Review Reports - Soil Hydrology Characteristics among Forest Type, Stand Age and Successive Rotation in Eucalyptus Plantations in Southern China

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

1. The research carried out can be important for the choice of species in the studied area.

2. There are numerous other researches with similar subjects, which can be found in the bibliography.

3. I ask the authors to specify what are the notable differences between the results obtained by them and other researchers.

4. Completing the conclusions with proposals regarding the degree of use of the eucalyptus species in forestry recultivation models.

Comments on the Quality of English Language

The English is easy to read and understand.

Author Response

Dear editor and reviewers

We thank all reviewers and editors for their thorough assessment of our manuscript and constructive feedback. All the recommended modifications have been integrated into our manuscript, highlighted in red, and the manuscript format has been switched to the Forest format. Below we provide a point-by-point response to all reviewers’ comments (in blue).

Reviewers/Editor comments:

Reviewer 1

Reviewer #1 comment: Comments and Suggestions for Authors

Reviewer #1 comment1: The research carried out can be important for the choice of species in the studied area.

Response: Thank you for your thorough review of our study, we appreciate your positive feedback regarding the work of the article.

Reviewer #1 comment 2: There are numerous other researches with similar subjects, which can be found in the bibliography.

Response: Yes, although there are many similar studies, there are few studies on the effects of eucalyptus on soil hydrology in Guangxi, even though Guangxi is the largest province in China with eucalyptus forest plantings. Our research focuses on the impact of eucalyptus age and rotation on soil hydrology and physical and chemical properties in Guangxi, where eucalyptus is widely planted, providing reference value for regional scientific management of eucalyptus management.

Reviewer #1 comment 3: I ask the authors to specify what are the notable differences between the results obtained by them and other researchers.

Response: Thank you for your insightful comment. Guangxi is the largest province in China with Eucalyptus forest plantings. The management of Eucalyptus plantations is significant to the regional ecological environment. However, a few studies focused on the influence of eucalyptus forests on soil hydrology. So, in this study, we focused on the impact of different eucalyptus forest ages and rotations on the hydrology of soil and litter.

First, In terms of water-holding capacity, the maximum soil water retention of the three forests (Eucalyptus, Cunninghamia lanceolata and Pinus massoniana) in our study (381.45-458.05g kg−1) is significantly lower compared to other ecosystems, such as meadow ecosystems (863.82–1318.87 g kg−1) [2], secondary forests, and other natural forests. (Lines 304-307). These differences in soil hydrological properties are attributed to the substantial impact of soil physicochemical properties, which are influenced by the aboveground canopy and belowground root systems of different plant types [37,38]. (Lines 307-310).

Second, we found a significant influence of Eucalyptus stand age on the soil hydrological characteristics. Specifically, as the stand ages advance, a noticeable increase in bulk density occurs (p < 0.05). While capillary porosity, total porosity, and water holding capacity (capillary, minimum, and maximum) significantly decrease (p < 0.05). This is because the increasing age of Eucalyptus forests leads to a greater demand for soil moisture by Eucalyptus trees, reducing soil moisture content and increasing soil bulk density (Lines 345 -350).

Lastly, we demonstrated that successive rotation of Eucalyptus forests on soil hydrological properties is increased with rotations. Our findings indicated that the 2nd rotation of Eucalyptus trees displayed superior hydrological characteristics compared to the 1st and 3rd rotations. This could be attributed to the highest total porosity in the 2nd rotation (Lines 382-384).

Reviewer #1 comment 4: Completing the conclusions with proposals regarding the degree of use of the eucalyptus species in forestry recultivation models.

Response: Thank you for your suggestions. We have refined and improved the conclusions and given reasonable suggestions (see lines 414-418).

New text: “Notably, the water-holding capacity of forest soil is a crucial indicator for assessing the ecological functions of forest ecosystems. Therefore, to balance eucalyptus production while maximizing the hydrological function of the soil, we recommend retaining as much of the plant residues on the soil as possible and harvesting after 5-7 years of cultivation.”

