Chemical and Mechanical Differences between Historic and Modern Scots Pine Wood
Round 1
Reviewer 1 Report
The authors focus on interesting problematics, namely chemical and mechanical changes in old (historic) pine wood as compared to present (modern) wood. The obtained results are in any case beneficial from the point of view of deepening the knowledge about these changes and obtaining the basis for possible targeted protection of historical buildings. Personally, I like the articles with such a focus, the results obtained and the relevant application as a whole.
Even so I would suggest to make few corrections and additions.
Formal shortcomings:
- poor quality of figures.
Missing requisites:
- photodocumentation of the examined material (beams, and eventually reinforced small test samples for the compression test), scheme of cutting samples, etc.,
- statistical significance of the obtained results, e.g. in the pressure test, there were four samples from each of the six beams, calculation through a quantile of Student distribution (e.g. level 0.95), related variability of measurement (COV) and selected accuracy of measurement (e.g. 5%); moreover, the basic descriptive statistics is completely missing, which does not matter much, because the average values and related variability are evident from the graphs,
- by comparing the obtained results with the “normal” current pine wood, it would be beneficial to have information about density as a basic physical variable, respectively one of the factors affecting other properties.
I consider the used research methods and the introduction, to be appropriate and sufficient. I consider the use of FTIR spectrometric analysis to be completely relevant. The explanation of changes at the chemical level is quite logical and clear, see degradation of mannan (skeleton types of hemicelluloses), reduction of acetyl content, etc. As for the stiffness analysis on small samples using "Tinius Olsen 6...", I would rather use for Dynamic mechanical analyzer, or eventually analysis at the level of cell walls (AFM - atomic force microscopy, DMT module determination and subsequent prediction of mechanical properties). However, I acknowledge the use of modern research technologies in general and the relevant discussion on results. Nevertheless, I would really add statistical significance to the results. If the number of samples within a given series (properties) is below 30, then it is necessary to verify the statistical significance of the obtained results (see above).
The reproducibility of the results is also difficult to estimate, especially due to the high variability of wood properties, specific climatic conditions, and many other specific factors. It will therefore always be bound to specific conditions, like in this case. However, the principle is clear and obvious, and even if the results were overvalued or undervalued, I consider them to be definitely beneficial.
Author Response
The authors focus on interesting problematics, namely chemical and mechanical changes in old (historic) pine wood as compared to present (modern) wood. The obtained results are in any case beneficial from the point of view of deepening the knowledge about these changes and obtaining the basis for possible targeted protection of historical buildings. Personally, I like the articles with such a focus, the results obtained and the relevant application as a whole.
Even so I would suggest to make few corrections and additions.
Formal shortcomings:
- poor quality of figures.
Response 1: All images have been replaced with images at a higher resolution and improved quality. Additional images have also been added.
Missing requisites:
- photodocumentation of the examined material (beams, and eventually reinforced small test samples for the compression test), scheme of cutting samples, etc.,
Response 2: Figure 2 has been included that shows the compression testing apparatus and a sample of timber.
- statistical significance of the obtained results, e.g. in the pressure test, there were four samples from each of the six beams, calculation through a quantile of Student distribution (e.g. level 0.95), related variability of measurement (COV) and selected accuracy of measurement (e.g. 5%); moreover, the basic descriptive statistics is completely missing, which does not matter much, because the average values and related variability are evident from the graphs,
Response 3: As the reviewer points out, the average values and related variability are shown in the graphs. Additional statistical information has been included both in the text itself and in the figure legends
- by comparing the obtained results with the “normal” current pine wood, it would be beneficial to have information about density as a basic physical variable, respectively one of the factors affecting other properties. We are unclear if the reviewer is referencing FTIR or compression tests in this instance. If the former, we would direct the reviewer to Auty et al (2014), Models for predicting wood density variation in Scots pine. Forestry 87:3, pp 449-458.
I consider the used research methods and the introduction, to be appropriate and sufficient. I consider the use of FTIR spectrometric analysis to be completely relevant. The explanation of changes at the chemical level is quite logical and clear, see degradation of mannan (skeleton types of hemicelluloses), reduction of acetyl content, etc. As for the stiffness analysis on small samples using "Tinius Olsen 6...", I would rather use for Dynamic mechanical analyzer, or eventually analysis at the level of cell walls (AFM - atomic force microscopy, DMT module determination and subsequent prediction of mechanical properties). However, I acknowledge the use of modern research technologies in general and the relevant discussion on results.
