Review Reports - Assessing Forest Degradation in the Congo Basin: The Need to Broaden the Focus from Logging to Small-Scale Agriculture (A Systematic Review)

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Excellent paper, reads well and very relevant topic. I found it difficult to find the sources in the paper of the findings in the abstract "Shifting agriculture emerged as the most significant driver, accounting for 50–75% of canopy opening, 75–85% of surface carbon loss, and 3–50% of tree species diversity loss over a 5–60 years period." but eventually understood this is displayed in Figure 2. This made me understand the canopy opening quote is based on 3 studies but I wasn't able to retrieve which 3 studies, perhaps I missed this but the paper would benefit from making this link to the sources clearer. Would be interesting also to compare against national estimates (e.g. Rep of Congo FREL) The focus on logging in studies could be because the data is useful for management plans, ie there may be a commercial drive behind. Please spell out UAV.

Author Response


We sincerely thank you for the time you spent reviewing our manuscript. We also appreciate your constructive comments on our manuscript. We have incorporated the improvements into the final version of our manuscript. Please find below our responses to the various comments and suggestions.

I found it difficult to find the sources in the paper of the findings in the abstract "Shifting agriculture emerged as the most significant driver, accounting for 50–75% of canopy opening, 75–85% of surface carbon loss, and 3–50% of tree species diversity loss over a 5–60 years period." but eventually understood this is displayed in Figure 2. This made me understand the canopy opening quote is based on 3 studies, but I wasn't able to retrieve which 3 studies, perhaps I missed this but the paper would benefit from making this link to the sources clearer.

Response: In the new version, we have added the reference sources in Table 4 (line 466), which replaces Figure 2. Table 4 facilitates interpretation of the results with the following columns: sample size (n), mean, standard deviation (SD), minimum value, median, maximum value and References. The results in the summary of the new version are adapted using mean values ± SD (lines 18-21) instead of the approximate values of Q1-Q3.

Would be interesting also to compare against national estimates (e.g. Rep of Congo FREL)

Response: We have, of course, exploited certain national reports on the REDD+ process (lines 57-60) demonstrating a lack of consensus at regional level on the definition of forest degradation. Many of these reports are also particularly literature-based. For this reason, we preferred to compare results directly from recent original articles.

The focus on logging in studies could be because the data is useful for management plans, ie there may be a commercial drive behind.

Response: Yes indeed, in the new version, we're thinking of emphasizing this differently in section 1 and 3.2.1 (lines 38-40; 208-209; 212-216).

Please spell out UAV.

Response: In the new version, we spell out the word UAV where it first appears in the text on line 400.

Reviewer 2 Report

Comments and Suggestions for Authors

Assessing Forest Degradation in the Congo Basin: the need for 2 a shift of focus from logging to small-scale agriculture (A Sys-3 tematic Review)

Manuscript ID forests-3649474

Reviewer 1:

Comment 1: Abstract: line 17 only includes anthropogenic causes of deforestation

Comment 2: Line 26 , why only for short period 0-5 years? Please provide reason

Comment 3: Knidly include GIS map of study area

Comment 4: The collection of non timber forest products , line 291 unsustainable harvesting techniques leads towards what?............. means forest pathogens attack or any other reason

Comment 5: line 302 is excellent, the relationship between regeneration and harvesting

Comment 6: Hunting: line 307 empty forests a very good point , However, our results demonstrate that studies on forest degradation related to hunting 318 represent only about 8% of the studies reviewed .

Yes, very less studies are reported on hunting

Comment 7: line 334 , the field of land scape ecology is good point

Comment 8: canopy opening : how its happening in Congo Basin?

Comment 9: all the 23 indicators are very good chosen, In addition to these , more indicators may be or not?

Comment 10: over all quality of review article is good

Comments for author File: Comments.pdf

Author Response

We sincerely thank you for the time you spent reviewing our manuscript. We also appreciate your constructive comments on our manuscript. We have incorporated the improvements into the final version of our manuscript. Please find below our responses to the various comments and suggestions.

Comment 1: Abstract: line 17 only includes anthropogenic causes of deforestation

Response: Yes, the study included only the anthropogenic causes of forest degradation identified in previous reviews, with the aim of assessing methods for monitoring them and their respective magnitudes.

