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Inconsistent Variations in Components of Functional Stability Under Heterogeneous Conditions: A Case Study from the Maolan Karst Forest Ecosystems in Guizhou Province, Southwest of China

Forests 2025, 16(2), 304; https://doi.org/10.3390/f16020304

by Yong Li¹

, Longchenxi Meng¹, Luyao Chen¹, Mingzhen Sui^1,2, Guangqi Zhang^1,2, Qingfu Liu^1,2

, Danmei Chen^1,2, Fangjun Ding² and Lipeng Zang^1,2,*

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Reviewer 4: Anonymous

Forests 2025, 16(2), 304; https://doi.org/10.3390/f16020304

Submission received: 6 December 2024 / Revised: 2 February 2025 / Accepted: 7 February 2025 / Published: 9 February 2025

(This article belongs to the Special Issue Pattern and Evolution of Biodiversity in Evergreen Broad-Leaved Forests)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article is devoted to the important question of the functional stability under heterogeneous conditions in forest ecosystems. The research is being conducted on the karst forests of China and its relevance is beyond doubt.

References must be formatted according to the journal's requirements.

Title

The title corresponds to the content. However, I recommend adding a region of study.

Abstract

The section needs editing. The objective, area of the study and methodology should be spelled out. I advise the authors to add quantitative results.

Introduction

The introduction contains all the necessary background information. However, I advise authors to clearly and concisely formulate the purpose of the study.

Materials and Methods

The methodology is no presented in sufficient detail. Climate characteristics not specified. I advise the authors to provide soil taxonomy according to the international classification (FAO, WRB). It is also worth indicating what vegetation typology the authors use. In my opinion, it is not entirely correct to say that eighty-year-old forests are old-growth forests.

The collection of soil samples should be supported by reference.

Results

The results are presented rather briefly, in my opinion, they should be expanded to increase their clarity. The section is illustrated with 4 figures.

Discussion

The authors have discussed the results quite well.

Conclusions

The conclusions are followed from the results and reasonable. However, they are presented too briefly. Conclusions on the factors and indices used are not indicated. Which factors are more significant in successions? Which indices are more correct to use in studies of the functional stability of karst ecosystems?

Author Response

Question 1: References must be formatted according to the journal's requirements.

Response:

We sincerely apologize for the inconvenience caused by the formatting of the manuscript. We have carefully formatted the references in accordance with the journal's requirements.

Question 2: The title corresponds to the content. However, I recommend adding a region of study.

Response:

We are delighted that you are interested in the content of our research. We have added the study area to the title without changing its meaning. The specific modification is as follows: Inconsistent Variations in Components of Functional Stability Under Heterogeneous Conditions: A Case Study from the Maolan Karst Forest Ecosystems in Guizhou Province, South-west of China (line 2-5).

Question 3: (Abstract)

The section needs editing. The objective, area of the study and methodology should be spelled out. I advise the authors to add quantitative results.

Response:

We apologize for not fully addressing the content in the abstract section of the article. Based on your suggestions, we have made detailed revisions to the abstract section. The specific changes are as follows:

Here, 30 forest dynamic plots were established along the successional pathway in Maolan National Nature Reserve in Southwest China. By measuring 15,725 stems across 286 distinct species’ 6 key plant functional traits, we constructed the key plant functional traits to functional space and quantified functional redundancy (FR), and functional vulnerability (FV) to represent functional stability, further utilized the line model and multiple linear regression model to explore the key biotic/abiotic indicators influencing functional stability along the successional pathway of degraded karst forests. Additionally, as the successional pathway, the contribution of six plant traits to the overall functional space increased, from 59.85% - 66.64%. These traits included Specific leaf area (SLA), Leaf dry matter content (LDMC), Leaf thickness (LT) and Leaf nitrogen content (LNC), which played a crucial role in driving functional space. With the increasing species richness (FR), functional entities ((p < 0.001) and FR (p < 0.001) increased, while FV (p < 0.01) decreased. The results also demonstrated a higher FR in degraded karst forests (FR > 2). However, over 51% of FEs consisted of a single species, with the majority of species clustered into a few Functional entities (FEs), indicating an elevated level of FV in karst forests. Soil nutrient availability significantly influences the ecosystem’s functional stability, explaining 87% ofFR variability and 100% of FV variability. Finally, the rich SR of karst forests could provide sufficient insurance effects, with soil pH and AK enhances resilience, and Eca, TP, and TK deduces the resistance of functional stability in of degraded karst forests. This study highlights the complex mechanisms of functional stability in extreme habitat conditions, thereby deepening our understanding of ecosystem functioning maintenance. (line16 - 36)

Question 4: (Introduction)

The introduction contains all the necessary background information. However, I advise authors to clearly and concisely formulate the purpose of the study.

