Past Logging and Wildfire Increase above Ground Carbon Stock Losses from Subsequent Wildfire
Round 1
Reviewer 1 Report
Understanding how wildfires will affect C stability in the ecosystem in relation to previous disturbances (e.g., logging or wildfire), as well as changes in management, fire severity, or other stand characteristics, is important for the management of C stocks. In this paper, the authors took advantage of a sampling conducted before the large fires that swept through E Australia in 2019-2020 aiming at quantifying C stocks. Subsequent sampling after the wildfire permitted addressing the question of how wildfires affect them. Although not all stands sampled before the wildfires could be sampled, there were enough of them to warrant a robust estimation of the changes caused by fires. The work has been well designed and carried out. The data are well analyzed, the results succinctly presented, and the discussion and conclusions reflect well the findings. The paper merits being published by Fire.
Despite the above, the paper is not amicable for the reader, and at times difficult to understand. It would have benefitted if in an annex table it would have been provided the basic information of all stands. That is, location, elevation, slope, time since disturbed (logged or burned), hazard reduction burning, etc. This information would have clarified how exactly the stands were sampled. As it is presented now, I could not know whether the stands had been either logged or burned by wildfire. This uncertainty was transferred over the analysis. Presenting the data as a function of time since logging or burning is misleading (Figure 4) further complicates understanding how the sampling was done. This must be clarified to make sure what is at stake.
While succinctness in reporting results is appreciated, the authors need to provide sufficient information about their methods and outcomes from the analysis so that everyone can judge by himself/herself and be able to reproduce the analysis. The information provided about statistical assumptions and outcomes is minimal and insufficient.
Additional comments:
1-3: The title is misleading and does not fully represent the results obtained. It needs to be changed since the effect of logging was small and the effect of wildfire virtually nil.
47: Unclear, of to?
48-54: Not everyone will be familiar with the species you are studying. Therefore, you may want to clarify and differentiate whether the species resprout or not and from which organs, because this will affect the structure of the forest.
110-111: You may want to specify the purpose of this survey, and the types of sites that had been selected (i.e., previously burned or logged?).
120-128: As indicated above, please, provide in an appendix the sites sampled, their coordinates, and main characteristics (elevation, dominant tree, etc.), years since logging or wildfire, fire severity, etc.
195: What is hazard reduction fire? In which stands they are carried out and how? Please, provide further explanation about this variable.
205-206: It is unclear how you sampled wildfire and hazard reduction. This needs to be clarified.
213-218: Please clarify this; time since logging is the only factor that you had sampled, as indicated above. Later, you refer in this same paragraph to time since wildfire of hazard reduction. There is no way to understand what you are aiming to test. Here and throughout this section, a clarification on the dependent variables (time since logging and time sin wildfire) needs to be given.
226-230: You need to provide information about the methods, assumptions, and priors used, and provide sufficient information from the modeling outcomes so that anyone could reproduce your analysis and results. The information provided is insufficient to do it properly.
270-271: Please, as per the above comments, you need to clarify how you sampled wildfire history and why and how you stratified your logged history by wildfire history. This is very confusing.
276: There is not an independent plotting for time since fire.
310: Please, clarify which history is behind this assertion.
312-314: But differences were very minimal. Please, abide by your results which showed very little tendency to change in response to ANY of the factors investigated.
Author Response
Reviewer 1
Comments and Suggestions for Authors
Understanding how wildfires will affect C stability in the ecosystem in relation to previous disturbances (e.g., logging or wildfire), as well as changes in management, fire severity, or other stand characteristics, is important for the management of C stocks. In this paper, the authors took advantage of a sampling conducted before the large fires that swept through E Australia in 2019-2020 aiming at quantifying C stocks. Subsequent sampling after the wildfire permitted addressing the question of how wildfires affect them. Although not all stands sampled before the wildfires could be sampled, there were enough of them to warrant a robust estimation of the changes caused by fires. The work has been well designed and carried out. The data are well analyzed, the results succinctly presented, and the discussion and conclusions reflect well the findings. The paper merits being published by Fire.
Despite the above, the paper is not amicable for the reader, and at times difficult to understand. It would have benefitted if in an annex table it would have been provided the basic information of all stands. That is, location, elevation, slope, time since disturbed (logged or burned), hazard reduction burning, etc. This information would have clarified how exactly the stands were sampled. As it is presented now, I could not know whether the stands had been either logged or burned by wildfire. This uncertainty was transferred over the analysis. Presenting the data as a function of time since logging or burning is misleading (Figure 4) further complicates understanding how the sampling was done. This must be clarified to make sure what is at stake.
