HETEROFOR 1.0: a spatially explicit model for exploring the response of structurally complex forests to uncertain future conditions – Part 1: Carbon fluxes and tree dimensional growth

Jonard, Mathieu; André, Frédéric; de Coligny, François; de Wergifosse, Louis; Beudez, Nicolas; Davi, Hendrik; Ligot, Gauthier; Ponette, Quentin; Vincke, Caroline

doi:https://doi.org/10.5194/gmd-13-905-2020

Articles | Volume 13, issue 3

https://doi.org/10.5194/gmd-13-905-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/gmd-13-905-2020

© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 13, issue 3

Model description paper

|

05 Mar 2020

Model description paper |

| 05 Mar 2020

HETEROFOR 1.0: a spatially explicit model for exploring the response of structurally complex forests to uncertain future conditions – Part 1: Carbon fluxes and tree dimensional growth

Mathieu Jonard, Frédéric André, François de Coligny, Louis de Wergifosse, Nicolas Beudez, Hendrik Davi, Gauthier Ligot, Quentin Ponette, and Caroline Vincke

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Final revised paper (published on 05 Mar 2020)
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Interactive discussion

Status: closed

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

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RC1: 'Comments', Anonymous Referee #1, 30 Jun 2019
- SC1: 'Reply to comments of Anonymous Referee #1', Frédéric André, 04 Jul 2019
RC2: 'Comments on Jonard et al. HETEROFOR model paper', Anonymous Referee #2, 09 Jul 2019
RC3: 'Comments', Anonymous Referee #3, 03 Aug 2019
AC1: 'Final response to referee comments', Mathieu Jonard, 04 Sep 2019

Peer-review completion

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

AR by Mathieu Jonard on behalf of the Authors (09 Sep 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (11 Sep 2019) by Min-Hui Lo

RR by Anonymous Referee #4 (24 Sep 2019)

Suggestions for revision or reasons for rejection

I very much appreciate the development and implantation of a new individual tree model that is physiology based and can be applied over periods that allow to judge the development of species mixtures under changing environmental conditions. I feel however that considerable improvements in the model description, presentation and discussion could still be achieved.

Model description

The model description in general would also benefit from a better explanation about which processes are run in which time steps. While photosynthesis is calculated hourly, time steps for allocation are not explicitly addressed. They may be done annually, similarly to dimensional calculations. If this is true (I couldn’t find any statement about it), it raises some yet unexplained questions: Where is the foliage compartment outside the vegetation period and how does it respire? Is the biomass at the end of the year abruptly changing or are empirical functions used to distribute the growth over the year? Shouldn’t the fact that biomass is actually changing during the year be reflected in the maintenance respiration calculations? If, however, allocation is done hourly or daily, how is the first leaf flushing justified in deciduous trees when there is not yet any photosynthesis? In particular since there seems to be no reserve compartment. The best model description is in the caption of figure 1 but I think this (and more) information needs to be in the text too.

I also noticed that in many equations, parameters are given as alpha, beta, gamma and delta letters without further indication - which is a bit strange and sincerely against common rules since this kind of notation is not specific. In my opinion, also empirical parameters (including a, b, c…) should be unmistakably identifiable and should also be given and explained (including sources) in a table somewhere.

Model demonstration and discussion

I appreciate that examples for demonstrating the model’s performance are based on a number of stands that differ somewhat in their structure. I was a bit disappointed though that only different model approaches (such as different photosynthesis schemes) have been compared and no parameter sensitivity has been done. I admit, however, that this might be a very comprehensive demand and should possibly be restricted to completely new model formulations. On the other hand, the tests are still limited to two tree species and more or less only one climate area. If no other sites will be incorporated (which would be good but which is something I don’t really expect), the issue should be carefully acknowledged as a limited demonstration of model performance.

In addition, existing literature should be better considered for the following topics: 1) the linear relationship between NPP and GPP has been recently discussed by Collalti et al. 2019; 2) the allometry depends on competition issues that need to be treated based on individual tree situations, which is a likely explanation for the relatively bad performance of increment calculations (see e.g. del Rio et al. 2019), 3) an hierarchical allocation approach that distributes carbon into different compartments has certain disadvantages, so that source-sink approaches or other approaches needs to be at least discussed as possible alternatives (e.g. Carl et al. 2018, Thurm et al. 2017). These points are particularly important in in a single-tree model than in a stand model.