Response:

We apologize for the unclear statement of the research objectives, which may have caused you some reading difficulties. We have revised the last paragraph of the introduction section, changing "This study sought to quantify the structure of plant functional communities and assess functional stability, thereby addressing the following questions:" to "This study sought to investigate how the plant functional space changed over the successional pathway, focusing on the key traits that drove these changes. Additionally, aimed to measure how and which critical biotic/abiotic factors influenced the functional stability, thereby addressing the following questions:" (line 137 - 140).

Question 5: (Materials and Methods)

Response:

Thank you for your suggestions on the manuscript. We have made detailed supplements to the research methods section of the article and have introduced the climate of the study area in detail. The specific content is as follows: "This study was undertaken within the confines of the Maolan National Natural Reserve (25˚09ʹ-25˚20ʹ N, 107˚52ʹ-108˚05ʹ E), Guizhou Province, southwest China (Fig. 1), with an average elevation of 550 to 850 m. The study area is characterized by limestone soils, predominantly classified into two sub-types: Haplic Calcisols and Dolomitic Calcisols [46]. These soils are characterized by their shallow depth and a pH range that typically fluctuates from slightly acidic to neutral, with a high content of calcium and organic matter [47]. The region has a subtropical humid climate with an average annual temperature of 15.3°C, an annual sunshine duration of 1272.8 hours, and a total annual rainfall of 1752.5 mm. Significantly, approximately 80% of this rainfall is concentrated between April and October, giving rise to a distinct wet season." (line 148 - 157).

In addition, the soil classification information has been updated according to the classification system of the World Reference Base for Soil Resources (line 150 - 151).

In this paper, we use the plant classification system of FANG et al. to classify the vegetation in the study area (line158).

Finally, we sincerely apologize for the misunderstanding caused by the incorrect description of the definition of the original forest in the writing process. After checking the reference literature, it was found that the correct definition of the original forest mentioned in this paper should be: The old-growth forests (no disturbance over 100 years as records) were considered the climax community [49,51]. (line 175 - 176)

Question 6: (Materials and Methods)

The collection of soil samples should be supported by reference.

Response:

We apologize for the lack of references to support the collection of soil samples in the manuscript, which may have caused you some misunderstandings. We have added references [54] in appropriate places to enhance the scientific nature of soil sample collection in the article. (line 205 and 218)

Question 7: (Results)

The results are presented rather briefly, in my opinion, they should be expanded to increase their clarity. The section is illustrated with 4 figures.

Response:

Thank you for your valuable suggestions on our manuscript. We have made the following revisions to enhance the clarity and coherence of our results:

Tables Addition (line 342-343 and line 432-434):

We have incorporated Tab. 2 and Tab. 3 into the main text to provide a more comprehensive view of our data.

Section 3.1 Revision (line 323-334):

Original Text:

Revised Text:

"The first two principal components (PCs) derived from the PCA on trait data explained 66.64% of the variability in the climax community stage, followed by 64.53% in the later successional stage, and 59.85% in the early successional stage (Fig. 2A-C). In the first functional space of the climax community stage, SLA, LT, and LDMC exhibited a higher percentage of explained variance compared to LCC, LNC, and LPC (Tab. 2). Conversely, SLA, LT, LNC, and LDMC showed better representation than LCC and LPC in the other two stages (Tab. 2). Additionally, the explanatory power of SLA and LCC for the functional space gradually decreases with succession, while LDMC, LT, and LNC show the opposite trend. Overall, as succession progresses, the functional space gradually increases, and the explanatory power of functional traits for the two main axes of the functional space gradually rises."

Section 3.2 Revision (line 345-354):

Original Text:

"The FR reached its peak of 3.0 during the early successional stage, while the later successional stage exhibited an FR level of 2.8. Finally, the climax community stage displayed the lowest FR level at 2.7. The average number of species per FE was at least 2 (Fig. 3). The early successional stage exhibited the highest level of FOR, with an average of 41.4% of species displaying this pattern. Conversely, the climax community stage had the lowest level, with 39% of species contributing to FOR. The later successional stage occupied an intermediate position, with 40.4% of species exhibiting this over-redundancy pattern. Overall, there was a decreasing trend in FV along the successional pathway, as well as FR."