Response 4: AFM needs considerable calibration against macroscopic methods to yield meaningful results even for modern wood samples, and such calibrations are not available for historic wood. In view of the changes observed in glucomannan acetylation and the hypotheses that such hemicelluloses have a key role in mechanical damping, DMA measurements would certainly have been interesting if we had access to the instrumentation. But complex results would be expected and such a DMA study would merit a separate publication in itself.
Nevertheless, I would really add statistical significance to the results. If the number of samples within a given series (properties) is below 30, then it is necessary to verify the statistical significance of the obtained results (see above).
The reproducibility of the results is also difficult to estimate, especially due to the high variability of wood properties, specific climatic conditions, and many other specific factors. It will therefore always be bound to specific conditions, like in this case. However, the principle is clear and obvious, and even if the results were overvalued or undervalued, I consider them to be definitely beneficial.
Response 5: As above, we have significantly increased the amount of statistical information that could be included. As noted in Kennedy (2015) - reference 9 - from historic buildings it is not always that case that a high number of samples can be obtained.
We thank the reviewer for their comments and have taken these suggestions on board.
Reviewer 2 Report
Heritage-713646
Chemical and mechanical differences between historic and modern Scots pine wood written by Kate Hudson-McAulay, Craig J. Kennedy and Michael C. Jarvis
This paper covers an interesting subject: Do historical wood materials still exhibit the same mechanical properties as living trees? The authors also examines the topic with regard to the chemical changes in the historical wood samples.
The title and the abstract sound interesting to me. I accepted the revision, even though I am not as comfortable with wood chemistry. Thus, I did not make comments on the chemical analysis and interpretation. Hopefully another reviewer can examine this aspect.
The layout of this manuscript is lacking several important elements.
The first is related to the structure: The introduction has no objective or hypothesis. Several paragraphs in the material and method part should be moved to the discussion section. There are no relevant informations in the results section. Sentences in the results section should be moved either, to the discussion or the introduction. Text parts in the discussion should be placed in the introduction, and others, moved to the conclusion. The second concern is related to the low number of analyzed samples: Only five or six (two different numbers were presented in the paper) wood samples have been taken from three historical buildings. No information is provided with regard to the number of modern Scot pine sampled. Is this sample depth enough for a publication? Furthermore, the sample age is anywhere mentioned (or number of tree-rings per cm). The mechanical resistance is directly related to the tree ring width (or more precisely to the latewood density). Thus, much more informations are missing from the analyzed samples. Inconsistency has been noted for the historical material: the author wrote in the material part that many samples of the historical material had visible signs of insect pest damage. In the discussion, this changed to fungus infestation. The limitation of this work has to be pointed out at the end of the discussion and I suggest to add a sentence to introduce future work which would be helpful to better understand the wood properties degradation in time. If the main objective of this paper is the compression testing of stiffness method as well as the spectral assignment analysis, the entire paper has to be reworked.
Due to this observation, I have to reject the paper in its actual form. I think by improving the entire paper, it should be worth for resubmitting.
Many comments are written directly into the manuscript.
Comments for author File: 
Comments.pdf
Author Response
This paper covers an interesting subject: Do historical wood materials still exhibit the same mechanical properties as living trees? The authors also examines the topic with regard to the chemical changes in the historical wood samples.
The title and the abstract sound interesting to me. I accepted the revision, even though I am not as comfortable with wood chemistry. Thus, I did not make comments on the chemical analysis and interpretation. Hopefully another reviewer can examine this aspect.
The layout of this manuscript is lacking several important elements.
The first is related to the structure: The introduction has no objective or hypothesis.
Response 1: An objective has been added to the introduction.
Several paragraphs in the material and method part should be moved to the discussion section. There are no relevant informations in the results section. Sentences in the results section should be moved either, to the discussion or the introduction. Text parts in the discussion should be placed in the introduction, and others, moved to the conclusion.
Response 2: The spectral assignment section has been moved out of materials and methods and into results. Results have been improved with the addition of the ANOVA information that gives additional statistical information and a table has been added that also adds to this. A section was moved from the discussion to the introduction.
