Climate Change-Driven Cumulative Mountain Pine Beetle-Caused Whitebark Pine Mortality in the Greater Yellowstone Ecosystem

Round 1

Reviewer 1 Report

Review of Macfarlane et al for Forests

Overview

     This is an ambitious paper which seeks to evaluate the present and persistent impact of Mountain Pine Beetle (Dendroctonus ponderosae) on Whitebark Pine (Pinus albicaulis) in the Greater Yellowstone Ecosystem by means of aerial photographic surveys combined with ground-truthed surveys. The paper is well written and the importance of Whitebark Pine is well presentedin the introduction. The survey methods appear appropriate and, whereas I am not an expert on geospatial statistics, the use of a tried and tested methods of interpolation (kriging) together with a justification (computation of Global Moran’s I statistic) seems justified and well executed. Importantly, classification of images and inter-observer variation was tested on an extensive sub-set of images using the Kappa statistic and was found to be excellent. Comparison with ground-truthed data was less convincing, but reasons for this are discussed fully. Overall, this is an important contribution to Forest Science and I recommend that the paper be published subject to some very few minor comments below.

Minor comments

Line 37: Global correction – insert taxonomic authority for binomial and year of description or cite flora for plant nomenclature.

Line 41: Global correction – for animal binomials cite taxonomic authority and year of description.

Line 50: “improve” should read “improves”.

Line 56: “A historically” should read “An historically”.

Line 79: “reordered” – should this read “recorded”.

Line 102: Check with editor or journal style guide, should seasons be capitalized i.e. “Fall” and “Spring”.

Line 115: “questions” – “hypotheses” is a better word to use here.

Line 166: “catchment” potentially confusing given the hydrological definition of “catchment”. Maybe note here whether or not this refers to a river catchment.

Line 268-269: Error noted here. Please address this error before publication.

Line 281-282: How much of the final map was interpolated? This is a very important point!

Line 326: Move the words “Figure 3).” to previous paragraph.

Line 354: “residual forests” What does this mean – please give an explanatory note, perhaps as a footnote.

Line 432-433: A majority were interpolated….How much as a percentage. Again, this is a very important point!

Line 472ff: Is there any hope for grey trees recovering or are they just standing dead wood????

Line 528: Why is this website highlighted in yellow?

Comments for author File: Comments.docx

English excellent. Some minor typos - included in review.

Author Response

Thank you very much for taking the time to review our manuscript. Your suggested edits will greatly improve the quality of the article. Please find the detailed responses below:

Line 37: Global correction – insert taxonomic authority for binomial and year of description or cite flora for plant nomenclature. Thank you. I will defer to the editor regarding how the journal would like this done.  

Line 41: Global correction – for animal binomials cite taxonomic authority and year of description. Thank you. I will defer to the editor regarding how the journal would like this done.  

Line 50: “improve” should read “improves”. Agreed and changed accordingly.

Line 56: “A historically” should read “An historically”. Agreed and changed accordingly.

Line 79: “reordered” – should this read “recorded”. Good catch! Agreed and changed accordingly.

Line 102: Check with editor or journal style guide, should seasons be capitalized i.e. “Fall” and “Spring”. My understanding is that they should not be capitalized.

Line 115: “questions” – “hypotheses” is a better word to use here. We decided to change this to “research questions” instead of “hypotheses” because we’re asking a question not stating hypotheses.

Line 166: “catchment” potentially confusing given the hydrological definition of “catchment”. Maybe note here whether or not this refers to a river catchment.  Yes, this does refer to a stream catchment and I believe that most people will not be overly confused.

Line 268-269: Error noted here. Please address this error before publication. Thank you for pointing this out. It has been addressed.

Line 281-282: How much of the final map was interpolated? This is a very important point! Thank you. 25% by area and can be found in results section on line 373.

Line 326: Move the words “Figure 3).” to previous paragraph. Done

Line 354: “residual forests” What does this mean – please give an explanatory note, perhaps as a footnote. I added a definition: residual forests (areas where the MBP outbreak cycle has ended).

Line 432-433: A majority were interpolated….How much as a percentage. Again, this is a very important point!  Great suggestion. 56% of the ground verification catchments were interpolated. This has been added to the text.

Line 472ff: Is there any hope for grey trees recovering or are they just standing dead wood???? Yes, just standing dead wood.

Line 528: Why is this website highlighted in yellow? This is highlighted yellow because it’s currently just a placeholder and the location will change once the editor has made the data available at the link.

