Functional Ecology of Forest, Heath, and Shrub Savannah Alternate States in Eastern Canada

Round 1

Reviewer 1 Report

The manuscript presents an interesting study comparing biodiversity through using traits. Overall, the manuscript clearly presents a story, but the analysis is insufficient to support their conclusions. In addition, this manuscript has a lot of writing flaws, please check the language.

Major comments

1. The title is not clear. It looks like a lab report title. Can you use your result or conclusion as the title? The abstract should be reformed and rewritten.
2. If the fire impact is an important part of your study, it is better to add more comparisons between pre- and post- fire traits. The method part confuses me. What is the role of fire in your study?
3. The post-fire soil conditions are greatly different from the pre-fire soil. Forest fires can create a lot of pyrogenic carbon through combustion (Jones et al. 2019; Wei et al. 2018). The tiny piece of pyrogenic carbon can increase soil pH and stimulate microbial activity (Certini, 2005). It is better to include this point in the discussion. How the changed soil conditions affect the plant traits?

Certini, G. (2005). Effects of fire on properties of forest soils: a review. Oecologia, 143(1), 1-10.

Jones, M. W., Santín, C., van der Werf, G. R., & Doerr, S. H. (2019). Global fire emissions buffered by the production of pyrogenic carbon. Nature Geoscience, 12(9), 742-747.

Wei, X., Hayes, D. J., Fraver, S., & Chen, G. (2018). Global Pyrogenic Carbon Production During Recent Decades Has Created the Potential for a Large, Long‐Term Sink of Atmospheric CO2. Journal of Geophysical Research: Biogeosciences, 123(12), 3682-3696.

4. Another important question is climate change. Are the pre- and post- fire climate conditions similar or changed a lot (e.g. precipitation, temperature)? Maybe the traits can be changed by climate change? I suggest that more climate information should be discussed.

Specific comments

Line 12: highest – the highest. Can you split this sentence and make it clearer?

Line 33-43: Please add a reference for each statement.

Line 77-84: Why you want to compare the biodiversity? What is the significance of your study (the study method or the scientific question)? Are there some other similar studies? Before this paragraph, a literature review is required to highlight the importance and application of your study.

Line 102-109: Can you add more information related to these fires (e.g. fire time, fire severity, fire type)? It is better to add a map to indicate your study area and the locations of these plots.

Line 125-128: Why these traits were selected? The explanation is insufficient.

Author Response

Forests Review comments

Reviewer 1

Major comments

1. The title is not clear. It looks like a lab report title. Can you use your result or conclusion as the title? The abstract should be reformed and rewritten.

Changed to “Functional ecology of post-fire forest, heath and wood savannah alternate vegetation states in eastern Canada”

We can consider another title based on the conclusion of this paper such as:

Alteration of natural fire regime negatively impacts ecosystem function

However, my concern with this title is that it is inferred from the conclusions of this paper. We do not present any fire regime change data per se in this paper, which has been reported in an earlier paper from my lab (Siegwart Collier and Mallik 2010). The present paper is builds on that and other papers (Mallik et al 2010; St. Martin and Mallik 2018).

There was no specific suggestion for rewriting Abstract. However, we have thoroughly rewritten the abstract with clearer hypothesis results and conclusions.  (see lines 10-30)

1. If the fire impact is an important part of your study, it is better to add more comparisons between pre- and post- fire traits. The method part confuses me. What is the role of fire in your study?

Unfortunately the reviewer appears to have missed the main focus of this paper. It is not about a comparison of pre- and post-fire vegetation, which has been published by many authors. Our focus here was to find out how fire-severity induced alternate vegetation states (forest, heath and wood savannah) vary functionally in terms of TD and FD. Pre- and post- fire traits of plants in this system have been described by our previous papers (see Siegwart Collier & Mallik 2010; St. Martin and Mallik 2018). These studies described the role of spatial distribution fire severity in the origin of the three alternate states. We have summarised these findings in lines 67-77. The present paper builds on these findings and seeks to explain trait filtering in these post-fire communities.

3. The post-fire soil conditions are greatly different from the pre-fire soil. Forest fires can create a lot of pyrogenic carbon through combustion (Jones et al. 2019; Wei et al. 2018). The tiny piece of pyrogenic carbon can increase soil pH and stimulate microbial activity (Certini, 2005). It is better to include this point in the discussion. How the changed soil conditions affect the plant traits?

Once again pre- and post-fire difference in plant and soil conditions in these communities have been reported by our previous studies (see Mallik Bloom and Mallik 2004, 2006). The papers cited by this reviewer deal with forest fires, carbon release and storage (as pyrogenic carbon) at a global scale, which may be related. However here we are dealing with a stand-level study. Nonetheless, as per this reviewer’s suggestion we added some texts in the Discussion explaining the role of charcoal (pyrogenic carbon) in soil pH and nutrient availability We also mentioned the role of charcoal in terrestrial carbon sink and cited the suggested references (lines 313-316)..

