Altitudinal Differentiation of Forest Resilience to Drought in a Dryland Mountain
Round 1
Reviewer 1 Report
Assistant Editor,
Forests
I have recently review the manuscript entitled “Altitudinal differentiation of forests resilience in a dryland mountain” written by Jie Li et al.
The manuscript presents an interesting study on the altitudinal differentiation of forest resilience to drought and its dominant climatic factors in the drylands of the Quilian Mountains. The authors established an interesting approach, at the ecosystem scale, to analyze the resilience and recovery time required by the system to drought disturbances. Droughts are the main climatic disturbances affecting forest ecosystems today, and the study of their impacts is urgent and has become the main focus of scientific research in recent years.
The authors asked three questions concerning the relationship between recovery time and drought intensity, altitudinal differentiation characteristics, to accurately find the key climatic factors of altitudinal differentiation; under the hypothesis that forest resilience to drought shows altitudinal differentiation in the Quilian Mountains. Although the authors did not analyze vegetation change along the altitudinal gradient, a brief mention of vegetation structure in the introduction would be useful to the reader. This could allow the main issues related to the mechanisms underlying in the hypothesis; mechanisms that are difficult to understand without an explicit mention, and are not so clear. In addition, drought resistance (although only evaluated at the ecosystem level) is determined by other factors rather than the climatic ones. The authors should mention this in the introduction.
The methodology is quite extensive with several equations that would be better if they stated in the appendix. For example, the calculation of PET and SPEI could be moved to the appendix. In addition, GAM equation should be shown in a more specific way and not in a general form.
Result section is clear, and the figures are enough. In figure 5 (and 4) it would be better to set the calendar year in the x-axes, as the time series are different. In addition, we need the table of the GAM model. Lines 372-379 is an explanation of GAM rather than an explanation of the results. In fact, RecPET at 1700-2600 and 2006-3000 should enter in the model without smooth.
The discussion is well written and attends to the objective. Authors discuss and highlight the limitations and perspectives. This is important due to the nature of the study focused in the ecosystem scale but tacking into account the role of the species differentiation along the altitudinal gradient.
Author Response
Reviewer 1：
1、The authors asked three questions concerning the relationship between recovery time and drought intensity, altitudinal differentiation characteristics, to accurately find the key climatic factors of altitudinal differentiation; under the hypothesis that forest resilience to drought shows altitudinal differentiation in the Quilian Mountains. Although the authors did not analyze vegetation change along the altitudinal gradient, a brief mention of vegetation structure in the introduction would be useful to the reader. This could allow the main issues related to the mechanisms underlying in the hypothesis; mechanisms that are difficult to understand without an explicit mention, and are not so clear. In addition, drought resistance (although only evaluated at the ecosystem level) is determined by other factors rather than the climatic ones. The authors should mention this in the introduction.
Our response：In the introduction of the revised draft, we added content of the impact of altitude on the distribution of forest species and forest growth. We also add the following content: The characteristics of multiple factors affecting the recoverability to drought, including climate variables, biotic variables as well as soil properties, etc., also show obvious elevation heterogeneity. Among them, climate variables change particularly significantly with increasing altitude and are extremely important in studying the attribution of vegetation changes. For instance, precipitation increases and temperature decreases as altitude rises in some dryland mountains. Two references are provided to support this content. The relevant content is updated in lines 59-67 of the revised manuscript.
2、The methodology is quite extensive with several equations that would be better if they stated in the appendix. For example, the calculation of PET and SPEI could be moved to the appendix. In addition, GAM equation should be shown in a more specific way and not in a general form.
Our response：Thanks for your suggestion! The calculation process of PET and SPEI was removed from 2.3.1. Standardized precipitation evapotranspiration index and moved to Appendix A. Please see Lines 171-180 and Lines 518-549. We have corrected the presentation form of the GAM equation. The forest resilience values follow the Gaussian distribution. Meanwhile, in order to avoid the influence of extreme values on the model, we applied the natural logarithm transformation to the forest resilience. In the GAM equation, the dominant climate factor within each altitude range is the independent variable, and the forest resilience is the dependent variable. The relevant updates are detailed in formula (17), formula (18) and lines 280-286.
3、Result section is clear, and the figures are enough. In figure 5 (and 4) it would be better to set the calendar year in the x-axes, as the time series are different. In addition, we need the table of the GAM model. Lines 372-379 is an explanation of GAM rather than an explanation of the results. In fact, RecPET at 1700-2600 and 2006-3000 should enter in the model without smooth.
