Patterns of Forest Species Association in a Broadleaf Forest in Romania
Round 1
Reviewer 1 Report
For never was a story of more woe than this of…
The problems associated with interactions between tree species at the undergrowth level have long worried the mind of scientists. Many poems, stories, articles, and books have been written. Many more will be written. Yet, there are still more questions than answers. Have the authors been able to meaningfully address any questions on this subject through their research? More likely to be no than yes. And here is why.
Extremely startled as to why wild cherry (Prunus avium) was included among the species investigated. This species does not reach the forest's first layer. Possibility in theory, but never in reality! Consequently, this species has its own strategy of settling, expanding, and developing beneath the forest canopy. Dissimilar to the species that make forests. Make a comparison between these different species?
This work ignores the fact that the tree species under study employ various strategies for dispersing their seeds. Some species have wind-dispersed seeds (anemochory). For example, Acer spp. Animals spread the seeds of other species (zoochory). For example, Quercus spp. and etc. It is hard to evaluate how the seeds are dispersed since there is a dearth of information on the placement of sample sites inside the stands. As a result, the cause of the presence or absence of particular species in the undergrowth cannot be ascertained.
No information is available on how the sample plots were placed inside the tree stand. Were they in the forest gap or under the canopy (closed or not?)? This impacts not just how a specific forest area settles, but also how some species growth and survive throughout the undergrowth stage.
What kind of undergrowth was studied? The height of the undergrowth? The age of the undergrowth? Some species' undergrowth can persist for a very long period beneath the forest canopy (including in a suppressed state). Contrarily, other species cannot survive the effects of adverse factors emerging beneath the forest canopy for an extended time.
The potential for these species to have both a vegetative and seed genesis in the undergrowth is not taken into consideration. All of this impacts how the undergrowth underneath the forest canopy is distributed.
Yes, the authors do a disclaimer at the end of their story that the purpose was only to evaluate the spatial position of the undergrowth of various species. However, for a forest scientist, this knowledge is of limited use because the distribution of undergrowth varies significantly not just between different types of forests but even within the same forest type. Nonetheless, the authors attempt to make broad generalisations regarding the biology and ecology of the researched species of woody plants based on this data, including their characteristics of mutual growth and development at the undergrowth stage.
Author Response
Dear Reviewer,
We thank you for the effort and the time spent reviewing our manuscript. We appreciate the valuable feedback and the opportunity to revise our paper on ‘Patterns of forest species association: a case study in a sapling community’. Your suggestions have been supportive, and we appreciate the constructive comments.
We have included the comments immediately after this short letter and responded to them individually, indicating exactly how we addressed each concern and describing the changes we have made. Both authors have approved the revisions. The changes are highlighted in the paper, and the revised manuscript and updated supplementary material are attached.
We hope our adjustments have resulted in a significantly improved manuscript that suits Forests journal better. Thank you again for the helpful input!
Sincerely,
Ciprian Palaghianu
May 13th 2023
Reviewer 1 - Comments and Suggestions for Authors
Extremely startled as to why wild cherry (Prunus avium) was included among the species investigated. This species does not reach the forest's first layer. Possibility in theory, but never in reality! Consequently, this species has its own strategy of settling, expanding, and developing beneath the forest canopy. Dissimilar to the species that make forests. Make a comparison between these different species?
[ADDRESSED] Thank you for your comment. In this study, we aimed to compare three different methods of characterising the species associations /co-occurrence at different scales. We focused on integrating the results from the three different approaches (co-occurrence indices based on binary data, local abundance examination by PCA, and spatial point pattern analysis of species distribution) and not on comparing the different species. Therefore, we selected a type of forest frequently encountered in the study area, with a common species composition in this development stage. We chose a sapling community because its complexity offered a robust "test platform" of comparison among the three methods we used. We did not want to focus on selecting or eliminating certain species from the study. Therefore, we started examining this community, considering it "as it is" with respect to its species composition. Moreover, we were led in this study considering the potential practical importance of this kind of investigation. The applied approach used in this study could be a first step in designing a future framework for investigating forest regeneration and providing forest restoration directions.
We considered your observation and integrated additional explanations in the introduction to clarify this particular aspect. Furthermore, we added to the supplementary material Table S1 which contains the species composition of each plot (the species percentage for each plot). This information may explain some of the results, so we updated the discussion section to link this new information with the results obtained.
