Tree-, stand- and site-specific controls on landscape-scale patterns of transpiration

Hassler, Sibylle Kathrin; Weiler, Markus; Blume, Theresa

doi:https://doi.org/10.5194/hess-22-13-2018

Articles | Volume 22, issue 1

https://doi.org/10.5194/hess-22-13-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

https://doi.org/10.5194/hess-22-13-2018

© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Articles | Volume 22, issue 1

Research article

|

04 Jan 2018

Research article |

| 04 Jan 2018

Tree-, stand- and site-specific controls on landscape-scale patterns of transpiration

Sibylle Kathrin Hassler, Markus Weiler, and Theresa Blume

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Final revised paper (published on 04 Jan 2018)
Preprint (discussion started on 01 Feb 2017)

Interactive discussion

Status: closed

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

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- Supplement

RC1: 'Review of Hassler et al., "Tree-, stand- and site-specific controls..."', Anonymous Referee #1, 06 Apr 2017
- AC1: 'Response to the comments of Referee #1', Sibylle Hassler, 22 Jun 2017
RC2: 'Manuscript review HESS-2017-47', Anonymous Referee #2, 10 Apr 2017
- AC2: 'Response to the comments of Referee #2', Sibylle Hassler, 22 Jun 2017

Peer-review completion

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

ED: Reconsider after major revisions (further review by Editor and Referees) (23 Jun 2017) by Nunzio Romano

AR by Sibylle K. Hassler on behalf of the Authors (14 Aug 2017) Author's response Manuscript

ED: Referee Nomination & Report Request started (17 Aug 2017) by Nunzio Romano

RR by Anonymous Referee #2 (18 Sep 2017)

Suggestions for revision or reasons for rejection

The authors have included the conversion to sap flow as suggested in the previous review. However, there are a number of points which still need to be addressed. With regards to the analytical approach, the relationship with soil moisture should be better explored and Fig. 4 should be improved to better depict the complexity of the dataset (co-variation of species, geology, aspect, etc; see my comments below). Moreover, there are several points to improve in the discussion, mainly the interpretations of species and aspect effects.

Specific comments

P. 5., L. 8. Could you specify which oak species was the allometry below derived from?

P. 6, L. 34. You have Q. robur and Q. petraea in your study site. Could you specify how many oaks from each species were measured in Table 1?

P. 8, L. 24-25. I think this analysis should be improved because soil moisture effects on transpiration are highly non-linear (Duursma et al., 2008) and here you’re relying on linear correlations. Moreover, in analysing sap flow vs soil moisture individually you’re not taking into account the variability due to variation in Epot. I suggest that:
You calculate SF/Epot, as sap flow relative to evaporative demand.
Optionally, rescale soil moisture values to relative values, obtaining relative extractable water or soil moisture deficit values (Granier et al. 1999; Granier & Loustau 1994)..
Plot SF/Epot as a function of (rescaled) soil moisture and check whether there is a threshold below SF/Epot starts to decline
Use an appropriate modelling approach to describe this behaviour: nonlinear models (e.g. sigmoidal, Sánchez-Costa 2015), piecewise/segmented regression (cf. Muggeo 2008) to detect possible breakpoints in this relationship, etc.

This analysis can be done to detect soil moisture effects both in the temporal and the spatial analysis.

Duursma, R., Kolari, P., Perämäki, M., Nikinmaa, E., Hari, P., Delzon, S., Loustau, D., Ilvesniemi, H., Pumpanen, J. & Mäkelä, A. (2008) Predicting the decline in daily maximum transpiration rate of two pine stands during drought based on constant minimum leaf water potential and plant hydraulic conductance. Tree Physiology, 28, 265–276.

Granier, A. & Loustau, D. (1994) Measuring and modelling the transpiration of a maritime pine canopy from sap-flow data. Agricultural and Forest Meteorology, 71, 61–81.

