Thermo-erosion gullies boost the transition from wet to  mesic tundra vegetation

Perreault, Naïm; Lévesque, Esther; Fortier, Daniel; Lamarque, Laurent J.

doi:https://doi.org/10.5194/bg-13-1237-2016

Articles | Volume 13, issue 4

https://doi.org/10.5194/bg-13-1237-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Special issue:

Freshwater ecosystems in changing permafrost landscapes

https://doi.org/10.5194/bg-13-1237-2016

© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 13, issue 4

Research article

|

01 Mar 2016

Research article |

| 01 Mar 2016

Thermo-erosion gullies boost the transition from wet to mesic tundra vegetation

Naïm Perreault, Esther Lévesque, Daniel Fortier, and Laurent J. Lamarque

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Final revised paper (published on 01 Mar 2016)
Preprint (discussion started on 05 Aug 2015)
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Interactive discussion

Status: closed

AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment

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RC C5009: 'Referee comment', Anonymous Referee #1, 07 Sep 2015
RC C5754: 'Review of the “Thermoerosion gullies boost the transition from wet to mesic vegetation” by Perreault et al.', Anonymous Referee #2, 24 Sep 2015
AC C7103: 'Response to Reviewers #1 and #2', Laurent Lamarque, 26 Oct 2015

Peer-review completion

AR: Author's response | RR: Referee report | ED: Editor decision

ED: Reconsider after major revisions (01 Nov 2015) by Warwick F. Vincent

AR by Laurent Lamarque on behalf of the Authors (17 Nov 2015) Author's response Manuscript

ED: Referee Nomination & Report Request started (18 Nov 2015) by Warwick F. Vincent

RR by Anonymous Referee #1 (25 Nov 2015)

Suggestions for revision or reasons for rejection

The authors strongly revised the manuscript and virtually responded to all my concerns and requests from the first submitted version. The methods, results and overall message of the study appear now clearly and I am confident this paper will significantly contribute to our better understanding of arctic ecosystem functioning and of the consequence of ongoing environmental changes.
However I still have a small problem with the presentation of the difference in polygon habitat responses to summer rainfall: the author still claim that intact and disturbed polygons responded positively to summer rainfall (reversely to mesic polygons, I guess) and justify it by no significant habitat x date interaction, both in the results (L196-197) and the discussion (L274-276). But it is a non-sense, íf the no significant interaction showed something it should be the similar response among the polygon types. I clearly understand that the variability can avoid the detection of such difference apparently demonstrated in a companion paper, but the data here does not support that idea. Did the authors try within polygon type date effect analyses? If there was a difference, it should be visible in F and p values of independent tests and could be an easy way out.
Eventually, I also have some minor comments:
-There still is some redundancy in the statistical results presentation between the text and figures and unnecessary specification: To me, the brackets L 197, L 206-206 and L232-233 (with the end of the sentence: and independently of the sampling location) can be deleted.
-Throughout the manuscript, some items are described using various denomination and even if it was a detail, it could lead to ask why the author used different words: ‘wet’ and ‘intact’ polygons, ‘site’ and ‘polygons’.
-Sentences L141-142 and 146-147 could be pooled for clarity.
- L 131 add a space between gully and RN08
- L 142 ‘70 x 70 cm’ instead of ’70 cm x 70 cm’ (same in the figure legned)
- L231 delete one ‘;’

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RR by Anonymous Referee #2 (07 Dec 2015)

Suggestions for revision or reasons for rejection

Review of the “Thermoerosion gullies boost the transition from wet to mesic vegetation” by Perreault et al.

This is my second review of the manuscript and I only have some very minor suggestions that I think will make the manuscript and its main story even stronger and more clear. The suggested references should help the authors to more clearly interpret their observations and to more effectively describe how their contribution complement and expand upon the existing literature.

L11-12: Clarify which sub-polygon feature the soil moisture and thaw depth observation was made (I assume the center pf the polygon?) as the variability within a single polygon can be substantial due to presence of raised or depressed center, rims and/or troughs.

L 16: Delete “therefore”

L17-18: Define/clarify “short period of time”

L 132. Centimeters (spelling error)

L 133: “..driven into..”

L125-: If I understand the authors correctly, all the authors’ measurements refer to the center of polygons. If so, it needs to be clearly stated in the paper (perhaps even in the title?) due to the large spatial variability that otherwise can be found between center, troughs and rims. I would actually encourage the authors to include “polygon centers” in the title, because of this. Especially considering recent literature that address ice wedge degradation and/or polygon types (see Lara, Mark J., et al. "Polygonal tundra geomorphological change in response to warming alters future CO2 and CH4 flux on the Barrow Peninsula." Global change biology 21.4 (2015): 1634-1651; and also Jorgenson, M. T., et al. "Role of ground ice dynamics and ecological feedbacks in recent ice wedge degradation and stabilization." Journal of Geophysical Research: Earth Surface (2015).) Changes in hydrology, vegetation and carbon fluxes can be completely different in troughs than in centers with ice wedge degradation.

L188-208: I would add the observation that soil moisture and thaw was similar (same?) between the two disturbed sites, despite the time since disturbance. Because this observation together with the clear difference in above ground biomass in figure 5 highlights a lag-time in vegetation response to the altered physical environment – a finding to be mentioned in both abstract and discussion/conclusion.

L197-200: Awkward sentence. I think the use of the word “driven” is what makes it confusing. Please find another word/rewrite.

