Response of Stand Spatial Structure to Nitrogen Addition in Deciduous Broad-Leaved Forest in Jigong Mountain
, Shenglei Fu 3,4, Liyong Fu 1, Lei Ma 3,4, Xiaowei Li 3,4 and Juemin Fu 5Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThe article is too simple, and the results are too thin. As a result, the description of the material methods and results is lengthy, and the description of the results in the discussion part is too much, and even new content is added in discussion part, which is not related to the results. There are only 2 tables and 1 figure in the results part. In my opinion, these two tables can be combined into one table or figure to display these results. In addition, there are some problems in the writing of the article, such as logical incomprehension and misplacement of figures. The overall quality of the article needs to be greatly improved.
Detailed comments are as follows:
abstract
line23-24，32-33 Please state that the comparison of 5 treatments is between the data of 2012 and 2017
introduction
line75-80 There's no logical connection
Matedals and methods
2.4 part. For the definition of each indicator, I do not think it is necessary, this part can be appropriately simple description
results
In the author's results, three influencing factors were set up (LINE 180-183), but the author only used one-way ANOVA in the result analysis, which did not involve one-way or multi-way ANOVA. I don't think this method of analysis is reasonable. Secondly, most of the author's results are presented in tables, it is suggested to present them in figures, which is more intuitive.
Table 2 Maybe the average±standard error is more reasonable
Table 3 It may be better to use a figure, because the table provides little useful information.
Figure 1 I don't know how this Frequency distribution came about. In my understanding of the material and method section, there are only 4 repetitions per year for each treatment, how can the authors make the distribution frequency? Authors need to explain clearly in the materials and methods section and provide frequency data. A difference analysis between 2012 and 2017 is required. And I'm not sure what the point of having data of two years here.
line237 figure 3 does not exist in the article.
line269-270 This sentence is useless
discussion
Too many descriptions of results
Figure 2 and line336-341, What is the relationship between them and the results? Its existence does not explain the results obtained. On the contrary, the authors put forward this figure only for comparison with previous studies? Without further discussion and analysis, I think this figure has no role in explaining the results, and its existence is of no value. In addition, there is no figure 4
line360 & Figure 2 The P value doesn't need so many decimals
Author Response
Please see the paragraph below or the attachment.
Response to the comments of reviewer 1 (round 1):
The article is too simple, and the results are too thin. As a result, the description of the material methods and results is lengthy, and the description of the results in the discussion part is too much, and even new content is added in discussion part, which is not related to the results. There are only 2 tables and 1 figure in the results part. In my opinion, these two tables can be combined into one table or figure to display these results. In addition, there are some problems in the writing of the article, such as logical incomprehension and misplacement of figures. The overall quality of the article needs to be greatly improved.
Detailed comments are as follows:
Response:
Thanks for your positive comments on our manuscript (MS). Your comments and suggestions have been very helpful to improve this MS. We took into account all of the comments when making the attached revisions.
Point 1: Abstract: line23-24，32-33 Please state that the comparison of 5 treatments is between the data of 2012 and 2017.
Response 1:
Thank you for this suggestion. We have added the description of year 2012 and 2017 in the revised MS. The revised sentences are “Enhancements in the average value of Crowding degree (C) and comprehensive spatial structure index (CSSI) between 2012 and 2017 were found in all five treatments, demonstrating statistical significance” and “All five treatments increased the proportion of C at maximum level (C=1), while decreasing the proportions at levels 0, 0.25, and 0.5 in 2017”.
Point 2: Introduction: line75-80 There's no logical connection.
Response 2:
Thank you for this suggestion. We have added a sentence in the revised MS as follow “indicating that N addition concentration affects forest growth”, which corresponds to the sentence “Furthermore, the effects of different nitrogen deposition rates on tree growth are also vary”. Combine the description in the previous section of this paragraph about the different responses of tree size to nitrogen addition, so finally we proposed “Therefore, long-term and multi-level experiments of N addition in temperate forests can better predict the effects of limiting elements on tree growth”.
Point 3: Materials and methods: 2.4 part. For the definition of each indicator, I do not think it is necessary, this part can be appropriately simple description.