Comment 2: Line 26, why only for short period 0-5 years? Please provide reason

Response: This short monitoring period mainly concerns the assessment of canopy opening as presented in the new version in figure 4. Some reasons for short-term monitoring of this indicator are given in lines 392-395.

Comment 3: Knidly include GIS map of study area

Response: In the new version, Figure 1, a GIS map, presents the study area.

Comment 4: The collection of non timber forest products , line 291 unsustainable harvesting techniques leads towards what?............. means forest pathogens attack or any other reason

Response: In the new version, we specify that these are “host species or providers of high-value NTFPs” (lines 305-307).

Comment 5: line 302 is excellent, the relationship between regeneration and harvesting

You're welcome

Comment 6: Hunting: line 307 empty forests a very good point, However, our results demonstrate that studies on forest degradation related to hunting 318 represent only about 8% of the studies reviewed.

Yes, very less studies are reported on hunting

Yes, indeed!

Comment 7: line 334, the field of land scape ecology is good point

You're welcome

Comment 8: canopy opening : how its happening in Congo Basin?

Response: We're not sure we understand the question. Nevertheless, openings in the forest canopy are generally created by the fall of trees because of anthropogenic or natural disturbance. However, the configuration of these openings can vary according to the type of disturbance. According to Molinario et al. (Ref.185) and Shapiro et al. (Ref 46) in the case of shifting cultivation, these canopy openings take the form of “isolated forest perforations” (IFPs) within a rural complex.

Comment 9: all the 23 indicators are very good chosen, In addition to these , more indicators may be or not?

Response: We believe that this list is not exhaustive, but the indicators listed in Table 3 are those identified in the short-list of articles analyzed for the context of the Congo Basin region

Comment 10: over all quality of review article is good

You're welcome

Reviewer 3 Report

Comments and Suggestions for Authors

Dear Authors! I with interest read your Review manuscript entitled: “Assessing Forest Degradation in the Congo Basin: the need for a shift of focus from logging to small-scale agriculture (A Systematic Review)”. The topic of article is actual (because studying forest degradation is important for ecosystem conservation, maintaining biodiversity and sustainable development) and fits to Forests journal scope; also it’s suitable for consideration in other MDPI journals like Sustainability, Applied science, etc. At almost the article written in good manner and structure, however I have some comments and suggestions.

I suggest to add the forest or land use map for Congo Basin. How many forest cover of Congo Basin in % and area. Probably need indicate where the Congo Basin located, and provide some short climate and soil characteristics.
Table 1. The citation should be provided as [] not like Murdiyarso et al. (2008), etc.
104. The selection of articles in Scopus and Google Scholar were not limited by date of publication? I mean you not choose a period like 1950-2024?
165. human abstract? Manually?
Table 2. Is a (Appendix A1) or not? L. 220.
It would be nice to make a graph or show in a table what a share or percentage of each factor (for example, logging, fire) contributes to the overall degradation in Congo Basin.
275. 3.2.5. Anthropogenic fires section. What about natural fires? How often it happens? Need to add this information. Another point, you know that after forest fires the soil became more suitable for erosion. Soil erosion is one factor of forest soil degradation, as well lead to change of soil properties. Please mention about it, you could see the following articles (Insect outbreak and long-term post-fire effects on soil erosion in mediterranean suburban forest; The Influence of Ground Fires on the Properties and Erosion of Forest Soils in the Southern Urals (Bashkir State Nature Reserve; Long-term fire effects on vegetation and topsoil properties in beech forests of Manjaca Mountain (western Bosnia and Herzegovina)).
Why you not considered a forest contamination (by any pollutants) as degradation factor? Probably some anthropogenic pollution is occurring in Congo Basin.
361. Lidar should be LiDAR. As well L. 395 and 396.
379. (De Wasseige and Defourny 2004, Bourbier et al. 2013; Hirschmugl et al. 2014). Please cite according to the journal rules.
409. See previous comment.
530-539. I suggest to compare recovery rates of reforestation also with some other part of planet (Trends in forest depletion, seed supply, and reforestation in Canada during the past four decades; Dynamics of Biomass and Carbon Stocks during Reforestation on Abandoned Agricultural Lands in Southern Ural Region; The evolution of reforestation in Brazil).
Please prepare references according to MDPI journal rules.

