Biomass Models and Ecosystem Carbon Density: A Case Study of Two Coniferous Forest in Northern Hunan, China
Round 1
Reviewer 1 Report
General comments
The purpose of this study was to construct biomass models and to compare de carbon density accumulated in four 19-year-old forests of two tree species (P. elliottii and C. lanceolata) in Northern Hunan (China). The subject of the paper is interesting, and the authors have made an important sampling effort. In general, this is a well written paper. Materials and methods are sound, but the biomass equations considered for analysis must be reconsidered. Discussion and conclusions are coherent with the results obtained although discussion must be revised. I am not able to appreciate the English grammar, but the manuscript is in general well understandable. However, for the reasons I cite below, the text must undergo what I consider major revision.
From my point of view, the paper present two main concerns: i) the biomass models and ii) the biomass or carbon density comparison framework. In relation to the first, authors fit specific biomass models to more accurately estimate the biomass. This is right, but since only four 19-year-old stands of each species are used to fit the models, they only can apply to these stands. Moreover, authors measured in the eight stands DBH, but not total height. Therefore, one cannot apply models depending on both variables. So, ¿why do the authors fit models dependent on DBH and H if later they are only going to use those dependent on DBH? Models depending on both DBH and H will be useful for other researchers if they had been considered more combination of age, plantation densities and site qualities in the data collection. Therefore, the authors should have tested more model formulations only dependent on DBH since they are the only ones applicable to the measured forest stands.
Regarding the second concern; as the authors knows, for a certain species or genotype, stand biomass growth depends on: i) stand age, ii) stand density, iii) site quality and iv) silvicultural treatments. So, in the discussion section (points 4.2 and 4.4) values ​​for age and stand density (and site quality if it is known) should be included when discussing the biomass and carbon values ​​obtained in this work in comparison with those found in other works (e.g., lines 342-347).
Specific Comments
Title
Since two forest plantations with the same age and specific plantation density ranges are analyzed, I recommend changing the current title to “Biomass models and ecosystem carbon density. A case study of two coniferous forest in Northern Hunan, China”
Introduction
I believe that the objective of this work should be the comparison of aerial and underground carbon density in each of the two types of forests, but not the fitting of biomass equations. This is a necessary step, but the same as soil carbon sampling. I understand that it is an instrumental aspect (necessary step of the work) but it should not be an objective.
Material and methods
Authors should be considered biomass equation formulations only depending on DBH.
Table 1: please provide the site quality of the stands if it is known and also the silvicultural treatments that have been carried out up to that time in the stands.
Author Response
Dear Reviewer (Professor),
Thanks for your insightful comments. We are impressed by your reviews extremely. Your suggestions are extremely valuable for improving this paper. We read your comments one by one and revised in the manuscript. The following is the process of modification.
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The paper brings currently highly demanded information about biomass and carbon modeling on the example of two selected tree species (representative of one coniferous and one deciduous tree species) from a selected region of China. I consider it important to constantly bring always new knowledge in this area from different regions around the world. I consider the presented models of biomass determination for selected trees to be very important.
I consider the problem to be the fact that the authors did not use the template for the Forests Journal, did not follow the required instructions of the journal, which should be self-evident when delivering the manuscript. I recommend authors go through the entire manuscript in detail and meet all MDPI requirements.
However, I find the content of the post to be good. Abstract meets the requirements,chapter Introduction is adequate (problem is mentioned required numbering references instead of current text). The methods used are appropriate, the results corresponding. The discussion is appropriate (again, I draw attention to the formal shortcomings in the requested adjustment). The number of references is by my Opinion above standard.
In Table 1 there are suspiciously low standard deviation values - please also indicate relative values - are they really such low numbers (2-3% by density, 5% by DBH)?!
The use of shrub and herb biomass measurement is not quite obvious in the methodology. According to the above methodology, it is more about determining the carbon ratio, not the determination of biomass itself (necessary collection of all biomass per unit area – please specify)
I recommend editing (mainly formal editing of the text) and commenting on my comments.
Author Response
Dear Reviewer (Professor),
Thanks for your insightful comments. Your suggestions are extremely valuable for improving this paper. We read your suggestions one by one and revised in the manuscript. We will also explain some contents that cannot be revised for the time being.
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The manuscript presents the study of carbon content in two forest plantations in subtropical region. The sample size are too small to have substantial and reliable results. The employed methods are appropriate but models and conclusions are too ambigious considering the sample size. The discussion could be better written. However, there is an intererest to the results of such study in the scientific community.
Author Response
Dear Reviewer (Professor),
Thanks for your insightful comments. Your suggestions are extremely valuable for improving this paper. We read your suggestions one by one and revised in the manuscript. We will also explain some contents that cannot be revised for the time being.
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
The authors have implemented the suggested changes and/or have adequately refuted those not made. Therefore, I consider the article in its current format suitable for publication in Forest.
Reviewer 3 Report
Thank you, the manuscript is much better now, I suggest to accept the manuscript in the journal "Forests".
