Nondestructive Techniques for Determination of Wood Mechanical Properties of Urban Trees in Madrid

Round 1

Reviewer 1 Report

I found the technical sections of the report to be very thorough and well presented.

My one requested change is that tables and discussion more clearly identify which density is being used: basic (bone dry), air dry (12% MC) and green (unseasoned).

I have one major and minor comment on the paper design and content.

The major comment is about the disconnection between the study’s overall aim and the technical methodology. The study's aim was framed around informing assessment of the physical and mechanical properties of urban trees. As stated, the structural integrity of urban trees is regularly an issue due to the safety and property implications of unexpected failure.

It is questionable if the AWV assessment of solid wood in the stem at breast height is likely to relate meaningfully to the likelihood of an urban tree's failure. I agree that that non-destructive methods can provide effective tools to estimate and evaluate the mechanical properties of wood in a standing tree. However, these are often deployed to estimate the likely structural properties of board recovered from the stem after harvest (as you have done). This is not directly relevant to the likelihood of failure of urban trees.

While I am not an expert in the area, tree failures are often large branches detaching from the stem in high winds due to loads across the grain at reaction wood and splitting of the stem due to significant decay pipes in the stem. The paper doesn’t explore either. I note that one section of log, Robinia pseudoacacia L., include a decay pipe, but the implications of this were not really explored. It potentially could be.

The logs were selected from ‘suspect’ trees, but I don’t recall you connecting your results to the basis of the tree being condemned. Also, I found it unfortunate that discussion of the difficulty of using the equipment in practice was confined to the last half of the paper’s final paragraph.

My minor comment is the referencing of material properties of urban trees to material from forest stands. Benchmarking properties from urban trees to forest material is of interest, but only in answering the obvious question.

Urban trees grow in such completely different circumstances to forest trees that any similarity measured across a few stems is pure chance. This point could be more clearly expressed.

Author Response

Consulte el archivo adjunto.

Author Response File: Author Response.docx

Reviewer 2 Report

The paper describes the determination of mechanical properties of certain tree species by static and dynamic methods and compares the obtained values and their correlations.

In the dynamic methods, ultrasonic methods from different manufacturers with different technological parameters are used. All methods have in common that they measure the travel time of the stress wave from the origin to the sink.

The article is written in a nice clear and flowing way. Despite the clarity of the article, it has very little use value. The results obtained with different ultrasound devices vary considerably. For example, the average values of the dynamic elastic moduli (Table 4) differ by up to 100% (Robinia pseudoacacia). The only useful value of the article is provided by Table 7, which gives the relationships between individual mechanical properties obtained with specific measuring devices and for a given tree species.

The major conclusion that can be drawn from the article is that ultrasonic methods cannot be used for absolute determination of the dynamic modulus of elasticity, but are only suitable for relative determination of mechanical properties and should be mentioned in the conclusion.

This fact is not sufficiently emphasised in the article, or rather the opposite is emphasised, i.e. »Various studies have shown that the use of nondestructive methods provides a highly effective tool with which to estimate and evaluate the mechanical properties of a standing tree.« (line 520-522)

 

Specific comments:

L 306- »For all trees studied, the indirect velocities in standing trees were found to be slightly  higher than the indirect velocities measured in logs, even though the measurements were taken at the same points« - table 2 shows opposite facts – the values in logs are higher than in standin trees

Figure 6- The charts should have the same scale (y axis)

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Review of the manuscript „Nondestructive techniques for estimation of physical and mechanical properties of urban trees in Madrid” submitted to the Forests Journal.

Overall, the topic of the article seems to be interesting. The analysis of the properties and issues related to urban trees in general is common in the literature in recent years. Due to the fact that the condition and quality of such trees should be monitored, the topic of the development of non-destructive methods is, in my opinion, justified. The paper contains minor linguistic errors. My suggestions are listed below:

-      In my opinion the word “estimation” should be replaced in the title since the study considers also a common laboratory tests. Maybe determination/investigation?

-      The abstract is informative, however, why authors give only Latin names? Moreover, the abstract should constitute a kind of summary and does not have to contain such specific values, but rather what the authors are able to conclude on their basis. Otherwise, we are dealing with a report, not a scientific work.

-      Line 35: “they progressively develop characteristics….” What kind of characteristics? In my opinion it would be valuable information for this study. Authors should be more specific.