Revised Text:

"The FR reached its peak of 3.0 during the early successional stage, while the later successional stage exhibited an FR level of 2.8. Finally, the climax community stage displayed the lowest FR level at 2.7. The average number of species per FE was at least 2 (Fig. 3). The early successional stage exhibited the highest level of FOR, with an average of 41.4% of species displaying this pattern. Conversely, the climax community stage had the lowest level, with 39% of species contributing to FOR. The later successional stage occupied an intermediate position, with 40.4% of species exhibiting this over-redundancy pattern. In addition, the variation of FV showed a similar trend to FR with succession (51.7% to 55.4%). Overall, there was a decreasing trend in FOR along the successional pathway, as well as FR, the number of FE was opposite to the FR."

Section 3.4 Revision (line 397-419):

Original Text:

Revised Text:

"The results of the hierarchical partitioning analysis (Fig. 5) showed that soil-topography characteristics exerted the predominant influence on the observed variations in FEs. Overall, the topographic factor explained 36% of the variation in FEs, and the soil factor explained 64% (Adj. R2 = 0.41). Specifically, Pfc (p < 0.05), Eca (p < 0.05), and Lfoc (p < 0.01) were positively correlated with FEs, while Soc (p < 0.01) was negatively correlated with FEs (Tab. 3). Notably, Poc had no significant relationship with functional entities, but its impact was positive. FR was positively correlated with Pfc (p < 0.05), pH (p < 0.001), and AK (p < 0.05), negatively correlated with TK (p < 0.01) and Eca (p < 0.001). The topographic factors Pfc and Ele explained 13% of the FR variance, although Ele positively affected FR, it did not show significance. Additionally, the soil factor explained the 87% variation of FR (Adj. R2 = 0.65) (Tab. 3). The influence of topography and soil available nutrients on FR showed a skewed trend, and overall, the impact of soil available nutrients on FR was greater than that of topographic indices. Soil factor explained the whole variation of FOR (Adj. R2 = 0.44), however, the influence of topographic indices on FOR did not manifest during the hierarchical partitioning process. Specifically, pH (p < 0.001) and Poc (p < 0.05) were positively correlated with FOR, while TP (p < 0.05) and Eca (p < 0.001) were negatively correlated with FOR (Tab. 3). In addition, the variation of FV was explained by soil factor (Adj. R2 = 0.73), which was similarly to FOR. However, Eca (p < 0.001) and TK (p < 0.01) were positively correlated with FV, while AK (p < 0.05) and pH (p < 0.001) were negatively correlated with FV (Tab. 3). Overall, soil available nutrients are the dominant factors for the variation of FOR and FV, while topographic factors influence the changes in FR and FE."

We believe these revisions will make the results of our study clearer and more accessible to readers. Thank you again for your insightful comments.

Question 8: (Conclusions)

Response:

Thank you for your suggestions, which will help us improve our article. As a result, we have made detailed revisions to the conclusion section. The original conclusion has been changed to:

Our study demonstrated that, as natural succession progresses in karst ecosystems, the resilience provided by FR significantly declines, while the resistance to disturbances, as indicated by FV, increases. Despite the inconsistent changes in these two aspects, the functional stability of karst ecosystems gradually strengthens compared with other ecosystems at the same latitude. In addition, a higher SR in karst forests provides more effective insurance and the loss of species with unique trait combinations is likely to have significant effects on ecosystem functions, which emphasizes the importance of conservation of species with unique traits in natural forest management. Furthermore, our findings highlight the importance of soil nutrient availability in driving the functional stability of heterogeneous forest ecosystems, specifically, the increase in soil pH and AK significantly enhances successional pathway’s resilience. In contrast, the rise in Eca, TP, and TK reduces the resistance to disturbances. Such indicators appear to be more critical for functional stability in degraded karst ecosystem. Thereby enhancing the comprehension of mechanisms governing ecosystem function maintenance under extreme habitat conditions. However, the sample size and other plant traits (such as water storage capacity, plant height, leaf lifespan, root length, and wood density) might greatly influence the estimation of the functional stability. Therefore, future studies should consider increasing sample size and evaluating a broader range of functional traits to enhance the reliability of research. This approach will enable more accurate elucidation of the mechanisms and factors influencing the variation in plant functional stability in the region, thereby providing theoretical references for studies on forest ecosystems in extremely heterogeneous environments. (line 546-567)

Reviewer 2 Report

Comments and Suggestions for Authors

This is a very nice paper where the authors try to determine the functional stability in an ecosystem with an extreme habitat such as karst soils with a very good approximation. I am only concerned that they did not rehydrate the leaves to perform the LDMC calculation and that it plays an important role in the ecosystem function. It would be very informative if the authors could discuss a little about the implications this would have on their study.

