Litterfall and Element Return in an Abies faxoniana Forest in Tibet—A Five-Year Study

Round 1

Reviewer 1 Report

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Comments for author File: Comments.pdf

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

 Overall, I found that the paper submitted for review [ID: forests- 1423326;  title "Litterfall and element return of Abies faxoniana in a Tibetan fir forest during five years"]  is interesting. The manuscript provides an analysis of the litterfall  (production; elements; nutrient return) pattern in a subalpine forest.  The topic, in general, is interesting, the data and analysis presented in this paper were interesting too. I think that the article has great scientific potential, but it should be improved. Some of the sections: introduction, methods, discussion, and conclusion need to be thought over,  expansion in some areas, and clarification in others.  

Below is a  list of corrections that should be made:

1. Introduction – Unfortunately, there is no precisely formulated research aim in the paper. Readers in the text (lines 226-231) may assume that the goal was to determine the amount of litter and nutrient return. In my opinion, in a scientific article, the aim of the work should be clearly defined, it is also worth for the authors to put forward at least one hypothesis.
2. Materials & Methods

2.1 Study site

The authors include Figure 1, but there is no reference to this figure in the text. In addition, the authors present in this Figure in detail the distribution of temperature and precipitation in the years 2016-2020, but in further work, they do not refer to climatic conditions. Hence, I have a question what was the purpose of such a detailed presentation of the climatic conditions. I would expect the results to be referenced to various weather conditions, mainly precipitation, in the years of the study.

Regarding Figure 1, I have a comment - please change the description of the OX axis, it is not readable.

2.4. Data analysis

In Line 392 the author wrot- To understand the characteristics of interannual and seasonal pattern litterfall and its components. –

Is it a subsection title or an unfinished sentence? If it is to be a sub-section title, it should be checked. If the authors intended to write a sentence, this should be reformulated.

 Lines 394- 396 – And the litter input of different components was tested by nonparametric test and LSD test (Fig. 2); independent sample T tests and LSD test were used to analyze the litter input in different seasons (Fig. 3); nonparametric test and Kruskal-Wallis test were used to analyze contents…

No information on what non-parametric test was used.

3. Results

In general, this section is  ok, however, some doubts may arise e.g

In lines- 410-411 the author wrote: The litter input tended to be larger in the non-growing season than in the growing season.

I have a question–on what basis did the authors write this? The authors studied the litter in five years, in three years the amount of litter was greater in the non-growing season, and in two years the amount of litter was greater during the growing season.

It would be worth supplementing this section with information on litter in 2018, the more so as the results for this year are different from other years (e.g. the smallest amount of litter, a large share of branches in October.

The caption for Figure 2 is not clear, please explain this part of the caption more precisely: different lowercase letters indicate that there were significant differences in the litter production by different components in a sample(P＜0.05).

In my opinion, the letters in this figure are hardly understandable for the reader, e.g. the letter “a” is used for leaf and branch. And one comment regarding legend,  it would be better to use the terms: leaves; branches; epiphytes.

 

4. Discussion-

In my opinion, this section should be improved. Below are the issues that in my opinion should be included in the discussion

1. Unfortunately, the authors do not explain in the discussion that there is a very large variation in the amount of litter in particular years. For example, in 2018 the amount of litter was about half less than in 2017. There is also no attempt to explain what could have caused such differences.
2. There is no explanation for the large variation in the share of litter accumulated in the non-growing season (around 75% in 2016 and 2017) to less than 50%
3. What factors caused the seasonal dynamics of litter input, seasonal dynamics of inputs of three litterfall components as well as proportions, and production of each litter component? Can it be related to the weather conditions, because you give their detailed characteristics, or were they other factors?
4. In lines 565-567 the authors wrote: “Comparison of the amounts of the litterfall indicated that the litter in the non-growing season generally contributed more than the litter in the growing season.– However, in two years out of five years of observation (2018, 2020), the situation was different. In such a situation, can it be assumed that more accumulates in the non-veterinary period? (Please see my question/doubt in the results section). The authors referred to the study by Fu et al. [41]. However, the quoted study [41] concerns the effect of gaps in the stand on the amount of litter. In the description of the research plot (lines 334-341), the authors did not mention any gaps. These lines contain information about the high degree of crown coverage [“The cover degree of trees is 90%,(line 337)],
5. Next lines 573-576– Because of the unique geographical location of the study area, a large number of fresh leaves and branches were moved to the ground surface by frequent extreme weather events in the growing season, forming green litter and increasing the litter input amount.– This explanation is questionable. The authors did not refer to climatic conditions in their work (despite their presentation in Fig. 1). There is no information on the frequency of extreme events, nor reference to the literature where such information could be found. Therefore, whether in 2018 and 2020 such events were more frequent than in other years?
6. Lines 84-586– The carbon content of litter collected in the growing season was generally higher than that of litter collected in the non-growing season, which is consistent with previous research results– literature is required.
7. Lines 599-600– This result is also consistent with the findings of previous studies, which showed that the amount of litterfall directly affects the element return amount.– literature is required.