Reviewer 2 Report

This paper describes the methods used to survey forest mortality in the GYE using aerial detection and presents results from the survey.  The authors also compare results from this survey with a similar survey from 2009 to make interpretations about the state of beetle activity then and now. 

The research is well conceived and the paper very well written.  The conclusions follow nicely from the results.  Overall this paper is an excellent contribution to the ecosystem scale understanding of the MPB outbreak and the subsequent aftermath that will be useful for guiding conservation of whitebark pine under climate change.

I have a few minor comments

49 – several typos

56 -might include something about “recent” or “recently”

79 – “recorded”

112 – “how widespread this reduction in MPB populations”

113- might specify “limited spatial extent of the field-monitored data”  Also, at “purpose” could start a new paragraph.

125- six national forests now.  Custer and Gallatin merged to become Custer-Gallatin a few years ago. Again at line 149.  This won’t matter much to anyone other than the managers of those (that) forest.

166- is catchment mapping described in  Macfarlane et al.[13]?  I’m trying to understand if the catchments were mapped by others or how exactly, as noted at line 177

209-“repeated when smoke free”  this implies an initial flight at some earlier time that is not mentioned.

218 -missing from the GPS enabled camera?

232 -were these changes applied consistently to each photo, or was each photo adjusted uniquely?  If unique adjustments were made to each photo, can you add a bit more detail to help readers understand how the adjustment process was applied to yield similarly interpretable results.  This seems important for discriminating healthy from diseased trees if the discrimination occurs along a continuum of color.  However, binning results into categories reduces the impact which could be mentioned here to help alleviate this concern.  This could also help alleviate concern about interpretations that might differ based on solar and camera angles.  See What is Bi-directional Reflectance? | Bi-directional Reflectance | Field-based Remote Sensing | School of Natural Resources | University of Nebraska–Lincoln (unl.edu). 

304 – units are English here, also a few other places elsewhere.

352- what is the evidence for this colder microclimate?

354- what is a “residual forest”?

359 – for discussion section: does this suggest the epidemic was interrupted by cold temps and thus the beetles did not “eat themselves out of house and home” at these locations?  Implying that epidemics could erupt in the future when conditions become favorable to beetles?  I think this is clear in the discussion and conclusions, but could reference this statement in discussion since it’s kind of catchy and the aerial survey seems to answer it.

377-“…with”?

385 –“collapse” does this refer to the loss of overstory trees, or is it meant to imply “unrecoverable population collapse” which is what collapse usually connotes?  Is near complete loss of mature trees synonymous with collapse when there is lots of regeneration (realizing of course that much of the regen is imperiled by multiple threats)?  If collapse includes the loss of cone bearing trees and the threats to not yet cone bearing trees please state that for clarity. 

477 – this sentence is unclear to me. “…with 2009…”?

479- formerly

481 – so the beetles have not yet “eaten themselves out of house and home” at least in some parts of the GYE?  This comment is a reference back to the interesting hypothesis mentioned earlier.  If that is the case, then the 2009 cold snap seems to have hit the reset button, but continued warming and associated outbreaks remain an important threat. That is clear as written but referring back to that quote helps drive home this conclusion.

484 – agreed!

512 – this is important for large diameter trees considering the emphasis on blister rust as the main threat

517 – yet another finding from this study that has important management implications.  This could not be done using ground based survey methods due to the massive area of the GYE.

518-521 – please be more explicit here.  Are you suggesting future outbreaks are likely to be more devastating in moderately affected areas and less devastating in severely affected areas because there are fewer live trees remaining in the severely affected areas?

Author Response

Thank you very much for taking the time to review our manuscript. Your suggested edits will greatly improve the quality of the article. Please find the detailed responses below:

49 – several typos Fixed typos on this line.

56 -might include something about “recent” or “recently” Added “recently” to the start of the sentence.

79 – “recorded” Agreed and have changed accordingly.

112 – “how widespread this reduction in MPB populations” I’m not sure what is being asked?

113- might specify “limited spatial extent of the field-monitored data”  Also, at “purpose” could start a new paragraph. Added “field-monitored” and made a new paragraph starting with “Purpose”.

125- six national forests now.  Custer and Gallatin merged to become Custer-Gallatin a few years ago. Again at line 149.  This won’t matter much to anyone other than the managers of those (that) forest. Agreed and have changed accordingly.