While succinctness in reporting results is appreciated, the authors need to provide sufficient information about their methods and outcomes from the analysis so that everyone can judge by himself/herself and be able to reproduce the analysis. The information provided about statistical assumptions and outcomes is minimal and insufficient.
We thank the reviewer for their support and constructive comments about the communication of our work. Detailed responses are provided to specific comments below.
Additional comments:
1-3: The title is misleading and does not fully represent the results obtained. It needs to be changed since the effect of logging was small and the effect of wildfire virtually nil.
We consider the title to be appropriate and indicative of the contents of the manuscript. No change made
47: Unclear, of to?
Typo, corrected.
48-54: Not everyone will be familiar with the species you are studying. Therefore, you may want to clarify and differentiate whether the species resprout or not and from which organs, because this will affect the structure of the forest.
Added “along the stem and branches” for clarification.
110-111: You may want to specify the purpose of this survey, and the types of sites that had been selected (i.e., previously burned or logged?).
Added “The initial surveys were stratified by time since logging and wildfire to determine the independent effects of these two disturbances on above ground carbon stocks.”
120-128: As indicated above, please, provide in an appendix the sites sampled, their coordinates, and main characteristics (elevation, dominant tree, etc.), years since logging or wildfire, fire severity, etc.
We have added a plot showing the time since logging, wildfire and hazard reduction fire for each site (figure 1b)
195: What is hazard reduction fire? In which stands they are carried out and how? Please, provide further explanation about this variable.
We have added “(planned fires to reduce fuel)” to the first mention in the manuscript. “Hazard reduction burning” has been used in other Fire publications without requiring further definition.
205-206: It is unclear how you sampled wildfire and hazard reduction. This needs to be clarified.
We wish to direct the reviewer to the second paragraph of the Methods, where we detail the stratification by logging and wildfire. For clarification we have added the following sentence “Hazard reduction burning (planned fires to reduce fuel) had also been applied at some sites, however we do not explicitly stratify our sample by this disturbance type, as it was not expected to have a significant effect on total carbon stocks.” We have also added figure 1b showing the specific stratification of our plots by disturbance history.
213-218: Please clarify this; time since logging is the only factor that you had sampled, as indicated above. Later, you refer in this same paragraph to time since wildfire of hazard reduction. There is no way to understand what you are aiming to test. Here and throughout this section, a clarification on the dependent variables (time since logging and time sin wildfire) needs to be given.
The first line of this paragraph states that we are assessing the effects of several variables (logging, wildfire hazard reduction and fire severity) on above ground carbon stocks. We suspect some earlier confusing around our stratification – which we have now clarified – may have led to the reviewer’s misunderstanding here.
226-230: You need to provide information about the methods, assumptions, and priors used, and provide sufficient information from the modeling outcomes so that anyone could reproduce your analysis and results. The information provided is insufficient to do it properly.
We have added that we used the default priors and details about minor settings to assist the model fitting process. The combination of these amendments and other details in this paragraph should contain all details sufficient to replicate our analysis.
270-271: Please, as per the above comments, you need to clarify how you sampled wildfire history and why and how you stratified your logged history by wildfire history. This is very confusing.
This comment has been addressed above.
276: There is not an independent plotting for time since fire.
With respect this is incorrect. We have plotted the interaction between logging and fire history in these figures. To plot the effects of fire history again would generally be considered duplication.
310: Please, clarify which history is behind this assertion.
Added “(logging and fire)” to reiterate the disturbances assessed in this study. Specific details follow this sentence.
312-314: But differences were very minimal. Please, abide by your results which showed very little tendency to change in response to ANY of the factors investigated.
Added “, although losses were generally small compared to the total above ground stocks in mature forests.”