Certini, G. (2005). Effects of fire on properties of forest soils: a review. Oecologia, 143(1), 1-10.

Jones, M. W., Santín, C., van der Werf, G. R., & Doerr, S. H. (2019). Global fire emissions buffered by the production of pyrogenic carbon. Nature Geoscience, 12(9), 742-747.

Wei, X., Hayes, D. J., Fraver, S., & Chen, G. (2018). Global Pyrogenic Carbon Production During Recent Decades Has Created the Potential for a Large, Long‐Term Sink of Atmospheric CO2. Journal of Geophysical Research: Biogeosciences, 123(12), 3682-3696.

4. Another important question is climate change. Are the pre- and post- fire climate conditions similar or changed a lot (e.g. precipitation, temperature)? Maybe the traits can be changed by climate change? I suggest that more climate information should be discussed.

Discussing climate change effects on trait filtering in these communities is difficult because we do not present long-term data on that in this paper. Our forest and heath sites were only 22-44 years old and wood savannah around 100 years old. It is hard to speculate how climate change would modify traits.

However, we can say that climate change induced change in vegetation (i.e., changing forest to heath or wood savannah) will certainly change overall community traits depending on the geographic extent.

Specific comments

Line 12: highest – the highest. Can you split this sentence and make it clearer?

Changed to the highest. We changed the sentence (lines 13-15)

Line 33-43: Please add a reference for each statement.

We added new references as suggested (see lines 79-87)

Line 77-84: Why you want to compare the biodiversity? What is the significance of your study (the study method or the scientific question)? Are there some other similar studies? Before this paragraph, a literature review is required to highlight the importance and application of your study.

These are adequately described in the Introduction. Please see lines 36-93.

Line 102-109: Can you add more information related to these fires (e.g. fire time, fire severity, fire type)? It is better to add a map to indicate your study area and the locations of these plots.

Table 1 of Siegwart Collier and Mallik 2010 [15] shows the fire history (date of fire, fire weather index, duration of fire, area burned etc.) of the study sites.

We have included a new Fig. 1 showing the distribution of study sites (lines 121-124)

Line 125-128: Why these traits were selected? The explanation is insufficient.

For a journal paper we feel that reasons for selection of the five plant traits are sufficiently described with appropriate reference for further details, please see lines 142-152.

Author Response File: Author Response.pdf

Reviewer 2 Report

In this study, the authors investigate plant species diversity, and plant functional diversity—based on 5 traits—in Newfoundland Canada, amount three community types: forests, wood savannah, and heath. Overall, this is a clear, well-executed study. The sample size is not large, but it is large enough to support their inferences. The sampling design is clear, the analyses executed area robust and appropriate. The authors do an excellent job relating their study to theoretical concepts they are addressing, including plant functional traits, and alternative stable states. I have suggested clarification in a couple places in the Methods section. Other than those minor suggestion,

123: A small table summarizing the number of sites, belt transects/replicates, 10x10 quadrats, and 1x1 quadrats for each plant community would help the reader quickly understand and evaluate your sample design.

125-135: Nice concise descriptions of each trait and why they matter.

Lines 148-150: “To calculate the functional composition of these anomalies one standard deviation of the mean of the site was applied to the non-applicable values.” What does applied mean in this context? Can you supply a little more justification for this approach, since it is a novel step to address the distribution of functional attributes of your dataset?

Lines 150-152: “Meanwhile, sites not containing any of the species in the functional trait matrix were represented as zero to maintain orthogonality in design and represent, not only the lack of functional contribution but also, the lack of functional diversity within certain communities.” So, there were some plots that only contained rare species? How many? Would it have been better to drop those plots completely?

153-156: Did you remove any rare species before calculating the taxonomical diversity indices?

Figure 4.: I see the high beta diversity in the WS. You assigned your groups before hand. If appropriate, consider addressing if any of the grouped woodland sites should be consider different community types?

266: “equal suggesting” – wrong verb tense? Or comma needed?

The discussion is excellent, and well supported by the results.

Author Response

Forests Review comments

Reviewer 2

In this study, the authors investigate plant species diversity, and plant functional diversity—based on 5 traits—in Newfoundland Canada, amount three community types: forests, wood savannah, and heath. Overall, this is a clear, well-executed study. The sample size is not large, but it is large enough to support their inferences. The sampling design is clear, the analyses executed area robust and appropriate. The authors do an excellent job relating their study to theoretical concepts they are addressing, including plant functional traits, and alternative stable states. I have suggested clarification in a couple places in the Methods section. Other than those minor suggestion,

We appreciate the reviewers encouraging comments

123: A small table summarizing the number of sites, belt transects/replicates, 10x10 quadrats, and 1x1 quadrats for each plant community would help the reader quickly understand and evaluate your sample design.

