Applicability of Thermal Dissipation Method in Sap Flow Measurement of Karst Shrub Community
, Qibo Huang 3, Yu Tan 1,2 and Suhui Liao 1,2Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsManuscript title:
Applicability of thermal dissipation method in sap flow measurement of karst shrub community
Specific comments:
Abstract:
Abstract section should be design again. I recommend giving the following information in the Abstract section:
1-Let us point out the main reason for the differences in the accurate estimation of sap flow density in special trees by the TDP method.
2-Where is the study area.
3- In which shrub or shrub group were TDP trials performed?
4-What is the number of experimental samples in creating the adjusted coefficients?
5- What is the statistical reliability rate of the newly created equations?
6- What is the limitation?
Introduction:
1- Introduction section is designed well.
Material and Methods:
1- By what method was the number of plant samples decided?
2- Is the number of plant samples sufficient to recommend this method?
Result and Discussion:
1- Please add to the text about the limitations of the suggested new formula
Conclusion:
1- The conclusions must respond to the work's hypotheses and be coherent with the objectives and methodology. These experiments were performed with limited number of plants. Practical suggestions should be written according to the results of the research.
Author Response
Dear editor and reviewers
Many thanks to the anonymous reviewers for their constructive comments on this manuscript, which led to an improved quality of the article and a better presentation of the content. In addition to these suggestions, we have revised the article references to ensure that they meet journal requirements. We have made extensive revisions to the article, which include the introduction, material and methods, discussion and conclusion. The related materials are also available in the appendix. Replies as follows (in black)：
Reviewer #1 comment (Remarks to the Author):
Abstract:
Reviewer #1 comment: Abstract section should be design again. I recommend giving the following information in the Abstract section:
1-Let us point out the main reason for the differences in the accurate estimation of sap flow density in special trees by the TDP method.
2-Where is the study area.
3- In which shrub or shrub group were TDP trials performed?
4-What is the number of experimental samples in creating the adjusted coefficients?
5- What is the statistical reliability rate of the newly created equations?
6- What is the limitation?
Response by authors: Thanks for your suggestions.
We have revised the text to make this clear in the line 12-28.
New text: “Although the thermal dissipation probe (TDP) method is prominent in forest transpiration studies, accurate estimation of sap flow density in particular trees with different wood structures remains highly variable. To verify the applicability of the TDP method in the measurement of transpirational water consumption of shrub communities in degraded karst areas in southern China, the Granier original formula was validated and corrected by the isolated stem segment method with Celtis sinensis, Xylosma congesta, Triadica sebifera, Paliurus ramosissimus, Pyracantha fortuneana, Sageretia thea and Phanera championii. Finally, the correction coefficients were analyzed about wood structural parameters. Our study revealed that the sap flow density estimated using Granier's original formula exhibited varying degrees of overestimation or underestimation compared to the measured sap flow density. The differences ranged from -78.9% to 114.2%, highlighting the need for formula correction. Consequently, we adjusted the coefficients α and β of the original formula (n=3-5), resulting in a revised range of 0.0047-0.0509 g cm-2 s-1 and 0.5882-1.9821 (R2=0.81-0.97), respectively. The conduit diameter was significantly correlated with the correction coefficient α. It is currently unknown whether the results obtained for a particular species can be applied to different growth environments and more prominent individuals of the same species. In conclusion, it is necessary to verify the applicability of Granier's original formula when estimating water consumption through transpiration in trees.”
Introduction:
Reviewer #1 comment:
1- Introduction section is designed well.
Response by authors: Thanks for the positive evaluation of our introduction.
Material and Methods:
Reviewer #1 comment: 1- By what method was the number of plant samples decided?
Response by authors: Thank you for your question.
General statistical experiments are greater than or equal to three samples. Due to the limitations of experimental instruments, sample access, and other factors, the designed replication of the experiment for each species is six. However, due to some uncontrollable factors, such as water leakage during the experiment, the experimental data of some samples were unavailable, resulting in inconsistent sample sizes among species.
Reviewer #1 comment: 2- Is the number of plant samples sufficient to recommend this method?
