Review Reports

Round 1

Reviewer 1 Report

It is a good sound paper that looks at numerous dimensional and other wood quality traits as a function of initial planting density as related to tree parentage.  It is not an enormous study from a sample perspective, but experimental design and findings are sound and the results are relevant.  So many papers focus on height, diameter, and stem volume without looking at the factors that impact utility of the fiber for product use.  They authors are correct in saying that research on "older" stands/stems is somewhat lacking, yet important.  "Older" of course is a relative term depending on typical rotation length and these are short-rotation trees.  The authors acknowledge that a grower or end-product user should approach the question "How densely should I plant these Chinese white poplars?" as an optimization question.  They state so in lines 332 and 333.  I would like to see them state that in the conclusions section in addition as it is a great summary point that can be gleaned from their results.

 

Author Response

Please see the attachment.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Summary of study

Authors analyzed the effects of planting density on various attributes (diameter, height, stem volume, wood density and fiber length of trees and compared the density effects on four hybrid clones of Populaus tomentosa in northern China. The experiment design applied is a two-factor complete block design, with three blocks replicates. Statistical analysis used in the study is analysis of variance. Authors found that with decreased planning density, there were significantly increased tree and stand attributes, except wood density and fiber length, which were not significantly affected by density manipulation.

General comments

Manuscript is written generally well, and regardless of the study methods used, which is not robust enough to be different from the previously published ones. Authors did not show the substantial advancement of existing knowledge, especially in the methodology, on the subject under consideration, as there have been similar studies carried out in the past, many of which are also cited in this manuscript. It is not clear whether clones used in the study have identical site and environmental factors existing in all the four studied clonal stands. As these factors have prominent effects on the tree attributes growth (diameter, height, volume, etc.), wood density, and wood fiber length, one should consider them in the analyses. Another thing, comparisons of stand density effects on the attributes should be made against any reliable standard or benchmark (e.g. site index, which is a good measure of site quality of the clonal stands). This may be estimated easily and expressed as a total height at any reference age for each clonal stand. Site index may be different for different clonal stands, and consequently, tree attributes growth should be different even if there are the same stand densities (number of individuals per unit area). In addition, there could be interaction effects of stand density and site index on the tree attributes growth, which has to be taken into account while investigating on the subject under consideration. Here, in the authors study, they considered only stand density, but disregarded site index and comparison was made without assuming any standard or benchmark.  Authors might have assumed site index class of each clonal stand was the same, which may not hold, as each stand could have different site qualities and tree growing environment. Most importantly, site index should be taken into account while studying the stand density effects on the tree growth attributes. If the authors compare the stand density effects for each estimated site index class of the clonal stands, study will be innovative, interesting and useful to the international audiences. Otherwise, the current study does not provide new knowledge to the international audience on the subject under consideration. The international readers of the journal could be attracted if the authors applied some scientifically robust methods, which are different from the previously published ones.  

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Strong improvements. clarifications are needed:

1) Make main results sound more innovative/ less trivial and also not controversial (l.25-28). Does density reduces yield or not?

2) Does genetical identity (table 1) affect the dependent variables here or not? Clarify

3) Is such an extensively descriptive table like table 2 really necessary?

4) Table 5 does not support the results at all (BWD appears to be quite insignificant to growth traits). 

5) Table 4 is also only descriptive and also does not seem to support the results

6) What kind of variables are "Clone" and "Clone × Initial planting density"? How were they quantified in table3?

7) How generalizable or limited are the results of the particular research design and sample? Such points (possible limitations) would be of importance in the conclusions.

The authors may take one more chance considering the comments above. 

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

Dear Authors, thanks for making the things more clear. As you clarified that all studied clones have grown at the identical site (Forest Tree Nursery) over the same growth period and guard rows were planted around the entire perimeter to reduce edge edge effects, no need to make the evaluation of site quality effects on the plant growth. This information has to be provided in the manuscript. Then manuscript become suitable for publication. 

Reviewer 3 Report

it is drastically improved