Size Composition, Stability, and Distribution of Metal Nutrient Elements of Soil Aggregates of Eucalyptus Plantations with Different Thinning Intensities

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1.      The background sentence should be rewritten as follows: “Eucalyptus plantations suffer from and reduced productivity due to soil degradation, short rotation cycles, and multiple generations of replanting.”. Moreover, this statement is not sufficient to lead to the objective statement. More efforts should be made in the background statement.

2.      While listing, “and” should be added before the last item. This should be checked throughout the manuscript.

3.      The connections between the two factors thinning intensities and soil aggregates are poor in the results of the abstract.

4.      The keywords should be arranged alphabetically.

5.      Although the introduction is well documented, many statements lack proper citations, especially in the third paragraph.

6.      The statement in lines 88–91 should be rewritten.

7.      Why were the four thinning intensities selected? (line 94).

8.      In Table 1, statistics are not necessary.

9.      Some abbreviated terms have not been defined.

10.  In the notes of tables and figures, significance should go along with a proper test.

11.  Please try different colors or patterns for figures and improve their quality. It is difficult to distinguish the bars.

Author Response

1. The background sentence should be rewritten as follows: “Eucalyptus plantations suffer from and reduced productivity due to soil degradation, short rotation cycles, and multiple generations of replanting.”. Moreover, this statement is not sufficient to lead to the objective statement. More efforts should be made in the background statement.

Response:

We sincerely appreciate the reviewer's comment. The description in this section has been revised and improved as follows. Please refer to the first paragraph of the Introduction section.

 

“Eucalyptus plantations face soil fertility decline mainly due to: imbalanced fertilization, soil structural damage from slash-and-burn clearing and comprehensive tillage, insufficient nutrient cycling caused by short rotation periods, scarce litter input coupled with intensified surface erosion during rainy seasons, and insufficient soil recovery time—all accelerating land productivity depletion [2].”

 

2. While listing, “and” should be added before the last item. This should be checked throughout the manuscript.

Response:

We deeply appreciate the reviewer's insight. We have conducted a check of "and" throughout the entire manuscript, and made adjustments where deemed inappropriate. Please check the revised manuscript with tracked changes.

 

3. The connections between the two factors thinning intensities and soil aggregates are poor in the results of the abstract.

Response:

We sincerely appreciate the reviewer's feedback. The description in this section has been revised as follows, please check the abstract.

 

“Overall, this study demonstrated that the thinning intensity not only impacts the stability of soil aggregates in Eucalyptus plantations, but also influences the accumulation of metal nutrient elements within these aggregates, which confirms the significance of macroaggregates as a reservoir for metal nutrient elements. To preserve and enhance soil macroaggregates, it is recommended to implement measures such as reducing the amount of mechanical disturbance, increasing the amount of organic matter, optimizing the stand structure, mitigating water erosion risks, and promoting biological activity, while conducting regular assessments of the aggregate stability.”

 

4. The keywords should be arranged alphabetically.

Response:

We sincerely appreciate the reviewer's comment. We have arranged the items in alphabetical order as follows.

 

“Eucalyptus; metal nutrient elements; soil aggregates; thinning intensity”

 

5. Although the introduction is well documented, many statements lack proper citations, especially in the third paragraph.

Response:

We deeply appreciate the reviewer's valuable insight. We have incorporated the following 13 references into the manuscript. Kindly refer to the third paragraph for these additions.

 