Besides the evaluations which are basically based on growth measurements that are very integrated outcomes from many underlying processes, I would like to see some curves of how different compartments of different trees or groups of trees are developing over time in dependence on climatic input. Do we see any climate or management impact here? Are different groups have different strategies or are developing differently? Is this development reasonably at all? Please elaborate.

There are a couple of other more specific things that caught my eye and may be corrected or answered:

P3L13: Another argument why forestry trials are not suitable to derive estimates for future conditions are that these future conditions, i.e. CO2 concentrations, simply cannot be observed in the present.

P4L13ff: The BALANCE model is described here as having no soil layers and is missing basic soil processes. This is wrong, as can be easily derived from Figs. 3 and 6 in Grote and Pretzsch 2002. I admit that neither weathering nor nutrients other than nitrogen are included but still the model hosts a full carbon and nitrogen cycle and calculations in different soil layers, considering different nutrient availability with rooting depth. Please correct.

P6L14: Does the model run when ‘no meteorological measurements’ (resp. scenario data) are provided as input? How can this work out reasonably?

P7L12ff (also in Fig.1, and P9): GPP is either derived by a radiation efficiency approach or with the Farquhar model? This is irritating. There should be a rule when the one or other method is applied. Has this something to do with the age/size or position of the tree similar to the differentiation of respiration?

P7L19: The expression ‘compartment’ or ‘tree compartment’ is used here and in other places but never defined. In P6L32 it is used for bark and foliage, P8L1 it is soil solution, at P12 it describes foliage and fine roots, and at P26 we learn that ‘structural compartments’ exist besides foliage and roots. The same holds for the expression ‘organ’ which is partly used as a synonym to ‘compartment’. Figure 1 caption tells us about ‘structural organs’ that are ‘roots, trunk, and branches’ and also later ‘organ’ development is described with equations throughout P11 to P13 without telling the reader what is actually meant.

P9L7 (and figure 1): Fruits are very interesting but seldomly considered as a separate and dynamic tree compartment that is explicitly modelled. From Fig. 1 and the description in P13 it seems that it is considered but how data on this compartment can actually be used to modify allocation pattern, needs to be described further (taking the carbon from all other compartments equally or selectively?).

P9L10: This indicates that photosynthesis is driven with daily meteorological data which for the Farquhar approach only makes sense if data are downscaled to hourly (or similar) time steps (also indicated in P10L18). Why is this not possible for the hydrological model then which explicitly requires hourly input?

P10L14: Possible relationships between Farquhar photosynthesis and soil water restrictions have been implemented before (see e.g. Granier, Knauer, van Wijk, Wang in references). I guess, that also the new implementation will be based on one of them which could be indicated here. Otherwise, I fear that a short description of how this is done is indispensable for understanding the carbon assimilation dynamics.

P11L4ff: I am a bit puzzled about these explanations. Why is it bad that ‘the crown to stem diameter ratio changes during the course of the tree development’ so that the npp/gpp ratio also changes. Isn’t this exactly what you want? And why is this index better although a relation of npp/gpp to this index has not been demonstrated?

P11L16ff: Maintenance respiration is taken from photosynthesis (according to equation 7), but its calculation is independent of carbon gain. So, the net gain might get negative. What’s happening then? Is there any reserve compartment?

P13L15/Eq.22: How is this parameterized and even how is the function itself derived? My question arises from the fact that fructification is highly variable and relates to specific climate conditions such as temperature in spring. Also, the parameter given in the appendix seems to be a variable based on this equation.

P13L30ff/Eq.26-28: How could height and diameter growth be derived from the total above structural carbon gain if diameter and height growth only depend on stem (trunk) development? I would expect that the dimensional growth depends on db_stem rather than db_structural. Given that the derivation of height and diameter increment is correct, has anybody checked if the biomass increase is actually supporting the dimensional change? Or does it imply a wood density change?

P14L30: Hounzandji et al. 2015 distinguish branches/twigs but not roots into three fractions of different diameter classes. The assumption that roots could be described with the same equations (and parameters?) without any additional data seems very bold to me. As it is, the description gives a false impression of what has been derived from literature. Furthermore, if a root fraction of 0-4 cm is assumed, it would include fine roots, which are, however, separately treated in the model. The differentiation is therefore inconsistent.

P17L17ff: The reconstruction is a nice feature but depends on the knowledge about how many trees have died and when they died during the investigated period. Otherwise, npp is underestimated since it only refers to the remaining trees. Could you acknowledge this in the paragraph?

