Woody Plant Structural Diversity Changes across an Inverse Elevation-Dependent Warming Gradient in a Subtropical Mountain Forest

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

If possible, make a list of exclusive and shared species between the three sampling sites.

I have no more comments

Comments on the Quality of English Language

no comments

Author Response

Thank you very much for your review. Your evaluation of our manuscript is helpful for our study.

Reviewer 2 Report

Comments and Suggestions for Authors

The authors present an interesting research study examining the changes in woody plant structural diversity along an inverse elevation-dependent warming gradient with these research questions 1) Does structural diversity differ along an inverse elevation-dependent warming gradient? (2) How patterns of species richness, total abundance, species diversity, size diversity, and species composition are affected by the inverse elevation-dependent warming? and (3) Can the communities be separated by certain structural parameters along a short-range elevational gradient?

Here are some suggestions to improve the paper:

While the results provided are informative, they don't clearly relate to the stated research questions. Connecting each result directly to the research questions would enhance clarity for readers.

For example, in Figure 2, it might be more informative to display the actual elevation data in meters alongside species abundance and richness, rather than using aggregated box plots. This also applies to Figure 3.

Regarding the use of PCA, it's worth considering alternative perspectives on its application. Elhaik's study, "Principal component analyses (PCA)-based findings in population genetic studies are highly biased and must be reevaluated," discusses potential biases in PCA-based analyses: Elhaik, Eran. "Scientific Reports 12, no. 1 (2022): 14683.

The authors might also consider briefly discussing the limitations of using PCA in their research.

 

For Figures 5 and 6, the captions could benefit from more detail to explain the purpose of these results and clarify the significance of the blue and red lines for readers.

It would benefit readers if the authors clearly separate the results and discussion sections. They should present the results in one section and then address each research question in the discussion section, supporting their answers with the findings from the results section.

Author Response

Thank you very much for you comments and suggestions. Below are the point-by-point response to your commnets. Thank you again.

Comments and Suggestions for Authors

Here are some suggestions to improve the paper:

While the results provided are informative, they don't clearly relate to the stated research questions. Connecting each result directly to the research questions would enhance clarity for readers.

For example, in Figure 2, it might be more informative to display the actual elevation data in meters alongside species abundance and richness, rather than using aggregated box plots. This also applies to Figure 3.

Response: Thank you for your comments. Actually, the research questions described in the introduction section have been responded to in the discussion and conclusion sections. As for Figure 2 and Figure 3, no pattern will be revealed in the figures by adding the actual elevation to each species, because the distribution ranges of species varies with overlaps, therefore we compared the indicators (total abundance and species richness) in three size categories of seedling, sapling, and adult trees, across communities which is characterized by average elevation, using Kruskal-Wallis ANOVA and visualized by Boxplots, in order to show the trends of change.

 

Regarding the use of PCA, it's worth considering alternative perspectives on its application. Elhaik's study, "Principal component analyses (PCA)-based findings in population genetic studies are highly biased and must be reevaluated," discusses potential biases in PCA-based analyses: Elhaik, Eran. "Scientific Reports 12, no. 1 (2022): 14683.

The authors might also consider briefly discussing the limitations of using PCA in their research.

Response: Thank you for the recommendation of this paper. This 35-page article is very helpful and we will use it as an reference in our new study, an on-going study that compares the efficacy of several ordination methods such as PCA, DCA (detrended correspondence analysis), PCoA (principal coordinate analysis), and NMS (nonmetric multidimensional scaling), in revealing the patterns of forest communities using our forest inventory data across an latitudinal gradient. But in the current article, we just use PCA to extract the ordination scores of Axis 1 and Axis 2 and overlay them with the warming index as PDIR (potential direct incident radiation) data (with the effect similar to a Pearson correlation analysis). Therefore, we argue that it is not necessary to further discuss the limitations of PCA in this context.

 

For Figures 5 and 6, the captions could benefit from more detail to explain the purpose of these results and clarify the significance of the blue and red lines for readers.