This work ignores the fact that the tree species under study employ various strategies for dispersing their seeds. Some species have wind-dispersed seeds (anemochory). For example, Acer spp. Animals spread the seeds of other species (zoochory). For example, Quercus spp. and etc. It is hard to evaluate how the seeds are dispersed since there is a dearth of information on the placement of sample sites inside the stands. As a result, the cause of the presence or absence of particular species in the undergrowth cannot be ascertained.
[ADDRESSED] Thank you for your observation. We acknowledged in our paper that many biotic and environmental factors shape juvenile forest communities. These different factors have already shaped the spatial patterns of the analysed community. Identifying these factors or how they created the existing pattern is beyond the scope of this study. Our analysis started with the present state - the current image of the spatial arrangement of species. This research aimed to see if the three methods used capture roughly the same realities and trends regarding the spatial distribution patterns of the species. We did not propose to examine the causes of these interactions, but only the ability of the investigative methods to capture specific patterns, and we want to observe if these patterns are consistent for different methods or at different scales of analysis. However, we considered your observation helpful and integrated additional explanations in the introduction and added in conclusion the need for more rigorous experiments to investigate the species associations in sapling communities (with complex observations of the micro-habitat conditions, species mechanisms of dispersions and regeneration and even the spatial pattern of the parent trees).
No information is available on how the sample plots were placed inside the tree stand. Were they in the forest gap or under the canopy (closed or not?)? This impacts not just how a specific forest area settles, but also how some species growth and survive throughout the undergrowth stage.
[ADDRESSED] Thank you for your comment. We realized that more specific information is needed about the studied area and the location of the plots. Therefore, we added a map of the area (as another reviewer suggested) and updated the information about the location of plots in the studied area:
2.1. Study site - “The stand was regenerated using the group shelterwood system, and the final removal cuts were applied six years before installing the sampling plots. In the study area, the seedlings had similar vegetation conditions. “(so, all the mature trees of the previous stand were removed six years before the inventory of the studied plots)
2.2. Data collection - “Within the cleared stand, a homogeneous area with a compact seedling cover was selected, where we set up a network of 10 plots in which all individuals were inventoried. The plots were positioned in two rows, with plot limits separated by 50 m. A buffer strip of 100 m was left from the stand boundary to prevent any specific composition irregularities due to the edge effect.”
What kind of undergrowth was studied? The height of the undergrowth? The age of the undergrowth? Some species' undergrowth can persist for a very long period beneath the forest canopy (including in a suppressed state). Contrarily, other species cannot survive the effects of adverse factors emerging beneath the forest canopy for an extended time. The potential for these species to have both a vegetative and seed genesis in the undergrowth is not taken into consideration. All of this impacts how the undergrowth underneath the forest canopy is distributed.
[ADDRESSED] Thank you for your comment. Our study was located in a homogeneous area with a compact seedling cover. The community of saplings is dimensionally uniform, the seedlings being installed after the final removal cuts were applied six years before sampling. The average height of the saplings is 98.01 cm (considering all individuals from the ten sampled plots), with a coefficient of variation of 54%. However, the size and age of the saplings were not considered relevant for achieving the objectives proposed in this species co-occurrence investigation. Therefore, the analysis used only individuals' presence, species and positions in each plot.
We considered your observation and integrated further explanations in the introduction to clarify our research objective. In the conclusions, we also expressed our interest in continuing this study through further experiments based on more complex observations of the micro-habitat conditions, species mechanisms of dispersions/regeneration or even the spatial pattern of the parent trees. Additionally, we inserted into the supplementary material Table S1 which contains the species composition of each plot as support information.
Yes, the authors do a disclaimer at the end of their story that the purpose was only to evaluate the spatial position of the undergrowth of various species. However, for a forest scientist, this knowledge is of limited use because the distribution of undergrowth varies significantly not just between different types of forests but even within the same forest type. Nonetheless, the authors attempt to make broad generalisations regarding the biology and ecology of the researched species of woody plants based on this data, including their characteristics of mutual growth and development at the undergrowth stage.
[ADDRESSED] Thank you for your comment. We integrated your observation in the abstract, introduction and conclusions sections.
Our study aimed to test three methods to assess species associations at different scales: the co-occurrence indices for binary presence-absence data, principal component analysis (PCA) on species abundance and point process analysis. We modified and included additional paragraphs in the abstract and the introduction section to emphasise explicitly our goal.
