Key Community Assembly Processes Switch between Scales in Shaping Beta Diversity in Two Primary Forests, Southwest China

Round 1

Reviewer 1 Report

I consider that the manuscript is important to understand better the relative importance of environmental and dispersal-based processes across spatial scales, life-history stages, and forest types in the community assembly.

The manuscript is in general well written and easy to understand. The Introduction is concise and focus, I like it. The hypotheses and objectives are clear. The results are clear and also the Discussion. The use of literature is correct.

However, methods are to brief in some aspects relative to experimental design and sampling procedure. I miss more information within the manuscript. In my opinion, the reference to literature is not enough to well understand the methodology used in this work.

Figures and tables could be improved, in quality, and in detail to do them self-explanatory.

You can see below some concerns that could be easily solved, and in my opinion, they would help improve the quality of the manuscript.

Specific comments

Abstract

Line 14: please changed “the understanding of” instead of “understanding of”

Introduction

Line 48: please change “within a single biogeographic region” instead of “within single biogeographic regions”

Lines 62-64: Yes, I agree with this sentence: “ontogeny has been found to help separate the consequences of different ecological processes for community structure [20–22]”. But also the ontogenetic stage of the species should be taken into consideration in order to avoid problems during establishment (Torroba et al. 2015; http://dx.doi.org/10.1016/j.ecoleng.2015.01.024) and thus increase the effectiveness of restoration of forest ecosystems.

Lines 78-82: Please homogenize the letter size in accordance with the rest of the manuscript.

Material and methods

Please explain more in-depth the experimental design and sampling, as well as the estimation of topographical variables used in the study for example slope in degrees?

Line 93: Please explain, at least briefly, the sampling protocol to can understand the experimental design at different spatial scales. It is very important to know clearly the experimental design and the sampling procedure at different scales to understand well the analyses of the data.

Line 97: please explain what convexity means.

Line 98: You say that you calculated the mean value for each topographical variables at each 20 × 20 m quadrat [28]”. However, you don’t mention anything about the sampling procedure or experimental design.  How many quadrats of 20x20 m did you take? And many quadrats of 10x10m, 50x50 m or 100x100m did you take. Please explain this in the manuscript, not only making reference to literature.

Lines 98-100: With this information, it is impossible for me to understand the soil sampling procedure, how many soil samples per 20ha plot, at which depth,

Lines 108-109: You say that based on the diameter size distribution of stems, you classify stems in different size classes but what is the size range included in each size class for the BB plot and for the ALS plot? Please explain.

Lines 113-114: Please revise this sentence I miss something to can understand.

Perhaps the word “and” is left-over.

Lines 117-118: Please explain better how you determine the exact location of trees into the sampling plots.

Line 142: You say that you calculated beta diversity both for the observed and simulated communities of each model for each DBH-size class at four different spatial scales (10 × 10 m, 20 × 20 m, 50 × 50 m, 100 × 100 m). However, you don’t mention previously in the manuscript at which different spatial scales you are going to work.

Line 146: You say “averaging the beta diversity of 100 simulated communities”, but from which become this number (100). For me it is impossible to understand without a previously good description of the experimental design and sampling. Please explain well before all necessary to can understand this number (100) at this point in the text.

Lines 154-158: Please correct the different letter sizes and line spacing.

Figure 1: Perhaps you can add some details for a better understanding of the figure, such as the abbreviation of Bubeng plot (BB) next to the name at the top of the figure, as well as to indicate that the four columns of graphs refer to life stages, and the row of graphs refers to spatial scales. Also, you can add in the legend the abbreviations used for the different models used. All of this can facilitate the interpretation of the figure.

The same comments for figure 2.

Also, perhaps the quality of figures 1 and 2 would be improved.

Table 2: Perhaps you can include the abbreviations of the four models in the first row of the table and in the table caption a brief description of the four models as you do in 119-122. In this way table 1 would be self-explanatory.

Discussion:

Line 208-209: It would be helpful to add the abbreviation of the model behind the explanation of what measures, for example: “Our results showed that the joint-effect of dispersal limitation and environment (IT model) produced good estimation…”, and to do the same latter in the discussion when other models are mention, e.g. Line 210: “while dispersal limitation alone (HT)…”

Appendix S2: Ecological process model

Please, use the abbreviations of the four models when describing, this helps to identify them easily.

Figures S3-S6: it is difficult for me to see the dotted lines of confidence intervals.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

This study (forest-948690) analyzed beta diversity patterns of tree species in two large forest plots in China, and examined the relative importance of community assembly processes (habitat filtering and dispersal limitation) among spatial scales, life stages, and forest types. The authors used different types of spatial point process model to reproduce species distributions under the influence of ecological processes, and then compared the observed beta diversity with the simulated patterns. The results suggest that the predominant community assembly processes change along spatial scales.

The research questions are clear and the manuscript is generally written well. On the other hand, I wasn’t convinced very well about conclusions. It could be sophisticated more by clarifying the links with the results. Also, there are some unclear points about the analyses, which should be clarified before publication. My specific comments were listed below. I hope those will be a help.