1. Li, X.H.; Wang, R.H.; Liu, K.L.; Zhou, Y.H.; Hu, J.Y. Effects of thinning on tree growth and soil physiochemical properties in Cunninghamia lanceolata plantation. Forest Res. 2023, 28, 251–259.
2. Li, Y.; Hong, S.X.; Fang, S.Z.; Cui, G.C. Thinning promotes litter decomposition and nutrient release in poplar plantations via altering the microclimate and understory plant diversity. For. Res. 2023, 66, 3–18
3. Mao, Z.H.; Zhu, J.J.; Liu, Z.G.; Tan, H.; Cao, B. Effects of thinning on plant species diversity and composition of understory herbs in a larch plantation. Frontiers of Forestry in China 2008, 3, 422–
4. Chen, R.Y.; Wei, P.; Liu, J.H. Utilization of compressed Chinese fir thinning wood. Chinese Journal of Applied Ecology 2005, 16, 2306–2310
5. Cheng, C.P.; Wang, Y.D.; Fu, X.L.; Xu, M.J.; Dai, X.Q.; Wang, H.M. Thinning effect on understory community and photosynthetic characteristics in a subtropical Pinus massoniana Can. J. Forest Res. 2017, 47, 1104–1115.
6. Shen, Y.F.; Wang, N.; Cheng, R.M.; Xiao, W.F.; Yang, S.; Guo, Y. Short-term effects of low intensity thinning on the fine root dynamics of Pinus massoniana plantations in the three Gorges Reservoir Area, Forests 2017, 8, 428.
7. Moore, M.M.; Casey, C.A.; Bakker, J.D.; Springer, JD; FuléZ.; Laughlin C.D.C. Herbaceous vegetation responses (1992—2004) to restoration treatments in a ponderosa pine forest. Rangeland Ecol. Manag. 2006, 59, 135–144.
8. Zheng, M.H.; Zhou, Z.H.; Luo, Y.Q.; Zhao, P.; Mo, J.M. Global pattern and controls of biological nitrogen fixation under nutrient enrichment: A meta-analysis.Global Change Biol. 2019, 25, 3018–3030.
9. Fu, X.L.; Yang, F.T.; Wang, J.L.; Di, Y.B.; Dai, X.Q.; Zhang, X.Y.; Wang, H.M. Understory vegetation leadsto changes in soil acidity and in microbial communities 27years after reforestation. Total Environ. 2015, 502, 280–286.
10. Chen, K.X.; Ye, Y.C.; Mo, L.J.; Huang, Q.L.; Shen, D.C.; Liu, S.S. Effects of thinning on physical and chemical characteristics,soil microorganism and soil enzyme activities of Eucalyptus urophylla Southwest China Journal of Agricultural Sciences 2017,30, 2277–2283.
11. Yan, Z.P. Effects of different tending thinning intensities on stands and soil properties of Eucalyptus plantations. .Master, Central South University of Forestry and Technology, Changsha, 2019.
12. Moorhead, D.L.; Rinkes, Z.L.; Sinsabaugh, R.L.; Weintraub, M. Dynamic relationships between microbial biomass, respiration, inorganic nutrients and enzyme activities: informing enzyme-based decomposition models. Front. Microbiol. 2013, 4, 223.
13. Wu, R.; Cheng, X.Q.; Han, H. The Effect of forest thinning on soil microbial community structure and function. Forests 2019, 10, 352.

 

6. The statement in lines 88–91 should be rewritten.

Response:

We sincerely appreciate the reviewer's feedback. The description in this section has been revised as follows. Please refer to the second paragraph on page 3 for these improvements.

 

“Although numerous studies on effects of thinning on size [36], proportion [37], stability [38], organic carbon, and nutrient distribution [35] of soil aggregates in plantations are well-documented, the impacts on metal nutrient element content and reserves remain unclear.”

 

7. Why were the four thinning intensities selected? (line 94).

Response:

We sincerely appreciate the reviewer's comment. This study was conducted in collaboration with forest farm production to determine the optimal thinning intensity for cultivating large-diameter eucalyptus timber. At that time, 60% was selected as the upper limit. However, this intensity may disrupt stand structure and stability. Therefore, to balance timber production and forest health in management selection cutting, medium intensity (45%) and minimum intensity (30%) were also chosen. A 15% intensity was not selected as it was considered that the difference might not be significant. Thus, the intensity gradients of 30%, 45%, and 60% were chosen in the experiment to cover a range of impacts from low to high and comprehensively assess the combined effects of different thinning intensities on tree growth, biodiversity, and ecological functions.

 

8. In Table 1, statistics are not necessary.

Response:

We sincerely appreciate the reviewer's comment. We have removed the standard deviations from Table 1 as shown below.

 

Table 1. Overview of Eucalyptus stands with different thinning intensities.

Thinning intensity	Number of trees （tree/ha）	Tree height （m）	Diameter at breast height （cm）	Aspect	Slope degree （°）
CK	1380	23	27	Northwest	25
30%	966	23	26	Northwest	27
45%	759	22	26	Northwest	23
60%	552	22	27	Northwest	24

 

9. Some abbreviated terms have not been defined.

Response:

We deeply appreciate the reviewer's valuable feedback. We have elaborated on the definitions of mean weight diameter (MWD) and geometric mean diameter (GMD) in the second paragraph on page 3 as follows. Additionally, we have revised all abbreviations under tables and figures throughout the entire manuscript. Kindly review these corresponding sections.

“MWD and GMD can reflect the quality of the soil structure, with larger values indicating better soil structure stability. Therefore, it can be inferred that stands under light density management will have better soil aggregate stability than those under heavy density management.”

 

10. In the notes of tables and figures, significance should go along with a proper test.

Response:

We sincerely appreciate the reviewer's insightful comment. We have added the following statement at the bottom of Table 2, Table 3, Figures 1-6, and Figures 8-9. Kindly review the corresponding sections.

 

"Lowercase letters indicate significant differences at the 0.05 level between different thinning intensities within the same soil aggregate size using one-way ANOVA with Duncan's multiple comparison test."

 

11. Please try different colors or patterns for figures and improve their quality. It is difficult to distinguish the bars.

Response:

We sincerely appreciate the reviewer's valuable feedback. We have redrawn Figures 1-9 in their entirety. Please refer to the revised manuscript for these updates.