Definitely, the results of our observational study revealed distinct co-occurrence patterns of forest species in the analysed sapling community. Even though all three methods of investigation highlighted several consistent positive and negative associations between species, we specified in the final paragraph of the conclusion section that the results are confined to the analysed community. We also modified the paper's title to explicitly underline that this investigation represents a case study. At the end of the discussion section, we updated the last paragraph "Nonetheless, we completed an observational study which was not intended to prove associations but to reveal and integrate the results from three methods about distinct species co-occurrence patterns without drawing conclusions about causal relationships."
Furthermore, in the conclusion we add that, for the moment, we cannot generalise our findings and we highlighted “… the need for more rigorous experiments to investigate the species associations in sapling communities, requiring complex observations of the micro-habitat conditions, species mechanisms of dispersions and regeneration, or even the spatial pattern of the parent trees.”
Observation: Additional modifications to those mentioned in this answer were made in the manuscript, introduced to address the observations suggested by the other two reviewers.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Check attached file
Comments for author File: Comments.docx
Author Response
Dear Reviewer,
We thank you for the effort and the time spent reviewing our manuscript. We appreciate the valuable feedback and the opportunity to revise our paper on ‘Patterns of forest species association: a case study in a sapling community’. Your suggestions have been supportive, and we appreciate the constructive comments.
We have included the comments immediately after this short letter and responded to them individually, indicating exactly how we addressed each concern and describing the changes we have made. Both authors have approved the revisions. The changes are highlighted in the paper, and the revised manuscript and updated supplementary material are attached.
We hope our adjustments have resulted in a significantly improved manuscript that suits Forests journal better. Thank you again for the helpful input!
Sincerely,
Ciprian Palaghianu
May 13th 2023
Reviewer 2 - Comments and Suggestions for Authors
Abstract
Kindly check minor spelling mistake. The abstract needs a better composition of words.
[ADDRESSED] Thank you for your comment. We modified the abstract, as suggested, and we think it better reflects our aim and findings now.
Introduction
Authors should explain why they chose saplings in this work.
[ADDRESSED] Thank you for your suggestion. We thoroughly explained in the introduction (lines 102-108) the reason we chose saplings for this observational study.
Although few studies investigated the particularities of juvenile forest communities, shaped by many biotic and environmental factors, we consider the potential practical importance of these association patterns not only for the insight into community assembly but also to provide forest restoration directions. Furthermore, our observational study focused on a sapling community because biotic interactions in these communities are highly complex and confined to limited spaces (Webb & Peart, 2000; Yamazaki et al., 2008), offering a solid "test platform" for our comparison among the different methods we used.
In this case, the limited space represents a nuisance, considering the effort of the data collection, but also an advantage for data analysis, as the interaction ranges are limited in space. Young cohorts are not shaped yet by environmental filtering (Webb & Peart, 2000). Its influence can be observed at larger scales, but the scale is narrower in the case of sapling interactions (Yin et al., 2021).
Material and methods
Insert the area studied in this experiment if possible.
[ADDRESSED] Thank you for your suggestion. We added Figure 1. Location of the study area.
Discussion
Could be more detailed. The lines should be more focused for highlighting the important finding of this work.
[ADDRESSED] Thank you for suggestion. We modified the discussions to be more focused on the important finding of the study. Furthermore, we integrated the reviewers' observations and added new references.
References
Strengthen the part of the discussion with 2 or 3 new references.
[ADDRESSED] Thank you for the suggestion. We added new relevant references that we integrated into the discussions and took into account the reviewers' observations.
Conclusion
Minor language issues must be addressed to improve quality of the MS.
[ADDRESSED] Thank you for comment. We checked the manuscript for language issues and corrected it.
Observation: Additional modifications to those mentioned in this answer were made in the manuscript, introduced to address the observations suggested by the other two reviewers.
Author Response File: Author Response.docx
Reviewer 3 Report
The manuscript entitled “Patterns of forest species association in sapling communities: a story of love and hate” addresses important ecological problems of the association of forest species in sapling communities. The authors have carefully and with scientific skill collected a serious amount of data in the field. They have used various methods of data analysis, taking into account different spatial scales and analytical approaches. The text of the article calmly and in-depth explains the successive stages of analysis and methodological intricacies. Unfortunately, material collected at a single site in a relatively homogeneous environment without environmental data significantly reduces the interpretability of the results obtained.