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Thank you for the opportunity to review "past logging and wildfire increase above ground carbon stock losses from subsequent wildfire." I found the manuscript easy to follow as the writing was crisp and clear. I would encourage the authors to pay more careful attention to details missing in the methods that are essential should researchers choose to replicate the approach and for cross checking to comparable studies. My comments are provided within the comments function of the pdf and can be summarized as follows. (1) Carbon stock transfers from live to dead - my experience in western USA fire adapted forests is most of the C stock transfers from live to dead in large trees - that is, only the outer bark, leaves, and some twigs are volatilized - so its not clear to me whether this happened or not given the authors did not include pyrogenic C but reference a study that may or may not be applicable (Satin: 2 to 27%) - I would have expected higher pool transfers given large trees in unlogged sites. (2) Duff and soil pools - since these were not measured, more discussion is warranted given in severe fires its actually the duff layer that is most combustible - maybe more so the case in highly productive sites and this should be discussed. (3) Logging history/methods - there is no discussion about what types of logging occurred - this is important and may explain much of the variation in the logged sites you reported - that is - was it clear felling, basal area removals, partial cuts, how much volume/basal area was removed, etc? (4) Severity classes need further definition - tree scorch is grouped into subjective categories and cited back to Gibson et al. 2020 - however, this needs further discussion about how it was applied in your study - were crown scorch percentages used or was it simply visually estimated and if so how (again if someone wants to replicate your study, they can't due to lack of descriptive methodology). (5) What is "hazard reduction fire?" I'm not familiar with this terminology. (6) Dead trees - you will see in my comments that this is a big issue for me in terms of not only transfer of C stocks across pools but it's surprising how little transferred based on Figure 2 - this seems like a really important area of discussion. (6) Allometric equations need further discussion - how relevant to your site conditions are they? (7) Time since logging - the scatter of points might be more explainable based on my comment above - what was the logging history/methods and how much of the variation can be attributed to logging methods vs. differences in site productivity, etc? Further details on my comments are provided in the comments function. Finally, I think you can expand the conclusions a bit by discussing whether changes in logging regimes are needed to reduce stock losses and if so how? Gentler logging? No logging? Longer rotations? Let trees grow bigger, leave more of the coarse woody debris?? The conclusions leaving me wanting more. Although I did not sign my review, I'm happy to work with the authors in seeing these changes improve the manuscript because of it is a novel contribution that will help inform forest management in the region of interest. Thanks
Comments for author File: Comments.pdf
Author Response
Reviewer 2
Review Report Form
Open Review
Comments and Suggestions for Authors
Thank you for the opportunity to review "past logging and wildfire increase above ground carbon stock losses from subsequent wildfire." I found the manuscript easy to follow as the writing was crisp and clear. I would encourage the authors to pay more careful attention to details missing in the methods that are essential should researchers choose to replicate the approach and for cross checking to comparable studies. My comments are provided within the comments function of the pdf and can be summarized as follows. (1) Carbon stock transfers from live to dead - my experience in western USA fire adapted forests is most of the C stock transfers from live to dead in large trees - that is, only the outer bark, leaves, and some twigs are volatilized - so its not clear to me whether this happened or not given the authors did not include pyrogenic C but reference a study that may or may not be applicable (Satin: 2 to 27%) - I would have expected higher pool transfers given large trees in unlogged sites. (2) Duff and soil pools - since these were not measured, more discussion is warranted given in severe fires its actually the duff layer that is most combustible - maybe more so the case in highly productive sites and this should be discussed. (3) Logging history/methods - there is no discussion about what types of logging occurred - this is important and may explain much of the variation in the logged sites you reported - that is - was it clear felling, basal area removals, partial cuts, how much volume/basal area was removed, etc? (4) Severity classes need further definition - tree scorch is grouped into subjective categories and cited back to Gibson et al. 2020 - however, this needs further discussion about how it was applied in your study - were crown scorch percentages used or was it simply visually estimated and if so how (again if someone wants to replicate your study, they can't due to lack of descriptive methodology). (5) What is "hazard reduction fire?" I'm not familiar with this terminology. (6) Dead trees - you will see in my comments that this is a big issue for me in terms of not only transfer of C stocks across pools but it's surprising how little transferred based on Figure 2 - this seems like a really important area of discussion. (6) Allometric equations need further discussion - how relevant to your site conditions are they? (7) Time since logging - the scatter of points might be more explainable based on my comment above - what was the logging history/methods and how much of the variation can be attributed to logging methods vs. differences in site productivity, etc? Further details on my comments are provided in the comments function. Finally, I think you can expand the conclusions a bit by discussing whether changes in logging regimes are needed to reduce stock losses and if so how? Gentler logging? No logging? Longer rotations? Let trees grow bigger, leave more of the coarse woody debris?? The conclusions leaving me wanting more. Although I did not sign my review, I'm happy to work with the authors in seeing these changes improve the manuscript because of it is a novel contribution that will help inform forest management in the region of interest. Thanks
We thank the reviewer for their comments, which we believe will assist in making this paper more accessible to an international audience. We have added further discussion to the Management implications section of the Discussion to indicate how silvicultural management can change carbon losses from wildfire. Other specific responses are provided below.