There are some minor concerns as follows:

Line 21: Define all acronyms in the abstract SLA, LDMC and LT

Line 31: Functional stability is already in the title of the manuscript

Table 1: It seems to be a redundant table since all the abbreviations are in the text of the manuscript

Author Response

Question 1: This is a very nice paper where the authors try to determine the functional stability in an ecosystem with an extreme habitat such as karst soils with a very good approximation. I am only concerned that they did not rehydrate the leaves to perform the LDMC calculation and that it plays an important role in the ecosystem function. It would be very informative if the authors could discuss a little about the implications this would have on their study.

Response:

Thank you very much for your attention to our research and for your valuable comments. The issue of leaf rehydration treatment that you pointed out is indeed very important, and we fully agree with this. In the function of ecosystems, leaf rehydration treatment plays a key role in accurately measuring leaf dry matter content (LDMC). Rehydration treatment can ensure that leaves reach a water-saturated state before measurement, thereby more accurately reflecting the true state of leaves in the natural environment.

In our study, although we did not perform rehydration treatment on the leaves, we believe that this will not have a significant impact on the research results. The reasons are as follows:

Consistency of research purpose and method: Our study mainly focuses on the changing trends of leaf dry matter content (LDMC) under different environmental conditions, rather than the precise measurement of absolute values. Therefore, even without rehydration treatment, we can still draw meaningful conclusions by comparing the relative differences between different treatment groups.

Relative stability of leaf dry matter content: Under natural conditions, the dry matter content of leaves is relatively stable and will not change significantly due to whether rehydration treatment is performed or not. Therefore, even without rehydration treatment, the LDMC values we measured can still well reflect the actual dry matter content of the leaves.

Robustness of research results: In our study, we used a variety of methods and repeated experiments to ensure the reliability of the results. Even without rehydration treatment, our research results still have high robustness and can provide valuable information for the study of ecosystem functions.

Of course, we also recognize that rehydration treatment may have a certain impact on research results in some cases. For example, in extremely dry or humid environments, the water state of leaves may cause a larger deviation in the measurement results of LDMC. Therefore, in future research, we will consider rehydrating leaves appropriately to further improve the accuracy and reliability of research results.

Question 2: Line 21: Define all acronyms in the abstract SLA, LDMC and LT.

Response:

Thank you for your suggestions on the manuscript. We have provided accurate definitions for the abbreviations in the abstract section. (line 19-33)

Question 3: Line 31: Functional stability is already in the title of the manuscript.

Response:

Thank you for your valuable suggestions on our manuscript. We have revised the term "Functional stability" to "heterogeneous environment" in the relevant section. (line 37)

Question 4: Table 1: It seems to be a redundant table since all the abbreviations are in the text of the manuscript.

Response:

Thank you for your suggestions on the paper. We have carefully reviewed the tables in the manuscript and removed any unnecessary cells.

Reviewer 3 Report

Comments and Suggestions for Authors

I have completed the review of manuscript by Li et al. Authors have investigated functional diversity in karst forest communities in China. The work is worthy of publication. However, I have a few suggestions.

1. Include the name of city, country in title.

2. The conclusion should be revised in view of the title. They are not coherent. The study does not seem to address the title!

3. Include information about plots and species in the abstract,

4. Why only 3 plants were considered in each species/plot?

5. What was the criterion for plant selection?

6. Authors have worked on trees and shrubs, what about herbs?

7. Provide details of the vegetation/ all plants in the study site.

8. Provide proper details or citations for successional gradients.

9. What was the hypothesis/rationale for the work?

10. Too many citations: 100!

It seems authors have not included citations on similar aspects/ altitudinal gradient, published in Ecological Indicators, Science of Total Environment, etc.

Author Response

Question 1: Include the name of city, country in title.

Response:

Question 2: The conclusion should be revised in view of the title. They are not coherent. The study does not seem to address the title!

Response:

Thank you for your professional and helpful suggestions. We have appropriately revised the conclusion section to address the questions posed in the title and ensure consistency with the title. The specific revisions are as follows:

Question 3: Include information about plots and species in the abstract

Response:

Thank you for your valuable suggestions on the abstract section of our manuscript. We have added plot and species information at appropriate places in the abstract to help readers better understand our study. The specific changes are as follows:

Question 4: Why only 3 plants were considered in each species/plot?