How the conclusions are supported by the results is not well explained. I don’t mean I’m against these conclusions, but do believe stronger arguments would be needed to make the conclusions convincing. The first conclusion says “dispersal alone and in concert with environment shapes beta diversity, respectively, at large and small spatial scales”. However, the observed distance-to-dissimilarity patterns show deviations from the simulated ones (Fig. 1 and 2), while the difference between the observation and simulations is variable depending on spatial distance. Although your conclusion may be right, others might draw a different conclusion from these patterns. For the second conclusion about life stages, it is difficult to judge whether the dissimilarity patterns are same (or similar). At least, there are some difference in the shape of curve between the small and large classes in ALS plots at 10 x 10 m level: dissimilarity saturated at about 200 m and even decreased thereafter in the small class, while it kept increasing in the large class. The third conclusion about forest types is difficult to be supported by the current study setting: a single plot for each forest type. I would avoid the generalized conclusion about forest type.

I’m not an expert of spatial point process, and may misunderstand something. But I think the current explanations are unclear and bit confusing. I can understand AIC was used to evaluate how well point process models explain spatial distributions of each species. But, I’m not sure how AIC can be used to evaluate how well the point process models represent the observed beta diversity patterns. More detailed explanation would be needed. In addition, if the point process models were fitted to each species as described at page 5, AIC was computed for each species. However, a single AIC value per model is listed in Table 1. I’m wondering whether the authors averaged the AICs for species, or the models were fitted to all individuals for all species.

According to the results, this study didn’t find the evidence for changes in ecological processes among life stages. Meanwhile, in another study in the same sites (Asefa et al. 2020 doi.org/10.1111/jvs.12819), the authors have reached another conclusion: the ecological processes associated with community assembly were influenced by life stages. I can understand it could be happened when analyzing community assembly by different approaches. I guess the authors could have a good discussion about why the contradictory conclusions were reached between the studies and how these can be reconciled.

 

Minor comments

- Lines 146-149: the explanation here is duplicated with the next section (2.6 Goodness-of-fit of the models).

- Lines 165-167: it is unclear which figures or table correspond to this sentence.

- Line 172: some explanations would be needed for the p-value (where is it from?)

- Line 242: But the citation [14] says that ecological processes can change among life stages.

- References: Yuan et al. 2011 is listed twice: [26] and [39]

- Figure 1: “Observed” may be better rather than “Real” for consistency.

- Figure 1: I’d use the DBH class name consistently: “Small” and “Large” instead of “Lower” and “Higher” as Fig. 2

- Table 1: it is difficult to understand where we should see: using asterisks or boldfaces would be helpful.

- Fig. S1: what is the third (northernmost) red point?

- Fig. S1: the tick-mark labels (“100” and “200”) on the scale-bar are touched each other.

- Finally, I’m just curious about how species interactions can be interpreted in your approach. Is that involved in habitat filtering process? Or reflected in dispersal limitation? Other readers may also be interested in this topic. Therefore, it would be great if the authors could add some arguments on this.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 3 Report

This is a very interesting manuscript with very relevant data and results. I added some minor comments for improvement.

 

• The abstract needs to include at least a sentence with the analytical methods used.
• The text between lines 82 and 87 (last sentence of Introduction belongs to the Material and methods section
• The Bray-Curtis dissimilarity is one of the most well-known ways of quantifying the difference between samples, but it does not satisfy the triangle inequality axiom. The variation in species composition among sites, or beta diversity, can be decomposed into replacement (true beta) and richness differences. A debate is ongoing in the literature concerning the best ways of computing and interpreting these indices. The authors in the introduction should mention the possibility of partitioning the components of beta diversity (Carvalho et al., 2013; Legendre, 2014). Indeed, these indices can help researchers understand different aspects of ecosystem functioning even putting some of results in Supplementary materials. Alternatively, in the Methods explain better the merits of using Bray-Curtis dissimilarity.

 

 

Some detailed corrections:

-In Abstract there is a space problem in

“ Abstract :Environmental…” that should be “ Abstract: Environmental”

-In Lines 78-82 text is in a different size letter. The same problem seems to occur in lines 154-159

-The size of text in References is different from remaining text

 

 

References

Carvalho, J.C., et al. (2013). Measuring fractions of beta diversity and their relationships to nestedness: a theoretical and empirical comparison of novel approaches. Oikos, 122: 825–834.

Legendre, P. (2014). Interpreting the replacement and richness difference components of beta diversity. Global Ecology and Biogeography, 23(11), 1324-1334.

 

Author Response

Please see the attachment

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

I thank the author's efforts to reply to my previous comments. Now, I understand this study conducted two types of analysis: species level and community level. I had confused these two viewpoints. The author's response letter solved my confusion. But, in the manuscript, the two viewpoints (species/community levels) are not explicitly stated and not distinguished well. It may be better to explicitly state this at the end of Introduction or somewhere in Methods: e.g. "We analyzed ecological processes both species and community levels. At species levels, we carried out xxxanalysis... At community level, we carried out ###analysis". Such explicit explanations would be helpful for readers (like me!).

I'm fine for the other parts of the manuscript.

 

 

Author Response

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Author Response File: Author Response.docx