It would benefit readers if the authors clearly separate the results and discussion sections. They should present the results in one section and then address each research question in the discussion section, supporting their answers with the findings from the results section.

Response: Thank you for the comment. Both Figure 5 and Figure 6 are clear in their present state. They showed the results of the relationship between warming index and PCA axis 1 scores or Axis 2 scores (Figure 5), and the relationship between PDIR and PCA axis 1 scores or Axis 2 scores (Figure 6). The blue lines represent the 95% confidence limit and the red lines represent the fitted line of the correlation, as in most other figures.

 

Reviewer 3 Report

Comments and Suggestions for Authors

This study is of great importance as the relationship between warming and changes in structural diversity and species composition of woody plant communities in a subtropical broadleaved forest is analysed. Such approaches can be used as a tool to model the consequences of climate change and address the critical contemporary challenges concerning climate change. However some improvements have to be done :

1. Introduction

An important role of scientists in the assessment of climate change, its factors and consequences should be emphasised. I recommend adding one paragraph describing the role of different disciplines in such studies. For example, historical land use reconstructions play an essential role, e.g. Gaillard, M. J., Sugita, S., Mazier, F., Kaplan, J. O., Trondman, A. K., Brostroem, A., ... & Strandberg, G. (2010). Estimating global land use change over the past 300 years: the HYDE database. Global biogeochemical cycles, 15(2), 417-433. Your studies are of great importance as, based on diversity in vegetation, future changes could be predicted. Also, specialists representing other disciplines could help, e.g. historical geographers – see: Sobala, M. (2024). Reconstructing of historical land cover based on contemporary cartographical materials. Journal of Historical Geography, 84, 14-26. As was indicated in this paper, good knowledge of historical land use trends is vital to understanding their impact on global warming. There is a growing need for spatially explicit descriptions of vegetation and land cover in the past on a continental and global scale to evaluate and improve dynamic vegetation and climate models (global and regional). I hope the abovementioned references will help prepare the suggested paragraph.

2.1. Study sites.

A map of the study area's location must be included for readers from different parts of the world.

Please also add more information on the region, such as what the potential and real vegetation are. A map would also be necessary to show the variation in vegetation distribution.

2.2. Sampling Design and Data Collection

A figure presenting the location and division of plots should be added to clarify the method applied.

Line 98 – Are centimetres correct for describing the tree diameter? I have never been in this study area, but it seems to be very thin. A photograph of the forest community could be added as it helps to know what type of vegetation is analysed.

Please explain why a nonparametric test was used – what was the size of the sample?

What could be the influence of factors other than altitude on change in temperature along the studied profile (local topography, aspect, slope gradient, etc.)? How did you deal with this problem?

How was the altitude measured?

4. Discussion

There is a lack of connection between the results obtained and the papers discussed. Please discuss your results, explaining them following results of other studies cited in your paper.

Describe also the strengths and weaknesses of your research. Are there any limitations connected to the features of the study area? How did you deal with them? How do they impact the results obtained?

5. Conclusions

This chapter should be strengthened when the Discussion chapter will be rewritten. Also information on result implications should be added.

 

Author Response

Thank you very much for you comments and suggestions. Below are the point-by-point response to your commnets. Thank you again.

Comments and Suggestions for Authors

1. Introduction

An important role of scientists in the assessment of climate change, its factors and consequences should be emphasised. I recommend adding one paragraph describing the role of different disciplines in such studies. For example, historical land use reconstructions play an essential role, e.g. Gaillard, M. J., Sugita, S., Mazier, F., Kaplan, J. O., Trondman, A. K., Brostroem, A., ... & Strandberg, G. (2010). Estimating global land use change over the past 300 years: the HYDE database. Global biogeochemical cycles, 15(2), 417-433. Your studies are of great importance as, based on diversity in vegetation, future changes could be predicted. Also, specialists representing other disciplines could help, e.g. historical geographers – see: Sobala, M. (2024). Reconstructing of historical land cover based on contemporary cartographical materials. Journal of Historical Geography, 84, 14-26. As was indicated in this paper, good knowledge of historical land use trends is vital to understanding their impact on global warming. There is a growing need for spatially explicit descriptions of vegetation and land cover in the past on a continental and global scale to evaluate and improve dynamic vegetation and climate models (global and regional). I hope the abovementioned references will help prepare the suggested paragraph.