Response 3:
Thank you for this suggestion. We have simplified the description of four spatial structure indexes (M, U, W and C) in the revised MS. This change is mainly due to the deletion of the description of each indicator and the retention of the calculation formula.
Point 4: Results: In the author's results, three influencing factors were set up (LINE 180-183), but the author only used one-way ANOVA in the result analysis, which did not involve one-way or multi-way ANOVA. I don't think this method of analysis is reasonable. Secondly, most of the author's results are presented in tables, it is suggested to present them in figures, which is more intuitive.
Response 4:
Thank you for this suggestion. Maybe there was a misunderstanding due to the unclear description in this paragraph. We have changed the description from “The nitrogen deposition factor included three types” to “The data processing of nitrogen deposition included three types” in the revised MS. It's true that only one factor was taken into account in the data analysis. A comparative experiment with nitrogen addition methods (understory addition of N (UN) and canopy addition of N (CN)) and nitrogen addition intensities (at addition rates of 0, 25 and 50 kg N ha-1 yr-1) were conducted, including five treatments: 1) CN at 25 kg N ha−1 yr−1 (CN25); 2) CN at 50 kg N ha−1 yr−1 (CN50); 3) UN at 25 kg N ha−1 yr−1 (UN25); 4) UN at 50 kg N ha−1 yr−1 (UN50); and 5) a control (CK, without N addition). Due to the shortly 5-year interval, we analyzed the influence of different N addition methods, namely CK, CN (combining CN25 and CN50), and UN (combining UN25 and UN50). Similarly, we analyzed the influence of different N addition intensities, namely CK, N25 (combining CN25 and UN25), and N50 (combining CN50 and UN50). Therefore, there are three types of data structure, each of which was analyzed using one-way ANOVA.We have added Figure 2 before table 3 in the revised MS, which shows the difference between 2012 and 2017 of stand spatial structure index under three types ((1)three nitrogen addition intensities, CK, N25 and N50. (2) three nitrogen addition methods, CK, CN and UN. (3) five nitrogen addition treatments, CK, CN25, CN50, UN25 and UN50).
Point 5: Table 2 Maybe the average±standard error is more reasonable.
Response 5:
Thank you for this suggestion. We have added standard error in table 2 in the revised MS.
Point 6: Table 3 It may be better to use a figure, because the table provides little useful information.
Response 6:
Thank you for this suggestion. We have added Figure 2 before table 3 in the revised MS, which shows the difference between 2012 and 2017 of stand spatial structure index under three types, and tags the results of multiple comparisons. In addition, I think table 3 should be retained, which shows the results of one-way ANOVA.
Point 7: Figure 3 I don't know how this Frequency distribution came about. In my understanding of the material and method section, there are only 4 repetitions per year for each treatment, how can the authors make the distribution frequency? Authors need to explain clearly in the materials and methods section and provide frequency data. A difference analysis between 2012 and 2017 is required. And I'm not sure what the point of having data of two years here.
Response 7:
Thank you for this suggestion. The relevant description is not accurate enough in the paragraph. The data processing object level is no longer the plot but the trees in the plot. So we have changed the description in this paragraph in the revised MS, as follow, “Figure 3 illustrates the average values and standard deviations (error bars) of the stand spatial structure index (M, U, W, and C) at different levels (0, 0.25, 0.5, 0.75, and 1) of trees in each plot under five nitrogen treatments (CK, CN25, CN50, UN25 and UN50) in 2012 and 2017”.
Point 8: line237 figure 3 does not exist in the article.
Response 8:
Thank you for this suggestion. This is really our carelessness in the figure number reference. Two figures are added before this section, leading that the number here is 3.
Point 9: line269-270 This sentence is useless.
Response 9:
Thank you for this suggestion. We have removed this sentence and added a description in subsequent sentence in each section in the revised MS, as follow, “The frequency distribution of M in 2012 and 2017 exhibited a consistent pattern (Figure 3 M column)”, “The frequency distribution of U in 2012 and 2017 under the five nitrogen treatments exhibited a uniform distribution (Figure 3 U column)”,”The frequency distribution of W in 2012 and 2017 initially increased and then decreased with increasing W levels (Figure 3 W column)” and “The frequency distribution of C in 2012 and 2017 increased with the increase of C level (Figure 3 C column)”.