The second concern is related to the low number of analyzed samples: Only five or six (two different numbers were presented in the paper) wood samples have been taken from three historical buildings. No information is provided with regard to the number of modern Scot pine sampled. Is this sample depth enough for a publication?
Response 3: As referenced by Kennedy (2015) – reference 9 – sampling from historic buildings often yields low numbers of samples, or small samples. To counteract this difficulty additional statistical information in the text and figure legends were included. The previous publication discussed that there were 4000 FTIR spectra in the modern calibration set.
Furthermore, the sample age is anywhere mentioned (or number of tree-rings per cm). The mechanical resistance is directly related to the tree ring width (or more precisely to the latewood density).
Response 4: Ring width and density are also listed in the previous paper. A sentence to this effect has been included in the manuscript.
Thus, much more informations are missing from the analyzed samples. Inconsistency has been noted for the historical material: the author wrote in the material part that many samples of the historical material had visible signs of insect pest damage. In the discussion, this changed to fungus infestation.
Response 6: The text has been clarified to be clear that both fungal and insect attack were noticed in the sapwood and that this study relates to the heartwood. More than one reviewer mentioned this point, and so these changes have improved the manuscript.
The limitation of this work has to be pointed out at the end of the discussion and I suggest to add a sentence to introduce future work which would be helpful to better understand the wood properties degradation in time. If the main objective of this paper is the compression testing of stiffness method as well as the spectral assignment analysis, the entire paper has to be reworked.
Due to this observation, I have to reject the paper in its actual form. I think by improving the entire paper, it should be worth for resubmitting.
Response 7: We thank the reviewer for these comments. These allowed us to make significant changes and improvements to the manuscript, particularly with regards to the statistical information included and clarity of the manuscript as a whole. This has meant that the manuscript is greatly reworked and improved.
Reviewer 3 Report
The title describes the content properly. The abstract summarizes the content well. Methodology is correct, however the number of historic pine samples for compression test is very low (only 4 for each beam). It is questionable that this is enough for the statistical analysis.
However, samples have similar age (16th century), but they are originating from three different buildings from different locations. That means three different past/antecedents. You did not make difference between the samples of three different origin during the presentation and discussion of the results. You have to clear, why you did not differentiate your results according to the origin of the tested material.
Figures are very low quality in the manuscript. Labels and legends are difficult to read. Please change them to high quality images!
You mention several times the possible fungal decay. Was the presence of fungus stated in the material? If yes, please describe. If not, you cannot refer to this during the explanation of your results. To mention the possible decay in the manuscript is interesting, because you state in the introduction part, that you have tested undecayed material (row 71-72). Please clear this contradiction!
Author Response
The title describes the content properly. The abstract summarizes the content well. Methodology is correct, however the number of historic pine samples for compression test is very low (only 4 for each beam). It is questionable that this is enough for the statistical analysis.
However, samples have similar age (16th century), but they are originating from three different buildings from different locations. That means three different past/antecedents. You did not make difference between the samples of three different origin during the presentation and discussion of the results. You have to clear, why you did not differentiate your results according to the origin of the tested material.
Response 1: The common factor being examined here is samples that are modern and samples that are historic. Modern samples were examined to provide a “sense check” and to compare with literature values. Across all samples the same result was shown – a loss of compressive strength relative to modern samples. As such we chose to present the results in this manner.
Figures are very low quality in the manuscript. Labels and legends are difficult to read. Please change them to high quality images!
Response 2: All images have been replaced with new, high resolution images. Additional images have also been included.
You mention several times the possible fungal decay. Was the presence of fungus stated in the material? If yes, please describe. If not, you cannot refer to this during the explanation of your results. To mention the possible decay in the manuscript is interesting, because you state in the introduction part, that you have tested undecayed material (row 71-72). Please clear this contradiction!
Response 3: The text has been clarified to be clear that both fungal and insect attack were noticed in the sapwood and that this study relates to the heartwood. More than one reviewer mentioned this point, and so these changes have improved the manuscript
We thank the reviewer for these comments, as we feel these have allowed us to improve the manuscript.