Reviewer 2 Report

Comments and Suggestions for Authors

The paper presents an insightful study on the particle size composition, stability, and distribution of metal nutrient elements in soil aggregates of Eucalyptus plantations under different thinning intensities. It contributes significantly to the understanding of soil health and nutrient cycling in managed forest ecosystems. However, certain aspects require revision to enhance clarity, methodological rigor, and the overall manuscript. Below are specific comments and suggestions for improvement.

 

General Technical Comments

1. The paper is generally well-written, but there are some areas where the language could be more concise. For example, the introduction contains several long sentences that could be broken down for better readability.
2. Some technical terms are used without sufficient explanation, which could confuse to readers who are not familiar with soil science or forestry. For example, terms like "mean weight diameter" and "geometric mean diameter" could be briefly explained when first introduced.
3. There are a few grammatical errors and awkward phrasings throughout the paper. For example, in the sentence "The fast growth and high nutrient demands of Eucalyptus, coupled with poor nutrient bases in forest lands, lead to excessive nutrient depletion and long-term deficiencies, resulting in land degradation and reduced productivity [2]".
4. In the results section, some sentences are overly complex and could be simplified. For example, "The MWD index of soil aggregates in stands with different thinning intensities ranged from 3.201 to 3.502, and the GWD index ranged from 1.807 to 2.163".
5. There are some inconsistencies in the use of terminology. For example, the term "metal nutrient elements" is used interchangeably with "metallic nutrient elements." It would be better to stick to one term throughout the paper.
6. Some references are cited with full author names, while others use "et al." after the first author.

Abstract

1. In the abstract and further in the text it is necessary to correct: ">2 mm, 0.25-1 mm, 1-2 mm and <0.25 mm" should be ">2 mm, 1-2 mm, 0.25-1 mm and <0.25 mm".

Introduction

2. The introduction provides a thorough background on Eucalyptus plantations and the issues related to soil degradation. However, the current introduction is broad and could be more concise in linking thinning practices directly to soil health.
3. The hypothesis is clearly stated, but it would be helpful to include more specific expected outcomes based on the thinning intensities.

 

Materials and Methods

4. The experimental design is well-described, but the rationale for selecting the specific thinning intensities (30%, 45%, 60%) could be better explained. Why were these particular percentages chosen? Are they based on previous studies or practical management practices?
5. The description of the soil sampling and analysis methods is thorough, but it would be beneficial to include more details on the statistical methods used, particularly the redundancy analysis. How were the environmental factors selected for the RDA? Were any preliminary analyses conducted to determine which factors to include?
6. It is necessary to clarify which method of dry sieving was used. It is written "Shavelov dry sieving method" or "Savelov dry sieving method", which is correct? Reference on the method is needed, the text contains 2 references, which is not to the method itself, but to papers, where it was used. It would be useful to discuss any potential limitations of this method, especially in relation to the specific soil types in the study area.

 

Results

7. The figures could be improved for better readability. For example, the labels on the axes in Figures 2 and 3 are quite small and could be enlarged. the color coding in Figures 10 and 11 could be more distinct to aid in differentiation.
8. The discussion of the results is thorough, but it would be helpful to include more comparative analysis with previous studies. How do the findings compare with other research on Eucalyptus plantations or similar forest systems?

 

Discussion

9. The discussion effectively interprets the results, but it could be strengthened by addressing potential confounding factors. For example, how might the understory vegetation or microclimate change due to thinning affect the soil aggregates and nutrient distribution?
10. The conclusion that large aggregates are crucial for nutrient storage is well-supported, but it would be beneficial to discuss the implications of this finding for forest management practices. How can this knowledge be applied to improve soil health and productivity in Eucalyptus plantations?

 

Overall, the paper presents valuable research on the effects of thinning on soil aggregates and nutrient distribution in Eucalyptus plantations. the paper could benefit from a more focused discussion on the practical implications of the findings and a more concise and clear presentation of the results. Additionally, some improvements in language and clarity would enhance the readability of the paper. With some revisions, this paper has the potential to make a significant contribution to the field of forest management and soil science.

Comments on the Quality of English Language

1. The paper is generally well-written, but there are some areas where the language could be more concise. For example, the introduction contains several long sentences that could be broken down for better readability.
2. Some technical terms are used without sufficient explanation, which could confuse to readers who are not familiar with soil science or forestry. For example, terms like "mean weight diameter" and "geometric mean diameter" could be briefly explained when first introduced.
3. There are a few grammatical errors and awkward phrasings throughout the paper. For example, in the sentence "The fast growth and high nutrient demands of Eucalyptus, coupled with poor nutrient bases in forest lands, lead to excessive nutrient depletion and long-term deficiencies, resulting in land degradation and reduced productivity [2]".

Author Response

The paper presents an insightful study on the particle size composition, stability, and distribution of metal nutrient elements in soil aggregates of Eucalyptus plantations under different thinning intensities. It contributes significantly to the understanding of soil health and nutrient cycling in managed forest ecosystems. However, certain aspects require revision to enhance clarity, methodological rigor, and the overall manuscript. Below are specific comments and suggestions for improvement.

