Multi-Elemental Analysis for the Determination of the Geographic Origin of Tropical Timber from the Brazilian Legal Amazon

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This research aimed to investigate the application of multi-elemental analysis combined with PCA to discriminate the provenance of tropical timber in the Brazilian Legal Amazon. They used Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to observe elements like Ca, Sr, Cr, Cu, Zn, and B, and PCA to cluster them in groups.

However, there are still some opportunities to improve the manuscript before final publication:

Major Comment: The element profile depicts the source of elements (Soil properties) as indicated in the discussion section. However, no soil analysis was added to the comparison for confirmation. Even the soil properties are not indicated in the introduction section or discussed in the discussion section.

Minor comment:

L31-37 Template paragraph not removed

Section 2.1: Line 84-92, “individuals” may be replaced by samples  

L-98: How to design or select “Subsamples”?

Table 1: In row 0%, what does it mean “Fe e Cr”, similarly in the next rows “Cr e Ba”, “Ba e Ce”, and so on

L164: “S2 e S3”,  I guess “e” actually for “and”.

 

Author Response

Dear, 

About major comment we agree with this comment, therefore, regarding soil properties the following paragraph was inserted in lines 53–59, page number 2 to address the reviewer’s comments:

“The Amazon exhibits a wide variability of soil classes according to the Brazilian Soil Classification System (SiBCS), with a predominance of highly weathered, acidic, and nutrient-poor Oxisols, Ultisols, and Entisols. Even in these deep profiles, regional geochemical studies have shown that the elemental signature of the parent material is still detectable in the soil matrix, creating pedogeochemical mosaics that can be distinguished at the landscape scale.”

Regarding soil analysis, the study did not cover this aspect due to lack of resources and logistics.

About minor comment:

L31-37 Template paragraph not removed

Response: has already been removed

Section 2.1: Line 84-92, “individuals” may be replaced by samples 

Response: We agree with this suggestion. Thus, we have replaced the word, in lines 90-98, page number 3. 

L-98: How to design or select “Subsamples”?

Response: With all due respect and consideration, I understand that the description of the methodology for collecting the subsamples in the lines 104-108, second paragraph of page 3 and the figure 2 clarify the question.

Table 1: In row 0%, what does it mean “Fe e Cr”, similarly in the next rows “Cr e Ba”, “Ba e Ce”, and so on

Response: The word "e" in Portuguese was translated to "and" in English. Therefore, the correction was made in all rows of the table 1.

L164: “S2 e S3”,  I guess “e” actually for “and”.

Response: We agree with your statement. In fact, the correct writting is "and" instead of "e". The correction was made in the article. 

Please note that the changes are written in red in the text of the article.

Yours Sincerely,

Marcos David Gusmão Gomes

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The work titled "Multielemental Analysis for the Determination of the Geographic Origin of Tropical Timber from the Brazilian Legal Amazon" is an excellent article that aims to develop a wood tracing tool to combat irrational and fraudulent exploitation of timber species.

This work has the great merit of using the chemical fingerprint method as a forensic tool to precisely determine timber origin, and ensure better monitoring and controlling of timber trade, which is a great challenge in the forestry sector and biodiversity conservation.

The study was very well conducted experimentally, from the collection and preparation of samples to the analyses carried out.

In terms of results, I think Table 1 is not very informative. I would suggest including the concentrations of each analyzed element on the different radial extensions considered. Also, the p-values ​​should appear clearly in this table, so that it is easier to see that the results are significant, instead of simply stating it as it was done.

In the discrimination figures (PCA), there are at least two instances where component 1 is not mentioned as such. Please check this.

In lines 148 and 163, table s1 and figures s1, s2, and s3 are mentioned; but they are not found anywhere in the manuscript.

Please remove the section "0. How to Use This Template" from lines 31-37.

 

 

 

Author Response

Dear,
I appreciate the comments and am glad you enjoyed the topic and the development of the work. Regarding Table 1, I included only the elements that showed significant differences.
The table with the concentration of each element in the different radial extensions considered is too large to be included in the article, as are the tables with the p-values ​​of each element compared pairwise. The tables are in Supplementary Materials, Table S1.
On lines 154-155 of the first paragraph of the results topic, the phrase "supplementary materials" was inserted in red to indicate that the tables are attached. Regarding the ACP components, when checking the figures, I noticed that in all of them components 1 and 2 appear with their respective percentages.

In the article, the section "0. How to Use This Template" was removed.

Yours Sincerely,
Marcos David Gusmão Gomes

 

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

Review of Gomes et al.

