Chemical Thinning and Fisheye Clip for Managing Light Intensity in the Understory of Forest Restoration

Round 1

Reviewer 1 Report (Previous Reviewer 4)

Dear Authors

As you have adequately responded to all my comments so that the manuscript can be accepted now.

Best regards

Reviewer 2 Report (Previous Reviewer 3)

The manuscript has been significantly improved compared to the previous version. All the recommendations of the reviewers have been taken into account, both the description of the material and methodology and the discussion part have been significantly improved. Data processing methods have been improved as well. I have no objection to the publication of this manuscript.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This study presents results comparing the accuracy of smartphone hemispherical photography compared to more widely accepted photosynthetically active radiation (PAR) readings taken with a ceptometer in different basal area levels of chemically thinned tropical forest restoration plantings. This paper attempts to illustrate the utility of this smartphone technology and chemical thinning in tropical forest restoration, but it has serious flaws that do not warrant publication as presented. The writing makes readability and understanding of the manuscript difficult at times and not enough detail is provided in many sections where it is needed. 

The introduction section needs a better justification for the restoration system that is used in this study. Why are fast-growing species planted first followed by slower growing species? What are some example species in each of these groups? Are these restoration plantings restoring a historical forest type in this region or have they been developed to maximize economic and ecological benefits? More details (keep it brief) on the management and stand dynamics of these species mixtures to achieve desired objectives might be beneficial to readers (e.g. species planted, planting spacing, differences in growth rates among species, thinning techniques, and criteria used to cut and leave trees). More information on how stand density and species selection for removal have historically been decided upon needs to be mentioned in this section. More detail on chemical thinning should be included. I have given specific comments in the manuscript file. 

The two main study objectives could be stated better than they currently are.

The Methods section and Study Description section are lacking important stand description information (see specific comments), and the herbicide application needs more details in order to make the experiment more repeatable. The experimental design is not clearly stated. In addition, more detail on how the 15 PAR/hemispherical photography photo locations over the top of 15 different timber trees needs more description. Was a systematic grid used to determine where measurements would be taken?

In the results, you state that chemical thinning was successful for all species. Was this after one year? Based on trials I have done with undiluted glyphosate and hack and squirt applications, it is hard to believe that all trees were successfully killed after one year. Was resprouting an issue? It is difficult to determine which treatments are different from one another in Figure 1 as it is presented.

Some of the Discussions talking points are too general. For example, in the first paragraph you talk about succession, but more context on constituent species or forest and target species mixtures and structures should be provided. Par should not have been measured at the understory level when the leaves were not on the trees. Understory light levels cannot be accurately determined in deciduous forests when the trees are dormant. Restoration plans for tropical forests are mentioned in this section, but this topic should have been discussed more in the Introduction.

The conclusions section does a good job of highlighting the study’s main findings. Wording could be improved through this section though as some silvicultural terms are communicated correctly.

Comments and writing corrections are included in the pdf file.

Reviewer 2 Report

Barros Forests CHEMICAL THINNING AND FISHEYE CLIP FOR MANAGING LIGHT INTENSITY IN THE UNDERSTORY OF FOREST RESTORATION

This paper is grammatically well-written, but I had difficulty fully understanding the intent of the paper.   Based upon the title, Abstract, Introduction, and Discussion, I would have expected that there would presentation of the biological response of the shade tolerant trees of this system after chemical thinning, with added insights into the effectiveness of the camera technique.   Instead it reports almost exclusively on the light and canopy openness measures.   In this regard, the paper needs to focus on what the authors plan to present in the Results.  Perhaps another paper is planned on the biological responses.   As it is, I do not think that this paper makes sufficient contribution to the literature on light measurements to merit publication but perhaps there might be if the authors refocus their efforts on this matter.

L 128+  What was the reclamation site history, particularly, current vegetation and soil condition?  How were the fast and slow growing trees positioned?   Later the fast growing trees were systematically removed, so this is important.  What was the canopy height and tree density at the year(s) of measurement?   Can you give insight into crown length and overlap of canopy branches, i.e., was there evidence of crown shyness developing? 