General Technical Comments

1. The paper is generally well-written, but there are some areas where the language could be more concise. For example, the introduction contains several long sentences that could be broken down for better readability.

Response:

We deeply appreciate the reviewer's constructive feedback. We have meticulously reviewed the entire manuscript and split lengthy, complex sentences to enhance readability.

 

2. Some technical terms are used without sufficient explanation, which could confuse to readers who are not familiar with soil science or forestry. For example, terms like "mean weight diameter" and "geometric mean diameter" could be briefly explained when first introduced.

Response:

We deeply appreciate the reviewer's valuable feedback. We have elaborated on the definitions of mean weight diameter (MWD) and geometric mean diameter (GMD) in the second paragraph on page 3 as follows.

 

“MWD and GMD can reflect the quality of the soil structure, with larger values indicating better soil structure stability. Therefore, it can be inferred that stands under light density management will have better soil aggregate stability than those under heavy density management.”

 

3. There are a few grammatical errors and awkward phrasings throughout the paper. For example, in the sentence "The fast growth and high nutrient demands of Eucalyptus, coupled with poor nutrient bases in forest lands, lead to excessive nutrient depletion and long-term deficiencies, resulting in land degradation and reduced productivity [2]".

Response:

We sincerely appreciate the reviewer's comment. The description in this section has been revised and improved as follows. Please refer to the first paragraph of the Introduction section.

 

“Eucalyptus plantations face soil fertility decline mainly due to: imbalanced fertilization, soil structural damage from slash-and-burn clearing and comprehensive tillage, insufficient nutrient cycling caused by short rotation periods, scarce litter input coupled with intensified surface erosion during rainy seasons, and insufficient soil recovery time—all accelerating land productivity depletion [2].”

 

4. In the results section, some sentences are overly complex and could be simplified. For example, "The MWD index of soil aggregates in stands with different thinning intensities ranged from 3.201 to 3.502, and the GWD index ranged from 1.807 to 2.163".

Response:

We deeply appreciate the reviewer's valuable feedback. We have revised the sentence in the second paragraph on page 8 as follows.

 

“The MWD index of soil aggregates ranged from 3.201 to 3.502, the GWD index ranged from 1.807 to 2.163.”

 

5. There are some inconsistencies in the use of terminology. For example, the term "metal nutrient elements" is used interchangeably with "metallic nutrient elements." It would be better to stick to one term throughout the paper.

Response:

We sincerely appreciate the reviewer's valuable feedback. We have revised all instances of "metallic" to "metal" throughout the entire manuscript. Please refer to the revised version for these changes.

6. Some references are cited with full author names, while others use "et al." after the first author.

Response:

We sincerely appreciate the reviewer's valuable feedback. We have thoroughly checked all references and replaced all instances of "et al." with full author names. Please refer to the revised manuscript for these updates.

 

Abstract

1. In the abstract and further in the text it is necessary to correct: ">2 mm, 0.25-1 mm, 1-2 mm and <0.25 mm" should be ">2 mm, 1-2 mm, 0.25-1 mm and <0.25 mm".

Response:

We sincerely appreciate the reviewer's valuable feedback. We have made the following improvements to this description. Kindly review the abstract.

 

“>2mm, 1-2mm, 0.25-1mm, and <0.25mm”

 

Introduction

1. The introduction provides a thorough background on Eucalyptus plantations and the issues related to soil degradation. However, the current introduction is broad and could be more concise in linking thinning practices directly to soil health.

Response:

We deeply appreciate the reviewer's insightful comment. We have revised the description regarding the impact of thinning on soil health as follows. Please refer to line 3 on page 2 for these improvements.

 

“For example, moderate thinning operations in Eucalyptus plantations have been proven to significantly enhance soil water use efficiency, potentially due to reduced rainfall interception and weakened transpiration [25]. Thinning can also effectively increase light intensity within the forest, promoting an increase in soil temperature [27]. High-intensity thinning in Chinese fir plantations significantly increases soil porosity and moisture content, thereby optimizing soil structure and enhancing its water-holding capacity. Thinning also stimulates the growth of fine roots of trees and increases fine root biomass, which aids in the accumulation of essential nutrients such as N, P, K, and the enhancement of organic matter content in the soil [26]. Thinning improves nutrient utilization in understory soil, as the wooden residues with a high carbon-to-nitrogen ratio in thinning residues compensate for the loss of some organic matter in the thinned forests [41]. Thinning can enhance biological nitrogen fixation and increase active nitrogen content [42]. The buffering capacity provided by the regeneration of understory vegetation can mitigate soil acidification [43]. These changes in environmental factors further affect soil enzyme activities, such as enhancing soil acid phosphatase and urease activities [36], but potentially decreasing invertase activity [21]. Under thinning conditions, competition for water and available nitrogen sources between trees and soil microorganisms decreases, leading to increased available nitrogen content, promoting microbial proliferation, and enhancing soil microbial biomass [51]. Thinning also affects the diversity and structure of soil microbial communities [38]. These changes are not only closely related to nutrient cycling within the soil but are also jointly influenced by seasonal variations and regional characteristics, exhibiting diverse response patterns and complex ecological interactions.”

