Causes of Decline in the Korean Fir Based on Spatial Distribution in the Mt. Halla Region in Korea: A Meta-Analysis
Round 1
Reviewer 1 Report
The paper addresses the mortality of Korean fir (Abies koreana) in the Mt. Halla Region in Korea using spatial analysis. Specifically, the paper offers a map identifying individual Korean fir, which is quite original and great. The subject is interesting, the approach used commendable, and within the scope of Forest journal. Unfortunately, the authors in their discussion have put unnecessary emphasis on growth, which diluted the main message of the paper, not to mention many loos statements. This makes the length of the discussion not justified by its content and this section clearly need to be more focused on the subject of the current research and shortened. Also, the paper did not sufficiently highlight the relevance of such a study, and a short background in this respect is needed in the introduction section.
Also, many figures are of poor quality making it difficult to assess some claims in the paper. In addition, some clarifications along with rephrasing are needed for the sake of clarity.
Please find below more specific comments on the paper.
General comments
All the Fig. except Fig. 6 are of poor quality. Please improve them.
- Introduction
At the beginning of the introduction, a little bit more background is needed about the rational of studying specifically the mortality of Korean fir i.e. why it is important in Korean context.
“Given that the mortality and density of the Korean fir on Mt. Halla varies depending on its aspect, as reported in previous studies…” Not clear to me what do you mean by aspect. It comes again throughout the paper so that it would be worthwhile to clarify it here.
- Material and methods
2.1 Study area
“Over the last 15 years (from 2003 to 2017)”, this seems to be 14 and not 15 years, isn’t it?
“Over the last 15 years (from 2003 to 2017), the average annual temperatures were approximately from 15 to 17 °C”. Please replace “were approximately from” with “approximately vary from”.
“and 12 °C in the mountain region (≥ 600 m above sea level); the average annual temperature lapse rates were – 0.61 °C/100 m on the northern aspects, and – 0.68 °C/100 m on the southern aspects of Mt. Halla.” Put all this in a new sentence. Please, rephrase it accordingly.
“The annual rainfall ranged from between 1,130 and 2,200 mm (coastal), 1,960 and 2,340 mm (mid-mountain), and 3,190 and 5,870 mm (mountain), showing a tendency to increase by approximately 230 mm/100 m with the increasing altitude [60].” Weird sentence, please rephrase.
2.3. Distribution map of the accumulated percent mortality rate for Korean fir on Mt. Halla
Replace “QGIS 2.18 program” with “QGIS 2.18 software”
2.4. Analysis of the distribution patterns of the Korean fir
2.4.1. General distribution of the Korean fir
About the t-test, are you comparing 1) highest vs lowest mortality and 2) highest vs lowest density? Also, this is not clear to me how the t-test was performed to slope, and solar radiation based on your classification according to mortality rate (two groups) and density (two groups). Please clarify.
Is statistical analysis also performed with SPSS?
2.4.2. Analysis of the altitudinal distribution of the Korean firs
“… and a t-test was conducted for the groups with respect to their mortality rate, density, terrain slope, and solar radiation...” Please see my comment above.
How do you compute APMR?
- Results
3.1. General distribution of the Korean fir on Mt. Halla
Fig. 1c. Poor quality Figure. I would add the altitude in some contour lines.
Fig. 2. Poor quality Figure. The legend and text inside the Fig. are fuzzy.
In Tab. 1 column 1, please omit “TTD” by replacing “TTD > 36 trees/3,600 m2” with “> 36 trees/3,600 m2”, and “TTD < 36 trees/3,600 m2” with “ < 36 trees/3,600 m2”.
“For each grid cell, the correlation between the factors such as the number of live firs, the number of dead firs, the density of Korean fir, mortality rate, terrain slope, solar radiation, and altitude were examined.” There is a slight difference with the corresponding statement in Material and Methods (2.4.1): “the correlation between the topographical factors and the distribution status of the Korean fir (number of live and dead firs, density, and mortality rate) were examined.”. Please fix and remove it from the Result section and keep it in the Material and methods.
