Early Selection of Tree Species for Regeneration in Degraded Woodland of Southeastern Congo Basin
, Michel Mpundu Mubemba Mulambi 3, Emery Kasongo Lenge Mukonzo 4, Mylor Ngoy Shutcha 3, Honoré Tekeu 1,5, Alphonse Kalambulwa Nkombe 3 and Damase Khasa 1,2,*Round 1
Reviewer 1 Report
This manuscript is within the scope of the journal and represents research important to reforestation. It is generally well-written and appropriately organized. The approach, experimental design (RCBD), and statistical analyses are adequate and appropriate. Seed handling, preparation, and storage are adequate for the study. There are numerous minor spelling and grammatical errors that need to be corrected prior to publication, but I feel that the overall quality of the data and the manuscript are good and recommend publication with minor revisions.
I am unfamiliar with Miombo woodland, and therefore cannot comment on the appropriateness of the species selected for inclusion in this study (Table 2). Brachystegia appears to be over-represented, but that may be representative of the area and I am happy to defer to the authors expertise on this issue. In any event, the three species recommended for planting based on biomass represent three genera, two from the pioneer early succession group and one from the late succession group, which seems appropriate to reforestation.
For future research, I would suggest refrigerated storage of seed if available, because germination rate will decreased rapidly when seed is stored at room temperature. Also, germination and survival in the field will be enhanced by a combined fungicide-insecticide seed treatment, if available, just prior to planting (seed germination will decrease if seed is treated and then stored).
The following specific items should be addressed.
Line 48: Rewrite: km2 is not a rate. Should be “estimated rate of 89 km2 / year” or other appropriate wording.
Line 56: Rewrite: “To conserve biodiversity and sustain multiple uses of local species”
Lines 71 – 79: This section should be re-organized/rewritten. The question (lines 75 – 77) is positioned as the main driver of this research, but I think that the final sentence in the preceding paragraph (lines 72 – 74) better summarizes the work.
Line 99: What is the soil depth? What is “pH water”? I think you mean just “pH”. We assume you add distilled water to get the reading. Please decimal-align the table. Numbers after the decimal should be consistent, at least within a factor. For example, for sulfur it should be 0.020 +/- 0.001; sand should be 24.00 +/- 1.41 or 24.0 +/- 1.4 might be more appropriate.
Line 147: Use of the term “stem/diameter ratio” is confusing, particularly when both stem and root diameter have been measured. It is really the ratio of the stem height to the stem diameter. The authors may consider changing the term to something like “stem height/diameter ratio”, “stem growth ratio,” or anything that is more clear. Even when terms are defined, it is best practice to make the meaning of the term obvious on its own.
Line 161 (and in Tables/figures): The word “all” should be inserted before the term “pairwise Tukey HSD tests”, or the word “pairwise” should be omitted. As written, it raises questions about whether Tukey was properly used, or manipulated to generate individual pairwise tests, which would not be appropriate and would provide artificially low p-values.
Line 180: I do not understand the sentence beginning “Seedling mortality….” Please rewrite.
Line 193: Survival is said to decrease “due to poor shoot growth.” That belongs in discussion, not results.
Verb forms need to be consistent (e.g. “was” in line 187 but “is” in 189. It should be “was” in both, using past tense to explain the current findings in this study. Present tense should be used when presenting what is known from the literature, e.g., “Trees produce seeds.” Capitalization should be consistent; do not use “p” and “P” both as in line 212. It should be “p”. Also be consistent among Tables. Lower case “ns” is used in line 213, but not in 252.
In scientific writing, please omit extra words that add no meaning. For example, omit “Briefly” (line 157), “In contrast” (line 159), “In comparison” (line 161), and “We have found that” (line 175).
Finally, various minor spelling and grammar errors exist throughout the manuscript. All of these are minor, but should be resolved prior to publication. Examples are given below, but I do not have time to identify them all:
Line 60: missing the word “is” before “used”
Line 61: omit “the” before “growth”
Line 69: change “are” to “is”
Line 96: change “by” to “of”
Line 120: change “as” to “was”
Line 157: change “compounds” to “compound”
Line 182: Change “seedlings number” to “seedling number”
Author Response
Response to reviewer comments, by Kaumbu JMK and al.
Line 48: Rewrite: km2 is not a rate. Should be “estimated rate of 89 km2 / year” or other appropriate wording.