 

2. The hypothesis is clearly stated, but it would be helpful to include more specific expected outcomes based on the thinning intensities.

Response:

We sincerely appreciate the reviewer's valuable feedback. We have made the following improvements to the hypotheses presented here. Kindly review the final sentence of the Introduction section.

 

“We hypothesized that the thinning intensity not only impacts the stability of soil aggregates in Eucalyptus plantations, but also influences the accumulation of metal nutrient elements within these aggregates.”

 

Materials and Methods

1. The experimental design is well-described, but the rationale for selecting the specific thinning intensities (30%, 45%, 60%) could be better explained. Why were these particular percentages chosen? Are they based on previous studies or practical management practices?

Response:

We sincerely appreciate the reviewer's comment. This study was conducted in collaboration with forest farm production to determine the optimal thinning intensity for cultivating large-diameter eucalyptus timber. At that time, 60% was selected as the upper limit. However, this intensity may disrupt stand structure and stability. Therefore, to balance timber production and forest health in management selection cutting, medium intensity (45%) and minimum intensity (30%) were also chosen. A 15% intensity was not selected as it was considered that the difference might not be significant. Thus, the intensity gradients of 30%, 45%, and 60% were chosen in the experiment to cover a range of impacts from low to high and comprehensively assess the combined effects of different thinning intensities on tree growth, biodiversity, and ecological functions.

 

2. The description of the soil sampling and analysis methods is thorough, but it would be beneficial to include more details on the statistical methods used, particularly the redundancy analysis. How were the environmental factors selected for the RDA? Were any preliminary analyses conducted to determine which factors to include?

Response:

We sincerely appreciate the reviewer's valuable suggestion. We conducted the RDA analysis using Canon 5.0, during which we screened factors through forward stepwise regression. The results of the contribution rates and explanation rates have been supplemented in Tables 4 and 5 of the manuscript (as shown below). Kindly review these updates.

 

Table 4. Explanation and contribution rates of individual factors to metal nutrient element contents of soil aggregates in RDA.

Soil factor	Explanation (%)	Contribution (%)	pseudo-F	P
SpH	66.3	68.3	90.7	0.002
SOC	22.6	23.2	91.5	0.002
ApH	3.5	3.6	20.3	0.002
ASOC	1.2	1.2	7.9	0.002
STN	0.4	0.5	3.1	0.052
MWD	0.6	0.6	4.4	0.058
GMD	0.2	0.2	1.8	--
SBD	0.6	0.6	5.1	0.062
SCP	0.9	0.9	9.6	--
SPS	0.2	0.2	2.2	0.096
PPS	0.2	0.2	2.3	0.100
TH	<0.1	<0.1	0.1	0.884
STP	<0.1	<0.1	0.4	0.662

 

Table 5. Explanation and contribution rates of individual factors to metal nutrient element stocks in soil aggregates in RDA.

Soil factor	Explanation (%)	Contribution (%)	pseudo-F	P
PPS	89.6	91.4	397	0.002
TSOC	3.6	3.6	23.4	0.002
ApH	2.2	2.2	20.5	0.002
STN	0.5	0.5	4.7	0.018
ASOC	0.4	0.4	4.7	0.034
SPS	0.3	0.3	4.0	0.028
SBD	0.3	0.3	3.5	--
MWD	0.3	0.3	3.8	0.056
SpH	0.2	0.2	3.0	--
DBH	0.1	0.1	1.8	0.166
STP	<0.1	<0.1	0.5	0.528
SNCP	<0.1	<0.1	<0.1	0.880

 

3. It is necessary to clarify which method of dry sieving was used. It is written "Shavelov dry sieving method" or "Savelov dry sieving method", which is correct? Reference on the method is needed, the text contains 2 references, which is not to the method itself, but to papers, where it was used. It would be useful to discuss any potential limitations of this method, especially in relation to the specific soil types in the study area.

Response:

We sincerely appreciate the reviewer's valuable suggestion. We have changed "Shavelov dry sieving method" to "dry sieving method". We have retained the following paper in the first paragraph on page 6.

 

[1] Yang, Q.; Zhu, D.Y.; Chen, J.; Chen, H. Effects of vegetation restoration models on soil aggregate and organic carbon stock. Journal of Forest and Environment 2022, 42, 631–639.

 

 

Results

1. The figures could be improved for better readability. For example, the labels on the axes in Figures 2 and 3 are quite small and could be enlarged. the color coding in Figures 10 and 11 could be more distinct to aid in differentiation.

Response:

We sincerely appreciate the reviewer's valuable feedback. We have redrawn Figures 1-11. Please refer to the revised manuscript for these updates.

