Compressive and Bending Strength Variations in the Properties of Portuguese Clear Oak Wood

Round 1

Reviewer 1 Report

Dear authors

Please check attachment.

Comments for author File: Comments.pdf

Author Response

Please find enclosed the pdf with the answers to your questions.

Thank you.

Author Response File: Author Response.pdf

Reviewer 2 Report

The publication aims to compare the properties of oak obtained from different areas of Portugal. Its primary purpose is to compare MOE, compressive and bending strength. Therefore, the number of samples used for testing is of great concern. The listed properties were determined for individual provenance on ten samples. The number of repetitions is small, considering that the samples came from only one tree. The analysis and discussion of the results are simple; it consists in comparing the results with several publications. It is not explained, for example, why the density of the S1 / P1 samples is so high, while the rest of the parameters are relatively similar.

From Figure 3, the angle of the top plate suggests that the sample planes are not parallel.

Author Response

The samples were collected from three different sites (S1, S2 and S3), a total of twenty trees were harvested. Ten trees from S1, three trees from S2 and seven trees from S3.

Regarding to the observation of figure 3, there is a of a sort of kneecap that, in the face of imperfections in the flatness of the tops of the specimens, adjusts the plates so that the load is carried out along the longitudinal axis of the specimens.

Round 2

Reviewer 2 Report

my previous comments were accepted.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

Dear authors

After reading throughout the paper, the main aim of study is to investigate the effects of locations of tree and positions of the samples cut on the compression and bending strength of oak wood. I think these factors on wood mechanical properties were already known before, not limited to oak, but also other wood species as the references you cited. The only highlight of this paper maybe the oak wood itself and its applications in your country. Besides, there are also some issues in details of presentation of the paper. See Followings.

1) In the Abstract

   Describe the factors and their levels in detail, such as location (1,2,3), and position (1,2).

   In your text” a provenance a significant …….., the other provenance no effects” which one, and why?

   Also the “resistance” is not clear, compression, bending and both?

   “The overall behaviour showed a noticeable correlation between the mechanical properties and density” is a common sence for researchers in this field, bot your result.

2) In the Introduction

  It is not suggested to use “[ ]” as a subject. Use author name or change the expression of this sentence.

 The introduction only focused on the Oak wood, did not provide sufficient background and did not include all relevant references. Other aspects relating to your study, such as compression and bending should be also discussed. And the other factors influencing the mechanical properties should be also added.

 Such as:

  “Vibrational characteristics of four wood species commonly used in wood products”

  “Size effect on the elastic mechanical properties of beech and its application in finite element analysis of wood structures”

3) In the Material and methods

  The information of trees was enough, but the sample size seems to be a nonstandard one, the commonly used one is 20*20*300 mm. The size will seriously affect the mechanical properties. See reference recommended in 2).

  The presentation of equation is not accepted.

  The testing procedure should be added in details including diagram or photos. The load rate and condition should also be added.

  The abbreviation of modulus of elasticity should be MOE.

4) In Results and Discussion section.

  The presentations of tables and figures must be improved.

  For fig. 5,6,7,8, the relationships between density and mechanical properties you studied were known. It is not new findings. Further explanations should be added.

5) In Reference section

 The reference style you used is not consistent with the template of the Forests. Most of citations are old. Please cite references published in the near years.

Author Response

We thank you for your revision that we found constructive. We did our best to incorporate all your revisions directly into the manuscript. We would like to emphasize that all the tests were done following the IPQ standard (1973) NP 619.  

Specifically addressing your question "For fig. 5,6,7,8, the relationships between density and mechanical properties you studied were known. It is not new findings. Further explanations should be added.", we intend to validate the information obtained for the Portuguese clear oak wood with the available in the literature for other oaks wood and relate the results to the different soil types. In this case a finer soil texture led to a more hydric stress which is reflected in the first layers of wood produced showing higher density.

Reviewer 2 Report

what is the age range of the trees used for the study? Is it plantation or natural regeneration stand, any silvicultural histroy of the sites?

The sample size (7 pieces) per radial position and 3 or 7 trees per sites 2 and 3 is very small and any outlier sample will significantly influence the interpretation of the results as evident in the boxplot. what is between tree variation per site?

what is accounting for the difference in properties between the samples from 10% and 90% in the radial positions for S1? Any reasons for the similitude in properties within the trees from sites S2 and S3? what is the wood anatomical variations among the sites?