Response: Thank you very much for your comments and the references you recommended. I agree that the impacts of climate change should be emphasized; however, the major goal of our study is to assess the changes of species diversity and community patterns across an inverse elevation-dependent warming gradient and not to directly analyze the effect of climate warming on vegetation patterns. Therefore this paper will be distracted from its focus if we expand the text with climate warming issues. Since our research interest includes the impact of climate change on terrestrial forest, the references you recommended are vital and very helpful and I have added them to my Endnote reference Groups.

 

2.1. Study sites.

A map of the study area's location must be included for readers from different parts of the world.

Please also add more information on the region, such as what the potential and real vegetation are. A map would also be necessary to show the variation in vegetation distribution.

Response: Thank you for your comments. As describe in this section, the vegetation type is evergreen broadleaved forest, as commonly distributed in the tropical and subtropical mountain areas. I agree that a map will help visualize the vegetation and the study sites, but a description with the latitude and longitude coordinates will also serve this purpose. Frankly, it’s quite difficult to prepare an appropriate map because it may raise other problems.

2.2. Sampling Design and Data Collection

A figure presenting the location and division of plots should be added to clarify the method applied.

Line 98 – Are centimetres correct for describing the tree diameter? I have never been in this study area, but it seems to be very thin. A photograph of the forest community could be added as it helps to know what type of vegetation is analysed.

Response: Thank you for your comments. The study area is located at the Yinpingshan Nature Reserve (22°52′–23°56′ N, 114°05′–114°15′ E) in South China. Vegetation type for the research is evergreen broadleaved forest. The tree diameter (by default, diameter at breast height or DBH) was measured in centimeter with a diameter tape. We placed three 1-ha plots at three different elevations. Each plot was further divided into 100 quadrats for plant census. Sampling design and plot arrangement were described in detail as in the Materials and Methods section.

 

Please explain why a nonparametric test was used – what was the size of the sample?

What could be the influence of factors other than altitude on change in temperature along the studied profile (local topography, aspect, slope gradient, etc.)? How did you deal with this problem?

How was the altitude measured?

Response: Thank you for your comments. Nonparametric test applies to data that may not meet some requirements or that are distribution-free. Rather than laboratory experimental studies, nonparametric methods are appropriate for data from field ecology study such as the current one. Therefore we used Kruskal-Wallis test (also called Kruskal-Wallis ANOVA in the Statistica software) instead of F test; MRPP (multi-response permutation process) instead of MANOVA (multivariate analysis of variance). The total sample size is 300 for three communities, each 100 quadrats. The elevation of each quadrat is the mean of elevations at the four corners of the quadrat, which were obtained during plot surveying with a total station. Aspect is also calculated from the elevation at the four corners of each quadrat, which in turn serves as the major factor in calculating PDIR (potential direct incident radiation) using HyperNiche 2.0. We have also assessed the influence of aspect.

Our results indicated that warming index (related to altitude change) is stronger than PDIR (related to aspect) in their correlations with species composition and community patterns (represented by the ordination scores of the first two PCA axes).

 

4. Discussion

There is a lack of connection between the results obtained and the papers discussed. Please discuss your results, explaining them following results of other studies cited in your paper.

Describe also the strengths and weaknesses of your research. Are there any limitations connected to the features of the study area? How did you deal with them? How do they impact the results obtained?

5. Conclusions

This chapter should be strengthened when the Discussion chapter will be rewritten. Also information on result implications should be added.