“The results showed that mortality rate had a positive correlation between density and altitude, but a negative correlation between slope and aspect (Table 2).” This sentence is confusing, here mortality does not have positive correlation, but the correlation is rather between density and altitude when the mortality is assessed. Please rephrase.
Table 1 is more than only about density, please fix the title.
“That is, the region with a higher mortality rate had higher tree density and less steep slopes.” Weird sentence. Please rephrase.
Tab. 2. What is the difference between APMR and “No. of dead firs”. I already asked somewhere above. If already answered, please omit this comment.
“The group of gird cells with the highest 50 % density...”. Please replace “gird” with “grid”.
Table 4. Is “sig.” stands for “significant? Shouldn’t be rather the probability at 5% (significant if lower than 5%, and not significant otherwise) or 1% (same reasoning as 5% earlier)?
3.2. Distribution of the Korean fir at varying altitudes
Later in the discussion section you may explain why mortality decreases between 1,400 and 1,600 m while the density still increased.
3.3. Distribution of the Korean fir on different aspects
Fig. 3 is of poor quality.
Replace “At the same altitude” with “At a same altitude”.
3.4. Distribution of the Korean fir in areas with heterogeneous topography
Replace “marked by a star” with “marked with a star”.
- Discussion
4.1. Accumulated percent mortality rate
“Considering the status of these dead Korean firs, the APMR that was obtained in this study, can be regarded as the APMR over the last 20 years.”. Would it be 15 rather than 20 years? The average mortality rate you obtained for the whole study area was 36.43 %, then closer to 37.9 % (for 5 to 15 years) of the reference you cited. I do acknowledge that mortality in higher altitude (1,300–1,400 m & 1,700–1,900 m, Tab. 5) or density (1.46 & 7.99-7.23 trees/100m2) can be regarded as having occurred over at least the last 20 years, but these are specific cases and not average values.
“This suggests that the APMR of the Korean firs across Mt. Halla has dramatically increased over the last 20 years (between November 1996 and April 2017)”. Some assumptions here are needed about the drastic mortality increase based maybe on the measured parameters in this study.
4.2Density
Add a space between “4.2” and “Density”.
“… with the altitude and solar radiation and negatively correlated with the terrain slope”. Please omit “correlated”. In addition, the correlation with solar ration is not significant.
“The decline in the diameter and crown growth”. Do you mean “crown diameter” or “stem diameter”?
“Considering the previous studies, the increase in density of the Korean firs across Mt. Halla with increasing altitude can be inferred to be related to the decrease in crown size (decrease in growth rate) with increasing altitude. If individual trees have relatively small crowns owing to low growth, this would reduce the crown-induced light blocking effect, providing space where a larger number of trees could grow within the same area, thereby increasing tree density (e.g., [37]).”.
I may agree with the hypothesis that recruitment may preferentially be stronger in higher altitude due to reduced competition for light, as stated. An alternative explanation can be explored, which would be that gaps induced mortality are likely to mostly occurred in higher altitudes (see Fig. 4) with probably larger diameter trees more sensitive to damage. This alternative is backed by your study which shows that mortality and density are both positively correlated with altitude.
“In areas with high solar radiation, this can be explained by the fact that excessive solar radiation causes stomatal closure, which in turn may lead to reduced photosynthesis and subsequently, a decline in plant growth”. This is conflicting with your Fig. 4c & 4f which suggest that radiation slightly change with altitude whereas tree density clearly increased. This later is consistent with Tab. 2 showing a nonsignificant relationship between APMR and ASR. They may be a confounding factor since lower temperatures negatively affecting photosynthesis, hence growth, mostly occur in higher altitudes. In addition you may explain how growth relate to mortality.
“Meanwhile, the high density of Korean firs observed on the areas with gentler slopes suggests that excessive soil moisture on less steep slopes may impede soil aeration, and thus lead to a decline in the growth rate [43-47].” I’m still wondering how growth rate affects density. Something may be missing. Presumably growth rate could be a proxy to assess the capacity of trees to withstand a stress and eventually collapse if the stress reaches a certain threshold. About this growth rate, you may elaborate a little bit.