 

2. The discussion of the results is thorough, but it would be helpful to include more comparative analysis with previous studies. How do the findings compare with other research on Eucalyptus plantations or similar forest systems?

Response:

We deeply appreciate the reviewer's insightful comment. When searching Web of Science using keywords such as "thinning," "aggregates," and "metal nutrients," we found limited research on this topic. Most studies focus on the adsorption of heavy metals by soil aggregates, often in non-forest ecosystems or without particle size fractionation. Therefore, it remains unclear whether our study is the first to evaluate the impact of thinning on the metal nutrient storage capacity of soil aggregates. Currently, there are no similar studies to ours. We hope that more research will join our efforts in the future, and we look forward to our study being cited by more peers. Once again, we sincerely thank the reviewers for their valuable suggestions, which have greatly encouraged us.

 

Discussion

1. The discussion effectively interprets the results, but it could be strengthened by addressing potential confounding factors. For example, how might the understory vegetation or microclimate change due to thinning affect the soil aggregates and nutrient distribution?

Response:

We sincerely appreciate the reviewer's valuable feedback. We have added descriptions regarding the effects of thinning on the understory environment and vegetation, and linked them to the stability of soil aggregates in our discussion. Please refer to the first paragraph on page 19 for these updates.

 

“However, some studies suggest that thinning can reduce stand density, effectively improving the growth space, water, light, and other environmental conditions of the stand. This creates favorable conditions for the survival of understory species, facilitating species colonization and habitat establishment, enhancing vegetation diversity, stabilizing overall function, and improving soil erosion resistance and aggregation [60,61]. A report from Zhang et al. [62] also showed that the removal of understory vegetation led to significantly lower macroaggregate mass but higher microaggregate mass, resulting in a decline in soil aggregate stability.”

 

2. The conclusion that large aggregates are crucial for nutrient storage is well-supported, but it would be beneficial to discuss the implications of this finding for forest management practices. How can this knowledge be applied to improve soil health and productivity in Eucalyptus plantations?

Response:

We deeply appreciate the reviewer's insightful comment. We have added a dedicated paragraph at the end of the discussion section to address how to protect soil macroaggregates for maintaining soil health in forestlands. Please see below:

 

“The findings of this study indicate that macroaggregates serve as the primary reservoir of metallic nutrients in Eucalyptus plantation soils. Therefore, integrated management measures should be adopted to preserve and enhance soil macroaggregates in Eucalyptus plantation management. These include (1) minimizing mechanical disturbance by prioritizing no-till or shallow tillage during land preparation and young stand tending to avoid structural damage from heavy machinery; (2) increasing the amount of organic matter through litter retention or organic fertilizer application to strengthen cementation via humus and microbial secretions (e.g., glomalin); (3) optimizing the stand structure by establishing mixed coniferous–broadleaf forests and retaining understory vegetation to stabilize aggregates through root penetration and exudates; (4) mitigating water erosion risks by regulating the canopy density to reduce the impact of raindrops and waterlogging damage; and (5) enhancing biological activities.

 

 

Comments on the Quality of English Language

1. The paper is generally well-written, but there are some areas where the language could be more concise. For example, the introduction contains several long sentences that could be broken down for better readability.

Response:

We sincerely appreciate the reviewer's valuable feedback. We have carefully reviewed the entire manuscript and split some lengthy, complex sentences to enhance the readability of the paper.

 

2. Some technical terms are used without sufficient explanation, which could confuse to readers who are not familiar with soil science or forestry. For example, terms like "mean weight diameter" and "geometric mean diameter" could be briefly explained when first introduced.

Response:

We deeply appreciate the reviewer's valuable feedback. We have elaborated on the definitions of mean weight diameter (MWD) and geometric mean diameter (GMD) in the second paragraph on page 3 as follows.

 

“MWD and GMD can reflect the quality of the soil structure, with larger values indicating better soil structure stability. Therefore, it can be inferred that stands under light density management will have better soil aggregate stability than those under heavy density management.”

 

3. There are a few grammatical errors and awkward phrasings throughout the paper. For example, in the sentence "The fast growth and high nutrient demands of Eucalyptus, coupled with poor nutrient bases in forest lands, lead to excessive nutrient depletion and long-term deficiencies, resulting in land degradation and reduced productivity [2]".

Response:

We sincerely appreciate the reviewer's comment. The description in this section has been revised and improved as follows. Please refer to the first paragraph of the Introduction section.

 

“Eucalyptus plantations face soil fertility decline mainly due to: imbalanced fertilization, soil structural damage from slash-and-burn clearing and comprehensive tillage, insufficient nutrient cycling caused by short rotation periods, scarce litter input coupled with intensified surface erosion during rainy seasons, and insufficient soil recovery time—all accelerating land productivity depletion [2].”