Reviewer 4 Report
I really enjoyed this article and read it with interest. I think it is important to understand the nature of wood degradation in constructions of historical buildings and its impact on strength characteristics. Especially in terms of the possibility of their appropriate protection. Nevertheless, I have some comments and recommendations to this work.
Introduction (literature review) is sufficient in my opinion. It explains the current state of knowledge and the reasons leading to the aims set in the article. However, I am not entirely sure that timber in historic buildings is comparable to paper degradation. After all, it is to geart extent an industrial product of completely different dimensions.
The Material and Methods are described sufficiently. I miss some pictures here. Firstly, illustrative photographs of the testing material, but above all a diagram of the sampling of beams. This should be definitely added. For a better understanding of the variability of the examined material, it would be useful to give a more detailed description of the examined material (beam dimensions, wood density, annual rings width, etc.)
The results of chemical change analyses are undoubtedly interesting and demonstrate changes in wood in the course of time. In my opinion, it is the most important and the most beneficial part of the article. It was not necessary to evaluate strength changes, at least in this form. The authors spent a lot of time and energy to determine the compression strength (modulus) using a method that is not standard and comparable with other studies. However, the achieved results are tricky to great extent. The variability of wood is enormous and the original properties of the evaluated material (pine wood) cannot be never determined. It was possible to take into account the width of annual rings and the proportion of the late wood. I can only agree with the last paragraph in the discussion and therefore the question is whether the issue of mechanical strength should be removed from the article. You mentioned in the Results that in some parts the stiffness was decreased by the fungal decay. If you had such samples (or even suspicion), they should be excluded from the analysis.
From a formal point of view, there are few pictures in the whole work, and very poor quality. This should be corrected. In general, the tables are missing. It means those numerical data as averages, coefficient of variation, etc. The results of statistical analyses should be also added.
Author Response
I really enjoyed this article and read it with interest. I think it is important to understand the nature of wood degradation in constructions of historical buildings and its impact on strength characteristics. Especially in terms of the possibility of their appropriate protection. Nevertheless, I have some comments and recommendations to this work.
Introduction (literature review) is sufficient in my opinion. It explains the current state of knowledge and the reasons leading to the aims set in the article. However, I am not entirely sure that timber in historic buildings is comparable to paper degradation. After all, it is to geart extent an industrial product of completely different dimensions.
Response 1: Whilst we agree with the reviewer’s point, we consider paper as a worthwhile comparison as it is cellulose based and has been extensively studies for it’s decay mechanism.
The Material and Methods are described sufficiently. I miss some pictures here. Firstly, illustrative photographs of the testing material, but above all a diagram of the sampling of beams. This should be definitely added. For a better understanding of the variability of the examined material, it would be useful to give a more detailed description of the examined material (beam dimensions, wood density, annual rings width, etc.)
Response 2: An image has been added of the testing apparatus, and a scheme showing the sampling regime also. Descriptions of ring widths etc. are given in reference 15; the text has been altered to point to this.
The results of chemical change analyses are undoubtedly interesting and demonstrate changes in wood in the course of time. In my opinion, it is the most important and the most beneficial part of the article. It was not necessary to evaluate strength changes, at least in this form. The authors spent a lot of time and energy to determine the compression strength (modulus) using a method that is not standard and comparable with other studies. However, the achieved results are tricky to great extent. The variability of wood is enormous and the original properties of the evaluated material (pine wood) cannot be never determined. It was possible to take into account the width of annual rings and the proportion of the late wood. I can only agree with the last paragraph in the discussion and therefore the question is whether the issue of mechanical strength should be removed from the article. You mentioned in the Results that in some parts the stiffness was decreased by the fungal decay. If you had such samples (or even suspicion), they should be excluded from the analysis.
Response 3: The issue with historic materials – as listed in reference 9 – is that access to materials from historic buildings is often difficult. Obtaining samples large enough for standardised tests such as those from the British Standards Institute are impossible, and as such a method that could examine samples that are available from historic buildings was developed and compared with modern samples.
The text has been clarified to be clear that both fungal and insect attack were noticed in the sapwood and that this study relates to the heartwood. More than one reviewer mentioned this point, and so these changes have improved the manuscript
From a formal point of view, there are few pictures in the whole work, and very poor quality. This should be corrected. In general, the tables are missing. It means those numerical data as averages, coefficient of variation, etc. The results of statistical analyses should be also added.