My main objection is that the main result, negative associations at small spatial scales and positive at larger scales, may be due to the fact that a higher number of seedlings was recorded on the larger plots and a lower number on the smaller plots. With a larger number of seedlings, there is a greater chance that more species will be represented and therefore the number of positive associations will increase. Conversely, with small plots, the number of individuals (and probably species) will be smaller, increasing the likelihood of negative associations. A similar problem occurs in biodiversity assessments, where small samples are less diverse than large ones (e.g. A. Chao et al. 2014).
My other comments are detailed below.
Line 65-66; 7172;74-77 This statement presents the rationale for the method used. In my opinion, it belongs in the Materials and Methods section rather than the Introduction.
Line 100 and 107. If the study plots were situated at 460 m a. s. l. what is the altitude 135-140 m?
Study site. Better study plot characteristics are needed, especially the species composition of each plot, as this may influence (or explain) the result obtained. For example, the absence of certain species on the same plots may explain the negative association.
Line 185-188. For data such as those presented in the manuscript, PCA compares the standardised species composition of the study plots by treating each species as a variable and then drawing the vectors of each variable (species) in the resulting multidimensional space. Obviously, if the vectors of two species are close together and have the same direction, this means that their occurrence is correlated, but the arrangement of the points on the plot and the axes drawn, as well as the species vectors, are influenced by all the species together, not by pairs of individual species. In other words, I think there are better ways of comparing the co-occurrence of species, taking into account their abundance, than PCA.
Figure 3. Why are the data of different pairs compared linked? I think a simple bar chart with data for all the pairs analysed would be better. On the other hand, this figure duplicates the data summarised in Table 1. Perhaps this graph should be moved to the supplementary material.
Lines 392 and 396. The text does not agree with the figures. Figure 7 shows Pa-Ac, Figure 8 Ac-Qr, whereas in the text it is the other way round.
Figure 5. Why is plot number 2 missing? Table 1 suggests that both species are present on this plot. However, Figure 4 suggests that both may be missing from this plot, in which case this information should somehow be included in Table 1.
Table 2. The table presents PCA ordination data, but in its current form it has no biological meaning. The correlation shown does not validate the co-occurrence of the species.
Line 464. Figure 6 shows 4 positive and 3 negative associations, but in reality it is out of 10 despite 4 non-significant cases.
Lines 521-527. This is the most convincing explanation for the results obtained.
Conclusion
I do not consider this manuscript suitable for publication in the journal Forests in its present state. I suggest that it be reconsidered after a major revision.
Author Response
Dear Reviewer,
We thank you for the effort and the time spent reviewing our manuscript. We appreciate the valuable feedback and the opportunity to revise our paper on ‘Patterns of forest species association: a case study in a sapling community’. Your suggestions have been supportive, and we appreciate the constructive comments.
We have included the comments immediately after this short letter and responded to them individually, indicating exactly how we addressed each concern and describing the changes we have made. Both authors have approved the revisions. The changes are highlighted in the paper, and the revised manuscript and updated supplementary material are attached.
We hope our adjustments have resulted in a significantly improved manuscript that suits Forests journal better. Thank you again for the helpful input!
Sincerely,
Ciprian Palaghianu
May 13th 2023
Reviewer 3 - Comments and Suggestions for Authors
My main objection is that the main result, negative associations at small spatial scales and positive at larger scales, may be due to the fact that a higher number of seedlings was recorded on the larger plots and a lower number on the smaller plots. With a larger number of seedlings, there is a greater chance that more species will be represented and therefore the number of positive associations will increase. Conversely, with small plots, the number of individuals (and probably species) will be smaller, increasing the likelihood of negative associations. A similar problem occurs in biodiversity assessments, where small samples are less diverse than large ones.
[ADDRESSED] Thank you for your comment. Although it is a more frequently encountered problem in biodiversity studies, we are aware that sampling problems related to different scales can influence the results of species association investigations. For example, Legendre & Legendre (Legendre & Legendre, 2012) suggested that it is more instructive to compare dominant or abundant species than rare taxa because the latter, having low frequencies of occurrence, are generally inadequately sampled.