Reply 1: Corrections have been made accordingly in the manuscript: “estimated rate of 89 km2 / year”
Line 56: Rewrite: “To conserve biodiversity and sustain multiple uses of local species”
Reply 2: The sentence has been rewritten as follows “To ensure sustainable use and sustainable management of the Miombo forest resources, local species must be integrated into the reforestation program”
Lines 71 – 79: This section should be re-organized/rewritten. The question (lines 75 – 77) is positioned as the main driver of this research, but I think that the final sentence in the preceding paragraph (lines 72 – 74) better summarizes the work.
Reply 3: the section has been re-organized/rewritten as follows:
In tropical habitats, like cleared and abandoned Miombo woodland, the secondary succession is made by early successional fast-growing species (e.g: Albizia, Combretum and Pterocarpus species), but the later successional species (e.g: Brachystegia and Julbernardia species in Miombo woodland) are sparse [7] and grow slowly as documented by Chidumayo [28].
Our core research question is whether seedlings of pioneer species (Chipya group sensu Lawton [31]), such as P. tinctorius and Combretum collinum Fresen. (weeping bushwillow, English; vaiërende boswilg, Afrikaans) exhibit better development compared to late species (Miombo group)? To answer this question, we evaluated the germination, survival, growth and productivity of seedlings, in a plantation from December 2010 to April 2014, in relation to the successional status (early and late species).
Line 99: What is the soil depth? What is “pH water”? I think you mean just “pH”. We assume you add distilled water to get the reading. Please decimal-align the table. Numbers after the decimal should be consistent, at least within a factor. For example, for sulfur it should be 0.020 +/- 0.001; sand should be 24.00 +/- 1.41 or 24.0 +/- 1.4 might be more appropriate.
Reply 4:
The soil depth is 20 cm ; pH water is a pH soil in a water dilution. The numbers after the decimal were corrected accordingly, with 2 or 3 number after the decimal (e.g: sand = 24.00 ± 1.41 and sulphur = 0.020 ± 0.001. The table 1 legend has been changed for OC: organic carbon, OM: organic matter.
Line 147: Use of the term “stem/diameter ratio” is confusing, particularly when both stem and root diameter have been measured. It is really the ratio of the stem height to the stem diameter. The authors may consider changing the term to something like “stem height/diameter ratio”, “stem growth ratio,” or anything that is more clear. Even when terms are defined, it is best practice to make the meaning of the term obvious on its own.
Reply 5 (line 147): “stem height/stem diameter ratio” is now used as suggested by the Reviewer
Line 161 (and in Tables/figures): The word “all” should be inserted before the term “pairwise Tukey HSD tests”, or the word “pairwise” should be omitted. As written, it raises questions about whether Tukey was properly used, or manipulated to generate individual pairwise tests, which would not be appropriate and would provide artificially low p-values.
Reply 6 (line 161): We have omitted. the word “pairwise”, accordingly
Line 180: I do not understand the sentence beginning “Seedling mortality….” Please rewrite.
Reply 7: Seedling mortality was noted from 60 days forward for all species, except P. tinctorius, the seeds of which germinated up to 75 days after planting
Line 193: Survival is said to decrease “due to poor shoot growth.” That belongs in discussion, not results.
Reply 8: The sentence has been deleted in the results section, accordingly
Verb forms need to be consistent (e.g. “was” in line 187 but “is” in 189. It should be “was” in both, using past tense to explain the current findings in this study. Present tense should be used when presenting what is known from the literature, e.g., “Trees produce seeds.” Capitalization should be consistent; do not use “p” and “P” both as in line 212. It should be “p”. Also be consistent among Tables. Lower case “ns” is used in line 213, but not in 252.
Reply 9: The verb “was” in the past tense is now used in both to explain the current findings in this study. As well, we are using “p” and “ns” throughout the the manuscript.
In scientific writing, please omit extra words that add no meaning. For example, omit “Briefly” (line 157), “In contrast” (line 159), “In comparison” (line 161), and “We have found that” (line 175).
Reply 10: We avoided using extra words that add no meaning throughout the manuscript
Finally, various minor spelling and grammar errors exist throughout the manuscript. All of these are minor, but should be resolved prior to publication. Examples are given below, but I do not have time to identify them all:
Line 60: missing the word “is” before “used”
Reply: Correction has been made, accordingly.
Line 61: omit “the” before “growth”
Reply: Correction has been made, accordingly.
Line 69: change “are” to “is”
Reply: Correction has been made, accordingly.
Line 96: change “by” to “of”
Reply: Correction has been made, accordingly.
Line 120: change “as” to “was”
Reply: Correction has been made, accordingly.
