for normality?

 

• Yes, they were; but we used non-parametric Mann-Whitney tests because some variables did not follow normal distributions.

 

 

Minor points

1. English language editing

Line 53 – economic loses   literal error

Line 107 – climate should be replaced to the climate

Line 113 – dry should be replaced to a dry

Line 146 – so as can be missed

Line 194 – in should be replaced to on

Line 253 – were should be replaced to was

Line 301 – where should be replaced to were

Line 314 – in situ should be written in Italics

Line 335 –comma is missed

Line 350 –comma is missed

Line 353 –opens should be replaced to opened

 

• We revised and corrected all minor points.

 

2. Figures

Figure 3     0.0 is not correct. You should change the format.

 Figure 5     The same point as in Figure 3.

 

• We revised both figures.

Reviewer 2 Report

Reversible impacts of a cold spell on forest cover, tree growth and carbohydrates in Mediterranean pine and oak forests

 

Jesús Julio Camarero * , Michele Colangelo , Cristina Valeriano , Manuel Pizarro

 

 

Major comments:

 

This manuscript is about the rarer extreme of climate change: cold spell. This topic is important even when the frequency, intensity, and duration of cold spells are much less than the dryer and warmer extreme. However, the authors should first give a more comprehensive review about the existing literature about climate changes and their consequences in the Mediterranean region (e.g. Fang, et al 2021. Hotter and drier climate made the Mediterranean Europe and northern Africa (MENA) region a shrubbier landscape. Oecologia: 1-16), then summarize any prior studies on cold spells—If this is more rarely studied in Mediterranean regions or elsewhere, this should be highlighted with references. Also, why should we care about it? Because, maybe existing forests may have adapted warmer and dyer climate, maybe a rare occasion of cold spells could be more devastating to trees than expected (here you should cite prior studies to support or not support such a speculation). At least, by the end of introduction, you should provide research questions and hypotheses with such a broader view. You should also revisit your overarching questions and hypotheses in Discussion/Conclusion sections.

 

Minor comments:

 

Abstracts:

1.     What is the purpose of using Pinus pinaster in non-defoliated area? It is not clear to me, and it feels like an ad-hoc decision.

2.     Prior to the cold spell, you mentioned defoliated pines grew more (2.73 mm), is this a mean? If so, you should also list standard deviations, and the Mann-Whitney test results (p value).

3.     You reported reduced radial growth in percentage (%) instead of absolute values (in mm). It is very hard to tell if you calculated the % reduction using long-term average or prior year growth. Also, you didn’t state whether they are statistically significant differences (no p-value mentioned).

 

Introduction:

1.     L30, are cold spells also more frequent, intense, and lasting? Any references? You need to work on this part of the literature review instead of only mention a couple of general studies.

2.     L39. “more frequent freeze-thaw cycles” any references? I was expecting you show some data on this based on your intro, but you didn’t. So you should modify your wording in the discussion about this topic ass well.

3.     L58-70 Most of this paragraph belongs to Methods section.

4.     L71-75. These hypotheses are really specific. You need to first present a more complete picture with a comprehensive literature review, then propose an overarching question and multiple hypotheses to address different facets of the question.

 

Methods:

1.     L85. “a by Pinus” should be “a nearby Pinus”, right?

2.     L100. I can’t tell whether you sampled 2 tree cores in Oct 2021 then two more again in 2022, or some trees were sampled in 2021, and other trees were sampled in 2022? If the later was true, you need to specify which ones were sampled when.

3.     L104-117 should be moved to Line 96 (before sampling and estimates). It’s still stie information, right? Also, it seems too long and of little use to your actual study.

4.     L123. If you downloaded your data from Google Earth Engine, you need to cite the data link, the original data source, its version, and resolution, etc. GEE is only a data hub.

5.     L155. “Comparison” of what? Not clear. Please specify.

6.     L166. Move the sentence “All analyses” to Line 163 before “Detrending”. Also, you need to mention the versions of R and R-Studio software.

7.     L170. Remove “,” after “nearby”; Also replace “also showing” with “which also showed”.

8.     L169. Is “damaged” the same as “defoliated”? Not clear. Please specify.

9.     L172. “spring” should really be early summer. It is already the end of June.

10.  L174. “between” should be “within”.

11.  L175. Please correct the grammar.

12.  L177. Please correct the grammar.

13.  L179. Change “collection” to “being collected”.

 

Results:

1.     L194. “In” should be changed to “On”.

2.     L199. Figure 1, you should add “Calamocha” and “Daroca” in the actual graphs (upper left conner of each frame). More importantly, the figure legend is very confusing. I guess the black line with solid dots are daily minimum air temperature during 12/1/2020-2/28/2021. And, error bars are means +- 1 standard deviation during 1993-2019 for Calamocha (Panel A) and during 1920-2019 for Daroca (Panel B). Right?