References

Carl, C., Biber, P., Veste, M., Landgraf, D. and Pretzsch, H. (2018). Key drivers of competition and growth partitioning among Robinia pseudoacacia L. trees. Forest Ecol. Manage. 430, 86-93.

Collalti, A. and Prentice, I. C. (2019). Is NPP proportional to GPP? Waring’s hypothesis 20 years on. Tree Physiol. 39, 1473-1483.

del Río, M., Bravo-Oviedo, A., Ruiz-Peinado, R. and Condés, S. (2019). Tree allometry variation in response to intra- and inter-specific competitions. Trees 33, 121-138.

Granier, A., Loustau, D. and Bréda, N. (2000). A generic model of forest canopy conductance dependent on climate, soil water availability and leaf area index. Annales des Sciences Forestieres 57, 755-765.

Knauer, J., Werner, C. and Zaehle, S. (2015). Evaluating stomatal models and their atmospheric drought response in a land surface scheme: A multibiome analysis. J. Geophys. Res. - Biogeosci. 120, 1894–1911

Thurm, E. A., Biber, P. and Pretzsch, H. (2017). Stem growth is favored at expenses of root growth in mixed stands and humid conditions for Douglas-fir (Pseudotsuga menziesii) and European beech (Fagus sylvatica). Trees-Struct. Funct. 31, 349-365.

Van Wijk, M. T., Dekker, S. C., Bouten, W., Bosveld, F. C., Kohsiek, W., Kramer, K., et al. (2000). Modeling daily gas exchange of a Douglas-fir forest: comparison of three stomatal conductance models with and without a soil water stress function. Tree Physiol. 20, 115-122.

Wang, Y.-P. and Leuning, R. (1998). A two-leaf model for canopy conductance, photosynthesis and partitioning of available energy I: Model description and comparison with a multi-layered model. Agric. Forest Meteorol. 91, 89-111.

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RR by Anonymous Referee #3 (29 Sep 2019)

RR by Anonymous Referee #1 (14 Oct 2019)

ED: Reconsider after major revisions (14 Oct 2019) by Min-Hui Lo

AR by Mathieu Jonard on behalf of the Authors (24 Nov 2019) Author's response Manuscript

ED: Referee Nomination & Report Request started (26 Nov 2019) by Min-Hui Lo

RR by Anonymous Referee #4 (09 Dec 2019)

Suggestions for revision or reasons for rejection

Thank you for considering some remarks and answering a number of questions raised before. I particularly appreciate the additional simulations.

Although I am still a bit concerned that the various options of the model (with and without water balance, LUE or Farquhar model, various alternatives in determining height growth and crown dimensions) may require more detailed instructions and evaluations, I acknowledge that this is difficult to carry out in a paper. Perhaps the authors can provide a commenting sentence?

Another issue that concerns me is that the nutrient cycle, a feature that makes the new model to some degree special, seems to affect respiration and allocation but not photosynthesis. Does this mean that with less nutrients the overall biomass growth is increasing? This would not only be counter-intuitive but also against experiences (e.g. Weinstein et al.).

In addition, while going through the text again I stumbled about a number of smaller issues and phrases that are uncommonly worded and difficult to understand, particularly in the new parts. This is certainly not covering any language problem and a general check is encouraged.