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Introduction

There is information that is repeated. If possible, summarize further the effects of Eucalyptus plantations on soil hydrological processes

Material and Methods

Lines 108 and 109: put the species scientific name in italics (about this point, review the entire text)

Line 125: write the scientific name of the species Chinese fir

Lines 122-129: “Three soil profiles were randomly selected in each plot at varying slope positions. Randomly choose three soil profiles with similar slope directions and locations” - better explain the selection of the geographic position of soil profiles.

Line 147: “quality” or quantity?

Line 151: “The thickness of water is 1000 kg m−3” thickness or density?

Results and Discussion

Table 1 To make the results easier to read, I suggest you create a separate table with information about the age and generations of eucalyptus plantations

Table 3 caption needs to be improved, as it does not provide precise information about the data presented therein. Also, the left column has to be clear about what the years represent and what the sequence 1st, 2nd, and 3rd represents.

Line 263: “For stand age of Eucalyptus plantation” or For rotations of Eucalyptus plantation!!!

Figures and Tables must be read independently, therefore the information contained in the captions must be improved. Please review all Figures and Tables in the article.

Discussion

Lines 309-310: Eucalyptus is an evergreen species!

Lines 318-320: “This lack of significance may be attributed to the inadequate differentiation of soil physicochemical 319 and hydrological properties at the chosen soil depth in our investigation”. Please explain better what you mean by this sentence!

Lines 381-382: “The decreasing soil moisture also led to a significant decrease soil capillary porosity (p < 0.05)”. The reasoning has to be done in reverse, that is, the decrease in the capillary porosity of the soil led to a decrease in soil moisture!

Author Response

Dear editor and reviewers

Reviewers/Editor comments:

Introduction

Reviewer #2 comment: There is information that is repeated. If possible, summarize further the effects of Eucalyptus plantations on soil hydrological processes

Response: Thank you for your suggestion; we summarized and deleted the part that is repeated in the introduction (see lines 71-84).

Line 71-84: “The stand age of Eucalyptus plantation influences root development and soil physical properties, affecting water uptake and soil infiltration rates [23,24]. For example, fine roots of the Eucalyptus tree could explore the soil down to a depth of 10 m throughout the entire rotation, contributing to high water use and potentially affecting water availability in the ecosystem [25]. Moreover, rotation-related factors, such as the frequency of harvesting and replanting, can impact soil nutrient availability and soil organic matter (SOM) content, influencing soil water-holding capacity and infiltration rates. Intensive management practices, including short rotation periods, which can lower SOM content [7] and alter soil hydrological characteristics [26]. Furthermore, removing trees during harvesting can expose the soil surface, increasing the risk of soil erosion and altering water runoff patterns [11]. Despite the significant influence of stand ages and rotations on aboveground biomass characteristics, as well as soil nutrient and physicochemical properties in Eucalyptus plantations, the effects of these factors on soil and litter hydrological properties have yet to be studied.”

Material and Methods

Reviewer #2 comment: Lines 108 and 109: put the species scientific name in italics (about this point, review the entire text)

Response: Thanks for your suggestion. Full text checked and corrected.

Reviewer #2 comment: Line 125: write the scientific name of the species Chinese fir

Response: Thanks for your suggestion. Corrected in the lines 118 and 150. Full text checked and corrected it.

Reviewer #2 comment: Lines 122-129: “Three soil profiles were randomly selected in each plot at varying slope positions. Randomly choose three soil profiles with similar slope directions and locations” - better explain the selection of the geographic position of soil profiles.

Response: Thank you for your point. We have now revised it in lines 120-123.

New text: “Soil sampling was carried out using a cutting ring and an aluminum box at 0-15 cm and 15-30 cm, respectively, to assess the physical properties of soil permeability in the laboratory. Three profiles were collected in each plot with similar slope directions and locations.”

Reviewer #2 comment: Line 147: “quality” or quantity?

Response： We have changed to “weight” in line 141.

