Relationship between the Radial Growth of Two Dominant Coniferous Species and GPP in the Arid Region of Northwest China
Round 1
Reviewer 1 Report
I consider that it is a great contribution to knowledge to analyze the association between GPP and the growth rings of two species. This is because it is normally done with climate, and a little with NDVI, however, the approach provided by the authors helps to understand the dynamics of carbon fixed by photosynthetic activity. In general, the article is very well done, I would just like to point out some aspects:
It does not present line numbering and that helps a lot for the reviewers.
The first paragraph of the discussion deals with results, not duplicating information.
More discussion related to the results of the GPP analysis and growth rings is missing.
Author Response
I consider that it is a great contribution to knowledge to analyze the association between GPP and the growth rings of two species. This is because it is normally done with climate, and a little with NDVI, however, the approach provided by the authors helps to understand the dynamics of carbon fixed by photosynthetic activity. In general, the article is very well done, I would just like to point out some aspects:
- It does not present line numbering and that helps a lot for the reviewers.
- The first paragraph of the discussion deals with results, not duplicating information.
- More discussion related to the results of the GPP analysis and growth rings is missing.
Response：
1.Thank you for your affirmation of our work. We added line number in the revision.
2.We deleted the first paragraph in discussion section.
3.We found that studies on tree rings and GPP were rarely conducted. Therefore, NDVI can only be used as an auxiliary. In addition, followed the comments of other reviewers, we added more comparisons with NDVI, while also pointing out the differences between the research results of GPP and NDVI. This may also indicate that the relationship between GPP and tree rings may have more physiological significance than that between tree rings and NDVI. L292-308
Reviewer 2 Report
Dear Authors,
I think authors undertook and interesting study to compare the tree ring width with the GPP. The tree ring width is an important indicator for the tree growth and its response to environment, which makes importance of this study.
The overall quality of the manuscript is good, however, there couple points that, I think, require clarification.
The study is based on the comparison between the tree ring data collected by authors on site and the satellite GPP and meteo data analysis. It is not clear what was the 8-day GPP choice for the study. Is this related to the temporal or spatial resolution of satellites? Cold you please clarify.
"The cores were then processed according to the international tree-
ring analysis method." It is not clear what methods were used for the core processing. Please clarify.
GPP = Assimilation + Respiration. These two parameters should cause opposite effects on the tree ring growth. I wonder is the authors only focused on the correlation in assimilation but overlooked the opposite effect of respiration on ring shrinking. There is a general statement of the climate change, that could be further explored in the paper. This all could make their current analysis to become incomplete. Would it be possible to clarify this and provide some inside in the magnitudes of the possible issues?
The conclusion is too short and not representative to the study. I think it should provide information to make at least the qualitative decision on what was claimed to be done in the abstract and in the introduction as well.
Sincerely, yours
Dear Editor,
I think authors undertook and interesting study to compare the tree ring width with the GPP. The tree ring width is an important indicator for the tree growth and its response to environment, which makes importance of this study.
The overall quality of the manuscript is good, however, there couple points that, I think, require clarification.
The study is based on the comparison between the tree ring data collected by authors on site and the satellite GPP and meteo data analysis. It is not clear what was the 8-day GPP choice for the study. Is this related to the temporal or spatial resolution of satellites? Cold you please clarify.
"The cores were then processed according to the international tree-
ring analysis method." It is not clear what methods were used for the core processing. Please clarify.
GPP = Assimilation + Respiration. These two parameters should cause opposite effects on the tree ring growth. I wonder is the authors only focused on the correlation in assimilation but overlooked the opposite effect of respiration on ring shrinking. There is a general statement of the climate change, that could be further explored in the paper. This all could make their current analysis to become incomplete. Would it be possible to clarify this and provide some inside in the magnitudes of the possible issues?
The conclusion is too short and not representative to the study. I think it should provide information to make at least the qualitative decision on what was claimed to be done in the abstract and in the introduction as well.
Sincerely, yours
Author Response
Comments and Suggestions for Authors
Dear Authors,
I think authors undertook and interesting study to compare the tree ring width with the GPP. The tree ring width is an important indicator for the tree growth and its response to environment, which makes importance of this study. The overall quality of the manuscript is good, however, there couple points that, I think, require clarification.
Response：Thanks for your affirmation of our work. We have carefully referred to your feedback and made corresponding modifications in the main text, and have provided a detailed response below.