Response: Thank you for your comments. The current Discussion section concentrates on the impact of temperature change on structural diversity. Instead of comparing our results with particular published studies, we further discussed some issues of woody plant structural diversity across an inverse elevational gradient (hence a warming gradient). Although the Conclusion section is not lengthy, it actually reports the research conclusion that are drawn from the research findings in the Results section and that are corresponded to the research questions presented in the Introduction section.

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

First of all, I cannot see any changes in the manuscript, as they were not marked in the text. Hence, it is difficult to assess the revised manuscript. Was there a mistake during the uploading of the revised file?

Secondly, some of the responses could be clearer or more precise. The author wrote, “Frankly, it’s quite difficult to prepare an appropriate map because it may raise other problems.”. Actually, it is difficult to understand the difficulties in preparing a study area map and what other problems may arise. I used coordinates to find the study area on Google Maps, but I did not find any information on the Yinpingshan Nature Reserve there. A map of the study area is essential for each paper describing geographical sites. Without detailed location information, readers cannot understand the background of the studies. The basic environmental elements should be presented on the map: location within Dongguan and China’s Guangdong Province, location of the analysed slope (altitude) and the peak of Mount Yinping.

The authors did not answer this comment: “A photograph of the forest community could be added as it helps to know what type of vegetation is analysed”. A figure presenting the location and division of plots also has not been added to clarify the method applied.

Finally, the authors did not answer this question: “Are there any limitations connected to the features of the study area? How did you deal with them? How do they impact the results obtained? There are no descriptions of the strengths and weaknesses of the research. 

As a result, I cannot change my assessment of the manuscript, as the responses seem evasive.

Author Response

Dear Reviewer,

Thank you very much for reviewing our manuscript. Your comments are very useful and we very much appreciate your help. In response to your concerns, we have made some changes to the manuscript. Below are the explanations for the modifications. Thank you.

Comments and Suggestions for Authors

First of all, I cannot see any changes in the manuscript, as they were not marked in the text. Hence, it is difficult to assess the revised manuscript. Was there a mistake during the uploading of the revised file?

Secondly, some of the responses could be clearer or more precise. The author wrote, “Frankly, it’s quite difficult to prepare an appropriate map because it may raise other problems.”. Actually, it is difficult to understand the difficulties in preparing a study area map and what other problems may arise. I used coordinates to find the study area on Google Maps, but I did not find any information on the Yinpingshan Nature Reserve there. A map of the study area is essential for each paper describing geographical sites. Without detailed location information, readers cannot understand the background of the studies. The basic environmental elements should be presented on the map: location within Dongguan and China’s Guangdong Province, location of the analysed slope (altitude) and the peak of Mount Yinping.

Response: Thank you for your comments. In response to your concerns, we have added a map showing the location of the study sites. Unfortunately, the location graph panel does not have particular details for the Mount Yinping, because we are not permitted to publish a fine-scale map with particular details of that area, though we are permitted to set up forest census plots and perform study and monitoring there. In addition, we do not have access to Google maps here or it is not permitted to use such maps.

The authors did not answer this comment: “A photograph of the forest community could be added as it helps to know what type of vegetation is analysed”. A figure presenting the location and division of plots also has not been added to clarify the method applied.

Response: Thank you for your comments. We are not able to add such a photograph because we did not take such pictures during our first census two years ago. Normally, when we perform controlled experiments with pot plants, we will take pictures and use graphic analysis to show the growth of plants. Thanks to your comments, we will take pictures to show the physiognomy of the evergreen broadleaved forest with the aid of an UAV (unmanned aerial vehicle).

 

Finally, the authors did not answer this question: “Are there any limitations connected to the features of the study area? How did you deal with them? How do they impact the results obtained? There are no descriptions of the strengths and weaknesses of the research.

As a result, I cannot change my assessment of the manuscript, as the responses seem evasive.

Response: Thank you for your comments. In response to your concerns, we added a paragraph at the end of the Discussion section, which can serve as a description of the limitations connected to this study.

Author Response File: Author Response.pdf