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors

The authors have addressed a very important problem related to soil  degradation in their paper. In my opinion, the article contains a number of methodological errors which do not allow the article to be published in its present form. First of all, in the Study Sites section, there is a lack of important information on the soils studied. With this type of study, this is basic and fundamental information. I would ask the authors to clarify which soil types according to the WRB classification were present on the study sites.  The title of the article may mislead the reader. ‘Particle size composition’ most often refers to soil texture classes or particle size distribution. A more correct title should read ‘Soil aggregates composition,..... .

Did the authors determine the clay content in their study? This is a key parameter determining the stability of the aggregates. In the list of analyses, the authors did not mention an analysis of the granulometric composition of the soils.

Author Response

1. The authors have addressed a very important problem related to soil  degradation in their paper. In my opinion, the article contains a number of methodological errors which do not allow the article to be published in its present form. First of all, in the Study Sites section, there is a lack of important information on the soils studied. With this type of study, this is basic and fundamental information. I would ask the authors to clarify which soil types according to the WRB classification were present on the study sites. 

Response:

We sincerely appreciate the reviewer's valuable feedback. We have added the following description. Please refer to the first paragraph on page 4 for these updates.

 

“The soils predominantly consist of Acrisols (FAO & IIASA. 2023. Harmonized World Soil Database version 2.0. Rome and Laxenburg. https://doi.org/10.4060/cc3823en) soils derived from granite, with a soil depth ranging from 80 to 90 cm. The soils have undergone prolonged and intense leaching processes, resulting in low available nutrient content and pH levels between 4.0 and 5.0. Due to their susceptibility to weathering, primary minerals are thoroughly decomposed under leaching effects and gradually transformed into secondary minerals. Leaching also leads to distinct stratification within the soil profile. However, long-term and frequent forest management activities have caused obscured boundaries between these layers.”

 

2. The title of the article may mislead the reader. ‘Particle size composition’ most often refers to soil texture classes or particle size distribution. A more correct title should read ‘Soil aggregates composition,..... .

Response:

We sincerely appreciate the reviewer's valuable feedback. We have changed the title to "Size composition, stability, and distribution of metal nutrient elements of soil aggregates of Eucalyptus plantations with different thinning intensities". Please refer to the revised manuscript.

 

3. Did the authors determine the clay content in their study? This is a key parameter determining the stability of the aggregates. In the list of analyses, the authors did not mention an analysis of the granulometric composition of the soils.

Response:

We sincerely appreciate the reviewer's valuable feedback. Our research primarily focused on the distribution of element content and reserves, which led us to overlook the measurement of clay content. This is indeed a limitation. We initially intended to supplement this data, but unfortunately, the samples were exhausted. During the manuscript revision period, we specifically visited the original sampling forest stands. However, the forest farm staff informed us that these experimental forest stands were clear-cut last summer, and the soil had undergone site preparation for reforestation, resulting in significant disturbance. Therefore, we ultimately decided to abandon the plan to re-sample and measure clay content. Nevertheless, we are still very grateful for the reviewer's comment and will prioritize considering these factors in our future research.

Reviewer 4 Report

Comments and Suggestions for Authors

The manuscript corresponds to the subject of the journal, but cannot be published in its current form. It is uncorrect to use Bd in formula 3. Should be use density of each aggregate separately. In addition, the formula 3 assumes that the concentration of metals in aggregates of different sizes is the same. In this regard, there is no point in considering and discussing of soil aggregate metal nutrient element content . Due to this manuscript may transform to aggregate-afforestation relationship discussion but metal influence can be consider only like a differences between variants of afforestation. I recommend that the authors withdraw the manuscript and seriously revise it. Other comments in the text.

Comments for author File: Comments.pdf

Author Response

1. The manuscript corresponds to the subject of the journal, but cannot be published in its current form. It is uncorrect to use Bd in formula 3. Should be use density of each aggregate separately. In addition, the formula 3 assumes that the concentration of metals in aggregates of different sizes is the same.

Response:

We sincerely appreciate the reviewer's valuable feedback. We would like to clarify that soil aggregates of different sizes were obtained by passing intact 0-20 cm soil samples through sieves with different pore sizes. Therefore, the individual densities of aggregates of different sizes cannot be obtained. The soil bulk density used here was employed to calculate the soil mass of the 0-20 cm soil layer. After determining the soil mass, we calculated the mass of aggregates of different sizes in the 0-20 cm soil layer by multiplying the soil mass of the 0-20 cm soil layer by the mass percentage of aggregates of different sizes in the intact soil mass. Subsequently, by multiplying the mass of aggregates of different sizes by the respective element contents in aggregates of different sizes (as shown in Figure 2 and Figure 3), we obtained the reserves of each element in aggregates of different sizes.

As demonstrated in Figure 2 and Figure 3, the contents of the seven elements vary among aggregates of different sizes. We substituted these varying element contents into the formula to calculate the reserves of each element in aggregates of different sizes.