Reviewer #2 comment: Line 151: “The thickness of water is 1000 kg m−3” thickness or density?

Response： We have revised it as “density” in line 145.

Reviewer #2 comment: Results and Discussion

Reviewer #2 comment: Table 1 To make the results easier to read, I suggest you create a separate table with information about the age and generations of eucalyptus plantations

Response: We are very grateful for your suggestions. We have recreated the basic information on the physical and chemical properties of soil in eucalyptus plantations from Table 1.

Table 1. Physical properties of soil in different forest types (mean ± standard error, n = 3).

Factors		Soil depth (cm)	Bulk density (g cm⁻³)	Capillary porosity (%)	Non capillary porosity (%)	Total porosity (%)	Soil aeration (%)
Forest type	Eucalyptus	0-15	1.31 ± 0.03b	45.51 ± 0.70a	11.32 ± 0.57a	56.83 ± 0.94ab	41.17 ± 0.72a
	Eucalyptus	15-30	1.38 ± 0.02ab	45.55 ± 0.66a	10.62 ± 0.55ab	56.16 ± 0.80ab	40.14 ± 0.59ab
	Chinese Fir	0-15	1.36 ± 0.04ab	46.96 ± 1.42a	11.65 ± 0.82a	58.61 ± 1.63a	40.83 ± 0.93ab
	Chinese Fir	15-30	1.42 ± 0.04a	46.84 ± 1.06a	10.38 ± 0.77ab	57.22 ± 1.42ab	39.34 ± 0.95ab
	Pine	0-15	1.44 ± 0.04ab	43.97 ± 1.73a	9.71 ± 1.27a	53.68 ± 1.75ab	38.76 ± 0.94ab
	Pine	15-30	1.46 ± 0.02ab	45.89 ± 0.96a	7.98 ± 0.59b	53.87 ± 1.14ab	37.25 ± 0.90b

Values that share similar letters within a column are not significantly different at a 95% significance level.

Table 2. Soil physical properties of Eucalyptus plantations with different stand ages and generations (mean ± standard error, n = 3).

Factors		Soil depth (cm)	Bulk density (g cm⁻³)	Capillary porosity (%)	Non capillary porosity (%)	Total porosity (%)	Soil aeration (%)
Stand age	5-year	0-15	1.28 ± 0.04b	50.85 ± 0.95a	9.94 ± 0.83a	60.80 ± 1.12a	41.11 ± 0.87a
	5-year	15-30	1.38 ± 0.03b	49.97 ± 0.92a	8.77 ± 0.74a	58.74 ± 1.29a	38.93 ± 0.91a
	7-year	0-15	1.40 ± 0.10ab	44.73 ± 2.91ab	9.97 ± 0.64a	54.70 ± 3.03ab	37.86 ± 1.72a
	7-year	15-30	1.42 ± 0.08ab	45.28 ± 2.62ab	10.43 ± 1.34a	55.71 ± 2.56ab	38.34 ± 1.43a
	15-year	0-15	1.44 ± 0.05a	41.36 ± 0.69b	7.77 ± 0.83a	49.13 ± 0.52b	37.60 ± 0.61a
	15-year	15-30	1.49 ± 0.04a	41.76 ± 1.18b	7.25 ± 1.30a	49.01 ± 0.77b	37.08 ± 0.90a
Generation	1st	0-15	1.28 ± 0.04ab	50.85 ± 0.95a	9.94 ± 0.83b	60.8 ± 1.12ab	41.11 ± 0.87bc
	1st	15-30	1.38 ± 0.03a	49.97 ± 0.92a	8.77 ± 0.74b	58.74 ± 1.29ab	38.93 ± 0.91c
	2nd	0-15	1.16 ± 0.04b	47.79 ± 0.97ab	15.00 ± 1.04a	62.79 ± 1.46a	45.71 ± 1.20a
	2nd	15-30	1.27 ± 0.04ab	47.61 ± 1.07ab	15.07 ± 1.31a	62.68 ± 0.55a	45.41 ± 1.02a
	3rd	0-15	1.29 ± 0.05ab	44.03 ± 0.91b	14.67 ± 1.16a	58.70 ± 1.78ab	45.84 ± 1.28a
	3rd	15-30	1.38 ± 0.04a	43.86 ± 1.12b	13.32 ± 1.11a	57.18 ± 1.30b	43.57 ± 1.03b

Values that share similar letters within a column are not significantly different at a 95% significance level.