Point 10: Discussion: Too many descriptions of results.
Response 10:
Thank you for this suggestion. We have removed some descriptions in results, such as, “the responses of stand spatial structure indices M, U, and W were not significant (Table 3). In actuality, CN25, CN50, and UN25 had raised the averages of M and U, reduced the average of W, and the averages of U and W tend to be closer to 0.5 (Table 2)”, “The comprehensive spatial structure index CSSI responded significantly to nitro-gen addition treatments, with most declining in 2017, except for CN25 which margin-ally increased by 0.70% (Table 3)”, etc.
Point 11: Figure 2 and line336-341, What is the relationship between them and the results? Its existence does not explain the results obtained. On the contrary, the authors put forward this figure only for comparison with previous studies? Without further discussion and analysis, I think this figure has no role in explaining the results, and its existence is of no value. In addition, there is no figure 4.
Response 11:
Thank you for this suggestion. A simple linear regression analysis (line336-341) was conducted to explore the relationship between the difference of C from 2012 to 2017, and stand square average diameter (Figure 4 left). Before here, we considered the effect of forest regeneration on C. From another perspective, this is a further discussion of why there is a significant difference in the response of C on nitrogen addition treatments. The same considerations apply to CSSI. This is our carelessness in the figure number reference. Coincidentally, two figures are added before this section, so that the number here is 4.
Point 12: line360 & Figure 2 The P value doesn't need so many decimals.
Response 12:
Thank you for this suggestion. We have corrected this problem in the revised MS, changing 0.00077 to 0.0008.
Reviewer 2 Report
Comments and Suggestions for AuthorsOverall comment:
When I started reading the manuscript, I liked the idea of the research. Rising levels of climate pollution and other factors are leading to increased atmospheric nitrogen deposition. Therefore, the study is important since it evaluates the effect of N deposition on stand spatial structure of forest trees.
The paper is well written. The authors worked on an important topic that is atmospheric deposition of N on stand spatial structure of forest trees. The data interpretation or discussion part might need to be improved.
Specific comment:
Line 100 # Please rewrite the sentence
There is no ‘Figure 3’
My major concern was the overall data trend. There was not much difference in the frequency trend data for 2012 and 2017 (Fig 1).
Similarly, stand spatial structure index values are very close for 2012 and 2017. I think it might take years for trees to generate values that are significantly different. Therefore, the time period (5 years) used in this study might not be large enough to see the significant difference in the results. However, the paper was able to demonstrate the overall trend of stand spatial structure impacted by N deposition.
The references cited by the authors to support the discussion could be improved. For an eg. "The stand spatial structure index C responded significantly to nitrogen addition treatments, and generally exhibited an increase in 2017 (Table 3). This deviates from most literature where Crowding degree C diminishes (Hu et al., 2019; Chen et al., 2017). These studies primarily focused on the impact of thinning treatments on stand spatial structure, wherein thinning evidently reduced tree density and consequently diminished the crowding degree C." The reference the authors used here was for thinning of the plants. It would be interesting to know the reason for the increase in crowding degree with the addition of N fertilizer. What would be its importance on the natural plant population?
Also, Please use C in brackets like Crowding degree (C).
The overall discussion needs to be improved. Otherwise, the paper is well developed.
Author Response
Please see the paragraph below or the attachment.
Response to the comments of reviewer 2 (round 1):
When I started reading the manuscript, I liked the idea of the research. Rising levels of climate pollution and other factors are leading to increased atmospheric nitrogen deposition. Therefore, the study is important since it evaluates the effect of N deposition on stand spatial structure of forest trees.
The paper is well written. The authors worked on an important topic that is atmospheric deposition of N on stand spatial structure of forest trees. The data interpretation or discussion part might need to be improved.
Response:
Thanks for your positive comments on our manuscript (MS). Your comments and suggestions have been very helpful to improve this MS. We took into account all of the comments when making the attached revisions.
Point 1: Line 100 # Please rewrite the sentence.
Response 1:
Thank you for this suggestion. We have rewritten this sentence in the revised MS, as follow, “Deciduous temperate forest is the dominant vegetation in this area, characterized by Quercus acutissima Carruth., Quercus variabilis Bl., and Liquidambar formosana Hance as the predominant canopy tree species”.