Our response：Thanks for your recognition and suggestion of result section! Due to the increase in the number of diagrams during the revision process, Figure 5 (Figure 4) in the original manuscript corresponds to Figure 6 (Figure 5) in the updated manuscript. The diagram used as the calculation process of recovery time in the updated manuscript does not involve the specific calendar year, and since the recovery time unit obtained in the study is T (T=1 month), Months is set in the x-axes (see Figure 5 in the text). In Figure 6 of the updated manuscript, we set the calendar year of the study period in the X-axes according to your comments, and SPEI-3 in the vertical axis because the time scale of SPEI is 3 months (see Figure 6 of the text).
We supplement the main results of the GAM model in table (see Table 2 in the text), including standard error, F-value, P-value, and variance explained. The lines 372-379 lines in the original manuscript reflect the complexity of the smoothing function by the value of edf, which has been moved to the diagram note in Figure 11 (see lines 367-373 of the updated manuscript). We have added specific values of edf in the 3.3. Dominant climate factors of forest resilience and relationships of results to more directly determine the relationship between the dominant factors and forest resilience. Please see Lines 346-361.
For a long time, the response of vegetation to climate is mostly based on linear models. However, as you mentioned, theoretically speaking, the impact of climate change on vegetation exhibits a significant nonlinear pattern due to the sensitivity and adaptability of vegetation. In recent years, a large number of scholars have tried to prove this hypothesis by using statistical methods such as threshold effect and multi-factor coupling. Figure 11a, 11d and 11e in the manuscript also verify the nonlinearity of this process.
However, the edf values of 1 in figure 11b and 11c indicated a linear relationship. We recognize that this result is related to the insufficient sample size in the altitude range of 1700-2600m and 2600-3000m (FIG. 1), which is difficult to fully reflect more detailed nonlinear information. Please see Figure-1. In order to comprehensively consider the response of resilience to precipitation in this altitude range and avoid overfitting phenomenon, the edf value of 1 is more in line with ecological phenomena, reflecting the overall trend of positive correlation. Although our results show a linear relationship at altitudes of 1700-2600 m and 2600-3000m, this does not deny the existence of nonlinear responses. We hope to further explore the nonlinear relationship between resilience and potential evapotranspiration at this altitude range with sufficient sample size in the future research.
Figure-1. Relationship between forest resilience and RecPET based on GAM in 1700-2600m and 2600-3000m. The red dots represent the actual sample points.
4、The discussion is well written and attends to the objective. Authors discuss and highlight the limitations and perspectives. This is important due to the nature of the study focused in the ecosystem scale but tacking into account the role of the species differentiation along the altitudinal gradient.
Our response：Thanks for your recognition and suggestion of discussion section! In the discussion section, we improved more physiological explanations of the influence of dominant climate factors on forest resilience and different physiological mechanisms of major forest species in QMNP to cope with drought events, hoping to fully explain the mechanism behind the results of our study. Please see Lines 411-458 and Lines 460-471.
Reviewer 2 Report
In the manuscript, “Altitudinal differentiation of forest resilience to drought in a dryland mountain” the authors have presented a well-designed study about the variation of altitude in response to drought stress. I have no qualms recommending this manuscript for acceptance. However, I'd suggest that authors carefully read and correct all typos and grammars mistakes throughout the manuscript. In addition, please correct the references section and align properly, also, correct in-text citations according to the journal's guidelines. The introduction and discussion part needs special attention. More mechanistic explanation should be given instead of superficially covering the topics.
Abstract
It should briefly mention the results obtained. A concluding line representing the future directions should be added.
Introduction
Introduction is written well. Some grammatical and typographical errors are present in this section. Please enrich your introduction section with recent literature.
Please increase resolution of fig 1.
The introduction is not balanced. Please mention case studies related to drought.
Abbreviation should be elaborated where first mentioned in the manuscript. Please don’t write full-forms again and again. Rectify in the entire manuscript.
Mention number of replicates if used.
Discussion
This needs special attention from authors. An interesting explanation from the biochemical perspective is not represented at all. I hope the authors can purify the discussion by giving mechanistic explanation.
Remove all typo errors.
Conclusion
The authors should avoid repeating what has already been presented in results and discussion. Please, avoid using abbreviations and acronyms in this section. Remember that the conclusions must be self-explanatory. The conclusions should highlight the novelty and implication of your study.
References
Please follow to the referencing style of the journal.
Lot of typographical errors are present in the reference section. Please rectify them.
Scientific names must be written in italics. Please check them.
Tables and Figures
Remember that tables and figures must be self-explanatory. That is, all statistics and abbreviations used must be clearly explained. All tables and figures must present standard error and suitable statistical analysis where appropriate. Absolute values of the tables must be presented with the replications and standard error.