- The study is based on the comparison between the tree ring data collected by authors on site and the satellite GPP and meteo data analysis. It is not clear what was the 8-day GPP choice for the study. Is this related to the temporal or spatial resolution of satellites? Could you please clarify.
Response：Yes, the temporal resolution of remote sensing images is mainly determined by the orbit of the satellite, while the resolution of remote sensing data products is also determined by the research objects and weather conditions. For example, the MODIS is a sensor on the two satellites named “terra” and “aqua”. The difference in transit time between the two satellites is eight days. Thus, the MODIS products typically achieve a time resolution of 8 days. Other satellites can achieve higher time resolution, such as weather satellites, which can reach minutes or hours. GPP data does not require high time resolution, so it is usually monthly data, with a small number of products offering 8-day resolution. For this issue is somewhat complex and the calculations for GPP products are much more complex, it is difficult to explain in detail in the manuscript. In this reason, we modified the text as: “these two remote sensing-based GPP products provide a high time resolution of 8 days”. L79-80.
- "The cores were then processed according to the international tree-ring analysis method." It is not clear what methods were used for the core processing. Please clarify.
Response: We have removed the “international tree-ring analysis method” statements, and added the sampling and lab processing in details.L116-127
- GPP = Assimilation + Respiration. These two parameters should cause opposite effects on the tree ring growth. I wonder is the authors only focused on the correlation in assimilation but overlooked the opposite effect of respiration on ring shrinking. There is a general statement of the climate change, that could be further explored in the paper. This all could make their current analysis to become incomplete. Would it be possible to clarify this and provide some inside in the magnitudes of the possible issues?
Response：Yes, GPP considers assimilation and respiration, while NPP is GPP minus respiration. In this study, we mainly focused on the relationship between canopy activity and tree trunk activity. So we did not employ the effects of respiratory. But your comment is really constructive. If respiratory effects can also be incorporated into model analysis, more interesting results will be obtained. Thank you and we will consider relevant works in the future.
- The conclusion is too short and not representative to the study. I think it should provide information to make at least the qualitative decision on what was claimed to be done in the abstract and in the introduction as well.
Response：Thank you for your suggestion. We rewrote the conclusion in revision. L359-L371
Reviewer 3 Report
The paper deals with the relationship between radial growth and canopy dynamics by two conifers depending on changeable climate factors. I can say that the whole study is well designed and includes a lot of different statistical methods. However, there are some questions which need to be answered. Why didn’t you select the same sample? You namely took 55 cores from 31 spruce trees and 35 cores from 19 Chinese pine. Within Discussion, in part 4.1., you stated „both spruce and Chinese pine were closely related to canopy activity from late February to early March, which is consistent with previous studies based on tree-ring data and monthly NDVI data of spruce or Chinese pine“, but there is no any reference that confirms it. After that, you mentioned relationship between radial growth of studied species and NDVI, but it is not related to February-March. You mentioned that water supply at the beginning of the growing season has a big influence to tree rings width of these species. But we know that spruce has a very shallow root system which means it uses water just from rainfalls, not from groundwater. Can you explain that a bit? Maybe conclusions should be a little bit extended.
Author Response
Comments and Suggestions for Authors
The paper deals with the relationship between radial growth and canopy dynamics by two conifers depending on changeable climate factors. I can say that the whole study is well designed and includes a lot of different statistical methods. However, there are some questions which need to be answered.
Response：Thank you for your affirmation of our work. We have carefully referred to your feedback and provided a detailed response.
- Why didn’t you select the same sample? You namely took 55 cores from 31 spruce trees and 35 cores from 19 Chinese pine.
Response：The distribution of the two tree species is different. The spruce distribution is concentrated, so suitable samples can be easily collected. However, Pinus tabulaeformis is relatively dispersed, resulting in a relatively small sample size. However, the statistical characteristics of both chronologies have reached the threshold, so it can be considered that the relevant analysis is reliable. We added these information in revision in L213-215.
- Within Discussion, in part 4.1., you stated “both spruce and Chinese pine were closely related to canopy activity from late February to early March, which is consistent with previous studies based on tree-ring data and monthly NDVI data of spruce or Chinese pine”, but there is no any reference that confirms it. After that, you mentioned relationship between radial growth of studied species and NDVI, but it is not related to February-March. You mentioned that water supply at the beginning of the growing season has a big influence to tree rings width of these species. But we know that spruce has a very shallow root system which means it uses water just from rainfalls, not from groundwater. Can you explain that a bit? Maybe conclusions should be a little bit extended.