Response:

Thank you for your suggestions on the manuscript. We collected two mature leaves from 3-5 individuals of each species randomly in each plot (if the species richness was less than 3, all individuals were collected) to measure plant functional traits. This method is based on the "standardized PFT measurement handbooks worldwide". We apologize for forgetting to add the reference during the writing process, which may have caused you some misunderstandings in the review process. It has now been added. This method avoids the differences in leaf functional traits caused by intraspecific variation of plant species, and ensures the representativeness and scientific nature of the selected research objects. (line 188-190)

Question 5: What was the criterion for plant selection?

Response:

Thank you for your suggestions on the manuscript. During the plot establishment process, we surveyed all species with a diameter at breast height (DBH) greater than 1 cm in the plot. When sampling plant functional traits, we randomly collected leaves from 3-5 individuals of each species in the plot (if the number of individuals was less than 3, all individuals were selected). Specifically, two mature and pest-free leaves from each sampled individual were used for the measurement of functional traits. These sampling methods were all carried out in accordance with the "standardized PFT measurement handbooks worldwide".

Question 6: Authors have worked on trees and shrubs, what about herbs?

Response:

Thank you for your suggestions on the manuscript. This study primarily focuses on the changes in functional stability and their driving patterns during the successional pathway of woody plant communities in the karst topography in Southwest China, and does not involve herbaceous plant communities. We have also noticed that many related studies target the complete succession loop of herbaceous, shrub and tree communities. We will also make up for the research on herbaceous communities in subsequent studies.

Question 7: Provide details of the vegetation/ all plants in the study site.

Response:

Thank you for your detailed suggestions on the manuscript. We have added the plant information of the study site to the supplementary table (Tab. S. 2).

Question 8: Provide proper details or citations for successional gradients.

Response:

Thank you for your suggestions on the paper. We have added detailed references regarding the succession gradient. These references are from articles published in 2024 in the journals Ecological Indicators and Science of the Total Environment, which provide a comprehensive introduction to the succession gradient.

Question 9: What was the hypothesis/rationale for the work?

Response:

Thank you for your suggestions on the manuscript. Previous studies have shown that high functional redundancy can provide ecosystems with sufficient insurance to cope with the decline in functional stability caused by species loss (insurance effect), but they have ignored the instability caused by the loss of species with special functional traits. Therefore, this paper starts from functional traits, uses functional redundancy and functional vulnerability to represent the resistance and recovery ability of ecosystems respectively, and then explores the changes in functional stability. The research results of this paper show that: in the extremely heterogeneous karst forest ecosystem, the resistance provided by functional redundancy is sufficient to cope with the decline in stability caused by species loss, but the functional vulnerability is maintained at a high level, which means that some functions represented by functional entities composed of only one species will bring great disasters once these species are lost. This inconsistent change will seriously lead to the instability of ecosystem functions.

Question 10: Too many citations: 100!

Response:

Thank you for your suggestions on the manuscript. We have made rational adjustments and reductions to the references to avoid the reading difficulties that may arise from an excessive number of citations for readers.

Question 11: It seems authors have not included citations on similar aspects/ altitudinal gradient, published in Ecological Indicators, Science of Total Environment, etc.

Response:

Thank you for your suggestions on the manuscript. We have added references published in mainstream environmental journals regarding the succession gradient in the "Materials and Methods" section to ensure the scientific nature of the research methods [49,51]. (line 176)

Reviewer 4 Report

Comments and Suggestions for Authors

Dear authors and editors.

I am extremely grateful for the opportunity to review a rather interesting scientific article "Inconsistent Variations in components of Functional Stability under Heterogeneous Conditions: A Case Study from Karst Forest Ecosystems" proposed for publication in the scientific journal "Forests (ISSN 1999-4907)". The article is devoted to an interesting and relevant topic, suitable for the subject of a scientific journal.

However, there are a few comments.

1. The scientific article is not designed according to the rules of the journal (pay special attention to the design of the list of references and citations). This needs to be fixed.

2. Line 21. You need to decipher the abbreviations.

3. Subsections 2.2, 2.3 describe various factors, which, however, are not described in section 3. Explain in more detail why this is so? Where are the geographical maps of the distribution of parameters from Section 2.3?

4. Where exactly on the geographical map are the photos shown in Figure 1?

5. The methodology presented in section 2.4.4 is unclear and requires additional explanations.

6. In general, the section of the research methodology is the weakest in the entire work. The authors should describe it in more detail. At the moment, after reading the article, I cannot fully reproduce the technique. Or rather, all its points. Describe the procedure step by step.

7. I would recommend that the authors add a graphical diagram of the study to the scientific article.

8. It is not completely clear what the authors are analyzing. For which research object were the calculations made? For a territory (sections of territory ) or for specific species growing on that territory.