While our findings are consistent with other studies, which found at small scales negative associations (Yin et al., 2021; Fajardo et al., 2006; Zhou et al., 2009), we admit that scale sampling could affect the results. Therefore, we explicitly integrated your opinion in the discussion section (lines 575-580). Moreover, in the Data analysis section, we pointed out in the manuscript that several studies (Fortin et al., 1990; Koleff et al., 2003; Blanchet et al., 2020) highlighted the sensitivity of species association patterns to the influence of scale (lines 173-174). Nonetheless, studies have not found an explicit link between small scales and statistically significant negative associations of species as a direct result of lower abundances in smaller plots. But the suggested scale issue remains intriguing and can also be extended towards ecological dominance. We admit ecological dominance might influence the spatial distribution patterns of species because dominant individuals have more frequent interactions than others (and we covered this topic in the discussion section).
Line 65-66; 71-72;74-77 This statement presents the rationale for the method used. In my opinion, it belongs in the Materials and Methods section rather than the Introduction.
[ADDRESSED] Thank you for your suggestion. We appreciate your opinion, and therefore we moved and updated those lines in the Materials and Methods section.
Line 100 and 107. If the study plots were situated at 460 m a. s. l. what is the altitude 135-140 m?
[ADDRESSED] Thank you for your comment. It was just a typo (the value 460 m) and we made the correction. We also added Figure 1. Location of the study area (as requested by another reviewer), and we specified the GPS coordinates to precisely identify the study area.
Study site. Better study plot characteristics are needed, especially the species composition of each plot, as this may influence (or explain) the result obtained. For example, the absence of certain species on the same plots may explain the negative association.
[ADDRESSED] Thank you for your suggestion. We added to the supplementary material Table S1 which contains the species composition of each plot (the species percentage for each plot). This information may partially explain some of the results, such as the negative association between several species in specific plots, considering that rare taxa are affected by sampling issues because of their low frequency of occurrence. We also updated the discussion section to link this new information with the results obtained.
Regarding the absence of certain species on the same plot - if both species are missing in the same plot, that particular plot is no longer included in the point process analysis (Ripley K function is calculated for a minimum of 10 individuals in the plot for each species) because it did not meet the requirement of having at least ten individuals of each species in a plot. However, in the case of the Jaccard index, based on presence-absence data of species, the number of individuals does not limit the calculation of the index. Therefore, in this case, only the quadrats where both species are missing are not included in the calculation (negative matches), as specified in the methodology.
As stated above (comment about the scale), scale issues can also extend to ecological dominance; therefore, species composition per plot is relevant information considering dominant individuals have more frequent interactions than others. We also pointed out that (lines 575-580): In our case study, the hornbeam (Cb) has a disproportionate weight (55%) compared to the other species in the analysed sapling community. Possibly as a result of ecological dominance, hornbeam (Cb 55%) is found in many of the positive associations, while sycamore (Ap 1%) is in most of the negative ones, as other rare species.
Line 185-188. For data such as those presented in the manuscript, PCA compares the standardised species composition of the study plots by treating each species as a variable and then drawing the vectors of each variable (species) in the resulting multidimensional space. Obviously, if the vectors of two species are close together and have the same direction, this means that their occurrence is correlated, but the arrangement of the points on the plot and the axes drawn, as well as the species vectors, are influenced by all the species together, not by pairs of individual species. In other words, I think there are better ways of comparing the co-occurrence of species, taking into account their abundance, than PCA.
[ADDRESSED] Thank you for your suggestion. We aimed to compare three different methods in characterising the species associations or co-occurrence. PCA is a powerful and versatile method widely used in ecology studies to analyse community data (Legendre & Legendre, 2012). This Euclidean-based ordination method also has a good potential in assessing similarity coefficients based on species presence-absence or abundance data, but despite its frequent use might not be the most suitable for investigating the association of species (Legendre & Gallagher, 2001). In the case of our study, we consider PCA does not provide adequate results, but we used this method to compare it with the other two and to observe if the results are in line with the outcomes of the other methods. Nonetheless, we agree with you, and we think PCA would not be the first choice in analysing species co-occurrence or associations. Therefore, we added further explanations in the methodology section (lines 228-233), and we explicitly integrated your observation in the discussion section. (lines 657-661).
Figure 3. Why are the data of different pairs compared linked? I think a simple bar chart with data for all the pairs analysed would be better. On the other hand, this figure duplicates the data summarised in Table 1. Perhaps this graph should be moved to the supplementary material.
[ADDRESSED] Thank you for your suggestion. The chart was inserted in that particular form for its visual impact in identifying the positive or negative associations between species. However, most of the information in the chart is summarized in Table 1. Therefore, we moved the chart to the supplementary material (Figure S1: The variation of cumulative values of the Jaccard co-occurrence index describing pair-species associations for different quadrat sizes). Moreover, we used your suggestion to use a simple cumulative bar chart.