L134-135  The semideciduous canopy has 20-50% of trees losing their foliage annually.    Is the range among the species or individuals of the species planted in this study?   Later, were the planted species also semideciduous?

L137  It appears that all the experiment was conducted on 1.2 ha.   Can we say that the work was pseudo-replicated, especially for the vegetation response part of the study?

L 150  Was the open PAR measured immediately adjacent in a large opening?.    When was it measured relative to the time of measurements under the canopy?  Was this before each plot measurement?

L154-163  Readers need to know something about the phone model and  camera settings.

Results – was there any evidence of mortality of non-herbicided trees, i.e., chemical transfer via root connections.

Figure 1  While there was upward trend in canopy openness/light with 30% treatment, it is perhaps lower than expected.   OK, why? Branch intertwining?  Rapid response of the canopy post thinning?  Either the 3 month measure was at the semi leaf-off phase or the canopy has rapid response after a year.

Figure 2 This is a remarkably noisy relationship comparing two measures aiming at the same goal of assessing canopies.  I would expect considerable discussion about the value of each type in this paper which one might be better at measurement of canopy.   Insight into the explanation of the residuals?

L210 Discussion of semideciduous nature of the forest?   Were any measures of light in this deciduous phase?

L257+  We finally begin discussion of the data reported in this paper, but then it quickly reverts to biology again.

English is fine

Reviewer 3 Report

The study is rather simple and narrowly focused on two very specific targets, however, the manuscript is of good quality and research is described very nicely. The objective of the study is well justified and the experiment as a whole is described in adequate detail for others to undertake it. The data analysis methods are appropriate for this kind of research by my opinion. Discussion is in good language and well framed. Amount of literature cited in the research paper is adequate.

Thera are only few things than can be advised for improvement of the manuscript. For international reader is hard to imagine how the five-year old plantation can look in tropical Brazil. Stand parameters of experimental sites (height, DBH, volume?) could help to better understand the material. “15 fast-growing” and “11 slow-growing” tree species also seems to be too simple description of material. Please list the tree species properly. Please describe the effect of applying herbicide more detailed: was the dieback of the treated species instant and what time it took to defoliate the trees. I can not distinguish in the Fig. 1 the grey colors indicating the significant differences.

Reviewer 4 Report

Using two different instruments, this manuscript assesses the importance of chemical thinnings in graduating the light available in tropical forest restoration projects. The paper's aims and objectives fit into this journal's editorial policy. After reading the manuscript, I cannot recommend publication in its current form. My comments are the following:

General Comment: The manuscript is too short in some critical Sections, such as Material and Methods and Results Sections. A reader needs more explanation to replicate this study. In short, the case study and the statistical methods are deficiently introduced in the manuscript. 

 

Major comments:

• Introduction: l. 78. An economic analysis is necessary to deal with this idea. Maybe species selection can be a critical issue

• I miss details about the cost of chemical thinning practices compared with other mechanical options. Besides, the use of glyphosate is controversial in some countries. Why do the authors not mention other practices to kill trees? I mean girdling or ring-barking. They are more “natural options” in order to change the stand composition and structure. 

• Material and Methods: a list of species planted, initially and after the thinning, is required

• Statistical methods are not well explained. It seems the authors only wish to describe the software used without explaining the reasons for using some techniques. For example, a list of explanatory variables and the hypotheses surrounding the linear models used must be mandatory. 

• Results: this Section is very poor. Nothing is said about linear models, ANOVA, correlation matrix, etc.

• Discussion Section: l. 244: what means “invasion” here?

• The study offers a conclusion regarding the minimum intensity of the thinnings for this treatment to be effective. Still, it is unclear if this percentage may depend on the species that were initially present or on the age at which the thinning is carried out. Any comments on this would be welcome.