Line 157: change “compounds” to “compound”
Reply: Correction has been made, accordingly.
Line 182: Change “seedlings number” to “seedling number”
Reply: Correction has been made, accordingly.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Your paper, "Early selection of woody species for regeneration in degraded woodland of southeastern Congo Basin," present a well designed and replicated common garden study comparing the survival and growth of 8 different native species.
I think the approach the research is valid and hopefully useful to local foresters looking for native alternatives to exotic species for planting and restoration. The paper fairly well written, easy to understand and easy to follow for the most part. There are some areas that could be improved, particularly providing more context for your study and results in the introduction and discussion that make the contributions of this study clear. The study design was appropriate, it is only unfortunate that you were not able to replicate it at more than one site which limits the conclusions you can draw. You should include a few sentences about the limitations of your conclusions in the discussion. I have also uploaded some specific detailed comments and some minor corrections.
Comments for author File: Comments.pdf
Author Response
Response to the reviewer’s comments, by Kaumbu JMK and al.
Line 73 – 74: I suggest providing some background and explanation on why successional status might be important.
Reply (line 74 – 77): In tropical habitats, like cleared and abandoned Miombo woodland, the secondary succession is made by early successional fast-growing species (e.g: Albizia, Combretum and Pterocarpus species), but the later successional species (e.g: Brachystegia and Julbernardia species in Miombo woodland) are sparse [7] and grow slowly as documented by [28].
Also, you need to be explicit about what the species you are selecting are "best" for. As you note, there are multiple uses for many of the native species.
Reply: The multiple uses for the species used in the present study are listed in table 2 (see line 61)
Line 75-77: Suggest rewording. Maybe, "Our core reserach question is..."
Reply (line 78 -80): Correction have been made in the manuscript, accordingly.
Our core research question is whether seedlings of pioneer species (Chipya group sensu Lawton [31]), such as P. tinctorius and Combretum collinum Fresen. (weeping bushwillow, English; vaiërende boswilg, Afrikaans) exhibit better development compared to late species (Miombo group)? To answer this question, we evaluated the germination, survival, growth and productivity of seedlings, in a plantation from December 2010 to April 2014, in relation to the successional status (early and late species).
Line 93: Stapf
Reply: Hyparrhenia diplandra (Hack.) Stapf. is the scientific latin name and authorities of bush arrow [family Poaceae]
Line 99: What is the soil depth?
Reply: The soil depth is 20 cm
Line 105:
Reply: We used only early and late successional species, which were respectively Chipya (ES) and 105 Miombo (LS), based on functional trait and seed availability.
Line 114: few more words on a random selection procedure
Reply: Correction has been made, accordingly. Seed collection was carried out on 10 trees, selected for their desirable characteristics (e.g: healthy tree, straight stem, seed availability and viability)
Line 117: Did you standardize the number of seeds per individual?
Reply: Yes, we did. The seeds were sorted, and mixed to form a composite sample of 1500 viable seeds per species (150 per individual).
Line 134: Only watered this year?
Reply: In order to obtain a good survival rate and growth, plants were watered during the four-year and only the dry season.
Line 139 - 140: How did you select the seedlings to keep? Did all species in every block have at least three seedling you could keep?
Reply: We selected three vigorous seedlings for all species based on their diameter and height
Line 141: Do you mean competing vegetation?
Reply: We mean, regrowth on thinned seedlings and competing vegetation
Line 157 - 160: Please specify why you log transformed the data. I assume it was to improve normality?
Reply: To validate the statistical model in our data, we log transformed the data because data normality along with homoscedasticity are perquisites for the ANOVA. However, ANOVA is not very sensitive to moderate deviations from normality. Simulation studies, using a variety of non-normal distributions, have shown that the false positive rate is not affected very much by this violation of the assumption (Harwell et al. 1992, Lix et al. 1996).
Line 168: I thought you defined the growth strategy a priori based on previous studies?
Reply: Yes, in the introduction. The previous studies do not address successional status (ES, LS) and growth strategies as determinants of species growth, because tree seedlings slowly growth from seed for typical Miombo species (LS) [30]. At the seedling phase, the biomass allocation in root growth is a main drive of the slow shoot growth, as observed to B. spiciformis and J. paniculata seedling [19].
Line 176: How is this variable defined/measured? Days since planting to emergence?
Reply: This variable was defined by estimating the time (in days) from the planting to emergence.
Line 178: averaged?
Reply: Yes, we mean averaged. Thank you !
Line 180: 60 days forward?
Reply: Yes, we mean “60 days forward”. Thank you !