“This can be interpreted to mean that the increasing number of individuals growing within a given space during the same time period resulted in a higher density”. I don’t know what you mean.
4.3. Density and mortality rate
“Kim et al. found a significant decrease in the distribution of the Korean fir”.
What do you mean by “distribution”?
In addition, the whole sentence needs to be rephrased. Please replace “Kim et al. found a … areas with a relatively low density” with “Kim et al. reported a significant decrease in the distribution (??) of the Korean fir in a densely populated area, and a slight decrease or increase in areas with a relatively low density”.
“relatively unfavorable growth conditions for Korean fir.”. What are those “unfavorable growth conditions”?
“The results showed that the densely populated areas have relatively … as particular climatic conditions exceeded the species’ physiological threshold (e.g., Allen [55]).”. Too many speculations here. You may explore the fact that higher density also means higher competition for resources as e.g. soil water, nutrients, and light, which may lead to slower growth and/or induce higher mortality.
Also, mortality decreases between 1,400 and 1,600 m while the density increases, this should be discussed.
“In this study, persistent heavy rainfall and the consequent excess soil moisture, are presumed to be the main causes for the sharp increase in the mortality of the Korean fir.”
Not convincing. Although locally mortality and slope are negatively correlated, at a broader scale, mortality increases with altitude. Are higher altitudes less steep?
Replace “factors that increase their density and factors that increase their mortality rate.” with “factors that increase both their density and mortality rate.”.
“Above, we had discussed possible links … particular climatic conditions exceeded the species’ physiological threshold (e.g., Allen [55])“. What are the “unfavorable growth conditions”? You may rather pinpoint the growth conditions you are referring to.
In addition, you assumed that “drought-induced mortality” may somehow explain higher mortality as altitude increases, which corroborate the fact that altitude and mortality are positively correlated (see my comment above: “ Are higher altitudes characterized by less steep terrains?).
Figure 7. “… Annual precipitation deviation from the blue dashed regression line in Figure (a)…. ”.
Replace “in Figure (a)” with “in panel (a)”.
Improve the quality of the Fig.
“This study focused on the distribution of Korean fir. Therefore, demonstrating a direct causal relationship between the mortality of the Korean fir and soil moisture was outside the scope of this study.”. Then wouldn’t be better to more focus on variables that have been measured in the study instead of extensively speculate on soil moisture (a few lines are enough)?
“However, some studies have addressed the effects and the additional physical pressures caused by the typhoons”. The study is not about growth rate and you may not give it such an emphasis, unless you provide clear link between both. I would omit all this paragraph.
4.4. Comprehensive analysis efforts regarding the distribution of the Korean fir in areas with heterogeneous topography
I don’t see your point in this section.
- Conclusion
Replace “no consistent correlation was observed with solar radiation” with “no significant correlation was observed with solar radiation”
Adjust conclusion to changes made in the discussion.
Author Response
We thank you for the constructive suggestions and insights. The manuscript has benefited from these insightful suggestions.
The manuscript has been rechecked and the necessary changes have been made in accordance with your comments.
Thank you for your consideration. I look forward to hearing from you.
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
1) Text needs to be split into more paragraphs. For example, section 3.3 should be minimum split into para per figure, maybe into more. Page 18 is single paragraph for almost whole page!
2) Some edits tagged in manuscript
3) Methods description needs detail on:
- APMR is described as "within 30m radius". What is the centre of this radius? According to Fig. 2 (a), APMR looks to be a regular grid. Given the other analysis talks of 60m cells, what is the rational for one analysis being radius-based (circular)?
- the selection process of the rectangular sections in 2.4.3 and Fig 2 (d) needs more explanation. Which cardinal directions (aspects) were covered? How many cells with min 36 trees per rectangle?
4) Fig 2 maps are quite small
5) Fig 6, at least for area B, need to state its aspect
Comments for author File: 
Comments.pdf
Author Response
We thank you for the constructive suggestions and insights. The manuscript has benefited from these insightful suggestions.
The manuscript has been rechecked and the necessary changes have been made in accordance with your comments.
Thank you for your consideration. I look forward to hearing from you.
Please see the attachment.
Author Response File: Author Response.docx