Response by authors: The sample size of each species is no less than three, and the adjusted R2 (0.81-0.97) results of the corrected fitting formula are good enough to recommend this method.
Result and Discussion:
Reviewer #1 comment: 1- Please add to the text about the limitations of the suggested new formula
Response by authors: We have revised the text to clarify this in lines 304-316.
New text: “This study focused on a limited number of samples and small diameter karst shrub communities, with a probe length of only 10 mm, and the applicability of the results for the same species in other growth environments and larger individuals is not yet known. Subsequent studies can be conducted on the same species in different growth environments and individuals of different sizes to investigate the effects of probe length, conduit size, conduit density and radial variation in sapwood on the sap flow correction formulae, with a view to obtaining more systematic correction results.”
Conclusion:
Reviewer #1 comment: 1- The conclusions must respond to the work's hypotheses and be coherent with the objectives and methodology. These experiments were performed with limited number of plants. Practical suggestions should be written according to the results of the research.
Response by authors: We have revised the text to make this clear in lines 319-343.
New text: “Our findings indicate that the values of FG showed varying degrees of overestimation or underestimation compared to the measured values of FC. The errors ranged from -78.9% to 114.2%, highlighting the unavailability of Granier's original formula in the transpiration estimation of the karst shrub community and the necessity of calibration before accurate estimation. To address this, the coefficients α and β in Granier's formula were corrected in seven typical species of karst shrub communities in southern China. The corrected values for α ranged from 0.0047 to 0.0509 g cm-2 s-1, while the corrected values for β ranged from 0.5882 to 1.9821. These corrected Granier’s formulas showed good performance and led to an obvious improvement in the accuracy of sap flow estimation, highlighting the applicability of the TDP method in measuring the transpiration of the shrub community following calibration. Furthermore, a significant correlation between wood conduit diameter and the calibration coefficient α was found in this study, suggesting the diameter of the wood conduits plays a significant role in determining the sensitive coefficient of Granier’s formula. As a result, it is important to verify the applicability of Granier's original equation when estimating transpirational water consumption in woody plants, especially when the wood structure (such as conduit diameter) of the studied species varies considerably from that of species in which the Granier's original equation established. Whether the calibrated Granier’s formula and the relationship between wood conduit diameter and coefficient α found in this study are suitable for other environments needs more study in the future. The results found in this study broadened the applicability of the TDP method in transpiration measurement in shrub communities. Considering water shortage is the main factor limiting plant growth and community succession in degraded karst and other drought ecosystems, this study is also helpful for comprehending the water use strategies of plants in such environments and further analyzing the role of shrubs in the water cycle of drought-prone ecosystems.”
Reviewer 2 Report
Comments and Suggestions for Authors2.2. Calibration experiment.
Could you comment if the selected trees for each species have similar age, DBH, and tree height? I think it is essential to describe these characteristics to consider if the size of the trees could be a controlling factor. You can add that information in Table 1 or just include a general comment.
Lines 20-21, pag 113. “The initial height of the water head in the rubber pipe above the stem segment was about 1.8 m”. It is essential to be more specific in this section. The water column is on the lower section of the segment so that the induced water flow follows that of the sap flow (from the roots to the crown). Could you describe this better in your text?. I also wonder about the rationale for using 1.8 m of water column. Is there any reference to support the selection of a 1.8 m water column and a 10cm gap to reload the water column? Please comment on this.
Lines 122-124. “This was repeated more than 3 times, and the measurement time was more than 5 h. A container was placed under the stem section to collect the water run-off from the stem, which was weighed every 5 min using an electronic balance”. This section must be improved. Figure 1 depicts many measuring points of sap flows for each selected study species. Could you improve this section so that one can understand better how do you obtain so many measuring points? Please comment on this.
2.4. Data extraction and statistics
3.1. Comparison between the actual measured sap flow density and that calculated through Granier's original formula.
I suggest that the boxes in Figure 1 and Figure 2 should be arranged in the order of species presented in each section's text. This will make it easier for the reader to follow your descriptions. Additionally, in Table 2, please include the number of samples for each species validation in the "n" column. The "n" should be equal to the number of observations shown in Figure 1.