Reviewer #2 comment: Table 3 caption needs to be improved, as it does not provide precise information about the data presented therein. Also, the left column has to be clear about what the years represent and what the sequence 1st, 2nd, and 3rd represents.

Response: thank you for your suggestion; we added more detailed information in the caption of Table 4.

Table 4. Physical and hydrology characteristics of litters in different forest types, Eucalyptus plantations with different stand ages and generations (mean ± standard error, n = 3).

Factors		Dry litter weight (g m⁻²)	litter moisture content (%)	Litter maximum water holding capacity (%)
Forest type	Eucalyptus	811.91 ± 45.91a	8.51 ± 0.18b	1054.14 ± 71.80a
	Chinese Fir	564.41 ± 91.24b	8.36 ± 0.19b	800.93 ± 119.95b
	Pine	611.08 ± 87.78ab	9.72 ± 0.67a	897.25 ± 126.99ab
Stand age	5-year	604.76 ± 56.27b	7.64 ± 0.13b	666.91 ± 58.98c
	7-year	1220.94 ± 106.6a	8.63 ± 0.28a	1637.39 ± 126.82a
	15-year	788 ± 82.39b	9.01 ± 0.24a	1045.33 ± 131.55b
Generation	1st	604.76 ± 56.27a	7.64 ± 0.13c	666.91 ± 58.98a
	2nd	584.36 ± 39.66a	8.21 ± 0.39b	665.64 ± 51.81a
	3rd	709.17 ± 94.69a	10.22 ± 0.38a	724.83 ± 81.27a
F Value	Forest type	8.521***	6.945**	3.739*
	Stand age	30.990***	21.24***	42.830***
	Generation	2.159	38.15***	0.591

Where 5-year, 7-year and 15-year are the stand ages of the Eucalyptus plantation; 1st, 2nd and 3rd are the generations of the Eucalyptus plantation. Values that share similar letters within a column are not significantly different at a 95% significance level. *, p ＜ 0.05; **, p ＜ 0.01; ***, p ＜ 0.001.

Reviewer #2 comment: Line 263: “For stand age of Eucalyptus plantation” or For rotations of Eucalyptus plantation!!!

Response: Sorry for the wrong figure number; we revised Fig. 4a to Fig. 5a, so here it should be “for stand age of Eucalyptus plantation.” (Line 272)

Reviewer #2 comment: Figures and Tables must be read independently, therefore the information contained in the captions must be improved. Please review all Figures and Tables in the article.

Response: Thanks for your suggestion; as requested, we checked all table captions to improve readability and independence.

Reviewer #2 comment: Discussion

Reviewer #2 comment: Lines 309-310: Eucalyptus is an evergreen species!

Response: Thanks for your suggestion. We have corrected in line 320.

Reviewer #2 comment: Lines 318-320: “This lack of significance may be attributed to the inadequate differentiation of soil physicochemical and hydrological properties at the chosen soil depth in our investigation”. Please explain better what you mean by this sentence!

Response: Thank you for your suggestion; we revised this in lines 329-331.

New text: “This nonsignificant interaction may be attributed to the inadequate differentiation of soil physicochemical and hydrological properties of 0-15 cm and 15-30 cm in our investigation, as these soil layers contain a few of SOM.”

Reviewer #2 comment: Lines 381-382: “The decreasing soil mois/ture also led to a significant decrease soil capillary porosity (p < 0.05)”. The reasoning has to be done in reverse, that is, the decrease in the capillary porosity of the soil led to a decrease in soil moisture!