It is overstretch  to draw any conclusion considering the small number of trees and the samples per site.  

There are several information on oaks including Portuguese oak and this study do not provide anything new to the existing knowledge in it's present form. Additional trees and samples should be tested to improve the quality of the results and the conclusion. 

Author Response

We thank you for your revision that we found constructive. We did our best to incorporate all your revisions directly into the manuscript. We would like to emphasize that all the tests were done following the IPQ standard (1973) NP 619.  

Specifically answering your questions:

"What is the age range of the trees used for the study? Is it plantation or natural regeneration stand, any silvicultural history of the sites?"

There are no data on the silvicultural history of the sites regarding silvicultaural operations over the years. All the sites were natural regeneration.

"The sample size (7 pieces) per radial position and 3 or 7 trees per sites 2 and 3 is very small and any outlier sample will significantly influence the interpretation of the results as evident in the boxplot. What is between tree variation per site?"

The tree variation per site is related to soil composition and growth conditions.

"What is accounting for the difference in properties between the samples from 10% and 90% in the radial positions for S1?"

A different soil composition as compared to Site 2 and Site 3.

"Any reasons for the similitude in properties within the trees from sites S2 and S3?"

In figure 1 it is possible to verify that Site 2 is close to Site 3 and according to EPIC WebGIS Portugal the soil characteristics is almost the same.

"What is the wood anatomical variations among the sites?"

In Site 1 we have a finer soil texture which led to a hydric stress. This site condition is reflected in the first layers of wood produced showing higher density (high proportion of latewood in the growth ring) when we compare to Site 2 and Site 3.

"It is overstretch to draw any conclusion considering the small number of trees and the samples per site.  There are several information on oaks including Portuguese oak and this study do not provide anything new to the existing knowledge in it's present form. Additional trees and samples should be tested to improve the quality of the results and the conclusion."

Although we agree with the reviewer, it is not possible to obtain any more of the same material, in the exact same conditions in order to have no additional disruptive factors contributing for the data analysis.

Reviewer 3 Report

Latin names are usually written in italics. Please change throughout the text.

In the introduction, when citing other authors, please enter the author's name followed by a bibliographic footnote, eg [3].

Fig. 1: if you have already uploaded a map with the presence of oaks, it will be helpful to mark the points from which you took the material for research: S1, S2 and S3. The dark green color is almost invisible on this map.

In formulas or units, please take care of superscripts.

Formulas and symbols written carelessly. There are deficiencies, empty spaces, and inconsistencies in the symbols used.

Line 111: isn't it better to use "distance between supports" instead of "span"?

Lines 121-123: You obtained compression samples from samples damaged in the bend test. Was there no risk of cracks or damage in these samples? Was it not possible to obtain twin material?

In the methodology you wrote that 10 trees from S1 were cut. Were 7 bending samples obtained from 10 trees ?? (tab 1).

Inconsistent use of symbols. First the modulus of elasticity as Em, then MOE. It introduces disorder and chaos.

Figures  2, 3, 4 what are these dots in the chart? The charts present exactly the same data as the table. Mean values and standard deviation. It shouldn't present the same data in two ways. Please add information about the data on the box-and-whisker plot.

Lines 154-156: you wrote: “In other words, these figures represent the influence of pith distance for compressive strength (figure 2), bending strength (figure 3), and modulus of elasticity, MOE (figure 4) to site S1, S2 and S3 considering different locations in the cross-section (position 1 -10% of the radius and position 2 - 90% of the radius).”. This graph shows the variability between sites, it does not show the effect of the distance from the pith on the mechanical parameters.

It was previously written that the density has a positive correlation with the mechanical properties of wood. So why does your oak with such a high density (higher than the other lines: 183-184) have a lower MOE (lines: 173-178)?

The discussion of the results boils down only to the statement that your mechanical performance is similar to those marked on other oaks. However, the density of Portuguese oak is higher than that of others and its mechanical parameters are lower. Why is it like that? Is the structure of Portuguese oak different? Is the chemical composition similar?

In the charts 5,6,7, the coefficient of determination is quite low. Especially for the density-compressive strength relationship. How do you explain that?

The conclusions are far reaching. Out of 20 cut trees, 42 samples were tested. Why such a small number of samples? Were the trees several years old? The conclusions do not conclude with the title of the manuscript.