We added a table as suggested (please see line 140)

125-135: Nice concise descriptions of each trait and why they matter.

We appreciate that this reviewer agrees with us that the description of traits is sufficient.

Lines 148-150: “To calculate the functional composition of these anomalies one standard deviation of the mean of the site was applied to the non-applicable values.” What does applied mean in this context? Can you supply a little more justification for this approach, since it is a novel step to address the distribution of functional attributes of your dataset?

The term “applied” has been replaced with “added” to better describe the method. To make this more clear, the explanation has been rewarded as “To calculate the functional composition of these anomalies one standard deviation of the mean of the site was added to the non-applicable values in order to avoid representing low diversity values as zero diversity as per [18].” (line 165-167) to draw emphasis to what the modification achieves.

Lines 150-152: “Meanwhile, sites not containing any of the species in the functional trait matrix were represented as zero to maintain orthogonality in design and represent, not only the lack of functional contribution but also, the lack of functional diversity within certain communities.” So, there were some plots that only contained rare species? How many? Would it have been better to drop those plots completely?

Few plots did not contain any species that were present within the plant trait index. In this case it is best to keep these zero values because dropping these plots from analysis would introduce a bias towards higher average diversity into the study. It is important to include lack of dominant flora into the analysis. 153-156: Did you remove any rare species before calculating the taxonomical diversity indices?

No, it is difficult to include traits of all (including rare) species to calculate FD.  However, studies have shown that patterns of FD are often driven by the traits of the dominant species according to the Mass-Ratio hypothesis (Grime, 1998; Mokany et al., 2008; Li et al., 2015). Nonetheless, we recognize that the omission of rare vascular plants and cryptogams in calculation FD may have lost some information (St Martin and Mallik 2019). Trait analysis of cryptogams is challenging and in its infancy (St Martin and Mallik 2017). Please see lines 303-307.  Also, removal of rare species in taxonomic diversity indices would misrepresent how this method was applied. Since the objective of this study was to compare functional and taxonomic diversity among alternate states it is best to use common approaches to each method.

Figure 4.: I see the high beta diversity in the WS. You assigned your groups beforehand. If appropriate, consider addressing if any of the grouped woodland sites should be consider different community types?

Beta diversity was measured between plots within individual sites and the results the presented are an average of values. Hence, the high beta diversity in wood savanna represents localized spatial heterogeneity and not differences between study sites. Structurally, all wood savannah sites appear similar though each has high degrees of diversity variation between plots due to the prevalence of a vegetation mosaic. 266: “equal suggesting” – wrong verb tense? Or comma needed?

Corrected by using a comma.

The discussion is excellent, and well supported by the results.

We very much appreciate this encouraging comment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

My major concerns have been well answered. But the current manuscript has some minor errors. Please check the writing (e.g., Line 39: delete ‘can’, Line 43: [6] insert ‘.’). Figure 1. Can you use a clearer figure? I recommended that you may use ArcGIS to make a better map.

Author Response

The minor edirorial corrections were made and Fig. 1 has been redrawn with clarity as suggested.

Abstract was revised as follows: 

In eastern Canada alternation of wildfire regime due to fire suppression creates alternate vegetation states converting black spruce forest to heath, and wood savannah (WS). We compared taxonomic diversity (TD) and functional diversity (FD) of post-fire forest, heath, and wood savannah alternate states to determine if community FD can explain their persistence. We hypothesized that i) species diversity (TD and FD) will be the highest in forest followed by WS and heath due to decreased interspecific competition and niche differentiation, ii) differences between TD and FD indices will be greater in communities with high TD in forest due to high trait differentiation and richness, and iii) changes in community trait values will indicate niche limitations and resource availability. We conducted this study in Terra Nova National Park, Newfoundland, Canada. We calculated functional dispersion (alpha FD), functional pairwise dissimilarity (beta FD), Shannon’s diversity (alpha TD), and Bray-Curtis dissimilarity (beta TD) from species cover. We used five functional traits (specific root length, specific leaf area, leaf dry matter content, height, and seed mass) related to nutrient acquisition, productivity and growth. We found lower beta diversity in forest than heath and WS; forest also had higher species diversity and greater breadth in niche space utilization. Wood savannah was functionally similar to heath but lower than forest in functional dispersion and functional divergence. It had highest functional richness and evenness. There was no difference in functional evenness between forest and heath. Functional beta diversity was highest in forest, and did not differ between heath and WS. Resource acquisition and availability was greatest in forest and lowest in heath. We suspect that this might be due to forest having the highest functional trait turnover and niche utilization. We conclude that alternate vegetation states originating from alterations to the natural fire regime negatively impact ecosystem function.

Author Response File: Author Response.docx