L207-208: Unclear sentence. Please clarify/expand. Is the location of the “)” off?
I think the authors can increase their emphasis in the abstract about their finding that the observed changes occurred across a relatively short time frame (<5yrs after initialization of ice wedge degradation) and also expand/highlight (in the discussion/conclusion) on the observation about their finding of a gradual vegetation transition along the time since disturbance.

L231: Duplication of “;”

L251-253: I would not describe the soil moisture (nor the thaw) to have a gradient from the young and old disturbed site –they are the same! The biomass on the other hand shows a clear gradient (see my comment earlier about a lag in vegetation response).

L281: Delete “(see below)”

L 282-287: This contradiction can also be explained by subsidence of the ground surface as ice rich permafrost thawed (see Shiklomanov, Nikolay I., et al. "Isotropic thaw subsidence in undisturbed permafrost landscapes." Geophysical Research Letters 40.24 (2013): 6356-6361.) I would recommend to add this reference as a complementary explanation to the existing references.
I would also like to alert the authors on another relevant publication: Jorgenson, Janet C., et al. "Twenty-five year record of changes in plant cover on tundra of northeastern Alaska." Arctic, Antarctic, and Alpine Research 47.4 (2015): 785-806.

L393-403: As I mentioned earlier, I think the abstract and the conclusion can be strengthened, because in their current form, they do not provide justice to the presented results. For example, emphasize that the moisture and thaw is a relatively immediate change as they are similar between the old and young disturbed sites, while the vegetation response was slower. Also highlight the exact time scale (5 and 10 years, respectively). I would also like to see in the discussion and conclusion the authors commenting on whether the site (10 years after disturbance) is still undergoing a transition in the vegetation, ie has the vegetation at the old disturbed site yet reached an equilibrium with the hydrology and thaw regimes (which appears to have stabilized due to the similar values between the old and younger disturbed site)?

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ED: Publish subject to minor revisions (Editor review) (20 Dec 2015) by Warwick F. Vincent

AR by Laurent Lamarque on behalf of the Authors (24 Jan 2016) Author's response Manuscript

ED: Publish subject to technical corrections (01 Feb 2016) by Warwick F. Vincent

We are pleased to accept your manuscript for publication after the following corrections. PLease submit this final version without track changes.

Line 51: Allard

Line 139: rather dependent on …

Line 219: associated with

Line 230: Results on the environmental conditions of the 197 sampling sites were obtained regardless of the gully location (no-significant..)..
I do not understand this sentence. I suggest that it be contracted to :

There was no significant effect of gulley location (df = 2, LLR = 1.6, P = 0.21 for soil moisture, df = 2, LLR = 0.0, P=1.0 for thaw-front depth).

Line 260: 22.3 vs 9.3 g m-2;

Line 260: Figs 2 and 5a.

Line 290: changing the original polygon microtopography

Hasn’t = colloquial English
Line 293: although the full transition has yet to be reached

Line 323: This result, however, contrasts with

Line 456 This current state underscores the importance of long-term monitoring of permafrost and its associated vegetation

Please delete Fortier et al. 2015 (and from the text). It is an uncitable conference abstract only:
Fortier, D., Godin, E., Lévesque, E., Veillette, A. and Lamarque, L. J.: Thermal erosion of
583 ice-wedge polygon terrains changes fluxes of energy and matter of permafrost ecosystems, 584 American Geophysical Union fall meeting, San Francisco, United States of America, 2015.

The norm now is for all journal articles to be cited with a doi reference – this allows readers to click on the doi in the the reference list and instantly be connected with the article. Please insert these doi numbers for as many citations as possible. This is the format:
Bouchard, F., Pienitz, R., Ortiz, J. D., Francus, P., and Laurion, I.: Palaeolimnological conditions inferred from fossil diatom assemblages and derivative spectral properties of sediments in thermokarst ponds of subarctic Quebec, Canada, Boreas 42, 575–595, doi:10.1111/bor.12000, 2013.

Line 591L Phil. Trans. R 592 Soc. B, 368: 20120482, 12 pp., 2013 This does not look correct, please check.

Sarrazin, D. and Allard, M.: The thermo-mechanical behavior of frost-cracks over ice wedges:
771 new data from extensometer measurements, 68th Canadian Geotechnical Conference and
772 7th Canadian Permafrost Conference, Quebec City, Canada, 2015.
and
Veillette, A., Fortier, D. and Godin, E.: Contrasting patterns of thermo-erosion gullies formed
821 in syngenetic ice wedge polygonal terrains on Bylot Island, eastern Canadian Arctic: case
822 studies from three different sedimentary environments, 68th Canadian Geotechnical
823 Conference and 7th Canadian Permafrost Conference, Quebec City, Canada, 2015.
These are citable, published conference proceedings and can be retained, but please include page length of the articles (before the year at the end of the citation).

Table 1. Distribution of the studied polygons per habitat and per gully.

Table 3. Information of the Canonical Correspondence Analysis.
Delete ‘Information of the…
CCA of what? Perhaps:
Canonical correspondence analysis of the vegetation and environmental variables.

Figure 2. The four habitat types studied in the Qarlikturvik valley, Bylot Island, Nunavut.

END of corrections

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AR by Laurent Lamarque on behalf of the Authors (07 Feb 2016) Manuscript

Short summary

We investigated the impacts of climate change and thawing permafrost on vegetation dynamics in Bylot Island, Nunavut. The development of gullies has created new drainage systems within the wetlands, promoting the emergence of mesic plants at the expense of hydrophilic ones within 10 years after disturbance inception. The landscape transformation from wet to mesic plant communities can have substantial consequences on food availability for herbivores and methane emissions of Arctic ecosystems.