Point 2: There is no ‘Figure 3’.
Response 2:
Thank you for this suggestion. This is really our carelessness in the figure number reference. Two figures are added before this section, leading that the number here is 3.
Point 3: My major concern was the overall data trend. There was not much difference in the frequency trend data for 2012 and 2017 (Fig 1).
Similarly, stand spatial structure index values are very close for 2012 and 2017. I think it might take years for trees to generate values that are significantly different. Therefore, the time period (5 years) used in this study might not be large enough to see the significant difference in the results. However, the paper was able to demonstrate the overall trend of stand spatial structure impacted by N deposition.
Response 3:
Thank you for this suggestion. Indeed the 5-year interval is short. By increasing the number of plots, we analyzed the influence of different N addition methods, namely CK, CN (combining CN25 and CN50), and UN (combining UN25 and UN50). Similarly, we also analyzed the influence of different N addition intensities, namely CK, N25 (combining CN25 and UN25), and N50 (combining CN50 and UN50). Finally, we have added a figure about the difference between 2012 and 2017 of stand spatial structure index under three types (Figure 2) in the revised MS.
Point 4: The references cited by the authors to support the discussion could be improved. For an eg. "The stand spatial structure index C responded significantly to nitrogen addition treatments, and generally exhibited an increase in 2017 (Table 3). This deviates from most literature where Crowding degree C diminishes (Hu et al., 2019; Chen et al., 2017). These studies primarily focused on the impact of thinning treatments on stand spatial structure, wherein thinning evidently reduced tree density and consequently diminished the crowding degree C." The reference the authors used here was for thinning of the plants. It would be interesting to know the reason for the increase in crowding degree with the addition of N fertilizer. What would be its importance on the natural plant population?
Response 4:
Thank you for this suggestion. In the first paragraph of discussion, we introduce the background that scant direct research exists exploring the relationship between nitrogen deposition and stand spatial structure, but primarily focusing on the influence of thinning treatments or forest fire on stand spatial structure. Therefore, we directly compared the result of an increase C with thinning treatments or forest fire. Furthermore, we explained the reasons of an increase C in the later part of this paragraph. First we considered the effect of forest regeneration on C. Then a simple linear regression analysis was conducted to explore the relationship between the difference of C from 2012 to 2017, and stand square average diameter (Figure 4 left).
Point 5: Also, Please use C in brackets like Crowding degree (C).
Response 5:
Thank you for this suggestion. We have corrected the description about the references to abbreviated symbols in the revised MS.
Point 6: The overall discussion needs to be improved. Otherwise, the paper is well developed.
Response 6:
Thank you for this suggestion. We have changed some of the description and removed the comments on previous studies and re-presentation of the results in discussion.
Reviewer 3 Report
Comments and Suggestions for AuthorsThe manuscript submitted by Hong et al presents a study with an interesting and valuable topic. The study investigated the impact of nitrogen (N) addition on the spatial structure of a deciduous hardwood forest over a five-year period from 2012 to 2017. The results showed that N addition moderately influenced the spatial structure of the stand, with increases in some parameters, such as degree of crowding (M) and neighborhood comparison (U), and decreases in uniform angle index (W). Degree of crowding (C) and global spatial structure index (CSSI) increased significantly in all treatments. The distribution of the spatial structure index showed an optimization with some N treatments. In general, the addition of N improved spatial structure and stimulated growth of larger diameter trees. However, the short duration of the study suggests the need for longer-term research. N deposition could be a valuable tool for optimising forest management.
The introduction is well written and introduces the reader to the proposed topic. Previous studies are highlighted and also the objectives of this study.
Materials and Methods: At Study site a map has to be add.
Results and analysis: The results are presented in detail. Too much detail though considering that the same information is presented in the table/graph but also in the text.
Discussion
Remove the comments on previous studies but also the re-presentation of the results and refer to the results obtained and whether or not they are validated by results of similar studies in the same area but not only.
Conclusions: This section is well written and briefly presents the results and limitations of this study.
Author Response
Please see the paragraph below or the attachment.