Granier, A., Reichstein, M., Breda, N., Janssens, I., Falge, E., Ciais, P., Grunwald, T., Aubinet, M., Berbigier, P., Bernhofer, C. & others. (2007) Evidence for soil water control on carbon and water dynamics in European forests during the extremely dry year: 2003. Agricultural and Forest Meteorology, 143, 123–145.

Sánchez-Costa, E., Poyatos, R. & Sabaté, S. (2015) Contrasting growth and water use strategies in four co-occurring Mediterranean tree species revealed by concurrent measurements of sap flow and stem diameter variations. Agricultural and Forest Meteorology, 207, 24–37.

Vito M. R. Muggeo (2008). segmented: an R Package to Fit Regression Models with Broken-Line Relationships. R News, 8/1, 20-25. URL https://cran.r-project.org/doc/Rnews/.

P. 8, L. 31. With regards to this section and also to Fig. 4, I already suggested in the previous review that grouping data by species (or by aspects in the first panel) would support some of the points you make (see my comment below on P. 12., L. 25-32)
P. 10, L. 8-9. It seems that when you leave out species-specific predictors ( compare Fig. 6 with Fig. 8), geology seems to gain a prominent role in explaining variability. Is there an association between species distribution and geological substrate that could explain this result?

P. 10, L. 20-30. You don’t need to repeat the values of r, as they’re already shown in Table 2.

P.10, L. 39 - p. 11, L. 1. Temperate tree species as the ones in this study will show declining transpiration rates with decreasing soil moisture below a certain threshold, and well before any visual sign of foliar water stress. The fact that in given localities water stress has been detected yet you don’t find any soil moisture effect on sap flow rates seems a bit odd to me.

P. 11, L. 2-10. I agree that we often lack the most complete picture of the available water sources for plants, but I suspect that the reason you’re not detecting any soil moisture effect is because of the analytical approach employed (see my previous comment on the suggestion of Sf/Epot analysis).

P. 11, L. 29 - 31. I already commented on this in my first review, and there are different issues to discuss here. First of all, the heat ratio method is well known to underestimate sap flow density as the method plateaus (loses sensitivity) at ~ 45 cm3 cm-2 h-1 (Fuchs et al. ,2017, Vandegehuchte & Steppe, 2013). Deciduous Quercus have large earlywood vessels, highly conductive and possibly allowing large sap flow density values, compared to Fagus, which shows a diffuse porous wood anatomy. What I mean is that the HRM may be possibly missing these high sap flow densities in oaks and therefore leading to an underestimation.

Moreover, comparative studies between Q. petraea and F. sylvatica show higher sap flow density in the former (Aranda et al 2005), pointing towards higher sap flow density in deciduous oaks compared to beech. A rough estimation from published values for Q. robur (Bréda et al. 1993, Fig. 2) also shows mean daily values closer to 10 cm3 cm-2 h-1, higher than those shown in Fig. 4 for oak. There is an additional uncertainty arising from potential differences between oak species. Overall, these issues should at least be discussed when interpreting differences between beech and oak.

Aranda I, Gil L, Pardos JA (2005) Seasonal changes in apparent hydraulic conductance and their implications for water use of European beech (Fagus sylvatica L.) and sessile oak [Quercus petraea (Matt.) Liebl] in South Europe. Plant Ecology 179:155–167.

Fuchs S, Leuschner C, Link R, Coners H, Schuldt B Calibration and comparison of thermal dissipation, heat ratio and heat field deformation sap flow probes for diffuse-porous trees. Agricultural and Forest Meteorology. http://www.sciencedirect.com/science/article/pii/S0168192317301314 (16 June 2017, date last accessed ).

Vandegehuchte MW, Steppe K (2013) Sap-flux density measurement methods: working principles and applicability. Functional Plant Biology 40:213–223.

P. 12., L. 25-32. I find this reasoning a bit convoluted, because to explain the lower sap flow rates in southern aspects, you’re invoking long-term drought adaptations without having detected soil moisture limitation effect on sap flow. Moreover, you don’t provide any reference supporting possible mechanisms for these drought adaptations and how they could possibly influence sap flow density patterns (e.g. changes in hydraulic conductivity, adjustments in leaf-to-sapwood area ratios,etc.).