Line 182: Might be easier for quick interpretation to have this as percent? Since you planted 100-seeds, you don't even have to change the axis, just the label.
Reply: Correction has been made, accordingly. We made the change y-label, as Percent of seedlings
Line 193 - 194: Do you think this was competition induced? Your plots were quite small.
Reply: Indeed, because of the small plots the competition effect cannot be ruled out. However, we can say with evidence that herbivory by insects played a major role.
Line 195: Your site description was quite good, but I can't recall anything about dormancy. I assume that these plants will all grow year round? You should specify earlier.
Reply: Yes the plants will all grow year round in this warm temperate climate CW according to Köppen's classification with distinct dry season from March to September
Line 196: Shrubs, trees, or both? This should be clarified earlier in species selection.
Reply: All the woody species tested are trees according to Raunkiaer's life-form classification. Trees and shrubs belong to Phanerophytes with the difference that a shrub is a woody, perennial plant with a mature height of between one and a half and 12 feet but some exceptions can reach 20 feet or more and larger than 12 feet is a tree.
Line 219 – 222: This is confusing and needs re-written. The significance of these correlations in context of your study questions are hopefully discussed later.
Reply: Correction has been made in the manuscript as follows:
In Figure 3, the increase in variation (CV) in height was positively correlated with the variation in diameter for all species (Spearman’s rank correlation: rs = 0.738, n = 16, p = 0,02). The great variation was observed between 2 and 4 years for all species (CV = 100.4% and 71.1% for height and diameter, respectively). It was average between species for the same year 2 (CV = 66.9 and 40.2%) and 4 year (CV = 69.3 and 40.1%) for height and diameter, respectively.
Line 223 (figure 3): Maybe some color coding or grouping with boxes and/or labels to segregate the LS and ES species?
Reply: Correction has been made, accordingly. The coding of boxplot and the x-axis label have been modified
Line 256 – 257: Should probably qualify "early growth"
Reply: yes, we agree. ES have early growth (shoot and productivity) compared to LS, as reported for four tropical tree species (2 ES and 2 LS) from India
Line 258 - 261: need a period. You should bring in more discussion from the literature and ES and LS strategies of plants around the world. Do your results fit expectations or defy them based on previous research? Why? Your root observations are interesting and could use more context.
Reply: The section is discussed by integrating the results of two other studies, in India and another one with two Miombo tree species.
Line 266: Be more specific. Do they have similar survival?
Reply: Our results agree with other studies for J. globiflora (> 85%) [37], B. spiciformis (85%), J. paniculata (68%) [19], B. utilis, B. bussei. B. microphylla and J. globiflora (> 80%) [25].
Line 285 – 288: Do you think it could have been competition? Did you see evidence of herbivory in the field?
Reply: Competition cannot be ruled out. However, we can say with evidence that it is due to herbivory by insects.
Line 297 – 299: I think you need to provide more explanation for why you think there is a trade-off between being adapted to regenerating form stump sprouts and survival from seed.
Reply: Yes, our data explain less the relationship between survival and sprouting ability of J. paniculate stumps. The following explanation was adopted:
The low survival of seedlings can be explained by a low growth (height, diameter of the stem and root, Figure A2) positively correlated with survival (Table A1). Seedling did not accumulate considerable biomass in terms of height and diameter to resist desiccation in September 2011 (end of dry season), as reported by Chidumayo [19].
Line 312 – 315: Can you find anything in the literature that suggests how these two allocation strategies relate to development?
Reply: The ES species allocate the biomass to growth in diameter and length of the root, while the LS invest their biomass more in terms of root length which would explain a slow shoot growth during the development of the seedlings, as observed in Miombo seedlings trees (B. spiciformis and J. paniculata [19]). However, for 66 tree species of temperate forest, specific length of the root and root diameter were not clearly related to growth rate [45]. The relationship between stem growth and root traits requires more data and remains an open question for future research.
Line 318 – 319: This needs a little more explanation.
Reply: This study also reveals the low growth rate of LS species (in the genera Brachystegia and Julbernardia) compared to ES, due to low stem height/root length ratio, in the first growth phase, for all Miombo species (LS). Chidumayo [19] reports high allocation of biomass to roots growth during seedling development of Miombo species, in agreement with our findings.
Line 329: slow initial growth?
Reply: yes, we agree. Thank you
Line 344: metre
Reply: yes, meter
Line 353: greater growth
Reply: yes, Correction has been made, accordingly.
Author Response File: 
Author Response.docx