3.     L229. Why from 2008? Confusing. Will you discuss it in discussion? Maybe you did.

4.     L227-238, Section 3.3. Most of the tree ring growth were percentage (relative values). As I mentioned earlier, I can’t tell whether they were based on long-term average or the year prior to the droughts or cold spell. If you show mean +- sd, they should be absolute measures (in mm).

5.     L243 Table 1. Based on DBH, it seems smaller trees are more vulnerable. Or, more accurately, those individuals grew faster in a young age were less likely to endure (or less resilient to) harsh winter cold spell in later years. I see you discussed this later. I think this is an interesting finding and should be highlighted in the abstract.

6.     Also, Table 1, why do you compare defoliated vs non-defoliated? They were different by choice. Also, spell out AR1, MSx, Rbar.

7.     L266 Figure 5. It seems that authors conducted numerous correlation tests (14 X 3 X 3) which is not so appropriate. But I also don’t have a suggestion of a better solution.

8.     Also, Figure 5, where are your dotted lines? I only see dashed lines.

 

Discussion and Conclusion:

1.     Didn’t see you address the hypotheses proposed in the intro.

2.     Also, overall, would you conclude cold spell is a less a concern than drought plus heat waves? I don’t think cold spell is more frequent. You need to give a more broad speculation, and maybe mention that in the abstract.

 

 

Author Response

Comments and Suggestions for Authors

Major comments:

This manuscript is about the rarer extreme of climate change: cold spell. This topic is important even when the frequency, intensity, and duration of cold spells are much less than the dryer and warmer extreme. However, the authors should first give a more comprehensive review about the existing literature about climate changes and their consequences in the Mediterranean region (e.g. Fang, et al 2021. Hotter and drier climate made the Mediterranean Europe and northern Africa (MENA) region a shrubbier landscape. Oecologia: 1-16), then summarize any prior studies on cold spells—If this is more rarely studied in Mediterranean regions or elsewhere, this should be highlighted with references. Also, why should we care about it? Because, maybe existing forests may have adapted warmer and dyer climate, maybe a rare occasion of cold spells could be more devastating to trees than expected (here you should cite prior studies to support or not support such a speculation). At least, by the end of introduction, you should provide research questions and hypotheses with such a broader view. You should also revisit your overarching questions and hypotheses in Discussion/Conclusion sections.

• We have revised the Introduction to better introduce climate extremes in the Mediterranean region as you suggested. However, there are few studies on cold spells’ effects on forests in the region and we cited one of them published by our team (Camarero et al. 2015, in Ann Bot.). We have also cited the suggested reference. We have indicated why we should worry about cold spells in Mediterranean regions: because these rare climate extremes may also impact forests by impairing their capacity to recover after summer drought and particularly Mediterranean species of sub-tropical origin which are adapted to dry-warm conditions such as Pinus halepensis.
• We have revisited the hypotheses in the revised Discussion and Conclusions.

 

Minor comments:

 

Abstracts:

1. What is the purpose of using Pinus pinasterin non-defoliated area? It is not clear to me, and it feels like an ad-hoc decision.

• As indicated in the revised ms., this species is found in colder locations than halepensis and this can explain why it showed lower damage and less growth reduction after the cold spell as compared with the Mediterranean P. halepensis.

 

2. Prior to the cold spell, you mentioned defoliated pines grew more (2.73 mm), is this a mean? If so, you should also list standard deviations, and the Mann-Whitney test results (p value).

• Done, we added it.

3. You reported reduced radial growth in percentage (%) instead of absolute values (in mm). It is very hard to tell if you calculated the % reduction using long-term average or prior year growth. Also, you didn’t state whether they are statistically significant differences (no p-value mentioned).

• Done, we revised it and indicated the p value for the absolute growth data (in mm).

 

 

Introduction:

1. L30, are cold spells also more frequent, intense, and lasting? Any references? You need to work on this part of the literature review instead of only mention a couple of general studies.

• To the best of our knowledge there are no data on these issues regarding Mediterranean regions since these are rare climate extremes. But the cited general references indicate climate variability is increasing.

2. “more frequent freeze-thaw cycles” any references? I was expecting you show some data on this based on your intro, but you didn’t. So you should modify your wording in the discussion about this topic as well.

• We cited the only study we know on cold-spell impacts in Mediterranean forests. The reference to “freeze-thaw” cycles is also covered by that study since this is a general phenomenon in ecophysiology

3. L58-70 Most of this paragraph belongs to Methods section.

• Ok, we moved part of it to Methods but we left the description of the measures takne since they are necessary to introduce the hypothesis.