Response：
1.Because there is no GPP relevant studies can be referred to, we sited several studies about NDVI. However, there are certain differences in the research results between NDVI and GPP, and we have also discussed the difference in the revision. L292-308
2 Thank you for pointing out the root system.
We have found some papers which reported that spruce mainly utilizes groundwater of 15-90cm in dry periods. While during wet periods, it mainly utilizes soil moisture of 0-20cm. But it is not particularly relevant to the topic we are discussing. So we modified the content to:“that roots can access water more easily”（L313）. At the same time, we looked forward to the possibility of related differences in the conclusion:“In addition, there are differences in the results between spruce and Chinese pine, which may be related to differences in organic matter allocation strategies or differences in habits (spruce has shallow roots, prefers shade, while Chinese pine has deep roots, prefers sunlight).”（L359-371）.
Reference
- Cong Xie, Liangju Zhao, Fei Meng, et al. Plant water sources in the upper reaches of the Heihe River forest ecosystem [J]. Journal of Lanzhou University (Natural Science Edition), 2020, 56 (04): 502-508. DOI: 10.13885/j.issn.0455-2059.2020.4.010.
- Guofeng Zhu, Lei Wang, Yuwei Liu, Bhat Mohd Aadil, Dongdong Qiu, Kailiang Zhao, Liyuan Sang, Xinrui Lin, Linlin Ye. Snow-melt water: An important water source for Picea crassifolia in Qilian Mountains[J]. Journal of Hydrology, 2022, 613(PA). DOI: 10.1016/J.JHYDROL.2022.128441.
Reviewer 4 Report
Please describe more detailed how do you use samples. Did you make one core per tree? From which side, North, East, etc. If the trees are on stipe terrain or on flat terrain?
You write 55 cores from 31 trees. Is that mean 2 per tree than you miss some cores. Same for other species 35 – 19 miss 3 cores.
Why you tested only a period of 36 years if you have chosen trees without human influence? Maybe because climate data?
Do you have diameters of trees?
I cannot agree that 0.4 is highly correlated
You need detailed comment on Correlation coefficients
In Section 4.1 you write from Feb to March and you need a reference
And in Section 4.2 from November to March
In Conclusion you need a explain what is practical contribution of this work for practice
Author Response
- Please describe more detailed how do you use samples. Did you make one core per tree? From which side, North, East, etc. If the trees are on stipe terrain or on flat terrain? You write 55 cores from 31 trees. Is that mean 2 per tree than you miss some cores. Same for other species 35 – 19 miss 3 cores.
Resonse：Yes, two cores per tree. We have provided a more detailed description of the sampling method. For the sample size, some samples were severely fractured and unable to be dated, so they were discarded, resulting in 31 trees with 55 cores and 19 trees with 35 cores being used for subsequent analysis. We also pointed out this in revision. L116-127.
- Why you tested only a period of 36 years if you have chosen trees without human influence? Maybe because climate data?
Response：GPP products provide continuous data since 1982. Therefore, this study can only analyze the relationship between tree rings and GPP since 1982. We have added a description of 1982 in the text. (L198-199)
- Do you have diameters of trees?
Response：We measured the relevant diameters, but we did not use diameter data as we prefer to study interannual relationships.
- I cannot agree that 0.4 is highly correlated
Response：Yes, for GPP is the total primary productivity that needs to be used for respiration and the growth of branches, leaves, buds, stems, and roots, so theoretically, the correlation coefficient is indeed difficult to reach extremely high (i.e.,>0.8). Therefore, we have reviewed the entire text and removed the phrase 'highly'.
- You need detailed comment on Correlation coefficients
Response：We have indicated both the correlation coefficients and p values in the results. (Section 3.2 and 3.3)
- In Section 4.1 you write from Feb to March and you need a reference. And in Section 4.2 from November to March
Response：Due to the lack of relevant research on GPP for reference. Therefore, we can only choose NDVI, but there are also certain differences between the two, so we have conducted corresponding discussions in the main text. L292-308
- In Conclusion you need a explain what is practical contribution of this work for practice
Response：We rewrote the conclusion section. L359-371
Round 2
Reviewer 1 Report
comments were addressed
Author Response
Dear reviewers,
Thank you for your review and valuable feedback on this manuscript.
Reviewer 2 Report
Dear Authors, thank you for your review and provided corrections.
I think that the manuscript has a good improvement in both understanding of methods and conclusion addressing the requests, and it is good to be published in the Journal.
Sincerely,
Author Response
Dear reviewers,
Thank you for your review and valuable feedback on this manuscript.