Author Response

I suggest to add the forest or land use map for Congo Basin. How many forest cover of Congo Basin in % and area. Probably need indicate where the Congo Basin located, and provide some short climate and soil characteristics.

Response: Given that our study is a literature review following the method described, the methods for producing land use and land cover deviate from it. Nevertheless, In the new version, Figure 1, a GIS map, present the study area indicate where the Congo Basin located whit a background showing the vegetation cover.

Table 1. The citation should be provided as [] not like Murdiyarso et al. (2008), etc.

Response: In the new version, we have adapted the references citation according to MDPI journal rules.

104. The selection of articles in Scopus and Google Scholar were not limited by date of publication? I mean you not choose a period like 1950-2024?

Response: The problem of forest degradation is a recent topic in scientific research. This is why we have chosen the period 2000-2024 as specified in lines 86. In the new version we have added a paragraph and a figure (Figure 3) showing the historical evolution of the number of publications analyzed by year and by country (lines 174-185).

165. human abstract? Manually?

Response: yes, human is referring to manually. In the new version, This is now precise as” human or manually” (lines 168).

Table 2. Is a (Appendix A1) or not? L. 220.

Response: Not to be considered as an appendix. This has been removed from the new version (lines 234-235)

It would be nice to make a graph or show in a table what a share or percentage of each factor (for example, logging, fire) contributes to the overall degradation in Congo Basin.

Response: As our study is a review of the literature following the method described, the results presented are based in limited data from studies carried out at different spatio-temporal scales. For that, an upscaling could not be possible. However, by comparing the variation of the most measured indicators, we believe that Table 4 and Figure 5 attempt to address this concern. In addition, we argue that distinguishing the respective impact of forest degradation factors remains a challenge in this field of study (lines 469-484).

275. 3.2.5. Anthropogenic fires section. What about natural fires? How often it happens? Need to add this information. Another point, you know that after forest fires the soil became more suitable for erosion. Soil erosion is one factor of forest soil degradation, as well lead to change of soil properties. Please mention about it, you could see the following articles (Insect outbreak and long-term post-fire effects on soil erosion in mediterranean suburban forest; The Influence of Ground Fires on the Properties and Erosion of Forest Soils in the Southern Urals (Bashkir State Nature Reserve; Long-term fire effects on vegetation and topsoil properties in beech forests of Manjaca Mountain (western Bosnia and Herzegovina)).

Response: Yes you’re right, but the present study is focused on Anthropogenic factors and dense rain tropical forest of congo basin region. Any articles analyzed have highlighted this concern. Most studies addressed this issue in the context of soil fertility as an indicator of forest land degradation. In the region fires is most associated to small scall agriculture and hinting activities, when it’s uncontrolled is responsible for most ecological problems (lines 291-297).

Why you not considered a forest contamination (by any pollutants) as degradation factor? Probably some anthropogenic pollution is occurring in Congo Basin.

Response: Any articles analyzed have reported this concern in the context of congo basin region.

Lidar should be LiDAR. As well L. 395 and 396.

Response: We have corrected overall in the new version of the document (lines: 376; 409; 411; 420)

379. (De Wasseige and Defourny 2004, Bourbier et al. 2013; Hirschmugl et al. 2014). Please cite according to the journal rules.

Response: In the new version, we have adapted the references citation according to MDPI journal rules.

409. See previous comment.

Response: In the new version, we have adapted the references citation according to MDPI journal rules.

530-539. I suggest to compare recovery rates of reforestation also with some other part of planet (Trends in forest depletion, seed supply, and reforestation in Canada during the past four decades; Dynamics of Biomass and Carbon Stocks during Reforestation on Abandoned Agricultural Lands in Southern Ural Region; The evolution of reforestation in Brazil).

Response: Given that our study focuses on the dense tropical rainforests of the Congo Basin, we chose to compare recovery rates with recent studies conducted in ecologically similar regions, particularly within the tropical forests of the Amazon Basin (Ref. 245)

Please prepare references according to MDPI journal rules.

Response: In the new version, we have adapted the references citation according to MDPI journal rules.