166- is catchment mapping described in  Macfarlane et al.[13]?  I’m trying to understand if the catchments were mapped by others or how exactly, as noted at line 177. Yes, this is described in Macfarlane et al.[13]

209-“repeated when smoke free”  this implies an initial flight at some earlier time that is not mentioned. This sentence was changed to “In 2018 skies were smoky due to extensive fires during the flight period and therefore fights were repeated in 2019 when skies were smoke free.

218 -missing from the GPS enabled camera? Added “GPS enabled camera”

232 -were these changes applied consistently to each photo, or was each photo adjusted uniquely?  If unique adjustments were made to each photo, can you add a bit more detail to help readers understand how the adjustment process was applied to yield similarly interpretable results.  This seems important for discriminating healthy from diseased trees if the discrimination occurs along a continuum of color.  However, binning results into categories reduces the impact which could be mentioned here to help alleviate this concern.  This could also help alleviate concern about interpretations that might differ based on solar and camera angles.  See What is Bi-directional Reflectance? | Bi-directional Reflectance | Field-based Remote Sensing | School of Natural Resources | University of Nebraska–Lincoln (unl.edu). 

These changes were applied consistently to each photo therefore I do not believe I need to explain the photo adjustments in more detail.

304 – units are English here, also a few other places elsewhere. Agreed. This has been corrected.

352- what is the evidence for this colder microclimate? I added the following: The Beartooth Plateau is the largest contiguous area above 3000 m in the U.S. Rocky Mountains (Turiano 2003). This large, high plateau is extremely cold, with particularly long winters (Locke 1989).

354- what is a “residual forest”? Good question.  Added a definition: residual forests are areas where the MBP outbreak cycle has ended.

359 – for discussion section: does this suggest the epidemic was interrupted by cold temps and thus the beetles did not “eat themselves out of house and home” at these locations?  Implying that epidemics could erupt in the future when conditions become favorable to beetles?  I think this is clear in the discussion and conclusions, but could reference this statement in discussion since it’s kind of catchy and the aerial survey seems to answer it.

Thank you for the very thoughtful response. I added the following in the discussion section: This indicates that since 2009 significant post-outbreak level mortality has occurred to formerly healthy forests. This is an important finding indicating that at least in some areas beetles have not literally eaten themselves out of house and home and this lower-intensity but more insidious mortality will likely continue and could kill large swaths of remaining forest over time.

377-“…with”? I removed “with”.

385 –“collapse” does this refer to the loss of overstory trees, or is it meant to imply “unrecoverable population collapse” which is what collapse usually connotes?  Is near complete loss of mature trees synonymous with collapse when there is lots of regeneration (realizing of course that much of the regen is imperiled by multiple threats)?  If collapse includes the loss of cone bearing trees and the threats to not yet cone bearing trees please state that for clarity. 

I agree that clarification on what we believe collapse means is useful. I added the following definition: collapse: Near complete loss of mature cone bearing trees and regeneration that is imperiled by multiple threats including blister rust and future MPB outbreaks.

477 – this sentence is unclear to me. “…with 2009…”? Agreed, I changed it to as follows: In 2009, 5% of the catchments showed trace levels of mortality but by 2018-2019 trace levels of mortality had been reduced to only 1% of the catchments. This indicates that since 2009 significant post-outbreak level mortality has occurred to formerly healthy forests. In other words, beetles had not yet “eaten themselves out of house and home” at least in some parts of the GYE.

479- formerly Agreed and have changed accordingly.  Good catch!

481 – so the beetles have not yet “eaten themselves out of house and home” at least in some parts of the GYE?  This comment is a reference back to the interesting hypothesis mentioned earlier.  If that is the case, then the 2009 cold snap seems to have hit the reset button, but continued warming and associated outbreaks remain an important threat. That is clear as written but referring back to that quote helps drive home this conclusion.

See above in 477 where I used your good suggestion. Thanks!

484 – agreed! Thank you for the support.

512 – this is important for large diameter trees considering the emphasis on blister rust as the main threat. Agreed!

517 – yet another finding from this study that has important management implications.  This could not be done using ground based survey methods due to the massive area of the GYE. Agreed!

518-521 – please be more explicit here.  Are you suggesting future outbreaks are likely to be more devastating in moderately affected areas and less devastating in severely affected areas because there are fewer live trees remaining in the severely affected areas?

Yes, I added the following to be more explicit. Moreover, as climate once again becomes favorable for MPB, these sub-outbreak level populations are capable of explosive population growth, especially in currently moderately affected forests, increasing the likelihood of future MPB outbreaks.