3.3. Correlation between wood structure, CV and calibrated coefficient in Grainer’s formula
On page 6, line 199, it states that "In addition, there is a significant correlation between CV and calibrated α (P < 0.01)." However, based on Box "d" in Figure 3, the correlation is actually between CV and calibrated β. Please make the necessary corrections.
In Figure 3, you present data collected from seven species, along with data from other studies. Some boxes contain more or fewer species from other studies, and it would be helpful if you could explain why this is so. Additionally, since you mentioned in section 2.4 that you extracted data from tables and figures from other studies, it would be useful to know whether the methodologies used in those studies were similar to your methodology to calibrate coefficients (α and β). If they were not, please comment on whether the data is comparable and should be included in this figure.
Lastly, I suggest adding a table that provides basic information about the other studies, such as reference, year, species, and extracted values. This would make it easier to compare and interpret the data.
Comments on the Quality of English LanguageNONE
Author Response
Dear editor and reviewers
Many thanks to the anonymous reviewers for their constructive comments on this manuscript, which led to an improved quality of the article and a better presentation of the content. In addition to these suggestions, we have revised the article references to ensure that they meet journal requirements. We have made extensive revisions to the article, which include the introduction, material and methods, discussion and conclusion. The related materials are also available in the appendix. Replies as follows (in black)：
2.2. Calibration experiment.
Reviewer #2 comment: Could you comment if the selected trees for each species have similar age, DBH, and tree height? I think it is essential to describe these characteristics to consider if the size of the trees could be a controlling factor. You can add that information in Table 1 or just include a general comment.
Response by authors: We have revised Table 1 to make DBH and tree height clear.
Considering age estimation is difficult for shrubs in drought-prone ecosystems, the age information of selected trees was not included in this research.
Table 1. Plant sample information.
|
Species |
Wood type |
Sample size |
Peeling diameter（mm） |
DBH(mm) |
Tree height(m) |
|
C. sinensis |
ring-porous |
6 |
22.1±0.9 |
18.3±1.5 |
2.46±0.18 |
|
X. congesta |
semi-ring-porous |
4 |
19.5±1.9 |
20.4±1.6 |
2.78±0.23 |
|
T. sebifera |
semi-ring-porous |
4 |
20.6±1.8 |
24.4±2.1 |
2.44±0.17 |
|
P. ramosissimus |
semi-ring-porous |
4 |
20.2±1.6 |
20.1±2.7 |
2.79±0.67 |
|
P. fortuneana |
semi-ring-porous |
4 |
22.1±2.2 |
19.2±4.7 |
2.50±0.38 |
|
S. thea |
diffuse-porous |
5 |
22.4±1.6 |
20.4±2.0 |
2.13±0.36 |
|
P. championii |
vine |
4 |
21.2±1.3 |
22.7±3.7 |
3.39±0.92 |
Reviewer #2 comment: Lines 20-21, pag 113. “The initial height of the water head in the rubber pipe above the stem segment was about 1.8 m”. It is essential to be more specific in this section. The water column is on the lower section of the segment so that the induced water flow follows that of the sap flow (from the roots to the crown). Could you describe this better in your text? I also wonder about the rationale for using 1.8 m of water column. Is there any reference to support the selection of a 1.8 m water column and a 10cm gap to reload the water column? Please comment on this.
Response by authors: Thank you for your suggestions.
The height of the water column in Zeng et al. (2022) and Zhang et al. (2017) flow correction study is limited to a fixed height (15, 30, 50, 70, and 90 cm), while the sap flow of plants in nature is constantly changing. In order to obtain a large range of sap flow density values and more test points, we adopted two times the conventional water column height and an unfixed water column height to obtain sap flow data between 1.8-0.1m water column.
Reviewer #2 comment: Lines 122-124. “This was repeated more than 3 times, and the measurement time was more than 5 h. A container was placed under the stem section to collect the water run-off from the stem, which was weighed every 5 min using an electronic balance”. This section must be improved. Figure 1 depicts many measuring points of sap flows for each selected study species. Could you improve this section so that one can understand better how do you obtain so many measuring points? Please comment on this.