Line 8: temporarily - wildfire is a temporary reduction of stocks while much of the stocks transfer from live to dead pools - logging involves more of the C transferring to the atmosphere
We understand the reviewer’s comment, however once antecedent disturbance has been accounted for, some carbon losses may be effectively permeant. For example, this may occur where repeated fire causes a shift towards smaller tree/shrub species. Given this is relevant to our research, we have not made any changes.
Line 50 cite Keith et al. 2009 - https://www.pnas.org/content/106/28/11635
The Keith paper is for non-resprouting eucalypt forest and therefore not suitable for this statement. We have instead added a reference to Roxburgh et al (2006), which does show large carbon stocks in resprouting eucalypt forest.
Line 69 this is a stretch for the reasons stated previously - large trees hold on to most of their carbon - so it's not likely that longer undisturbed forests will emit more as they have larger trees
The reviewer makes a valid point, however this has not been clearly demonstrated one way or the other in resprouting eucalypt forest and requires further investigation. It is a possible response, given that carbon in older forests may be stored in fire sensitive understorey species, dead and fallen vegetation, foliage, bark and litter, which can all be consumed by fire and amount to a large carbon loss.
Line 89-92: I think this yellow highlight should be in the intro and discussed as part of the scope of the project introduction more than in the methods - so I would move this up higher
The highlighted sentences have been moved to the start of the second paragraph of the introduction.
Line 107 how was severity defined? This needs to be discussed in the methods - soil severity, tree canopy severity? If so, what levels were used for each of the severity categories - this study cannot be replicated by others or related to other studies without knowing severity measures used.
We describe how we measured severity in the ‘Site data’ section below, including references to the source of our definitions. For further clarification we have added that we consider fire severity to be “(scorch and consumption of vegetation by the fire)” in this section.
Line 128 this needs to be repeated in the discussion and abstract
Added “Carbon losses and predicted effects of disturbance may be underestimated in some cases due to the accumulation of carbon at sites between pre- and post-fire surveys.” to the abstract.
This subject is already discussed towards the end of the 3rd paragraph of the discussion.
Line 132 given these were present on sites, I remain concerned about the lack of recognition for carbon passing from live to dead pools - why isn't that discussed or accounted for?
We have altered this sentence to state that we were looking for trees that were large relative to most trees on site. So they were not necessarily ‘exceptionally’ large. These trees were also not necessarily killed by fire. As to the reviewer’s concerns about the transfer of carbon from live to dead trees, we measured all dead and fallen trees on site, and these issues are more specifically addressed in the Discussion and associated responses to reviewer comments.
Line 133 this makes no sense to me - a severe fire never removes a large tree - the large trees are not combusted - mostly branches and leaves but the trunks remain even in the high severity patches - again, there is a need to recognize this
I am uncertain as to what the reviewer is concerned about specifically. The section of text they refer to states that large trees are ‘unlikely to be completely removed from the site by a single fire’ which is in agreement with the reviewers comment.
Line 159 please discuss the relevance of the allometric equations used at least for studies conducted outside the region or at continental scales - this needs to be discussed as levels of uncertainty
We have added text to the following paragraphs discussing whether each equation was developed for our study area or not, and if not how it may influence our data.
Table 1 paul these are continental scale allometrics - relevant??
See above.
Table McCarthy outside the region - is it relevant?
See above.
Line 189 as noted - this needs further explanation - these are subjective categories - are there percentage canopy scorch figures assigned to each? If so, please include those and a bit more explanation than simply citing Gibson et al
Further detail about specific definitions used to classify severity has been added.
line195 what does this mean?
Changed to “mapping of the area of past logging and fire”
Line 238 this pertains to my comment above - since most of the tree is still present after severe fire, I would think the carbon transfers live to dead pools and shouldn't be reflected as a negative - perhaps I'm misunderstanding something here but it should be discussed that the trees haven't been combusted and are still standing - at least the large ones are - and so carbon stock is mostly still present - please explain
As indicated in the manuscript, these statistics refer to the change in carbon stocks between the surveys for the total above ground stock and for each sub-component. That is, if a tree is killed by fire, that carbon is lost form the live tree pool, and at least partially transferred to the dead tree or coarse woody debris pool. We have added some text to this sentence to further clarify that we are talking about the change between pre- and post-fire surveys. We also articulate this point in the second sentence of the ‘Analysis’ section of the methods, and have altered the second sentence of the Discussion to further clarify the point.