Response 4: All images have been improved and replaced. Additional images have been added. Further statistical information has been included in both the text and figure legends.
We thank the reviewer for these comments as we feel they have helped improve the manuscript a great deal.
Reviewer 5 Report
Line 96: Using right unit! (MICRO meter, I guess)
Figure 1B: Description does not clearly fits the picture. Description: difference spectra (modern-historic) after normalization. In Picture: inner, outer Heartwood and sapwood (of modern? Or historic?, No differences of modern and historic pine can be seen
Line 146/147 Introducing an new developed and optimized method. – In chapter results it is missing, to show that this new method works well/ is comparable with large scale standard/ has no underestimations as mentioned tensil testing in lines 144,145…. Discussion of the potential of new method is also meaningful
Line 182/183 „… due to fungal degradation“ Do you have any signs/evidences (macroscopic or microscopic) for fungal attack. You should mention in chapter Material as you did for signs of insect attack. Otherwise you should express such assumptions with more caution.
Line 184 Due to brown rot attack the relative content of lignin always increased at least. The same will happen for soft rot as well!!! (I would avoid „sometimes“ in this context
Line 249-251 „...but no increase in total aromatic content was observed even in the sapwood. The fungal decay there was possibly due a white rot species, Please be careful! During fungal dagradation just the relative percentage contents of main components will be changed. No increases of total aromatic (or other) contents are possible because no aromatics will be added!!!!! Suggestion: No higher absorbance values at the aromatic characterizing peaks/wavenumbers could be detected compared to modern pine. A possible reason fort hat could be an attack of an simultnously degrading white rot species, which degrades all wood component at the same time. But a macro- or microscpic or even microbiological evidence for fungal degradation does not really exist. (….someting like this)
Author Response
Line 96: Using right unit! (MICRO meter, I guess)
Response 1: This has been changed.
Figure 1B: Description does not clearly fits the picture. Description: difference spectra (modern-historic) after normalization. In Picture: inner, outer Heartwood and sapwood (of modern? Or historic?, No differences of modern and historic pine can be seen
Response 2: We thank the reviewer for pointing out this error. We have replaced this figure (now figure 3b) with a difference spectra as outlined by the reviewer.
Line 146/147 Introducing an new developed and optimized method. – In chapter results it is missing, to show that this new method works well/ is comparable with large scale standard/ has no underestimations as mentioned tensil testing in lines 144,145…. Discussion of the potential of new method is also meaningful
Response 3: This has been covered at length in reference 44 (Kate Hudson-McAulay's PhD thesis). We feel that this would be too long and complex to include in this article.
Line 182/183 „… due to fungal degradation“ Do you have any signs/evidences (macroscopic or microscopic) for fungal attack. You should mention in chapter Material as you did for signs of insect attack. Otherwise you should express such assumptions with more caution.
Response 4: The text has been clarified to be clear that both fungal and insect attack were noticed in the sapwood and that this study relates to the heartwood. More than one reviewer mentioned this point, and so these changes have improved the manuscript
Line 184 Due to brown rot attack the relative content of lignin always increased at least. The same will happen for soft rot as well!!! (I would avoid „sometimes“ in this context
Line 249-251 „...but no increase in total aromatic content was observed even in the sapwood. The fungal decay there was possibly due a white rot species, Please be careful! During fungal dagradation just the relative percentage contents of main components will be changed. No increases of total aromatic (or other) contents are possible because no aromatics will be added!!!!! Suggestion: No higher absorbance values at the aromatic characterizing peaks/wavenumbers could be detected compared to modern pine. A possible reason fort hat could be an attack of an simultnously degrading white rot species, which degrades all wood component at the same time. But a macro- or microscpic or even microbiological evidence for fungal degradation does not really exist. (….someting like this)
Response 5: A version of these words has been included.
We thank the reviewer for these comments which have allowed us to both improve the manuscript and eliminate a couple of errors that we had not spotted. As such this reworked manuscript is much improved.
Round 2
Reviewer 2 Report
The quality of the paper has been improved but a lot of work is still to be done.
Many comments are marked in the manuscript.
Comments for author File: Comments.pdf
Author Response
Comments to reviewer 2.
