Effect of Forest Edge Cutting on Transpiration Rate in Picea abies (L.) H. Karst.

Round 1

Reviewer 1 Report

This study reported the effect of forest edge cutting on sap flow of Norway spruce using the trunk heat balance method and simultaneously monitored bark surface temperature and soil water potential following the edge cutting. The results indicated that a 50-m edge cutting led to increased bark surface temperatures and sap flow of trees in the first and second rows of the new forest edge. While this effect was marginal on inner trees (e.g., in the third row of the new edge). I think the study overall is well-designed and conducted, and the manuscript is well-prepared. Though the sample size is limited (a total of 6 trees in treatment plots, and 9 in control plots) due to sensor failure, which is common in sap flow studies, the results could be quite useful for forest management and provide insights into controlling bark beetle infestation. Please see my detailed suggestions as follows:

1. In the abstract, I think the experiment design is a bit over-described, but some information like the research background of this study (usually should be given in the first line), which method was used for sap flow measurement, is missing.

2. L39. Change ‘i.e.’ to ‘e.g.’ since sap flow is only one of plant physiological responses.

3. L48-49. It would be good to have a reference for these statements.

4. L50-51, ‘can have similar…. Creating a forest edge’. I do not quite follow here. Did you mean the high density could lead to more forest edges?

5. L53-55. Well, again I do not quite follow the two hypotheses formulated here. For H1, did you mean the forest edge trees would decrease their sap flow due to more direct sunlight exposure? For H2, did you mean the competition for resources (e.g., light, nutrients, and water) would be released for trees in the forest edge then lead to increased sap flow? Please clarify.

6. L64. Please give plot size, also any criteria for establishing plots? Just randomly located in the stand?

7. L83. In table 1, please indicate which are treatment plots and which are control plots. If possible, please provide the average DBH and height for the plots.

8. L96. In this section, please double-check all units for meteorological parameters, superscripts e.g.,’-2’ etc.

9. L105. Please move the manufacturer information right after the SWP sensor. And give sensor type.

10. L106. Add ‘stored in” Microlog SP3 data logger.

11. L109. Please also mention the information on the data logger used for bark temperature measurement.

12. L114. I thought you have a balanced design, e.g., five trees per plot, but due to the sensor failure you only had 6 and 9 from treatment and control plots. Please clarify this.

13. L117. Please indicate the height of the installation for sap flow sensors. At DBH?

14. L127. How did you define/determine the zero flow condition? What method/criteria?

15. L132-135. I do not quite follow the method used here (i.e., how the regression equation is derived). Which trees are interior ones? And how many of them? What goes to the general file?

16. L144. I do not see you conducted any model selection.

17. L157. Did you conduct any statistical test (e.g., Wilcox test/t-test) on environmental factors between 2019 and 2020? If yes, please indicate the statistical significance in the table.

18. I think a figure to show the fluctuation of the monthly/daily value of these environmental variables between 2019 and 2020 could be very informative. And could add information on the seasonal pattern of environmental drivers.

19. Again, in table2, it is interesting to see a slightly wetter year (1.9 mm daily average rainfall in 2020 vs. 1.7 mm in 2019) had drier soil (i.e., more negative SWP). Please add some discussion regarding this.

20. L175. Please indicate statistical significance using e.g., ‘letters’ in table 3. Also, add a unit for temperature.

21. L179. Did you test the correlation of the diurnal pattern of sap flow between treatment and control plots? By how? This is not mentioned in the statistical analyses. And consider giving a figure to show the diurnal pattern of sap flow, it would be quite straightforward for readers to see if there is any difference in diurnal patterns between treated and control plots, and between years.

22. L188. Please remove the extra period (‘.’) after ‘canopy’.

23. L188-190. “In other words, as the rate of…of the trees increases.’ This is repetitive, consider deleting it.

24. L219. It is interesting to see Herbst et al reported no edge effect on oak trees, did they mention any underlying mechanisms? If yes, please include them.

25. L223-224. Since I do not really understand the H1 formulated in the introduction, I also do not quite follow these related statements here.

26. L230. Are these 3% and 8% statistically significant?

27. L239. Please add some numerical results for canopy change in the first and second rows vs. in the third row.

28. L258-259. Provide a reference for ‘Moreover, reduction in…into diterpenes”.

29. L259-260. “as they are part of…can lead to death.’. Hard to follow, please rephrase.

30. L275. Is ‘slightly decreased’ significant?

31. L279. Add a period after ‘stress on forests’.

Author Response

For reviewer 1.

