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Thanks for your work in revision; I believe you've addressed reviewers' questions and suggestions fully and appropriately and am pleased to accept the current version of the manuscript.
Most of the reviewers' suggestions and questions are straightforward and should be easily attended to. I would ask you to give particular attention, however, to the second reviewer's request that you clarify how this paper builds from and goes beyond your previous publications from 2013. While reviewers are clear that new material here merits publication, it is important that readers understand how the current manuscript is related to previous publicatioins.
This article developed tree-level and knot-level models based on detailed knot measurements using CT-scan. Simulation of knot growth for different scenarios were also provided. The article is well written. It provides sufficient introduction and background information on how this work is related to and based on, and the methods are well described, and the discussion is appropriate.
The article describes an original work which clearly defines question and methods.
No comments
This article developed tree-level and knot-level models based on detailed knot measurements using CT-scan. Simulation of knot growth for different scenarios were also provided. The article is well written. It provides sufficient introduction and background information on how this work is related to and based on, and the methods are well described, and the discussion is appropriate.
Comments:
1. P7, L4: "from the stem's pith (l)" looks like "l" is pith position. This may confuse readers with "radial position (l)" in P7, L21 and also in P8, L3.
2. P7, L5-6: reword this sentence to make it more clear.
3. P8, L3-4: "x-axis" is not defined in the article. Define the axes, including Z and X. A figure defining the knot parameters in a coordinate system may help understanding.
4. P9, L13: "one of the cardinal directions" -- I believe this refers to "one of the two cardinal directions" in the previous sentence that has been chosen as the reference to measure the angle. Confirm this.
5. P10,L14-15: is the knot diameter measured here the same knot diameter recorded in P7, L3-4? Clarify it.
6. P12,L8-16: Models 2 and 3 use only 2 variables. Are they already the results of the backwards elimination process? Clarify it
7. Did you consider separating ramicorn knots from normal knots in the modelling? Ramicorn knot seems quite common in spruce trees, and they have very different characteristics, especially "trajectory" or insertion angle, from normal knots.
8. You used 75% of the data for fit, and 25% for model evaluation. I may have missed it, but did you report the evaluation results?
Models were developed for predicting branch growth and knot properties of black spruce in Canada. The models were used to test hypothesis on branch autonomy. The study is well designed and documented. The manuscript is logical and fluently written. The results are logical and clearly presented according to the research questions posed. However, the following points caused concern when reading the manuscript.
The authors have already published similar results (Duchateau et al. 2013a, 2013b) based on the same trees as those used in this study. In the previous paper (Duchateau et al. 2013a), it is said that “we aimed to develop models describing knot size and curvature that could be linked with the characteristics of the tree and branch to which they are attached. Models are intended for integration into a tree growth simulation system to quantify the effects of silvicultural treatments on knot morphology and inform future forest management decisions.” That is about the same aim as in the manuscript at hand. The authors should, therefore, explain in detail what was already in the previous paper and what the new contribution of this manuscript is.
The sampling and measurements are relevant for the study. The material and methods are clearly described and the necessary details mainly given (but see the comments below). Based on the description, it would be possible to repeat the study.
Pages 6-10. The details of the measurement approach were already explained in the previous papers (Duchateau et al. 2013a, 2013b). The description could, therefore, be considerably condensed here.
Page 6, Lines 11-12. A total of 41 logs (2.5-m long) were scanned. Thus, on average 10.25 m from each stem was scanned (41 logs * 2.5 m / 10 trees). The average height of the stems was 16.22 m (Table 1), i.e. approximately 6 m from each tree was not scanned, probably the uppermost part of the stem. Because the modelling approach requires annual height and radial increments to be measured along the stem, part of the knot data could not be used. However, the authors only mention the total number of the knots measured, not the share of the usable data. Please, explain in detail.
There is sufficiently new knowledge in the paper to merit its publication. The problems of the branch autonomy theory have already been demonstrated in several previous papers. However, the study is somewhat innovative, and a valuable confirmation of the existing knowledge. Advanced modelling approaches were used, but the new contribution of the manuscript should be demonstrated compared with the previous models.
Page 3, Lines 6-16. The text here is very general in its statements and does not allow a deeper insight in the context of the study. Remove.
Page 7, Lines 1-5. Are terms ‘central axis of a knot’ and ‘geometrical centre of a knot’ synonyms? If yes, stick to only one term, if not explain the terms properly.
Page 11, Lines 9-12. Weiskittel et al. (2011) is definitively not the first paper reporting the effects of stand density on diameter and height increment.
Equations 2 and 3. An error term for individual annual rings (Eq. 2) and years (Eq. 3) is missing.
Page 12, Lines 7-8. The tree level error term was already explained below Eq. 2. Remove the sentence.
Page 13, Lines 1-3. The division into sections is explained below, when describing the models in detail. Remove the sentence.
Page 13, Line 19. Replace ‘could be’ by ‘was’.
Equations 4 and 5. Add a separate tree level random variable. Now, there are only knot and annual ring level variables.
Page 19, Line 23. Do nodal or internodal branches form pseudo-whorls?
Table 1. Define the crown base.
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