4. L71-75. These hypotheses are really specific. You need to first present a more complete picture with a comprehensive literature review, then propose an overarching question and multiple hypotheses to address different facets of the question.

• We followed your suggestion and presented a more general hypothesis regarding the pre-Mediterranean, sub-tropical origin of the species most affected by the cold spell such as Pinus halepensis.

 

Methods:

1. “a by Pinus” should be “a nearby Pinus”, right?

• Ok, we corrected it.

 

2. I can’t tell whether you sampled 2 tree cores in Oct 2021 then two more again in 2022, or some trees were sampled in 2021, and other trees were sampled in 2022? If the later was true, you need to specify which ones were sampled when.

• Ok, we corrected it. We sampled 2 cores per tree in the last date.

 

3. L104-117 should be moved to Line 96 (before sampling and estimates). It’s still stie information, right? Also, it seems too long and of little use to your actual study.

• Ok, we moved it. We think it is necessary to accurately describe climate conditions of the study sites.

4. If you downloaded your data from Google Earth Engine, you need to cite the data link, the original data source, its version, and resolution, etc. GEE is only a data hub.

• Ok, we cited it.

5. “Comparison” of what? Not clear. Please specify.

 

• Ok, we corrected it.

 

6. Move the sentence “All analyses” to Line 163 before “Detrending”. Also, you need to mention the versions of R and R-Studio software.

• Ok, we moved it. We did not use R-studio.

7. Remove “,” after “nearby”; Also replace “also showing” with “which also showed”.

 

• Ok, we corrected it.

 

8. Is “damaged” the same as “defoliated”? Not clear. Please specify.

• Ok, we replaced it by “defoliated”.

 

9. L172. “spring” should really be early summer. It is already the end of June.

 

• Ok, we corrected it.

 

10. L174. “between” should be “within”.

 

11. L175. Please correct the grammar.

 

12. L177. Please correct the grammar.

 

13. L179. Change “collection” to “being collected”.

 

• Ok, we corrected them.

 

Results:

1. “In” should be changed to “On”.

 

• Ok, we corrected it.

 

2. Figure 1, you should add “Calamocha” and “Daroca” in the actual graphs (upper left corner of each frame). More importantly, the figure legend is very confusing. I guess the black line with solid dots are daily minimum air temperature during 12/1/2020-2/28/2021. And, error bars are means +- 1 standard deviation during 1993-2019 for Calamocha (Panel A) and during 1920-2019 for Daroca (Panel B). Right?

 

• Ok, we revised and corrected the figure and its legend. Thank you.

 

3. Why from 2008? Confusing. Will you discuss it in discussion? Maybe you did.

• Yes, we discussed it since we think this was a lagged response to the 2005 drought.

 

4. L227-238, Section 3.3. Most of the tree ring growth were percentage (relative values). As I mentioned earlier, I can’t tell whether they were based on long-term average or the year prior to the droughts or cold spell. If you show mean +- sd, they should be absolute measures (in mm).

• Ok, we removed the percentages.

5. L243 Table 1. Based on DBH, it seems smaller trees are more vulnerable. Or, more accurately, those individuals grew faster in a young age were less likely to endure (or less resilient to) harsh winter cold spell in later years. I see you discussed this later. I think this is an interesting finding and should be highlighted in the abstract.

• We agree and highlighted this finding in the abstract. Thank you.

 

6. Also, Table 1, why do you compare defoliated vs non-defoliated? They were different by choice. Also, spell out AR1, MSx, Rbar.

• You are right. We removed that comparison and spelt out the statistics..

 

7. L266 Figure 5. It seems that authors conducted numerous correlation tests (14 X 3 X 3) which is not so appropriate. But I also don’t have a suggestion of a better solution.

• You are right and that’s why we show the 0.05 and 0.01 significance levels. More conservative (Bonferroni-corrected) tests could be considered but the important results are the correlations.

 

8. Also, Figure 5, where are your dotted lines? I only see dashed lines.

• We plotted horizontal dashed (0.05) and dotted (0.01) lines.

 

Discussion and Conclusion:

1. Didn’t see you address the hypotheses proposed in the intro.

• We reframed and addressed the hypotheses proposed in the introduction.

 

2. Also, overall, would you conclude cold spell is a less a concern than drought plus heat waves? I don’t think cold spell is more frequent. You need to give a more broad speculation, and maybe mention that in the abstract.

• OK, we did it in the revised conclusions.

Round 2

Reviewer 1 Report

I am completely satisfied with the new revised version of the manuscript.