-      Line 45: Low cost of what?

-      Line 46: Does it mean that no laboratory equipment is needed to perform the analysis? Or just a standard one?

-      Line 52: Why the only determinant of quality mentioned is decay, since there are others that concern standing trees to a greater extent?

-      Line 68: Equipment manufacturers are not given.

-      In summary, in my opinion the introduction should also focus on issues related to acoustic methods, correlations between the different methods, morphological features (some of them could be an issue in the case of urban trees) that may affect the results. There are many examples in literature.

-      Line 75: Can you provide a photographic documentation of these cracks in bark and cavities in the trunk because they can indicate many other things. Did you assessed the condition of tree crown for example? What was the main criterion for selecting the representatives. The description seems insufficient.

-      Line 81: Which heights? It is of great importance. As the authors of this and other publications focused on the properties of trees in urban or polluted territories emphasize many times, factors related to the habitat may significantly affect the results, it should be characterized more. Without it, the methodology is partially incomplete.

-      There are no symbols in equation 1 and 3, equation 2 is missing.

-      Line 142: There is no need for providing the whole name of the standard.

-      How much specimens were tested?

-      Line 208: Was there a time limit for the sample to break?

-      The number of repetitions is missing in practically every description.

-      The title contains information about the physical properties. They seem to be missing.

-      At the moment, very little attention has been paid to the control of density as for research focused on mechanics of wood.

-      Figure 6,7,8 should be readable in black and white version.

-      Lines: 343-347; 400-403 belong to methodology

-      In results and discussion section, authors mainly comment on the results presented in the tables. The element of scientific discussion, summaries, conclusions are missing here. There is no need to refer to values, authors should focus more on the scientific elaboration of this data.

-      Line 512: “…of a specific area of the tree can be determined by performing measurement of longitudinal indirect velocities.” As authors themselves mention, on the basis of such small number of repetitions and trees, the lack of more advanced statistical analysis, uncontrolled environmental or morphological conditions related to wood, stating such a conclusion on the basis of presented studies is, in my opinion, impossible. It may be, but not can be determined. Moreover, in my opinion, the other conclusions do not fully correspond to the title of the paper.

Author Response

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Reviewer 4 Report

The authors focus on quite interesting problematics to me, namely the prediction of the mechanical properties of the wood of urban trees using non-destructive methods that work on the principle of ultrasound propagation in the material environment. Although this is not a particularly innovative problematics, it is clearly known and used (including, for example, in Arboriculture). In any case, an article with this focus, and it can said with theoretically reproducible application outputs, has the potential to impress the reader.

I welcome the use of basic book literature related to the given problematics (for example, Bucur) as well as a sufficient number of relevant professional articles. I only have a few suggestions for modification, mostly in the form of recommendations.

1.      Consider changes in the title of the article. There is no prediction of the physical properties of wood, only the mechanical properties. Moreover, you are not predicting the properties of the tree, but of the wood. One of the possible titles is, for example, "Non-destructive techniques for estimation of wood mechanical properties of urban trees in Madrid".

2.      State the affiliation (manufacturer, city, state) for all used devices.

3.      Was it not necessary to take into account the time correction for the zero distance of the probes in the speed calculations?

4.      I would use Figure 3 in the style of Figure 4, i.e. focusing on the device and the test sample rather than the personal service.

5.      I would modify the graphic outputs in Figures 7 and 8 so that the main outputs are not at the top right, but fill more space (graph area). For example, in Figure 7, start on the x-axis from a velocity value of 2000 m/s and on the y-axis from a modulus of elasticity value of 6000 MPa.

6.      Correctly round individual quantities, including statistical ones, for density, velocity and modulus to a whole number, and strength characteristics to one decimal place.

7.      Conclusions also include concrete essential results. So I recommend at least using the last sentence in the abstract.

I could imagine possibly differently evaluated correlation dependencies, but that is a matter of opinion.

And I did not quite understand the inclusion of destructive tests of wood in compression and tension, the justification of which is minimal in my opinion, at least the tensile ones.

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 2 Report

The authors have made all necessary corrections.

Reviewer 3 Report

Thank you very much for your corrections, I'm glad to see them in your manuscript and thank you for the answers. Good luck with your studies on urban trees because the topic itself is very interesting on one hand, and very difficult and complex on the other. In my opinion article is ready for publication.