Response by authors: We have revised the text to make this clear in lines 128-144.
New text: “The water column height of the existing sap flow calibration experiment is limited to a fixed height (15, 30, 50, 70, and 90 cm). To expand the range of sap flow density values and increase the number of test points, we utilized a water column height twice the conventional measurement and an adjustable water column height to capture sap flow data within the range of 1.8-0.1m. The initial height of the water head in the rubber pipe above the stem segment was about 1.8 m. The water column is positioned in the lower section of the segment to align with the direction of the induced water flow, corresponding to the sap flow from the roots to the crown. A container was placed under the stem section to capture the actual sap flow, which was weighed every 5 min (Consistent with CR1000 recording frequency) using an electronic balance with an accuracy of 0.01 g. Subsequently, the height of the water column diminishes over time due to gravitational effects. When the height of the water column dropped to about 10 cm, the water was added to 1.8 m. This was repeated more than 3 times, and the measurement time was more than 5 h. Acidic magenta dye was added to stain the sapwood at the end of calibration for the determination of sapwood area (As, cm2). At the end of each measurement, the maximum temperature difference (∆Tm) between the heated probe and the reference probe was recorded at zero water pressure.”
2.4. Data extraction and statistics
Reviewer #2 comment:3.1. Comparison between the actual measured sap flow density and that calculated through Granier's original formula.
I suggest that the boxes in Figure 1 and Figure 2 should be arranged in the order of species presented in each section's text. This will make it easier for the reader to follow your descriptions. Additionally, in Table 2, please include the number of samples for each species validation in the "n" column. The "n" should be equal to the number of observations shown in Figure 1.
Response by authors: The boxes in Figure 1 and Figure 2 have been arranged in the order of species presented in each section's text. The number of samples for each species verification has been added in Table 2.
Figure 1. Comparison between sap flow density of measured (FC) and calculated through Granier’s original empirical formula (FG).
Figure 2. The CV varied with the K value.
Table 2. Formulae calibration and validation for different species.
|
Species |
Fd=αKβ（g cm-2 s-1） |
Validation |
|||||
|
α |
β |
R2 |
n |
R2 |
RMSE |
n |
|
|
Granier’s Original coefficient |
0.01199 |
1.231 |
|
|
|
|
|
|
C. sinensis |
0.0300 |
1.9821 |
0.97 |
5 |
0.90 |
0.004 |
1 |
|
X. congesta |
0.0141 |
1.5697 |
0.86 |
3 |
0.64 |
0.001 |
1 |
|
T. sebifera |
0.0076 |
1.6654 |
0.95 |
3 |
0.95 |
0.002 |
1 |
|
P. ramosissimus |
0.0047 |
0.5882 |
0.81 |
3 |
0.62 |
0.001 |
1 |
|
P. fortuneana |
0.0065 |
1.4802 |
0.90 |
3 |
0.94 |
0.000 |
1 |
|
S. thea |
0.0198 |
1.8844 |
0.91 |
4 |
0.98 |
0.002 |
1 |
|
P. championii |
0.0509 |
3.0391 |
0.87 |
3 |
0.69 |
0.037 |
1 |
Reviewer #2 comment: 3.3. Correlation between wood structure, CV and calibrated coefficient in Grainer’s formula
On page 6, line 199, it states that "In addition, there is a significant correlation between CV and calibrated α (P < 0.01)." However, based on Box "d" in Figure 3, the correlation is actually between CV and calibrated β. Please make the necessary corrections.
Response by authors: There are two y-axis in each figure in Figure 3. The left and right y-axis are α and β, respectively. The left y-axis in Figure 3d shared the same title with Figure 3c. The fitted line in Figure 3d represents the significant correlation between CV and calibrated α.
Reviewer #2 comment: In Figure 3, you present data collected from seven species, along with data from other studies. Some boxes contain more or fewer species from other studies, and it would be helpful if you could explain why this is so. Additionally, since you mentioned in section 2.4 that you extracted data from tables and figures from other studies, it would be useful to know whether the methodologies used in those studies were similar to your methodology to calibrate coefficients (α and β). If they were not, please comment on whether the data is comparable and should be included in this figure.