Lines 392 and 396. The text does not agree with the figures. Figure 7 shows Pa-Ac, Figure 8 Ac-Qr, whereas in the text it is the other way round.
[ADDRESSED] Thank you for your observation. We checked and it was a typo, therefore we modified the text as suggested.
Figure 5. Why is plot number 2 missing? Table 1 suggests that both species are present on this plot. However, Figure 4 suggests that both may be missing from this plot, in which case this information should somehow be included in Table 1.
[ADDRESSED] Thank you for your comment. Regarding the missing plot number 2 - this situation is caused by a calculation limitation of the Ripley function (to limit the spatial positioning errors), which uses a minimum of 10 individuals in the plot for each species (as we specified between lines 283-287: In addition, several other plots were also eliminated in the case of point process analysis from particular species analyses because they did not meet the requirement of having at least ten individuals of each species in a plot.). Figure 5 presents the results of Ripley for Fe-Tc relationship (and in plot 2 the condition of a minimum of 10 individuals for each species was not met, and as a result, plot 2 was not included in the analysis). However, in the case of Table 1 the method used (Jaccard index) is based on presence-absence data of species. The number of individuals does not limit the calculation of the Jaccard index, and in this case, only the quadrats where both species are missing were eliminated from the calculation (negative matches), as specified in the methodology (lines 195-196: In our analyses, we selected the Jaccard index, a classical index of co-occurrence that does not incorporate negative matches (quadrats where both species are missing).).
Table 2. The table presents PCA ordination data, but in its current form it has no biological meaning. The correlation shown does not validate the co-occurrence of the species.
[ADDRESSED] Thank you for your comment. Your observation is correct and very useful. We tried to use a more objective (numerical) form of presenting the information provided by PCA in order not to interpret the association of species based only on the visual analysis of the grouping of variables. However, the numerical values in the table are not so relevant for the co-occurrence of the species. Therefore, we modified the information presented initially in Table 2 and considering its lower relevance, we moved the table to the supplementary material (Table S2 - The explained variance of PCA for different quadrat sizes and the most significant pair-species correlation).
Line 494. Figure 6 shows 4 positive and 3 negative associations, but in reality it is out of 10 despite 4 non-significant cases.
[ADDRESSED] Thank you for your observation. We corrected as suggested: “…but positive associations are present in 4 of the ten plots (Figure 6)”
Lines 521-527. This is the most convincing explanation for the results obtained.
[ADDRESSED] Thank you for the suggestion. We are glad you appreciate these lines as convincing. Therefore, we highlighted these ideas and integrated them into the conclusions and the paper's abstract.
Observation: Additional modifications to those mentioned in this answer were made in the manuscript, introduced to address the observations suggested by the other two reviewers.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The authors attempted to revise their history considering the questions and comments mentioned during the initial round of review. Thanks to the authors for their efforts. However, most questions and comments cannot be accepted because they do not materially alter the content.
The authors repeatedly state that the study's goal was to examine the three methods of estimating the spatial distribution of the undergrowth without considering the biological and ecological properties of the undergrowth itself. Nonetheless, the authors attempt to make broad generalisations regarding the biology and ecology of the researched species of woody plants based on this data. Therefore, it is still unclear why wild cherries were included in this study. Many species of woody plants thrive beneath the forest canopy but never reach the primary (main) layer of stands! European mountain-ash (Sorbus aucuparia), Barcelona-nuts (Corylus avellana), crab apple (Malus sylvestris), etc. Why then did the research exclude other species of woody plants growing in the undergrowth?
"However, the size and age of the saplings were not considered relevant for…" Perhaps for the authors that may be true. However, this knowledge about the undergrowth relationships is much more significant than its simple spatial location. Especially because the height of the undergrowth varied greatly even within the sampling plots ("…with a coefficient of variation of 54%..."). I suggest the authors describe the undergrowth (at least in the appendix). Represent the average height of the undergrowth individually for each woody plant species studied. Moreover, present the age characteristics of the undergrowth being studied.
It is unknown what type of stands existed before the final removal cuts. The species composition of the stands? The age of the stands? Mean DBH? Were the tree stands closed?