Response to the comments of reviewer 3 (round 1):
The manuscript submitted by Hong et al presents a study with an interesting and valuable topic. The study investigated the impact of nitrogen (N) addition on the spatial structure of a deciduous hardwood forest over a five-year period from 2012 to 2017. The results showed that N addition moderately influenced the spatial structure of the stand, with increases in some parameters, such as degree of crowding (M) and neighborhood comparison (U), and decreases in uniform angle index (W). Degree of crowding (C) and global spatial structure index (CSSI) increased significantly in all treatments. The distribution of the spatial structure index showed an optimization with some N treatments. In general, the addition of N improved spatial structure and stimulated growth of larger diameter trees. However, the short duration of the study suggests the need for longer-term research. N deposition could be a valuable tool for optimising forest management.
Response:
Thanks for your positive comments on our manuscript (MS). Your comments and suggestions have been very helpful to improve this MS. We took into account all of the comments when making the attached revisions.
Point 1: The introduction is well written and introduces the reader to the proposed topic. Previous studies are highlighted and also the objectives of this study.
Response 1:
Thank you for this positive comment.
Point 2: Materials and Methods: At Study site a map has to be add.
Response 2:
Thank you for this suggestion. We have added Figure 1 about the distribution map of permanent sample plots in the revised MS.
Point 3: Results and analysis: The results are presented in detail. Too much detail though considering that the same information is presented in the table/graph but also in the text.
Response 3:
Thank you for this suggestion. We have simplified some descriptions in the revised MS.
Point 4: Discussion: Remove the comments on previous studies but also the re-presentation of the results and refer to the results obtained and whether or not they are validated by results of similar studies in the same area but not only.
Response 4:
Thank you for this suggestion. We have removed the comments on previous studies, such as, “Hu Xuefan et al. (2019) used the comprehensive index CSSI to evaluate comprehensively the response of the spatial structure of secondary Mongolian oak forests to different thinning treatments. The results showed that both traditional management and two target tree management treatments optimized the stand spatial structure”, “Li Xiaowei et al. (2021) found that canopy nitrogen addition (CN) significantly in-creased the fine root biomass of plot trees compared to understory nitrogen addition (UN)”, etc. Also, we have removed the description in results, such as, “the responses of stand spatial structure indices M, U, and W were not significant (Table 3). In actuality, CN25, CN50, and UN25 had raised the averages of M and U, reduced the average of W, and the averages of U and W tend to be closer to 0.5 (Table 2)”, “The comprehensive spatial structure index CSSI responded significantly to nitro-gen addition treatments, with most declining in 2017, except for CN25 which margin-ally increased by 0.70% (Table 3)”, etc.
Point 5: Conclusions: This section is well written and briefly presents the results and limitations of this study.
Response 5:
Thank you for this positive comment.
Round 2
Reviewer 3 Report
Comments and Suggestions for Authors287-297 does not belong in Discussion. Compare previous results with those obtained in this study.
In an overall the Discussion is not well presented. Rewrite this section according to journal standards.
Otherwise, I noticed that the manuscript has been improved.
Author Response
Response:
Thanks for your comments on our manuscript (MS). Line 287-297, we have replaced some content to section Introduction (see lines 65-73 in revised MS), and deleted the remaining content, “This research utilized five nitrogen addition treatments (CK, CN25, CN50, UN25, UN50) on the canopy simulated nitrogen deposition platform to analyze the alterations in the spatial structure indices of Mingling degree (M), Neighborhood comparison (U), Uniform angle index (W), and Crowding degree (C), as well as the comprehensive spatial structure index (CSSI) in 2012 and 2017”.
This paragraph in Discussion was rewritten into a new one, “One-way analysis of variance in this study showed that CN25, CN50, and UN25 had a beneficial impact on the stand spatial structure indices of Mingling degree (M), Neighborhood comparison (U) and Uniform angle index (W) (Table 2), albeit insignificant (Table 3). This might be attributable to the 5-year time interval being relatively short, such that changes in the stand spatial structure induced by tree growth could not be reflected timely. The effect of short-term nitrogen addition on tree growth was not significant, which was also reported in other literature (Zhou, et al.,2019; Kjønaas et al., 1998). Therefore, the effect of nitrogen addition on the stand spatial structure needs to be continuously observed and studied”.