Line 50. The reviewer asks “how” in relation to damage done my acetic acid in enclosed spaces.
Response: Line 52 and reference 8 demonstrate that damage done by acetic acid on heritage materials can be significant. In that study acetate-based efflorescences were identified on glass, lead and calcareous artefacts.
Line 67-8. The reviewer states “not clear”.
Response: The sentence:
“However, a basic problem with such tests is that to maintain an adequate length:width ratio (aspect ratio) the width of the samples needs to be comparable with, or smaller than, a single annual ring.”
Has been replaced with:
“However, one issue with such tests is that the length:width ratio needed is high. With the length of the sample restricted by the size of sample taken, the width of the sample will need to be extremely small; of a similar scale to a single annual ring. “
Lines 76-80. The reviewer states “Omit. Finish the introduction with the objectif. Otherwise reword and place this earlier.”
Response: This paragraph has been deleted.
Lines 85-90. The reviewer states “Same comment as before. Not relevant for your study to go in to detail about your buildings. Present only the name of the buildings. Furthermore this is plagiat from the paper of Hudson-McAulay et al 2018”
Response: This section has been reduced to the names of the buildings, their locations in Scotland and their dates. For a heritage-related article we feel that this is the minimum level of detail that is appropriate.
Line 93. The reviewer states “This is in disagreement with your objectif”.
Response: We disagree. The objective states “This leads to the objective of this current study: is the heartwood of pine, which shows no signs of insect or fungal degradation, altered with age? And if so, in what way?” The sentence highlighted states “Many, but not all of these historic samples had visible signs of insect pest damage (larval holes), restricted to the sapwood that was located mainly at the corners of the beams”. Throughout the manuscript we have made clear that this study is focussed on the heartwood, that the sapwood is included only for comparison purposes, and as such the key element of this study is unaffected by insect or fungal decay.
Line 100. The reviewer states “I do not follow you. Did you apply the compression test with the same method for the modern and the historical material? You should at least say how many samples were tested for the modern material.”
Response: The sentence “Eight samples of modern Scots pine, derived from two trees, were utilized for development of the compression testing method.” Has been added.
Line 110. The reviewer asks “Are the outermost samples in the sapwood zone or in the outer part of the heartwood? This is important to know, as the interpretation of the results will differ”.
Response: As states in lines 98 and 131, samples were taken “in the sapwood”. This is to allow comparison between heartwood and sapwood. For additional clarity both lines have been altered to state that the samples were taken from the heartwood.
Line 135. The reviewer asks for more information on ring width and density.
Response: The sentences “In short, for heartwood there is little difference in density between modern and historic samples. However, historic samples displayed narrower ring-widths than samples taken from modern plantation-grown Scots pine.” Have been added.
Line 172. The reviewer asks for a picture of better quality.
Response: Unfortunately for logistical reasons we cannot take a new picture of this equipment. We wish to keep the existing image in, as other reviewers asked for it and it was added for this reason.
Lines 204, 224 and 233. The reviewer points out that we are interpreting the results and that this could take place in the discussion.
Response: The journal’s Instructions for Authors states that the results section should “Provide a concise and precise description of the experimental results, their interpretation as well as the experimental conclusions that can be drawn.” We have underlined the contentious part. Given this definition we feel we have adhered to these instructions faithfully.
Lines 213-216. The reviewer recommended deletion of two sentences and moving a reference to a figure.
Response: We have done this in accordance with the reviewer’s comments.
Figures 5 and 6. The reviewer suggests deleting these and replacing with just the p values.
Response: These figures have been removed and the p value inserted
Figure 8. The reviewer state that s/he did not see where samples were taken from the pith.
Response: The materials and methods section now states “Four samples from each historic beam were prepared for compression testing, located in the heartwood as close as possible to the pith, in the sapwood, and at two equally spaced intervals (inner heartwood and outer heartwood) between the pith and sapwood edge.” These correspond to the four points shown on this image.
We accept that our description of the sample positions in the methods section was previously incorrect, and this was responsible for the reviewer being confused. We thank the reviewer for pointing out this error and allowing us to make this correction.
Line 280. The reviewer suggests changing the discussion to perspectives and conclusion.
Response: We have followed the journal’s instructions for authors with regards to section headings and content.