Author Response
Dr. Ciprian PALAGHIANU
Ștefan cel Mare University of Suceava
Forestry Faculty
Phone: +40 745 614 487
Email: cpalaghianu@usv.ro
Subject: Reviewing of a manuscript for publication in Forests Journal
Article title: Patterns of forest species association: a case study in a sapling community
Authors: Ciprian Palaghianu and Cosmin Coșofreț
Dear Reviewer,
We thank you again for the effort and the time spent reviewing our manuscript. We appreciate the valuable feedback and the opportunity to revise our paper on ‘Patterns of forest species association: a case study in a sapling community’. Your suggestions have been supportive and useful in polishing an article that involved a lot of work. We consider your help decisive in completing this investigation and writing a better paper.
We have included the comments immediately after this short letter and responded to them individually, indicating exactly how we addressed each concern and describing the changes we have made. Both authors have approved the revisions. The changes are highlighted in the paper, and the revised manuscript and updated supplementary material are attached.
We hope our adjustments have resulted in a significantly improved manuscript that suits Forests journal better. Thank you again for the helpful input!
Sincerely,
Ciprian Palaghianu
May 17th 2023
Reviewer 1 - Comments and Suggestions for Authors
It is unknown what type of stands existed before the final removal cuts. The species composition of the stands? The age of the stands? Mean DBH? Were the tree stands closed?
[ADDRESSED] Thank you for your suggestions. We believe this information is relevant and can clarify some uncertainties related to how the understory/seedlings evolved. Therefore, we added a table in the supplementary section with relevant additional information about the parent stand - Table S3. Synthesis of information about the parent stand (species percentage, age, DBH, and canopy cover). We also added further details in the paper (2.1. Study site section) regarding the characteristics of the parent stand.
In summary, we studied in a temperate broadleaf managed forest, an even-aged stand with a representative species composition for this region. The stand was naturally regenerated using the shelterwood system, and the final removal cuts were applied six years before our inventory. At that moment, before the felling, the forest management unit recorded the stand composition: pedunculate oak (50%) and hornbeam (30%), with small-leaved lime (10%) and common ash (10%). In the forest administration records the species with a proportion of less than 10% are not registered explicitly. The age at which the stand was completely eliminated was 130 years for the oak and 110 for the other species (the age is being appreciated in the records of the forest management unit as multiple by ten years). For this type of stand, quite regular for this area, the forest technical regulations require that the age at which the harvesting may begin should be 110-120 years (but the entire regeneration process lasts 10-15 years, depending on masting years and the evolution of seedling regeneration). The stand canopy cover was of 0.6.
In this case, the final removal cuts were synchronised with a relatively abundant masting year for oak. Furthermore, to complete the information on this particular stand, no other year of masting was recorded after the last cut (the technical regulations oblige the forest administrators to carry out the annual controls of the regeneration, which also follow the intensity of seed masting).
We chose this regular stand type to minimise confounding factors and accurately study the species association from the statistical point of view. Therefore, we selected a case study in an even-aged stand, with consistent regeneration in terms of age and size and representative species composition for this habitat type.
I suggest the authors describe the undergrowth (at least in the appendix). Represent the average height of the undergrowth individually for each woody plant species studied. Moreover, present the age characteristics of the undergrowth being studied.
[ADDRESSED] Thank you for your suggestions. Unfortunately, we failed to include information about the height of the saplings in the paper, although we provided details in the previous answer. Therefore, we added a table in the supplementary section with additional information on saplings' average height per species - Table S2. We also added references to this information in the paper.
Regarding the age of the sapling - we considered your observation and integrated further explanations and new references into the paper. Our study was located in a homogeneous area with a compact seedling cover. The understory (the sapling community) in that area was relatively uniform in size and age, being the last part of the stand that was harvested. The regeneration cohort has installed immediately after the final removal cuts were applied, six years before our inventory. There is evidence of this regeneration cohort in the forest administration records because the forest technical regulations oblige the administrators to carry out an annual control of the regenerations and keep records of the regenerated species after harvesting. The same records showed no other masting year after the last cut. Additionally, as field practice, the tall saplings are cut during the final removal cut so as not to obstruct or overshadow the new wave of regeneration. And such tall saplings (called "wolves" by practitioners) are also eliminated because they will have inappropriate habitus, of low quality. This way, better conditions are created for the development of a fresh new cohort of seedlings.
