Effects of bryophyte and lichen cover on permafrost soil temperature at large scale

Porada, Philipp; Ekici, Altug; Beer, Christian

doi:https://doi.org/10.5194/tc-10-2291-2016

Articles | Volume 10, issue 5

https://doi.org/10.5194/tc-10-2291-2016

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

Special issue:

Changing Permafrost in the Arctic and its Global Effects in...

https://doi.org/10.5194/tc-10-2291-2016

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

Articles | Volume 10, issue 5

Research article

|

30 Sep 2016

Research article |

| 30 Sep 2016

Effects of bryophyte and lichen cover on permafrost soil temperature at large scale

Philipp Porada, Altug Ekici, and Christian Beer

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Final revised paper (published on 30 Sep 2016)
Preprint (discussion started on 01 Feb 2016)

Interactive discussion

Status: closed

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

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RC1: 'Referee comment', Anonymous Referee #1, 01 Mar 2016
RC2: 'Review', Anonymous Referee #2, 08 Apr 2016
AC1: 'Authors' response to reviewers' comments', Philipp Porada, 06 May 2016

Peer-review completion

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

AR by Philipp Porada on behalf of the Authors (12 May 2016) Author's response Manuscript

ED: Referee Nomination & Report Request started (15 Jun 2016) by Cathy Wilson

RR by Anonymous Referee #3 (27 Jun 2016)

Suggestions for revision or reasons for rejection

This is a very well written, clear and concise paper. The development work it reports on is well thought through. Choices made during the development stage are well justified. I only have some minor comments and suggestions, given below.

General.
- It is unclear to me which are the parameter values chosen in the "constant" simulation. Maybe they were given somewhere, but it did not find this even after looking twice. These values should be stated more clearly, as it would help interpreting the results.
- I would have liked to see a more detailed analysis of seasonal effects, in particular the difference between summer and the shoulder seasons (which might be a bit more humid?). As the paper is now, it is not shown convincingly that the dynamic hydric state of bryophytes (and its effect on soil temperature) is really required, i.e. that this effect cannot be taken into account by simply tweaking the average ("constant") heat conductivity and heat capacity.
- The bryophytes seem to have little effect in winter, which makes sense. Is bryophyte compaction by snow taken into account? (Probably not, and probably it wouldn't make any additional difference because snow insulation is strong, but it would be good to know).
- The discussion about the differences between mosses and lichen could be a little bit more detailed, in terms of how their properties change with general humidity etc.

Specific.
- Quite often two sentences are contracted to a single one, only a comma separating the two parts. Examples: P1, L7: "The model simulates .. on upland sites, wetlands are not included". Or:P5, L19: "D is the fraction of cover lost due to disturbance, it is set to 0.00083 per month.". It would be better to have two separate sentences in these cases.
- P1, L10: What is the "study region" mentioned here?
- P2, L26: Indeed in ORCHIDEE there is no bryophyte PFT but Koven et al. (GRL, 2009) do take into account soil thermal insulation but an organic layer.
- P3, L30: re-order the sentence: "… non-vascular vegetation model LiBry, described in detail by Porada et al. (2013), is integrated into JSBACH."
- P4, L2: What is poikilohydry?
- P5, L3 and P5, L7: These sentences on disturbance appear to be contradicting each other. The first sentence seems to say that the surface coverage is (brutally) set back to a small initial value, while the second one suggests a more gradual, regular disturbance. I think the second sentence is correct. Please clarify.
- P5, L15: The equation is difficult to read, with all the min and max. It might be useful to clarify right from the beginning that there are one positive growth term, one "negative growth" (senescence?) term and one disturbance term, and to define these separately.
- Figure 2: Might be useful to place the values for the "constant" simulation on this graph.
- P15, L19: It should be said clearly that there is absolutely no reason why you would expect the bryophytes to reduce the cold bias. In the discussion, it would be nice to get an idea about the possible reasons for this substantial bias.

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ED: Publish subject to technical corrections (06 Sep 2016) by Cathy Wilson

AR by Philipp Porada on behalf of the Authors (15 Sep 2016) Author's response Manuscript

Short summary

Bryophyte and lichen cover on the forest floor at high latitudes insulates the ground and thus decreases soil temperature. This can protect permafrost soil, stabilising it against global warming. To quantify the insulating effect, we integrate a novel, process-based model of bryophyte and lichen growth into the global land surface model JSBACH. We find an average cooling effect of the bryophyte and lichen cover of 2.7 K, which implies a significant impact on soil temperature at high latitudes.