Line 243 precisely my point - the carbon stocks are transferring across pools - live to dead - so did you account for this in the total carbon stock change? That is - was a dead tree counted as a negative stock change?
Yes, if carbon is transferred from one pool to another, it is still counted towards the total. We have added the following sentence to the ‘Analysis’ section of the methods to clarify how the total carbon stock is calculated: “Total carbon was calculated as the sum of the live tree, dead tree, understorey, coarse woody debris and litter carbon stocks for a given survey.”
Figure 2a it's surprising how little carbon stock change occurred in the dead pool - I would expect higher transfer amounts in high severity plots -what's going on here?
Firstly, these figures are for all sites, not just those burnt at high severity. Secondly, the loss of a live tree can contribute to the dead tree pool or the coarse woody debris pool, depending on whether it stays upright. These pools also experienced some losses because of the fire, thus the dead tree and coarse woody debris pools are the total of carbon lost and gained by each respective pool.
This influence of losses and gains from the dead tree and coarse woody debris pools is discussed throughout the Discussion.
Line 248 in unlogged site?
No, as outlined in the second paragraph of the methods, all sites have been logged and burnt by wildfire at some point in the past.
Line 258 wow - this is surprising too - must be the species you are working with don't have much insulating bark features - might be a good point for discussion
Stem size is discussed in the introduction and discussion. No Changes made.
Line 264 this needs further discussion - what were the logging intensities in these sites - did they all have the same basal area removals? Were they all clearcuts of the same patch sizes - this likely explains the variation and should be discussed
Details about silvicultural practises in the study area are provided in the first paragraph of the Methods. For further clarification we have added the following sentence “Unfortunately there was not reliable information on historic (i.e. prior to the 2019-20 fires) logging intensity or wildfire severity for each site” to this part of the methods.
We have added the following to the end of the ‘Disturbance history’ section of the Discussion: “Some of the variance in the data may be explained by variable logging intensity and wildfire severity prior to the 2019-20 fires. Variation in the impacts of these two antecedent disturbances would likely influence the quantity and stability of carbon stocks that were burnt by the 2019-20 fires. There are many variables and interactions to consider here, hence we do not speculate on how this may affect our results, other than to say that it is a likely source of unexplained variance.”
Line 338 this is a really important finding - what it says to me is that your estimates of stock change in unlogged high severity sites maybe over estimated due to postfire flushing and resprouting - that is another point to emphasize that may increase the difference in stock changes from unlogged to logged sites that remove the trees and most of the carbon
We are not entirely sure what the reviewer is arguing. However, as indicated in the text, most trees that had survived were producing new foliage and hence not capturing foliage loss was probably a minor point.
Line 338 "some?" My experience with high severity fires is most of the carbon transfers to dead pools, not some but I see that you cited Santin - how relevant is this to your study area though?
We note the reviewers experience with their surveys.
The reference to the Santin paper is to provide the reader with an idea of how much this may affect the results. No equivalent is available for our forest type.
Line 344 not sure about that - perhaps in the soils but certainly not in large dead trees
If the carbon was still within a dead or fallen tree it was captured within those pools.
Line 352 yes - good point -especially if you sampled right after fire - postfire flushing would have been missed - maybe mention how many of those plots were soon after fire
We have added that the surveys were conducted “(three to eight months post fire)”
Line 367 this needs further discussion as noted above - what were the stand ages logged, logging intensity, basal area removals, logging methods - this is key given how much the logged sites varied in stock changes
This has been addressed in previous comments.
Line 370 I keep coming back to how were these trees "lost" - large trees are not combusted fully - only twigs, bark, and leaves - the trunks are still on site and so is the carbon
This has already been rephrased in response to an earlier comment.
Line 376 here is your opportunity to discuss logging methods in more detail
Discussion has been added further down in response to earlier comments.
Line 400 it also could have come from the duff layer, which was not measured - my experience is mostly the duff layer is consumed in high severity fires
Our methods measure the depth of litter above the mineral soil surface. This captures most of the ‘duff’ layer, which is often negligible in eucalypt forests.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Thanks for addressing my comments.
Reviewer 2 Report
Thanks for responding to my suggestions. I believe the manuscript meets publication requirements and will make an important management/conservation contribution.