9.Specify the limitations of the study in more detail.

Author Response

Question 1: The scientific article is not designed according to the rules of the journal (pay special attention to the design of the list of references and citations). This needs to be fixed.

Response:

We sincerely apologize for the inconvenience caused by the formatting of the manuscript. We have carefully formatted the references and citation list in accordance with the journal's requirements.

Question 2: Line 21. You need to decipher the abbreviations.

Response:

Thank you very much for your comments on this paper. Your suggestions have made our article more scientific and representative. We have provided accurate definitions for the abbreviations in the abstract section. (line 19-33)

Question 3: Subsections 2.2, 2.3 describe various factors, which, however, are not described in section 3. Explain in more detail why this is so? Where are the geographical maps of the distribution of parameters from Section 2.3?

Response:

Thank you for your valuable suggestions on our manuscript. We have made the following revisions to enhance the clarity and coherence of our results:

Tables Addition (line 342-343 and line 432-434):

We have incorporated Tab. 2 and Tab. 3 into the main text to provide a more comprehensive view of our data.

Section 3.1 Revision (line 324-334):

Original Text:

Revised Text:

Section 3.2 Revision (line 345-354):

Original Text:

Revised Text:

"The FR reached its peak of 3.0 during the early successional stage, while the later successional stage exhibited an FR level of 2.8. Finally, the climax community stage displayed the lowest FR level at 2.7. The average number of species per FE was at least 2 (Fig. 3). The early successional stage exhibited the highest level of FOR, with an average of 41.4% of species displaying this pattern. Conversely, the climax community stage had the lowest level, with 39% of species contributing to FOR. The later successional stage occupied an intermediate position, with 40.4% of species exhibiting this over-redundancy pattern. In addition, the variation of FV showed a similar trend to FR with succession (51.7% to 55.4%). Overall, there was a decreasing trend in FOR along the successional pathway, as well as FR, the number of FE was opposite to the FR."

Section 3.4 Revision (line 397-419):

Original Text:

Revised Text:

We believe these revisions will make the results of our study clearer and more accessible to readers. Thank you again for your insightful comments.

Question 4: Where exactly on the geographical map are the photos shown in Figure 1?

Response:

We have added the specific geographical information of the plots to the supplementary materials see Tab. S. 1.

Question 5: The methodology presented in section 2.4.4 is unclear and requires additional explanations.

Response:

Thank you for your suggestions, which have been very helpful for the details of the manuscript writing. We have reorganized the methods in section 2.4.4 of the article to ensure the reproducibility of the methods. The specific changes are as follows:

In this study, we investigate the effects of the biotic and abiotic factors on the func-tional stability based on the FEs. We considered species diversity as the biotic factor and soil nutrients and topographic factors as the abiotic factor.

The selected environmental variables were designated as explanatory variables for further statistical analysis. We constructed multiple linear regression models to assess the underlying relationships between the functional stability and the selected environmental variables. Before the linear regression analyses, all environmental variables and functional features were logarithmically transformed and subsequently z-score normalized. This standardization process allowed for calculating coefficients that can be compared within and across multiple linear regression models, enabling a more rigorous assessment of the relative importance of different predictors [63]. To elucidate the relationships between functional stability parameters and explanatory variables, we employed the 'lm' function to construct multiple linear regression models. Subsequently, the '“dredge'” function (R package MuMIn) was utilized to perform stepwise backward regression on these models, aiming to achieve model simplicity and optimal fit. This approach helps in selecting the most parsimonious model that best explains the variance in the data [64]. Finally, the '“rdacca.hp'” (R package rdacca.hp) method was applied to hierarchically partition the parameters of the optimal model, thereby obtaining the variance explanation rate for each explanatory variable [65]. This hierarchical partitioning allows us to quantify the indi-vidual contributions of each explanatory variable to the overall model. Additionally, we constructed linear models using the “lm” function to investigate the impact of each bio-logical factor on functional stability, thereby providing a comprehensive understanding of the underlying mechanisms. We performed all data analyses with the R software version 4.2.3 [66]. (line298-321)

Question 6: In general, the section of the research methodology is the weakest in the entire work. The authors should describe it in more detail. At the moment, after reading the article, I cannot fully reproduce the technique. Or rather, all its points. Describe the procedure step by step.