We explicitly mentioned in the discussions that we did not systematically investigate the age of all the seedlings (nearly 7200), but our observations in the field showed that the age differences between the seedlings were limited to 1-3 years. We considered the sapling community to be rather homogeneous in age. The density of the first wave of regeneration became very high, with over 14 saplings per square meter at the moment of sampling. Therefore, the installation of the first cohort significantly reduced the chances of survival of the new seedlings, considering the limited space and access to light. Our observations were supported by studies on both deciduous (Ray et al., 1999) and coniferous species (Gaudio et al., 2011) that show that it is challenging to generate a new cohort of other ages because it is tough to survive due to low light availability even for shade-tolerant species. Ray (Ray et al., 1999) showed that the total stems peaked around five years after seed cutting, suggesting that most new individuals had initiated by that time. And by ten years, total stems were declining substantially, indicating that crown closure had occurred and growing space was becoming limiting within the new cohort.
Nonetheless, the authors attempt to make broad generalisations regarding the biology and ecology of the researched species of woody plants based on this data
[ADDRESSED] Thank you for your observation. An in-depth analysis of species traits was not the aim of our study. Therefore, we considered your observation and searched and removed the references from the text of the paper to the biology and ecology of the researched species. Furthermore, broad generalisations were also excluded from the content of the paper. Finally, we modified the paper's title and discussion section to emphasise that this investigation represents a case study, and no generalisation should be inferred or assumed.
Therefore, it is still unclear why wild cherries were included in this study. Many species of woody plants thrive beneath the forest canopy but never reach the primary (main) layer of stands! European mountain-ash (Sorbus aucuparia), Barcelona-nuts (Corylus avellana), crab apple (Malus sylvestris), etc. Why then did the research exclude other species of woody plants growing in the undergrowth? [ADDRESSED] Thank you for your comment. Our observational case study focused on integrating the results from the three different approaches to species associations. And our test object of study was a seedling population. Therefore, we selected a regular even-aged managed forest stand with a representative species composition for this region. All the seedlings (approximately 7200) from all the species present in the plots were inventoried.
These are the species we have found: pedunculate oak (Quercus robur L.), hornbeam (Carpinus betulus L.), small-leaved lime (Tilia cordata Mill.), common ash (Fraxinus excelsior L.), field maple (Acer campestre L.), wild cherry (Prunus avium L.) and sycamore maple (Acer pseudoplatanus L.).
We did not exclude any species of woody plants, with the exceptions of four species that were also identified in the field: dog rose (Rosa canina L.), common dogwood (Cornus sanguinea L.), common hawthorn (Crataegus monogyna Jacq.), and elder (Sambucus nigra L.). These species were excluded from the association analysis because they had too few individuals to allow the calculation of the association indices (at most, one individual per plot). In comparison, Prunus avium had over 120 individuals identified in the sampling plots. The species association (the Jaccard index or the L(t) function) cannot be mathematically calculated for one or two individuals of the same species per plot. We have added in section 2.2. Data collection an additional paragraph to clarify this aspect.
In conclusion, the listed species are the only ones found in the field. We did not meet other species (such as Sorbus aucuparia, Corylus avellana or Malus sylvestris, or any other species we did not list). Therefore, we examined the species association for all species where this was theoretically possible.
Additional references:
Ray, D. G., Nyland, R. D., & Yanai, R. D. (1999). Patterns of early cohort development following shelterwood cutting in three Adirondack northern hardwood stands. Forest ecology and management, 119(1-3), 1-11. doi: 10.1016/S0378-1127(98)00490-3
Gaudio, N., Balandier, P., Perret, S., & Ginisty, C. (2011). Growth of understorey Scots pine (Pinus sylvestris L.) saplings in response to light in mixed temperate forest. Forestry, 84(2), 187-195. doi: 10.1093/forestry/cpr005
Author Response File: Author Response.docx
Reviewer 3 Report
Most of the issues I raised have been clarified and corrected satisfactorily by the authors.
Author Response
Dear Reviewer,
We thank you again for the effort and the time spent reviewing our manuscript. We appreciate the valuable feedback and the opportunity to revise our paper on ‘Patterns of forest species association: a case study in a sapling community’. Your suggestions have been precise, supportive and extremely useful in polishing an article that involved a lot of work. We consider your help decisive in completing this investigation and writing a better paper.
Both authors have approved the revisions. The changes are highlighted in the paper, and the revised manuscript is attached. We also attached the updated supplementary material.
We hope our adjustments have resulted in a significantly improved manuscript that suits Forests journal better. Thank you again for the helpful input!
Sincerely,
Ciprian Palaghianu
May 16th 2023
Author Response File: Author Response.docx