Lastly, I suggest adding a table that provides basic information about the other studies, such as reference, year, species, and extracted values. This would make it easier to compare and interpret the data.
Response by authors: Thank you for your suggestions.
Since not all wood structure and CV parameters (α, β and conduit diameter, conduit density, wood density) can be found for some calibrated species in published references, the amount of data in the boxes of Figure 3 is inconsistent. In order to enlarge the data range, the published calibrated species that find only one or two structure parameters were also included in this analysis. To make it clear for readers, we add this information in “Data extraction and statistics”. Please refer to the attachment for the data in Figure 3.
Reviewer 3 Report
Comments and Suggestions for AuthorsDear all,
I reviewed the ms. "Applicability of thermal dissipation method in sap flow measurement of karst shrub community". The ms. focuses on the validation and correction of Granier's original formula used in the thermal dissipation probe (TDP) method for estimating sap flow density, particularly in the context of shrub communities in degraded karst areas. The ms identifies a critical gap in research related to the calibration of Granier's empirical formula for sap flow density, particularly in karst regions. I have minor suggestions:
Introduction:
The introduction provides a comprehensive background on the importance of accurate sap flow measurement in vegetation, particularly focusing on the use of the thermal dissipation probe (TDP) method in karst areas. But, I would like to recommend to clearly articulate why this research gap is significant and how addressing it can contribute to the field.
M&M:
The "Materials and Methods" section provides a detailed description of the study area, calibration experiment, wood structure analysis, and data extraction and statistics.
Table 1: Could the authors insert the crown area [CA] and height of trees? Especially CA is very important for these experiment.
Results:
For all Figures: Could you improve the Figures? It´s impossible to read it.
The "Results" section appears to provide a comprehensive and detailed account of the study's findings. The authors presented a detailed comparison between the actual measured sap flow density and the estimates provided by Granier's original formula, the calibration of parameters in Granier's formula, and the correlation between wood structure and the calibrated coefficients.
Discussion:
The Discussion delves into the implications of your findings, particularly focusing on the impact of non-calibration on sap flow density estimation, differences observed before and after calibration of Granier's formula, and the correlation between wood structure and calibration coefficients. The discussion effectively highlights the limitations of Granier’s original formula across different tree species, referencing various studies to support this. The discussion about how the deviation in sap flow estimation varies across species is crucial. Could the authors explore the ecological and methodological implications ?
The ms. should discuss the potential for future research, particularly in terms of extending the study to different species, growth environments, and tree sizes. This could include exploring the effects of probe length, conduit size, and radial variation in sapwood on sap flow correction formulas.
Also, it´s importante to Link to Objectives and Hypotheses. The discussion should explicitly refer back to the study's objectives and hypotheses, addressing how the findings support or refute these.
Conclusion:
The conclusion of your manuscript succinctly summarizes the main findings and their implications. The conclusion points out the necessity of verifying and calibrating Granier's original equation for different species, which is essential for researchers and practitioners in the field. I would like to suggest to expanding on how these findings can inform future research and forest management practices.
Author Response
Dear editor and reviewers
Many thanks to the anonymous reviewers for their constructive comments on this manuscript, which led to an improved quality of the article and a better presentation of the content. In addition to these suggestions, we have revised the article references to ensure that they meet journal requirements. We have made extensive revisions to the article, which include the introduction, material and methods, discussion and conclusion. The related materials are also available in the appendix. Replies as follows (in black)：
Reviewer #3 comment (Remarks to the Author):
Dear all,
I reviewed the ms. "Applicability of thermal dissipation method in sap flow measurement of karst shrub community". The ms. focuses on the validation and correction of Granier's original formula used in the thermal dissipation probe (TDP) method for estimating sap flow density, particularly in the context of shrub communities in degraded karst areas. The ms identifies a critical gap in research related to the calibration of Granier's empirical formula for sap flow density, particularly in karst regions. I have minor suggestions:
Response by authors: Thank you for your careful reading of our manuscript and recognizing its usefulness. We appreciate your recommendations and suggestions for improvement. We have carefully considered your feedback and will address each point to enhance the clarity and accuracy of the article.