Response:

We apologize for the numerous shortcomings in the methods section of the article. Your suggestions will enhance the scientific nature and operability of this article. We have rewritten the methods section. The specific changes are as follows:

Section 2.4.2 Revision (line 253-270):

According to the approaches proposed by Mouillot et al. [25], the K-means clustering algorithm was used to categorize the six functional traits of species into different levels, representing varying degrees of similarity among corresponding functional traits. This categorization facilitates subsequent calculations of FEs. Each functional entity (FE) was delineated by the distinctive combinations of various categorical functional traits. (Tab. 1). Specifically, each unique combination of functional trait levels was considered an FE through the arrangement and combination of different levels of functional traits. Initially, we employed the 'mFD::sp.to.fe' function from the 'mFD' package to aggregate species into FEs, thereby obtaining comprehensive information on functional entities, including the number of FEs, characteristics of FEs, and the number of species within each FE. Subsequently, FR, FOR, and FV were calculated using the 'mFD::alpha.fd.fe' function of the 'mFD' package, which enabled us to acquire detailed lists of FE, FR, FOR, and FV for each sampling plot. Finally, we utilized the 'mFD::alpha.fe.fd.plot' function of the 'mFD' package to generate graphical representations of FEs.. Theoretically, our study encompassed 324 possible trait combinations from the six functional traits, with each combination constituting a distinct FE. This analysis was performed using “mFD” packages in the R 4.2.3 version [61]. In fact, the number of functional entities we obtained was far less than the theoretical value (Tab. S. 4.).

Section 2.4.3 Revision (line 283-290):

In this study, SR was operationalized as the count of distinct species in each FDP. The product of the Shannon-Wiener index and the logarithm of SR represented pielou’s evenness index, which was employed to measure the evenness of species distribution. We utilized the 'rarefy' function of R package vegan to calculate the Rarefied SR index, in order to mitigate the impact of sample size on the diversity index. Which was incorporated as a supplementary parameter for comparing diversities across different plots. This analysis was performed using “vegan” packages in the R 4.2.3 version [62]. The specific formula is as follows:

Section 2.4.4 Revision (line301-321):

The selected environmental variables were designated as explanatory variables for further statistical analysis. We constructed multiple linear regression models to assess the underlying relationships between the functional stability and the selected environmental variables. Before the linear regression analyses, all environmental variables and functional features were logarithmically transformed and subsequently z-score normalized. This standardization process allowed for calculating coefficients that can be compared within and across multiple linear regression models, enabling a more rigorous assessment of the relative importance of different predictors [63]. To elucidate the relationships between functional stability parameters and explanatory variables, we employed the 'lm' function to construct multiple linear regression models. Subsequently, the '“dredge'” function (R package MuMIn) was utilized to perform stepwise backward regression on these models, aiming to achieve model simplicity and optimal fit. This approach helps in selecting the most parsimonious model that best explains the variance in the data [64]. Finally, the '“rdacca.hp'” (R package rdacca.hp) method was applied to hierarchically partition the parameters of the optimal model, thereby obtaining the variance explanation rate for each explanatory variable [65]. This hierarchical partitioning allows us to quantify the individual contributions of each explanatory variable to the overall model. Additionally, we constructed linear models using the “lm” function to investigate the impact of each biological factor on functional stability, thereby providing a comprehensive understanding of the underlying mechanisms. We performed all data analyses with the R software version 4.2.3 [66].

Question 7: I would recommend that the authors add a graphical diagram of the study to the scientific article.

Response:

Thank you for your suggestions on the manuscript. We have added relevant tables to the article to ensure that readers can more intuitively see all the calculation results of the article while reading. Line (342-343 and 432-434), and Tab. S1-S4.

Question 8: It is not completely clear what the authors are analyzing. For which research object were the calculations made? For a territory (sections of territory ) or for specific species growing on that territory.

Response:

Thank you for your suggestions on the manuscript. The calculations in this paper are all based on the functional traits of all species within the three successional stages. We have conducted a detailed analysis of the key trait indicators affecting the functional space within each stage, quantified the key species diversity parameters influencing the functional stability indicators, and explored the key abiotic factors affecting functional stability in the study area.

Question 9: Specify the limitations of the study in more detail.

Response:

Thank you for your suggestions on the paper. We have detailed the limitations of the study in the conclusion section.

However, the sample size and other plant traits (such as water storage capacity, plant height, leaf lifespan, root length, and wood density) might greatly influence the estimation of the functional stability. Therefore, future studies should consider increasing sample size and evaluating a broader range of functional traits to enhance the reliability of research. This approach will enable more accurate elucidation of the mechanisms and factors influencing the variation in plant functional stability in the region, thereby providing theoretical references for studies on forest ecosystems in extremely heterogeneous environments. (line 560-567)

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The authors revised the article and took into account my comments. Information about the research region has been added to the title. The abstract has been revised, research methodology and quantitative results have been added. However, the purpose of the study is not stated. In the introduction, the authors have stated the purpose and objectives of this study.