I was thinking whether it could be an effect of oak, with lower sap flow density, being preferentially distributed in southern slopes, but I’ve seen in a response to Reviewer #1 that beech trees also show lower sap flow rates in southern aspects. I think that you should provide this information to the reader, not only to the reviewers, so the results can be discussed properly. One possible way would be to add conditioning factors (e.g. species, or aspect in the first panel) in the plots of figure 4. This is something I already proposed in the first version of the manuscript and which I mentioned in an earlier comment (on P. 8, L.31).

You mention geology as a possible influence on these patterns. Do the southern slopes sampled correspond to schist substrate (which seems to be associated with lower sap flow density)? It is not clear whether you mean this in your explanation of lines 32-34 (P. 12).

P. 12, L. 40-42. Then, Epot is not higher in southern slopes so one should not expect higher sap flow as discussed in the previous paragraph. These results here are more consistent with the fact that sap flow was not higher in southern aspects. Maybe you should integrate this part of the discussion in a single paragraph (e.g. from P. 12. L. 25 to P. 13, L. 2), because the ideas are very tightly linked.

P. 13, L. 23-25. See the issues on species comparisons mentioned in the comment on P. 11, L. 29 - 31.

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RR by Anonymous Referee #1 (18 Sep 2017)

Suggestions for revision or reasons for rejection

Review of manuscript hess-2017-47-version2

The authors have much improved their manuscript from the original (version 1) submission, and have sufficiently addressed my previous concerns. I congratulate them on fine work and offer only a handful of minor suggestions:

1) page 1, line 19: I think “modelled” should be “measured”

2) page 1, lines 21-23: This makes it sound like species and diameter were important for velocity but not for flow — but really it’s just that you didn’t include species and diameter in the regressions for flow. I understand that you made that choice because the variables would not be independent, but perhaps with a caveat to the reader (e.g. saying that some portion of the relationship between flow and DBH or species is inherent to the assumed allometric relationships), it would be better to include species and diameter (and height) in the flow regressions anyway. After all, the goal is to learn which controls are most important, and species and DBH are probably important controls. As written, the text suggests that flow is less related to DBH than velocity is, which is the opposite of the truth. The same issue affects page 13, line 14.

3) page 1, line 30: delete the word “to” before “65%”.

4) page 1, line 31-32: We disagreed about this sentence in the original version, but let me make one more appeal. The day-night change in solar input is typically enough to make transpiration go from its maximum value to near zero, even without the action of stomata; so it seems incomplete to say that the main controls on transpiration are plant-physiological and soil characteristics, omitting sunlight and atmospheric conditions. The latter are clearly extremely important controls too; no model could omit them and hope to reproduce measurement transpiration patterns. I understand from your response to my first review that you were thinking of the atmosphere and sun as drivers and you wanted to list the ‘resistance’ factors here — but that is just not what the sentence says.

5) page 2, line 32: delete “have been investigated”

6) page 2, line 41: I would use the word “effect” instead of “aspect” to avoid confusion with the landscape-scale characteristic category “aspect”

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ED: Publish subject to minor revisions (further review by Editor) (28 Sep 2017) by Nunzio Romano

AR by Anna Wenzel on behalf of the Authors (23 Oct 2017) Author's response Manuscript

ED: Publish subject to revisions (further review by editor and referees) (29 Oct 2017) by Nunzio Romano

ED: Publish as is (20 Nov 2017) by Nunzio Romano

Short summary

We use sap velocity measurements from 61 trees on 132 days to gain knowledge about the controls of landscape-scale transpiration, distinguishing tree-, stand- and site-specific controls on sap velocity and sap flow patterns and examining their dynamics during the vegetation period. Our results show that these patterns are not exclusively determined by tree characteristics. Thus, including site characteristics such as geology and aspect could be beneficial for modelling or management purposes.