Therefore, we have retained the original content. We hope you can understand, and thank you again for the reviewers' comments, which have been very helpful in improving the quality of our manuscript.

 

2. In this regard, there is no point in considering and discussing of soil aggregate metal nutrient element content. Due to this manuscript may transform to aggregate-afforestation relationship discussion but metal influence can be consider only like a differences between variants of afforestation. I recommend that the authors withdraw the manuscript and seriously revise it. Other comments in the text.

Response:

We sincerely appreciate the reviewer's valuable feedback. We would like to clarify the following: This study was conducted in collaboration with forest farm production to determine the optimal thinning intensity for cultivating large-diameter eucalyptus timber. At that time, 60% was selected as the upper limit. However, this intensity may disrupt stand structure and stability. Therefore, to balance timber production and forest health in management selection cutting, medium intensity (45%) and minimum intensity (30%) were also chosen. A 15% intensity was not selected as it was considered that the difference might not be significant. Thus, the intensity gradients of 30%, 45%, and 60% were chosen in the experiment to cover a range of impacts from low to high and comprehensively assess the combined effects of different thinning intensities on tree growth, biodiversity, and ecological functions.

By setting these four different thinning intensities, we aimed to quantify the content and reserves distribution characteristics of seven metal nutrient elements in soil aggregates and their relationships with environmental factors. It should be noted that the initial afforestation time, initial density, tree species, and management measures were all the same, with the only difference being the thinning intensities.

Thank you again for the reviewer's comment, which have been very helpful in improving the quality of our manuscript.

 

3. It is better to make the series ascending or descending

Response:

We sincerely appreciate the reviewer's valuable feedback. We have made the following improvements to this description. Kindly review the abstract.

 

“>2mm, 1-2mm, 0.25-1mm, and <0.25mm”

 

4. It is unclear. In soil particles form aggregates because there are aggregate size composition and particle size composition

Response:

We sincerely appreciate the reviewer's valuable feedback. We have revised "aggregate particle size" to "aggregate size" throughout the entire manuscript.

 

5. “artificial ”not only...

Response:

We sincerely appreciate the reviewer's valuable feedback. We have revised "artificial forests" to "plantations" in several instances throughout the entire manuscript.

 

6. aggregate particle size

Response:

We sincerely appreciate the reviewer's valuable feedback. We have revised "aggregate particle size" to "aggregate size" throughout the entire manuscript.

 

7. Table 1: Please round the averages to significant figures according to the rounding rules. in the whole table

Response:

We sincerely appreciate the reviewer's valuable feedback. We have rounded the tree height and diameter at breast height in Table 1 to the nearest integer. Please refer to Table 1.

 

Table 1. Overview of Eucalyptus stands with different thinning intensities.

Thinning intensity	Number of trees （tree/ha）	Tree height （m）	Diameter at breast height （cm）	Aspect	Slope degree （°）
CK	1380	23	27	Northwest	25
30%	966	23	26	Northwest	27
45%	759	22	26	Northwest	23
60%	552	22	27	Northwest	24

 

 

8. Table 2: See comment for table 1

Response:

We sincerely appreciate the reviewer's valuable feedback. Considering that if we retain integers, for example, the data for SBD's CK, 30%, and 60% treatments are all 1, and SNCP's CK and 60% treatments are both 8. Although STN's four treatments are all 1, the 30% treatment is significantly higher than the others. If we retain one decimal place, SpH's CK and 30% are both 4.4, and STP's CK and 45% are both 0.2. Given that many studies retain two to three decimal places, we have ultimately decided to retain two decimal places, as this helps to highlight the differences between the data from different treatments. Thank you again for your comment, which have significantly improved our manuscript.

 

9. Table 3: See comment for table 1

Response:

We sincerely appreciate the reviewer's valuable feedback. For the same reasons mentioned above, we have decided to retain two decimal places. Thank you again for your comment, which have significantly improved our manuscript.

 

10. “Note: SBD, soil bulk density; SCP, soil capillary porosity; SNCP, soil non-capillary porosity; STP, soil total porosity; SWC, soil water content; SpH, soil pH; SOC, soil organic carbon; STN, soil total nitrogen; STP, soil total phosphorus; SAN, soil ammonium nitrogen; SNN, soil nitrate nitrogen; SAP, soil available phosphorus. Lowercase letters indicate significant differences at the 0.05 level between different thinning intensities.”

Is it necessary to have a prefix S (soil) before each abbreviation?

Response:

We sincerely appreciate the reviewer's valuable feedback. Table 2 presents the physicochemical properties of intact soils, whereas Table 3 specifically presents the physicochemical properties of aggregates of different sizes. Additionally, both Figure 10 and Figure 11 include physicochemical indicators for both intact soils and aggregates. To differentiate between them, "S" was added to the intact soil indicators and "A" was added to the aggregate indicators.

Round 2

Reviewer 4 Report

Comments and Suggestions for Authors

I am satisfied with the answers. I recommend publishing the article.