June 19 2025

 

This useful article contributes to the plausibility and feasibility of using elemental analysis for forensic provenance determination of Brazilian lumber species.   The practical value of this project and of future related work is obvious.  The technical aspects of the manuscript reveal skill and effort.  Please consider this a positive review with a few minor concerns and soft suggestions.  

My main concern is to request a more thorough explanation than lines 136-139 of the PCA methodology and outcomes, especially because two types of data are in the PCA-based figures 3-5 without much explanation.  (Incidentally,  those figures are a little difficult to see clearly, especially the pale locality symbols such as Itaituba.)    It is probably merely my failed comprehension, but as one reader, I’m not sure exactly how the multielemental values were determined for each PCA figure representing a different species and different radial portions.   Specifically where I’m unclear is that for each figure the green elemental axes reflect multiple localities, so how do multiple localities relate to those single green lines? What do the main axes in the PCA reflect?   A step by step walkthrough from data gathering  to  Figures 3-5 would help.   In that connection, line 138, distinct groups of what?

I’d suggest including authorship, family, taxonomic reference, and maybe a little additional info for each mentioned species. Perhaps in a table? Or in the SM?

Lines 68, 69---results reportedly differ for different Ipe species, so on line 87 is it a problem that the 16 Ipe samples unidentified as to species?   Are there vouchers?   Could these be sent to someone familiar with Bignoniaceae for identification? On lines 219, 263 are the differences due to environmental heterogeneity, or possibly to being different species of Ipe?

Lines 100, 290 and perhaps elsewhere.  Tree trunks don’t really retain pith.  “Center of trunk?”

Micro-issues noted during reading:

Parts of the MDPI template remain in the ms.  (e.g. lines 31-37).   Line 39 (irrational? Or Illegal?), 44 (please define “Legal Amazon”), 67 (typo), 71 (give botanical name),  Fig. 2, lines 99, 107, 146, 168, 192, 288 (disc and disk used inconsistently),  “multi-elemental” (15, 221,315) vs. “multielemental”  (title,233) inconsistent.

 

A suggestion:

It goes without saying that an exploratory project has limits and cannot delve into every angle of a topic, so it would be offensive for a reviewer to ask, “why did you not look into this or that?”  Those obviously are questions for the future.  But perhaps an exploratory paper could benefit in terms of context and perspective by  offering specific pointers for future research questions, beyond the broad generality of lines 319-322.  

In any case, I think this paper with a little sandpapering with an eye to clarity will  be a valuable contribution.

Author Response

Dear,
I appreciate the comments. Respectfully, i understand that for the methodology topic, the explanation about PCA is clear, as the objective was to address its function and what is expected of the technique for the work in question.
The descriptions of Figures 3 to 5 provide a summary of the PCA content, as they are captions. Detailed descriptions of the figure content are provided in the results and discussion sections. The principal axes are component 1 (x-axis) and component 2 (y-axis), which are linear combinations of the original variables (concentrations of chemical elements) that explain most of the variability in the data. Each green line represents an original variable (e.g., Fe, K, Zn in mg/kg) projected onto the space of the first two principal components. In line 137, distinct groups refer to the identification of patterns (samples from locations with similar chemical signatures) that form aggregates and that clearly separate from other samples (locations) I appreciate your collaboration on the item detailing the species, but I understand that for the context of the work, addressing the botanical aspect of the sampled species will not be relevant. Regarding sample identification, the description of the ipê samples was only possible at the genus level. In the study (Moreira et al., 2024) I mentioned, I emphasize that the samples were collected from the same location. However, in my study, the locations are different, located approximately 220 km apart. Therefore, I suggest in the discussion of the work that environmental heterogeneity may be a contributing factor. In specialized literature, the central region of the trunk is referred to as the pith. Therefore, I used the nomenclature, which is already established in other scientific publications. In line 39, the term is illegal because it is in disagreement with the legislation that regulates forestry activity.

Legal Amazonia is a Brazilian region comprised of the States of Pará and Amazonas, the federal territories of Acre, Amapá, Guaporé and Rio Branco, and also the part of the State of Mato Grosso north of the 16th parallel, the State of Goiás north of the 13th parallel and Maranhão west of the 44th meridian. The terms wooden disc and multielement have been corrected to disk and multi-elemental, respectively. Please note that the changes are written in red in the text of the article.