Author Response

We thank you for your revision that we found constructive. We did our best to incorporate all your revisions directly into the manuscript. We would like to emphasize that all the tests were done following the IPQ standard (1973) NP 619.  

Specific answers to some of your questions:

"Lines 121-123: You obtained compression samples from samples damaged in the bend test. Was there no risk of cracks or damage in these samples? Was it not possible to obtain twin material?"

The samples were examined, and no damage found.

"It was previously written that the density has a positive correlation with the mechanical properties of wood. So why does your oak with such a high density (higher than the other lines: 183-184) have a lower MOE (lines: 173-178)?"

This difference may have a direct relation with the age and site conditions (growth conditions) of the oaks involved in the cited studies (138-214 years) and the oaks used for this study (34-60 years).

"The discussion of the results boils down only to the statement that your mechanical performance is similar to those marked on other oaks. However, the density of Portuguese oak is higher than that of others and its mechanical parameters are lower. Why is it like that? Is the structure of Portuguese oak different? Is the chemical composition similar?"

Differences in chemical composition may account for this fact.

"In the charts 5,6,7, the coefficient of determination is quite low. Especially for the density-compressive strength relationship. How do you explain that?"

This value may be related to the presence of small defects, such as small knots that was found to be present in some samples.

"The conclusions are far reaching. Out of 20 cut trees, 42 samples were tested. Why such a small number of samples?"

Because it is not possible to obtain any more of the same material, in the exact same conditions in order to have no additional disruptive factors contributing for the data analysis.

"Were the trees several years old?"

The Trees ages range from 34 to 60 years.

"The conclusions do not conclude with the title of the manuscript."

We are open to change our manuscript title if necessary.

Round 2

Reviewer 1 Report

Based on responses and corrections of authors, the paper has been much improved. Please double check the editing and gramma. 

Author Response

• Based on responses and corrections of authors, the paper has been much improved. Please double check the editing and gramma. 

  Thank you for your revision. We doubled checked everything.

Reviewer 3 Report

Line 51: something is missing in this sentence.

Lines 77-84: does this have to do with Portuguese oak? Unnecessary, at this point, an interruption.

Line 141: how do you measure sample deflection? On Fig 2 I can’t see any deflectometer.

Equation 3: h is a height of a sample? So in that case 60 mm?

Fig 3: is the tensometer necessary? You didn’t count MOE from compressive test.

In methods standards also have to be cited like publications and recorded in the reference list.

Table 1: you added 3 samples in location 1 for bending and 6 for compression. However, the values have not changed? What is the reason for this?

Figures 4,5 and 6 they contain the same data as table 1. What do the dots on these charts mean that are visible, for example, for S1-P1 in compression?

Line 198: you find significant differences between P1 and P2. However, I can't find the results of the analysis anywhere. It can be noted in Table 1 that such an analysis was carried out and the statistical differences were marked with different letters.

Author Response

Thank you for your revision.

•  Line 51: something is missing in this sentence.

   Added directly in the manuscript.

• Lines 77-84: does this have to do with Portuguese oak? Unnecessary, at this point, an interruption.

    Changed places directly in the manuscript.

• Line 141: how do you measure sample deflection? On Fig 2 I can’t see any deflectometer.

The mechanical testing was carried out using a Shimadzu AG-I universal machine and the  is the slope of the regression line. In this photo we took the deflectometer off in order not to damage the equipment, but it was used in the initial configuration.

• Equation 3: h is a height of a sample? So in that case 60 mm?

Yes.

• Fig 3: is the tensometer necessary? You didn’t count MOE from compressive test.

    We do not use this data in this manuscript, but we have obtained it for database data.

• In methods standards also have to be cited like publications and recorded in the reference list.

    Ok, we add in the reference list.

• Table 1: you added 3 samples in location 1 for bending and 6 for compression. However, the values have not changed? What is the reason for this?

  Because there was a mistake in the table, all values are ok.

• Figures 4,5 and 6 they contain the same data as table 1. What do the dots on these charts mean that are visible, for example, for S1-P1 in compression?

These points represent outliers due to a possible data input error during testing.

• Line 198: you find significant differences between P1 and P2. However, I can't find the results of the analysis anywhere. It can be noted in Table 1 that such an analysis was carried out and the statistical differences were marked with different letters.

We found a significant difference for the provenance S1-MOE and it is possible to analyze in figure 6, for example, but it is also possible verify this information in figure 4 and figure 5 for Compressive strength and Bending strength, respectively, through the boxplots.