Thanks
Should be improved
Author Response
1、In the manuscript, “Altitudinal differentiation of forest resilience to drought in a dryland mountain” the authors have presented a well-designed study about the variation of altitude in response to drought stress. I have no qualms recommending this manuscript for acceptance. However, I'd suggest that authors carefully read and correct all typos and grammars mistakes throughout the manuscript. In addition, please correct the references section and align properly, also, correct in-text citations according to the journal's guidelines. The introduction and discussion part needs special attention. More mechanistic explanation should be given instead of superficially covering the topics.
Our response：Thanks for your recognition and suggestion of our work! We have carefully reviewed the full text, corrected spelling and grammar errors, revised the format of references section and the format of in-text citations. We reorganized the introduction text, supplemented the drought-related recovery time and resilience studies, and enriched the introduction with the latest literatures, hoping to better sort out the research background, research highlights, and research significance. Please see Lines 48-58. In the discussion section, we improved more physiological explanations of the influence of dominant climate factors on forest resilience and different physiological mechanisms of major forest species in QMNP to cope with drought events, hoping to fully explain the mechanism behind the results of our study. Please see Lines 411-458 and Lines 460-471.
2、Abstract
It should briefly mention the results obtained. A concluding line representing the future directions should be added.
Our response：Thanks for your suggestion! Our updated manuscript briefly and directly supplemented the research results in the abstract: Altitudinal differentiation characteristics of forest resilience to drought, dominant climate factors of forest resilience, and relationships between forest resilience and dominant factor. Please see Lines 17-25. Combining the limitations and prospects of the research presented in the discussion section, Picea crassifolia Kom. and Sabina przewalskii Kom. exhibited stronger resilience to drought compared to Ulmus glaucescens Franch. and Pinus tabuliformis Carr. This may be related to their different physiological mechanisms. Therefore, it is necessary to study the quantitative effects of tree species on resilience. However, the response process of ecosystems to climate is complex, and the impact of species on this process is often multi-channel, involving changes in multiple indicators such as biomass, crown width, tree height, etc. (62,64). It remains a challenging task in ecology to accurately explore the quantitative effects of tree species on ecosystem scales using specific indicators. Therefore, quantitative studies of the effects of different tree species on resilience will be the focus of our future work. A concluding line representing the future directions has been added to the end of the abstract. Please see Lines 25-30.
3、Introduction
Introduction is written well. Some grammatical and typographical errors are present in this section. Please enrich your introduction section with recent literature.
Please increase resolution of fig 1.
The introduction is not balanced. Please mention case studies related to drought.
Abbreviation should be elaborated where first mentioned in the manuscript. Please don’t write full-forms again and again. Rectify in the entire manuscript.
Mention number of replicates if used.
Our response：Thanks for your suggestion! We have corrected grammatical and typographical errors in the whole article. We ensure that abbreviations are elaborated when first mentioned in the manuscript and subsequently appear as abbreviations. We have supplemented the drought-related recovery time and resilience studies in the introduction and enriched the introduction with the latest literatures. In figure 1, we supplemented the geographic environment information of QMNP and improved the resolution, hoping to highlight the ecological significance of QMNP more accurately. Please see Figure 1.
4、Discussion
This needs special attention from authors. An interesting explanation from the biochemical perspective is not represented at all. I hope the authors can purify the discussion by giving mechanistic explanation.
Remove all type errors.
Our response：Thanks for your suggestion! We have removed all typo errors in the whole article. In the discussion section, we improved more physiological explanations of the influence of dominant climate factors on forest resilience and different physiological mechanisms of major forest species in QMNP to cope with drought events, hoping to fully explain the mechanism behind the results of our study. Please see Lines 411-458 and Lines 460-471.
5、Conclusion
The authors should avoid repeating what has already been presented in results and discussion. Please, avoid using abbreviations and acronyms in this section. Remember that the conclusions must be self-explanatory. The conclusions should highlight the novelty and implication of your study.
Our response：Thanks for your suggestion! We revised the conclusion to highlight the innovation of this study in improving the resilience index based on recovery time and drought intensity, summarize the research process of this study, and list the research findings and their guiding significance, to make the conclusion more self-explanatory. We have added the significance of our research findings: Our study confirms the altitudinal differentiation of forest resilience to drought and the importance of the altitudinal perspective in studies of the dryland mountain evolution. Furthermore, the findings of this study provide a scientific basis for predicting the potential changes in vegetation resilience and developing policies for ecological protection in studies of the dryland mountains under future global climate change. Please see Lines 485-509. We have removed all abbreviations and acronyms in conclusion section.