Yours Sincerely,
Marcos David Gusmão Gomes
 

 

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

This study investigated the application of multi-elemental analysis combined with Principal Component Analysis (PCA) to discriminate the provenance of tropical timber in the Brazilian Legal Amazon. As multi-elemental composition can provide a chemical fingerprint for timber tracing, wood samples from Hymenaea courbaril (Jatobá), Handroanthus sp. (Ipê), and Manilkara huberi (Maçaranduba) were sampled across multiple locations for multi-elemental determination and PAC. The results showed significant differences in elemental profiles among locations, particularly when using the intermediate disk portions (25% to 75%) and especially the average of all five sampled portions, providing most effective in geographic discrimination of the trunk. However, several improvements can be made to enhance the clarity, completeness, and impact of the study.

1. Page 1, Line 31-37, the paragraph with the title “0 How to Use This Template” as the part of the template, is the Instructions for authors of Forests and should be removed.
2. Page 2, Line 54-56, as it was presented that “Multi-elemental analysis for origin determination relies on the absorption of chemical elements by an organism, which is directly related to the quantity of these elements in the soil [4]”, in this study these elements in the soil of multiple locations should be related to these in the wood samples of these multiple locations. Moreover, the three analyzed species presented genetic effect and genetic-environment-interaction (GEI) on these elements in their wood samples. It is suggested that the background of soil types across these locations and three analyzed species would be added in the Section 2 Materials and Methods. And the latitude, longitude, altitude of these locations would be also added together in the table.
3. Page 2, in Introduction, it is suggested that the methods based on the chemical analysis of the multi-elemental composition and their application for wood tracing would be mentioned, including the challenges, weaknesses and disadvantage associated with them. It would be imperative that the Introduction provides a concise overview of the substantial advancements made in the domain of multi-element analysis for the purpose of wood determination. Consequently, the number of citations in the literature would exceed twenty, including in these from the past five years.
4. Page 4, Introduction, Line 128-130, “This approach aimed to investigate significant differences and determine which dataset (individual or mean values for each wood portion) provided better origin discrimination.” Consequently, Discussion, Line 280-282, “These findings show that variability in wood elemental composition across species is largely influenced by specific soil characteristics, as environmental elemental abundance helps differentiate the geographic origin of timber species.” Furthermore, Line 302-304, “Moreira et al. [7] stated that such variations highlight specific characteristics within and among individuals that contribute to overall data variability, confirming that both species and wood tissues differ.” As previously mentioned, it could be posited that the variability in wood elemental composition is largely influenced by both the soil characteristics and the analyzed species. However, the present study did not investigate the soil characteristics and undertake a comprehensive analysis of the variation of the analyzed species.
5. As demonstrated in Figure 3-5, the range of the sum of PC1 and PC2 for PCA is from 39.7% (Jatobá, 25% radial portion) to 60.3% (Maçaranduba, 25% radial portion). The basis for selecting the first two principal components for visualization would be the subject for PCA analysis. The selection of the first three principal components for the purpose of judgement would be a preferable option when compared with the selection of the first two principal components. It is recommended to verify this using a rolling stone diagram.
6. It has been observed that some of the expressions employed in the supplementary material have not been translated into English. It is evident that certain texts have been superimposed on the figure.

Author Response

Dear, 

I appreciate the comments. Regarding item 2 of the commentary, the soil classes of the samples were inserted in Section 2 Materials and Methods. The coordinates of the samples are illustrated on the map of the study area, in Figure 1.

Regarding item 3 of the commentary, with all due respect, considering that there is a character limit in the article, i understand that the introduction presents a current overview of the use of multi-element analysis for attribution of geographic origin in a succinct and objective way, citing recent works (from 2020 onwards).

Regarding item 4 of the commentary, the study did not include analysis of soils collected in the sample areas. The association of the wood sample with the soil type in which the tree grew was made using webgis from the Brazilian soil classification system (Pronasolos).
Regarding item 5 of the commentary, the criterion adopted for selecting the PCAs was to provide the best discriminatory information for samples from certain locations, even in cases where the explained variance had a low percentage. Please note that the changes are written in red in the text of the article.

Yours Sincerely,
Marcos David Gusmão Gomes
 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

The concerned mistakes have been corrected. The manuscript is acceptable to proceed further.

Author Response

Dear,

The reviewer stated that "the errors in question have been corrected. The manuscript is ready to proceed." Therefore, there is no need to make any further corrections.

Reviewer 4 Report

Comments and Suggestions for Authors

The references would be update with these related four literature published in past three years.

Author Response

Dear,
To address the reviewer's comment, the following most recent references (from 2023 onward) were included in the introduction: reference 1, line 36; reference 2, line 40; and reference 3, line 53. Since there was already a reference from 2024 (reference 11, Moreira et al.), the author added three more references to meet the reviewer's request.

Added references are written in red. Sincerely,

Marcos David  

Author Response File: Author Response.pdf