Reviewer #3 comment: Introduction: The introduction provides a comprehensive background on the importance of accurate sap flow measurement in vegetation, particularly focusing on the use of the thermal dissipation probe (TDP) method in karst areas. But, I would like to recommend to clearly articulate why this research gap is significant and how addressing it can contribute to the field.
Response by authors: Thanks for your advice.
We added some information to make the significance of this research more clear. The outline of reasons to carry out this study in the introduction is as follows (lines 39-59).
New text: “The thermal dissipation probe (TDP) method is widely used in the research of forest transpiration, because it is simple to use, and has small destructive and continuous monitoring. The Granier empirical equation has been confirmed in some studies. Still, more and more studies have shown that the empirical equation will cause significant deviations in the estimation of sap flow density for some tree species. Even so, the calibration of the empirical equation for sap flow density estimation is rare. To reduce the measurement uncertainty of forest transpiration, it is necessary to verify the applicability of the Grainer’s original formula in various tree species, especially when the studied species obviously differ in wood structure and growth environment with the tree species used to establish the Granier’s original formula. Otherwise, it may induce unignorable errors in the estimating of forest transpiration and even conclude opposite water use strategies in some species.”
Reviewer #3 comment: M&M:
The "Materials and Methods" section provides a detailed description of the study area, calibration experiment, wood structure analysis, and data extraction and statistics.
Table 1: Could the authors insert the crown area [CA] and height of trees? Especially CA is very important for these experiment.
Response by authors: Thank you for your suggestion.
We have revised Table 1 and added DBH and tree height information.
The crown area was not determined during the experiment, and now it is winter; the crown width measured now is not representative, so this parameter not be included in Table 1.
Table 1. Plant sample information.
|
Species |
Wood type |
Sample size |
Peeling diameter（mm） |
DBH(mm) |
Tree height(m) |
|
C. sinensis |
ring-porous |
6 |
22.1±0.9 |
18.3±1.5 |
2.46±0.18 |
|
X. congesta |
semi-ring-porous |
4 |
19.5±1.9 |
20.4±1.6 |
2.78±0.23 |
|
T. sebifera |
semi-ring-porous |
4 |
20.6±1.8 |
24.4±2.1 |
2.44±0.17 |
|
P. ramosissimus |
semi-ring-porous |
4 |
20.2±1.6 |
20.1±2.7 |
2.79±0.67 |
|
P. fortuneana |
semi-ring-porous |
4 |
22.1±2.2 |
19.2±4.7 |
2.50±0.38 |
|
S. thea |
diffuse-porous |
5 |
22.4±1.6 |
20.4±2.0 |
2.13±0.36 |
|
P. championii |
vine |
4 |
21.2±1.3 |
22.7±3.7 |
3.39±0.92 |
Results:
Reviewer #3 comment: For all Figures: Could you improve the Figures? It´s impossible to read it.
Response by authors: Thanks for your advice.
The boxes in Figure 1 and Figure 2 have been arranged in the order of species presented in each section's text. Please refer to the attachment for the data in Figure 3.
Figure 1. Comparison between sap flow density of measured (FC) and calculated through Granier’s original empirical formula (FG).
Figure 2. The CV varied with the K value.
Reviewer #3 comment: The "Results" section appears to provide a comprehensive and detailed account of the study's findings. The authors presented a detailed comparison between the actual measured sap flow density and the estimates provided by Granier's original formula, the calibration of parameters in Granier's formula, and the correlation between wood structure and the calibrated coefficients.
Response by authors: Thank you for your positive and encouraging review of our paper. We greatly appreciate your recognition of the results.
Discussion:
Reviewer #3 comment: The Discussion delves into the implications of your findings, particularly focusing on the impact of non-calibration on sap flow density estimation, differences observed before and after calibration of Granier's formula, and the correlation between wood structure and calibration coefficients. The discussion effectively highlights the limitations of Granier’s original formula across different tree species, referencing various studies to support this. The discussion about how the deviation in sap flow estimation varies across species is crucial. Could the authors explore the ecological and methodological implications?