1. A sentence was added to the abstract to define the sap flow method used in the study, besides some minor changes made in the abstract to avoid over-describing.
2. In line 37, i.e. changed to e.g.
3. Reference added.
4. The sentence was clarified to avoid the misleading comparison with forest edge.
5. Hypotheses clarified
6. The sentence about the selection criteria for establishing of the plots was added.
7. New table was created
8. Done
9. Done and a sentence added about data loggers and sensor types used in the field study.
10. Done and a sentence added about data loggers and sensor types used in the field study.
11.  
12. It was indicated in the first version of the manuscript in section 2.2. The sentence was changed to have a briefer picture.
13. The height of the installation for sap flow sensors is indicated.
14. The zero-flow condition is pre-described in the software (mini32) supplied by the manufacturer. We take 03:00 a.m. as zero flow for the baseline process of sap flow data.
15. The method for creating calibration equations is described more briefly.
16. The model selection information and validation was given in the text.
17. We did not conduct any statistical test for environmental variables between 2019 and 2020.
18. A figure shows the fluctuation of the daily value of the environmental variables between 2019 and 2020.
19. A sentence was added to section 3.2 about this situation. Due to the lack of precipitation in September 2020 (only 2 mm precipitation was recorded in this month, Figure 2), the soil water potentials of the study plots were lower in 2020 than in 2019 (Table 2).
20. Statistical significance indicating using letters in table 3.
21. A figure was created to show the diurnal pattern of sap flow for measured Cp, Tp and predicted Tp.
22. Was deleted.
23. The repetitive sentence is deleted as recommended.
24. The underlying mechanisms were included
25. The sentence was rephrased in the introduction, and also, here was modified for more clarity.
26. Yes, 3% and 8% decreases are statistically significant and are stated in Table 4.
27. The range of values was added
28. The statement is from article no. 40, the reference was added
29. The sentence was rephrased.
30. The same with number 26.
31. The sentence was finished.

Reviewer 2 Report

 Specific comments:

1.      Lines 16, 86, 249 and 273. “-” is needed between 50 and meter.

2.      The Introduction needs to be improved or reorganized to highlight the significance of the current study.

3.      The English writing should be checked carefully throughout the whole manuscript, i.e., on line 54, “struggling” here is proper or not for scientific writing.

4.      The author mentioned “bark beetle Ips typographus (L.) infestation” in the abstract, but did not set up any hypotheses about it. Meanwhile, the scientific base raised for the bark beetle infestations at the end of Introduction is very abrupt.

5.      The resolution of Figure 1 is inadequate. In addition, the layout of this figure needs to be reorganized, for example, move the right one to the bottom.

6.      Line 87. Please list out the manufacturing information about LiDAR as detailed as possible.

7.      Lines 97 and 98. The unit of global radiation and wind speed need to revise.

8.      Line 100. The workflow of infrared thermometers needs to be detailed introduced.

9.      Lines 150. One space is needed between 711 and mm.

10.  Line 155. The style of the unit used in current manuscript should be the same.

11.  Lines 163-164. What kind of criteria of drought stress did the author use in this manuscript? Did the SWP reflect the drought stress? How about the soil water availability for plants?

12.  Before Figure 2 (still the matter is, bad quality of figure), why not draw a figure to show the continued observation of sap flow along with daily dataset for Tp and Cp?

13.  Lines 216 and 218. Please keep the usage of sap flow to replace the sap flux density.

14.  Lines 223-225. The current result of increases in sap flow is hard to link to the lack of concurrence for light, mineral nutrients, except for soil water, since the author did not conduct any survey on light, mineral nutrients and so on.

15.  Lines 273-275. When considering the tree position, i.e., the first and second rows of the Tp treatment (forest edge cutting), I think the samples are not enough to draw such a kind of conclusion. Also, for the next conclusion, the author did not perform any experiment to reveal the effects of bark beetle on sap flow. Therefore, such kinds of conclusions are not supported.

Author Response

For Reviewer 2.

1.”-“ inserted between 50 and meter

2. The introduction was improved and reorganized.
3. The world “struggling” was changed
4. The introduction was improved and reorganized.
5. The Figure was modified and reorganized, the resolution is appropriate now
6. A detail about LiDAR was added.
7. The unit of global radiation and wind speed was revised.
8. The manufacturer information and the distance of the sensors from tree bark were added to the manuscript. I assume the reviewer thought the bark surface measurement was conducted from a distance since the thermometers are infrared.
9. The space was created.
10. Units were unified.
11. The sentence was rephrased.
12. A figure was created to show a diurnal pattern of sap flow for measured Cp, Tp and predicted Tp.
13. All “Sap flux” terms changed to “sap flow” throughout the manuscript.
14. The sentence was rephrased.
15. The conclusion was modified. We kept a freer concept of the distance from the forest edge, emphasising the individually investigated values.

Round 2

Reviewer 1 Report

I only have a minor suggestion. For figure3, please consider using a more colorblind friendly palette.

Author Response

Thank you for all recommendations; they substantially improved the manuscript.

Author Response File: Author Response.docx

Reviewer 2 Report

I strongly require the author to go over the whole manuscript to revise what might have problems.

Author Response

For Reviewer 2 Round 2 (Minor Revisions)

 

We went through the whole manuscript once more and made following revises on the manuscript:

 

1-A sentence was added to introduction to emphasise the link between sap flow measurements and tree defence mechanism against bark beetle infestation.

2-) In material methods, the aspect of the cleared forest edge was indicated.

3-) A sentence was added to discussion to indicate the results of prior studies regarding the effect of forest edge clearing to the bark beetle infestations and sap flow.

4- A sentence was added to conclusions that further research could be useful to support the results of the current study with larger sample size, longer study period and with different scenarios.

Author Response File: Author Response.docx