P1L15: I think you mean ‘different’ instead of ‘contrasted’
P1L18: The “most empirical option for describing maintenance respiration provides the best results while … empirical approaches similarly perform for photosynthesis and crown extension.” What should the reader who cannot distinguish between ‘empirical’ and ‘most empirical’ gain from this? Rephrase.
P1L20: ‘driven by’ instead of ‘according to’? (also to avoid repetition)
P2L4: rephrase ‘make no doubt’ do you mean ‘will certainly happen’ or similar?
P2L6: Please indicate what Messier had proposed.
P2L12: After modification, this sentence doesn’t make any sense now. Rephrase.
P2L14ff: Pretzsch et al. don’t propose new models but a test of the (relatively few) models that are able to cover complex stands with empirical data. Reformulate!
P4L33: ‘within the frame of’ instead of ‘in’
P5L1ff: Repetition from P2L8ff
P6L4: grammar, rephrase
P6L6: Is it really only the annual time step that is stored and can be used for evaluation? Shouldn’t there be the option to read out at least daily data, e.g. for checking photosynthesis and drought development? Since later on ‘detailed budgets’ are mentioned, I think that the information should be elaborated.
P6L24ff: Repetition from the previous sentence. Shorten and rephrase.
P7L34: ‘On another hand’? Wrong phrase (perhaps consider ‘In addition’ or just skip?)
P10L11: I am still puzzled. Why is the hourly meteorology only loaded for water-balance calculations? It is needed for photosynthesis anyway, correct? If this is linked to the selection of the photosynthesis module, please note this here.
P11L15: How is the position of the leaf accounted for? Simple linear decreasing function? Exponential function using two additional parameters according to Schaefer et al.? Which parameters? Same for all species?
P14L4: ‘Allocation priority is given….’ Not ‘In the allocation, priority is given …’
P14L19: Either you skip the new half-sentence or you have to give a reference here. Perhaps look into Hacket-Pain et al.
P16L12: described not describe
P19L31: grammar, rephrase
P20L17ff: I may have missed it but after highlighting the special consideration of nutrients for growth in HETEROFOR, it should somewhere be stated explicitly that the state of nutrition has been kept constant for all presented simulations.
P20L19: replace ‘evolution’ by ‘development’
P21L8/9: grammar, rephrase
P23L3: what does ‘but not symmetrically’ mean? (also correct spelling)
P24L4 (Fig.4): I wonder why no simulation vs. measurement plots but only simulation and measurement vs. girth?
P25L6,L12,L13,L15: grammar, rephrase
P25L17ff: This information is very scarce and provokes some serious question. In order to judge the reason for the insensitivity to the climate scenarios, the reader needs to know in particular, if the water availability was different. The role of water balance is mentioned in the discussion referring to another paper. Still, I think that some information of increasing drought stress or vegetation length extension could be indicated here in the result section.
P25L18: ‘recognized’ instead ‘assessed’?
P30L1: ‘increase’ instead ‘increased’
P30L10: ‘maintain a stable npp to gpp ratio’, ‘On the other hand’ (never: on another hand – however, this phrase is usually only used if another sentence before has been started with: On the one hand, …)
P30L28: ‘evaluate the interest of this approach’?? Do you mean the significance, applicability, …?
P31L8: This is an unproven claim. You might however phrase it as a possible line of further investigations.
P31L16: provide instead provides
P31L20: ‘high computational demand’ instead ‘long computing times’
P31L24: rephrase ‘two errors were added’
P31L28: delete ‘noisily’
P31L29: ‘depict’ instead of ‘highlight’?
P32L3: ‘account’ instead of ‘accounts’
P32L5: replace ‘What came out’ by ‘The result’
P32L9,L12: grammar, rephrase
P32L13: Could? Or Should? Or Can?
P33L27: I don’t see the logical reasoning here. Also avoid to describe coupling as ‘perfect’.
P34L4/5: grammar, rephrase
P34L7: I would delete ‘predicts well individual radial growth and’ for language reasons as well as because I think that this feature has not been convincingly demonstrated (see comment to Fig. 4, also, prediction needs longer periods and independently set up sites).
P24L10: replace ‘overview’ by ‘impression’

Mentioned references
Hacket-Pain, A., Ascoli, D., Berretti, R., Mencuccini, M., Motta, R., Nola, P. et al. 2019 Temperature and masting control Norway spruce growth, but with high individual tree variability. Forest Ecol. Manage., 438, 142-150.
Weinstein, D.A., Beloin, R.M. and Yanai, R.D. 1991 Modeling changes in red spruce carbon balance and allocation in response to interacting ozone and nutrient stresses. Tree Physiol., 9, 127-146.

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ED: Reconsider after major revisions (17 Dec 2019) by Min-Hui Lo

AR by Mathieu Jonard on behalf of the Authors (20 Jan 2020) Author's response Manuscript

ED: Referee Nomination & Report Request started (21 Jan 2020) by Min-Hui Lo

RR by Anonymous Referee #4 (23 Jan 2020)

ED: Publish as is (27 Jan 2020) by Min-Hui Lo

AR by Mathieu Jonard on behalf of the Authors (30 Jan 2020) Manuscript

Short summary

To explore the forest response to new forestry practices under a changing environment, one needs models combining a process-based approach with a detailed spatial representation, which is very rare. We decided to develop our own model according to a spatially explicit approach describing individual tree growth based on resource sharing (light, water and nutrients). A first evaluation showed that HETEROFOR predicts well individual radial growth and is able to reproduce size–growth relationships.