Response by authors: Thanks for your positive comments and suggestions.
We now added and explored the ecological and methodological implications in lines 298-312.
New text: “According to the Hagen-Poiseuille law, the conduit size is an important factor affecting sap flux density. Yi and Xu’s study found that the calibration coefficient of the Granier equation would change with the vessel area. This study has similar results. Shinohara et al. demonstrated variations in the estimation parameters of C. japonica and C. obtusa across different sizes and regions. Therefore, applying the sap flow density correction factor of a smaller tree species to an individual of the same size in a larger tree species or in a different region may also cause uncertain errors. This study focused on a limited number of samples and small diameter karst shrub communities, with a probe length of only 10 mm, and the applicability of the results for the same species to other growth environments and more prominent individuals is not yet known. Furthermore, distinct research methods revealed varying error trends for different wood species. There are some fundamental differences in calibration approaches, including water movement through the xylem (i.e., negative vs. positive pressure) and calibration material (i.e., intact trees, stems with foliage, stem segments). Still, there is not enough data to determine fully how these differences may affect coefficients and subsequent water use estimate.”
Reviewer #3 comment:The ms. should discuss the potential for future research, particularly in terms of extending the study to different species, growth environments, and tree sizes. This could include exploring the effects of probe length, conduit size, and radial variation in sapwood on sap flow correction formulas.
Also, it´s importante to Link to Objectives and Hypotheses. The discussion should explicitly refer back to the study's objectives and hypotheses, addressing how the findings support or refute these.
Response by authors: Thanks for your advice.
We have presented the shortage of this study and pointed out the important areas needed to explore in the future in revised discussion. In addition, we also added the presentation to link objective.
New text: “lines 304-316: This study focused on a limited number of samples and small diameter karst shrub communities, with a probe length of only 10 mm, and the applicability of the results for the same species to other growth environments and more prominent individuals is not yet known. Subsequent studies can be conducted on the same species in different growth environments and individuals of different sizes to investigate the effects of probe length, conduit size, conduit density and the radial variation in sapwood on the sap flow correction formulae, to obtain more systematic correction results.”
New text: “lines 234-237: Validating these findings in a degraded karst region with the main tree species of shrub communities, FG exhibited significant errors ranging from -78.9% to 114.2% compared to FC. Hence, validating Granier's original formula for each tree species is imperative to ensure measurement accuracy.”
New text: “lines 255-261: In this study (Table 1 and Table 2), the calibration coefficients showed that for ring-porous species, they were larger than the original equation. In contrast, for semi-ring-porous species like X. congesta, the calibration coefficients were closer to the original equation. In the case of diffuse-porous species, the calibration coefficients were less different from the original equation. These variations in calibration coefficients suggest differences in wood characteristics, such as the distribution uniformity of microstructures in the sapwood cross-section, duct size, and efficiency of duct moisture transfer.”
New text: “lines 285-297: In this study, the calibration coefficient was positively correlated with the conduit diameter but significantly correlated with the coefficient α and not with the coefficient β. This may be due to the small specificity of coefficient β. There also showed an extensive range of variation in coefficient α and a slight variation in coefficient β. Furthermore, it has been observed that the CV exhibits a significantly negative correlation with coefficient α, whereas its correlation with β remains insignificant. This suggests that appropriate adjustments to α can effectively enhance the formula's estimation accuracy. The calibration coefficients were negatively correlated with conduit density, but the correlations were insignificant. This suggests that there is no clear correlation between wood characteristics such as wood density and correction coefficient, and that this result may be due to the limited number of samples from different wood types or the low specificity of the parameters between other tree species.”
Conclusion:
Reviewer #3 comment: The conclusion of your manuscript succinctly summarizes the main findings and their implications. The conclusion points out the necessity of verifying and calibrating Granier's original equation for different species, which is essential for researchers and practitioners in the field. I would like to suggest to expanding on how these findings can inform future research and forest management practices.
Response by authors: We have revised the text to make this clear in lines 338-343.
