Does the Process of Passive Forest Restoration Affect the Hydrophysical Attributes of the Soil Superficial Horizon?

Round 1

Reviewer 1 Report

Summary

The paper investigates whether passive regeneration of degraded tropical forests improves the hydrophysical properties of the soils, which would have beneficial effects on water infiltration, surface runoff/erosion and the overall water budget of catchments in the tropics. The authors conducted field studies and compared various soil-hydraulic and -physical properties of a degraded forest, forests under passive regeneration, and two fields under pasture and sugar cane cultivation. They conclude that hydrophysical properties are improved through passive forest regeneration, but that the required time spans are very long.

Broad comments

Strengths:

1. The topic is highly relevant. Information on how far passive regeneration helps in recovering original soil(hydrological) functions are a prerequisite for any management strategies aiming at improving runoff generation and water budgets of catchments with degraded forests.
2. The presented measurements are a valuable information that completes the soil-hydrological data available for tropical soils.
3. The chosen set of measurement methods is appropriate for the aim of the study.
4. The number of replicates is low, but sufficient to allow statistical analyses.

Weaknesses:

1. Introduction:
   1. The introduction does not logically lead to the research questions of the study.
   2. The study aims at understanding variations in infiltration capacity and other hydrophysical properties. The introduction refers exclusively to Ks as indicator “forest regeneration success”. It remains unclear from the introduction why (only) the parameter Ks is seen to be an appropriate indicator. Also, it is unclear from the introduction to which aim all the other hydrophysical parameters were measured and how they may indicate a soil’s degradation or regeneration status.
   3. Please give information on the processes behind observed changes in hydrophysical parameters due to land degradation/regeneration.
   4. Please refer to experience in the literature with respect to changes in those parameters.
   5. Please explain why you judge the chosen parameter as appropriate to evaluate the regeneration success.
   6. You use the term “passive regeneration”. What active regeneration measures one could think of? Are there experiences (in the literature) with active regeneration measures?
   7. The introduction should state the research questions or hypotheses investigated in the study (ideally, as the last paragraph of the introduction).
2. Materials & Method:
   1. Measurements of hydrophysical properties were undertaken only in the uppermost soil layer (0-10 cm mineral soil), why? Ks is, however, derived from infiltration experiments. What is the (assumed) maximum depth of the infiltration front during the infiltration experiments, i.e. over which depth does the derived Ks value integrate? Why was Ks not (additionally) measured at undisturbed soil samples from 0-10 cm?
   2. Basis soil properties (e.g. soil texture) differ between the sites. The effect of those variations needs to be included in the PCA.
   3. In order to fully understand why the investigated areas differ in their hydrophysical properties it is important to know not only their present land use, but also their history. Details on both are missing. For example, how much are the forest/regeneration areas disturbed by cattle grazing? What was the land use before regeneration started? How much compaction may be due to the former land use or site preparation?
3. Results:
   1. The description of the results contains a number of inconsistencies and logical errors (examples see below).
   2. Very often, differences between land uses are discussed although there are statistically not significant. Please refer when possible to statistical significances and explicitly state other differences as tendencies.
   3. The PCA provides the central results of the study. However, the paragraph on the PCA results is rather short
4. Discussion
   1. I miss a comparison of the measured data with data from literature. What are typical values for degraded vs intact soils under the investigated types of land use?
   2. Some interpretations of the results are misleading and do not correspond to the data in the result section, see examples below.
   3. The PCA results are not discussed. What are the parameters (of those that were measured) that were most influenced by land use and degradation/regeneration? How does this compare with literature?
   4. How do the variations of other soil properties such as soil texture blur the results?
5. Conclusions
   1. The conclusions are mostly comprehensibly, although very short. Some remarks on the ecological relevance of the results with respect to the problems stated in the introduction (rainfall infiltration, runoff generation, water budget, erosion,…) should be added.

Specific comments

1. The term “forest” is sometimes used for the degraded forest, sometimes for the regeneration areas, which makes it difficult for the reader to understand to which land use the authors refer to.
2. The abstract should include 1 or 2 sentences on the conclusions of the study.
3. Tab. 1: The table lists soil properties down to 30 cm. Why not deeper? What is the soil depth at the sites? Information on stone content and root densities would be informative as both strongly influence the hydrophysical properties.
4. Line 152: The distinction between macro pores and micro pores is somewhat misleading. By using a matric potential of -6 kPa, the parameter “Mic” also contains the meso-porosity.
5. Tab. 2: The table should contain also information on the standard deviation of the parameters. Based on Table 2 in the present form (without indications of standard deviation or other measures of variability) it is very difficult to follow the result description in the text. Also, the number of measurements must be stated.
6. The text between lines 188 and 218 contains a number of statements that are inconsistent with the information provided in Table 2. Examples: line 194: “The DFF presented Ks values between P and SC.” à DFF lies in the same group as SC (ab); line 209: “The highest values of OC were found in P and NR42, being statistically similar to each other.” à P and NR42 are in different groups according to the statistical test.
7. Fig. 3: It would be informative to have boxplots also for the other measured parameters. From Fig. 4 it seems that NR42 contains an outlier, which is, however, not visible in Fig. 3. Please state in the figure caption what is shown in the boxplot. What range is indicated by the whiskers? Are outliers shown?
8. Line 228: The hydrophysical data were measured at 0-10 cm depth, Ks integrates over a much deeper soil range. Why do you expect that there should be a significant relation between Ks and the other soil properties?
9. Line 236: “…demonstrated that the forest areas presented the best absolute values in the hydrophysical indicators…” à but Ks of DFF ranks 4 in Table 2!
10. Lines 316-319: this is not a conclusion, but a statement of the results.

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

See attached file "water-791240-re...."

Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The manuscript was largely improved, congratulations! I only have very little further comments, which I have typed directly under the authors' response in tha attached document.

Comments for author File: Comments.pdf

Author Response

Please refer to the file in attachment.

Thank you

Author Response File: Author Response.pdf

Reviewer 2 Report

See attachment

Comments for author File: Comments.pdf

Author Response

The authors wish to thank reviewer 2 for their comments on this manuscript and for accepting it in its present form.