Furthermore, we have changed the description about the impacts of nitrogen addition methods (CN and UN) and nitrogen addition intensities (N25 and N50) on stand spatial structure, as follow “In the present study, the impacts of nitrogen addition methods (CN and UN) and nitrogen addition intensities (N25 and N50) on stand spatial structure were consistent with the effects of nitrogen addition treatments, suggesting that stand spatial structure indices M, U, and W did not respond significantly to nitrogen addition methods and intensities, while C and CSSI respond significantly (Table 3). Furthermore, multiple comparison tests showed that the differences between different nitrogen addition methods or intensities and the control group were significant, possibly due to the differences in plot renewal and square average diameter (Table 1). However, the differences of stand spatial structure indices between nitrogen addition methods (CN and UN) and between nitrogen addition intensities (N25 and N50) were not found in this study, possibly because changes in stand spatial structure require a longer time to manifest”.
Round 3
Reviewer 3 Report
Comments and Suggestions for Authors332-341 compress the paragraph
342-352 delete the paragraph or add the necessary bibliographical references
353-361 delete the paragraph or add the necessary bibliographical references
Author Response
Response to the comments of reviewer 3 (round 3):
332-341 compress the paragraph.
Response:
Thanks for your suggestion on our manuscript (MS). We have compressed the paragraph in the revised MS, as follow “Our study's results showed that nitrogen addition treatments optimize the stand spatial structure, which align with the effects in Hu Xuefan et al. (2019). This may provide additional evidence that the size of the tree plays a significant role in its growth. Specifically, the larger the tree's diameter, the more vigorous and competitive it is, resulting in a higher CSSI. Actually, the data from 20 plots indicate a significant positive linear relationship between CSSI and the stand square average diameter (R2=0.4752, P=0.0008, Figure 4 right)”.
The original text is “Our study's results showed that nitrogen addition treatments optimize the stand spatial structure, which align with the effects in Hu Xuefan et al. (2019), although it appears to be a decrease in value, but compared to the control group CK, CN25, CN50, and UN25 all significantly alleviated the rate of degradation of stand spatial structure (Table 3), as confirmed in the multiple comparison test of the mean differences in CSSI. Furthermore, the data from 20 plots indicate a significant linear relationship between the comprehensive spatial structure index CSSI and the stand square average diameter (R2=0.4752, P=0.0008, Figure 4 right), and the comprehensive spatial structure index CSSI increased with an increase in stand square average diameter. This further corroborates that the size of the tree itself is an influential factor affecting tree growth, that is, the larger the diameter, the more vigorous of the tree, the more competitive it is, hence the comprehensive spatial structure index CSSI will be larger”.
342-352 delete the paragraph or add the necessary bibliographical references.
Response:
Thanks for this suggestion. We have deleted this paragraph except for the last sentence “However, the differences of stand spatial structure indices between nitrogen addition methods (CN and UN) and between nitrogen addition intensities (N25 and N50) were not found in this study, possibly because changes in stand spatial structure require a longer time to manifest”, which was incorporated into the next paragraph by rewriting it.
353-361 delete the paragraph or add the necessary bibliographical references.
Response:
Thanks for this suggestion. We have added three bibliographical references and adjusted the relevant description in the revised MS, as follow, “Studies have shown that the number of competing trees based on Euclidean distances can vary (Davies and Pommerening, 2008; Hu et al., 2021). This study utilizes a 4-neighbor method to calculate the spatial structure indices of trees, and further re-search is needed to determine the impact of their number on the rules affecting the spatial structure indices of trees and to establish the optimal number. Moreover, Li Xiaowei et al. (2021) found that nitrogen addition methods (CN and UN) have a significant effect on the fine root biomass of plot trees in the same platform. However, the differences of stand spatial structure indices between CN and UN was not found in this study, possibly because changes in stand spatial structure require a longer time to manifest. Therefore, the long-term impacts of different nitrogen addition treatments on stand spatial structure and other characteristic indices require longer-term plot data collection to obtain a more stable response pattern of stand spatial structure to nitrogen deposition, which will provide guidance and basis for the management of deciduous mixed forests in the North-South climatic transition zone of Dabie Mountains”