5. Conclusions - In my opinion, conclusions should be improved, especially sentence: There were greater litter inputs and returned amounts in the non-growing season than in the growing season, which may have an impact on the vegetation change caused by global change.- Please see my comments for the results and discussion section.

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The authors referred to my comments in the cover letter. Unfortunately, only part of my comments has been taken into account in the revised article. Some parts of the text may still be questionable and/or difficult to understand for the reader. So, in my opinion, the manuscript still needs to be improved. The work has great scientific potential, it is very interesting, but in my opinion, it cannot be published in this version. The weak points in the revision version are in the Discussion and appear to be in the language.  I give detailed comments below. The authors should re-read the work and rethink/re-edit the discussion. So I recommend one more improvement,   I suggest a minor revision.

Below I present a list of my comments on the revised version of the article

Introduction – ok

Study site:   Regarding Figure 1, the authors only partially referred to this comment :

• the description of the OX axis – ok

 unfortunately:

• there is no reference to this figure in the corrected text.
• Editor error in the Figure: “precupitation” – should be precipitation
• different colors of bars representing precipitation, unfortunately I do not understand the idea of ​​such a presentation of precipitation (e.g. purple for the precipitation in May 2016, then for the precipitation in April in 2017, and for the precipitation in February in 2019).

This should be corrected. Different colors weaken the readability of the Figure.

 Data analysis –

I have a question related to Table 1, how did you calculate the correlations between the  Litter Amount and Mean monthly air temperature/ Monthly rainfall? Did you calculate the correlations between all possible pairs of variables?  Is it a coefficient of multiple correlation?

Results

Table 1-  for improvement or clarification, in my opinion, the values ​​given by the authors in this table are not clear to the reader.

What do the authors understand by the term “monthly air temperature/monthly rainfall? What month was taken into account in the calculations? In the years 2016-2020, there were 10 litter inputs in the different seasons 910 values) and  60  values monthly air temperature/60 values monthly rainfall.  

Discussion –

Unfortunately, the authors still do not explain in the discussion why there is a large variation in the amount of litter in particular years. The authors explain this by the differentiation of rainfall in particular years. However, the correlations between the amount of rubbish and climatic factors are statistically insignificant (p> 0.05), and therefore they may be responsible for the differentiation to a rather small extent.

The authors wrote that (lines 235-237)  ‘Fluctuating trends in the amount of annual litter and different precipitation caused this wide range of litter production. With the lowest precipitation, the maximum litter production occurred in 2019 due to the high negative correlation between the annual litter amount and precipitation” -.

What precipitation in 2019  did the authors take into account? Total annual precipitation, precipitation in the growing season, precipitation in non-growing season, or maybe in some month?   

However, in lines 263-283 the author wrote that: “the greater precipitation occurred in the growing season from 2018 to 2020” – but as shown in Figure 1  the precipitation in the growing season in 2019 was low.

I think the authors should rethink the discussion. If the authors want to explain their results by precipitation conditions, they should once again analyze and present in the article correlations between the amount of litter and rainfall, e.g. with the sum of rainfall during the growing season, with the total rainfall during the non-growing season. In the light of the results presented by the authors [no significant correlation between the amount of litter and the total rainfall]- explanation of the differentiation of the amount of litter by precipitation conditions is not correct in my opinion

Perhaps it would be worth showing on the chart, for example, the amount of litter in a given year/season and the amount of rainfall in the corresponding growing / non-growing season - maybe then the explanation of the relationship between the amount of litter and rainfall will be clearer.

 Best regards,

Author Response

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Author Response File: Author Response.pdf