6、References
Please follow to the referencing style of the journal.
Lot of typographical errors are present in the reference section. Please rectify them.
Scientific names must be written in italics. Please check them.
Our response：Thanks for your suggestion! We have removed all typographical errors in the reference section. Scientific names in the updated manuscript texts and Figure 2 are written in italics and the references format is unified.
7、Tables and Figures
Remember that tables and figures must be self-explanatory. That is, all statistics and abbreviations used must be clearly explained. All tables and figures must present standard error and suitable statistical analysis where appropriate. Absolute values of the tables must be presented with the replications and standard error.
Our response：Thanks for your suggestion! We have reviewed and revised all tables and figures, and explained all statistics and abbreviations. “P” in Figure 6 shows the significance level of the Theil-Sen trend analysis and the Mann-Kendall trend test. The “R2” and “P” in Figure 8 show the degree of resilience curve fitted. The closer “R2” is to 1, the stronger the data fitting effect of the model is. The “P” represents the significance level of the resilience curve. Figure 10 shows the ranking results of the influence degree importance of dependent variables based on the random forest model. Because it is mainly based on the reduction of node impurity rather than the traditional statistical significance, reliable statistical analysis results were not obtained and listed in the figure. Figure 11 and Table 2 show the relationship between forest resilience and dominant factors in different altitude ranges, standard error and statistical analysis results based on the GAM model. The rest charts do not involve standard errors and statistical analysis.
Reviewer 3 Report
The article is titled “Altitudinal differentiation of forest resilience to drought in a dryland mountain”. In the study, the authors examined the resistance of forests to drought, taking into account differences in altitude. To this end, the authors adopted the Leaf Area Index (LAI) as an indicator of vegetation status in combination with a standardized evapotranspiration index (SPEI). The study was conducted for an area in the dry mountains. The article is interesting, but in my opinion it needs improvement. My comments are as follows:
- the research method is not fully described. For better understanding, I propose to present in the form of a diagram
- the authors did not explain why they adopted a 3-month cumulative period for SPEI Fig 1 to be corrected, the map is illegible,
- in Fig. 5 on the horizontal axis, specify specific years, while in the caption add that SPEI was calculated for a 3-month accumulation period, e.g. SPEI-3
- explanations of the axes in Fig. 6 are not clear to me
- the manuscript should be adapted to the requirements of the journal, appropriate styles for the text and tables should be used
Author Response
1、- the research method is not fully described. For better understanding, I propose to present in the form of a diagram
Our response: Many thanks for your suggestion! We have reorganized the Chapter 2.3.2 and added the schematic diagram of physiological basis of resilience curves (Figure 3) and resilience curve based on recovery time and drought intensity (Figure 4). These changes may be easier for readers to understand the research method in this manuscript. Please see lines 184-205.
2、- the authors did not explain why they adopted a 3-month cumulative period for SPEI Fig 1 to be corrected, the map is illegible,
Our response：Thanks for your suggestion! We have added to the reasons for choosing SPEI with a time scale of 3 months. Considering the seasonal characteristics of forest growth, we chose the SPEI with the time scale of three months (SPEI-3) that reflects short-term and medium-term moisture conditions, allowing us to study the characteristics of seasonal drought events and reveal the drought effects on ecosystems. Please see lines 174-177. Moreover, we reorganized and added the geographic environment information of Qilian Mountain National Park in Figure 1.
3、- in Fig. 5 on the horizontal axis, specify specific years, while in the caption add that SPEI was calculated for a 3-month accumulation period, e.g. SPEI-3
Our response: Many thanks for your suggestion! We have changed Figure 5 in the original manuscript to Figure 6 in new manuscript. And we set the years as the X-axis and SPEI-3 as the vertical axis in Figure 6.
4、- explanations of the axes in Fig. 6 are not clear to me
Our response：Thanks for your suggestion! We have changed Figure 7 in the original manuscript to Figure 7 in new manuscript. In new Figure 7a, the x-axis is recovery time, and the y-axis is the average drought intensity of historical drought events corresponding to recovery time. In Figure 7b, the x-axis is recovery time, and the y-axis is the number of historical drought events corresponding to recovery time. In Figure 7c, the X-axis are the different elevations, the brown y-axis is the drought frequency, the green y-axis is the co-occurrence frequency of drought and LAI anomalies, and the blue y-axis is the average SPEI-3 from 1982-1990.
5、- the manuscript should be adapted to the requirements of the journal, appropriate styles for the text and tables should be used
Our response: Many thanks for your suggestion! We change the manuscript according to the requirements of the journal.
Round 2
Reviewer 2 Report
Thanks for the Nice discussion.
Regards