Response: Thank you for your point; we revised lines 392-393 as required.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This paper is interesting, has a novelty, and is especially useful for decision-making stakeholders. The article has been prepared quite well, but small things need to be improved:

Line 93: units should be in metric (km² or hectares)

L 129: inconsistent in the use of terminology for ring knives; L 139= rings; L 148= cutting ring.

L 135: Figure 1 must be corrected. The map presented should be equipped with positions/observation points of eucalyptus, fir, and pine plantations.

L 143-152 need citation/references

L 147: quality ?

L 149: W1 is maximum water holding capacity (g kg−1), W2 is capillary moisture capacity (g g−1) but in L 172 W1 is the soil water content (g kg−1), W2 is the maximum water holding capacity (g g−1)

L 151: thickness ?

L 154-186 need citations indicating which methods the authors refer to. Each formula must be accompanied by citation/s.

- English writing should go through a review by a native speaker.

Comments on the Quality of English Language

English writing should go through a review by a native speaker.

Author Response

Dear editor and reviewers

Reviewers/Editor comments:

Reviewer #3 comment: This paper is interesting, has a novelty, and is especially useful for decision-making stakeholders. The article has been prepared quite well, but small things need to be improved:

Response: Thanks for the positive evaluation of our writing. It is useful for decision-making stakeholders.

Reviewer #3 comment: Line 93: units should be in metric (km² or hectares)

Response: We converted it into km2 in line 86.

Reviewer #3 comment: L 129: inconsistent in the use of terminology for ring knives; L 139= rings; L 148= cutting ring.

Response: Thank you for your valuable comments; we now uniformed the terminology as cutting the ring in lines 132 and 142.

Reviewer #3 comment: L 135: Figure 1 must be corrected. The map presented should be equipped with positions/observation points of eucalyptus, fir, and pine plantations.

Response: Thank you for your suggestion; we have now revised it.

Reviewer #3 comment: L 143-152 need citation/references

Response: Thank you for your suggestion; citation added in each parameter in the text (lines 134-140).

The cutting ring method measured soil bulk density [30], capillary porosity [30] and total porosity [31].

Pb = G × V

Pn = 0.1× (W1−W2) × Pb× Pw

Pc = 0.1 × W2 × Pb × Pw

P = Pn + Pc

Reviewer #3 comment: L 147: quality?

Response: Change to weight in the line 141.

Reviewer #3 comment: L 149: W1 is maximum water holding capacity (g kg−1), W2 is capillary moisture capacity (g g−1) but in L 172 W1 is the soil water content (g kg−1), W2 is the maximum water holding capacity (g g−1)

Response: Thank you for your point; we revised W1 (new line 162) as Wswc.

New text:

“Wswc = (G1−G2) × G2 × 1000

W1 = (G3−G1) × G1 × 1000

W2 = (G4−G1) × G1 × 1000

W3 = (G5−G1) × G1 × 1000

where Wswc is the soil water content (g kg⁻¹), W1 is the maximum water holding capacity (g kg⁻¹), W2 is the capillary moisture capacity (g kg⁻¹), W3 is the minimum water holding capacity (g kg⁻¹), G1 is the quality of the dried soil in-ring cutter (g).”

Reviewer #3 comment: L 151: thickness ?

Response: revised to density (line 145).

Reviewer #3 comment: L 154-186 need citations indicating which methods the authors refer to. Each formula must be accompanied by citation/s.

Response: Thank you for your point; we added a citation in each formula in the text (lines 134-136 and lines 158-161).

New text: “The cutting ring method measured soil bulk density [30], capillary porosity [30] and total porosity [31].” (lines 134-136)

“The infiltration and drying methods were used to sample unit weight, determining the mass water content of the soil [1], maximum water holding capacity [2], minimum water holding capacity [2], and capillary water holding capacity [2]. The calculation formula for each soil water retention index is as follows:” (lines 158-160)

Reviewer #3 comment: English writing should go through a review by a native speaker.

Response: We apologize for the language problems in the original manuscript. The language presentation was improved with assistance from a native English speaker with appropriate research background.