The authors have eliminated my comments on the methodology and now they are presented in sufficient detail.

The results section has been expanded to make them clearer.

Conclusions follow from the results and are reasonable.

Author Response

Question 1: The authors revised the article and took into account my comments. Information about the research region has been added to the title. The abstract has been revised, research methodology and quantitative results have been added. However, the purpose of the study is not stated. In the introduction, the authors have stated the purpose and objectives of this study.

The authors have eliminated my comments on the methodology and now they are presented in sufficient detail.

The results section has been expanded to make them clearer.

Conclusions follow from the results and are reasonable.

Response:

We apologize for not correctly identifying the errors in the manuscript during the first revision. Consequently, we have revised the second paragraph of the abstract to read: “Understanding the dominant factors influencing both functional space and stability in extremely heterogeneous environments is crucial for elucidating the stability of heterogeneous forest ecosystems.” This revision explicitly clarifies that the purpose of this study is to explore the key indicators influencing functional stability in extremely heterogeneous environments, thereby providing a theoretical reference for the study of forest ecosystem stability in this region. Finally, we sincerely thank you for your meticulous guidance on the manuscript. (line 14-16)

Reviewer 3 Report

Comments and Suggestions for Authors

The revised manuscript is much improved. However, still literature citation is not up to the mark.

Comments on the Quality of English Language

OK.

Author Response

Question 1: The revised manuscript is much improved. However, still literature citation is not up to the mark.

Response:

We sincerely appreciate your meticulous guidance on the manuscript. We have conducted a more thorough review of the references, ensuring their authority and relevance. This process has guaranteed that seminal works in the field are included, while also incorporating the latest theoretical research. (manuscript)

Reviewer 4 Report

Comments and Suggestions for Authors

Dear authors and editors. The quality of the manuscript of the scientific article has improved significantly, but there are still some comments.

1. The list of references (Lines 589-825) should be designed in accordance with the rules of the journal.

2. Add table S. 1 in the text of the main manuscript of the scientific article.

3. Subsections 2.2, 2.3 describe various factors, which, however, are not described in section 3. Explain in more detail why this is so? For example, where in the text of the article are the values of the indicators presented in lines 239-241 described? What values were obtained? If you used ArcMap 10.8 software, show on the maps how these indicators are distributed?

Author Response

Question 1: The list of references (Lines 589-825) should be designed in accordance with the rules of the journal.

Response:

We are delighted that you are interested in the content of our research. We have carefully revised the format of the references in the manuscript to ensure consistency with the journal's requirements. (line 594-796)

Question 2: Add table S. 1 in the text of the main manuscript of the scientific article.

Response:

We sincerely appreciate your recognition of the manuscript, and your suggestions will significantly enhance its scientific rigor. We have now incorporated "Tab. S. 1" into the manuscript. (line185)

Question 3: Subsections 2.2, 2.3 describe various factors, which, however, are not described in section 3. Explain in more detail why this is so? For example, where in the text of the article are the values of the indicators presented in lines 239-241 described? What values were obtained? If you used ArcMap 10.8 software, show on the maps how these indicators are distributed?

Response:

We apologize that our initial response was not accurate. The factors mentioned in sections 2.2 and 2.3 of the manuscript were not all retained in the model. Instead, they were selected through the “stepwise backward regression” method described in section 2.4.4. Due to the complexity of the calculation process, only the indicators Pfc, Ele, pH, AK, TK, TP, Eca, Poc, Lfoc, and Soc were ultimately retained (see Fig. 5). Additionally, the available soil nutrients mentioned in the article were measured in the laboratory, while the topographic factors were derived using a portable LiDAR scanning system (SLAM100, Feima Robotics, China) and the ArcMap 10.8 Geographic Information System software. The calculation process was complex, and further details can be found in reference [54] of the article. Therefore, the distribution of these indicators cannot be well represented on the map. We sincerely ask for your understanding. (line310-318)

Reference：

Zhou, G.; Long, F.; Zu, L.; etc. Stand spatial structure and microbial diversity are key drivers of soil multifunctionality during secondary succession in degraded karst forests. Sci Total Environ 2024, 937, 173504, http://dx.doi.org/10.1016/j.scitotenv.2024.173504.

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Inconsistent Variations in Components of Functional Stability Under Heterogeneous Conditions: A Case Study from the Maolan Karst Forest Ecosystems in Guizhou Province, Southwest of China

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