New text: “The results found in this study broadened the applicability of the TDP method in transpiration measurement in shrub communities. Considering water shortage is the main factor limiting plant growth and community succession in degraded karst and other drought ecosystems, this study is also helpful for comprehending the water use strategies of plants in such environments and further analyzing the role of shrubs in the water cycle of drought-prone ecosystems.”
Reviewer 4 Report
Comments and Suggestions for AuthorsThe paper is particularly focused on the assessment of sap flow in shrub species (in China) using the Granier’s formula (thermal dissipation technique) and compared with stem segment method.
The paper is of interest for sap flow studies in forest trees, although, in my opinion, the study is based on limited sampling. This issue should be included in the “Discussion” section.
It is well reported that the thermal dissipation technique has important limitations (e.g. due to variability in radial profile, natural gradients, wood parameters). It is therefore more informative to compare relative rather than absolute sap flow values.
“Introduction“ section: It should be added some information about other sensors/tecnhniques to measure sap flow (e.g., Kumar et al., 2022; Front. Plant Sci.)
Author Response
Dear editor and reviewers
Many thanks to the anonymous reviewers for their constructive comments on this manuscript, which led to an improved quality of the article and a better presentation of the content. In addition to these suggestions, we have revised the article references to ensure that they meet journal requirements. We have made extensive revisions to the article, which include the introduction, material and methods, discussion and conclusion. The related materials are also available in the appendix. Replies as follows (in black)：
Reviewer #4 comment (Remarks to the Author):
Comments and Suggestions for Authors
The paper is particularly focused on the assessment of sap flow in shrub species (in China) using the Granier’s formula (thermal dissipation technique) and compared with stem segment method.
Response by authors: Thank you for your careful reading of our manuscript and recognizing its usefulness. We appreciate your recommendations and suggestions for improvement. We have carefully considered your feedback and will address each point to enhance the clarity and accuracy of the article.
Reviewer #4 comment: The paper is of interest for sap flow studies in forest trees, although, in my opinion, the study is based on limited sampling. This issue should be included in the “Discussion” section.
Response by authors: We have revised the text to make this clear in lines 304-316.
New text: “This study focused on a limited number of samples and small diameter karst shrub communities, with a probe length of only 10 mm, and the applicability of the results for the same species to other growth environments and more prominent individuals is not yet known. Subsequent studies can be conducted on the same species in different growth environments and individuals of different sizes to investigate the effects of probe length, conduit size, conduit density and radial variation in sapwood on the sap flow correction formulae, to obtain more systematic correction results.”
Reviewer #4 comment: It is well reported that the thermal dissipation technique has important limitations (e.g. due to variability in radial profile, natural gradients, wood parameters). It is therefore more informative to compare relative rather than absolute sap flow values.
Response by authors: We have revised the text to make this clear in lines 237-244.
First, one of the aims of this study is to improve absolute sap flow estimation in karst shrub community using TDP method. Relative sap flow is not the scope of this study. Calibration is still helpful when using relative sap flow values, as added in the revised text: “Although not all sap flow applications necessitate absolute water use estimates, calibration can also yield benefits. One of the hypotheses in comparing relative sap flow among trees is that the error is constant in simple trees. However, the sap flow error varies with the sap flow rate, as found in this study (Figure 1). Considering the natural variation of sap flow under fluctuating environmental drivers, calibration of Granier’s formula can alter the pattern of relative sap flow and lead to different results when compare water use among trees even they belong to the same species with similar age, size and growing environment.”
Reviewer #4 comment:
“Introduction“ section: It should be added some information about other sensors/tecnhniques to measure sap flow (e.g., Kumar et al., 2022; Front. Plant Sci.)
Response by authors: We have revised the text to make this clear in lines 37-39.
New text: “Various methodologies are available for assessing trunk sap flow, such as heat pulse, heat balance, heat-field deformation, and thermal dissipation.”
Round 2
Reviewer 2 Report
Comments and Suggestions for Authors
I am pleased to see the modifications made to this paper. Just a small recommendation for figure 3.
Page 7 Line 218. Note: Correlation is calculated based on the data measured in this study and collected from published papers.
Suggested text :
Note: Correlation is calculated based on the data measured in this study and collected from published papers (see: Supplementary Table S1).
