the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Disentangling future effects of climate change and forest disturbance on vegetation composition and land-surface properties of the boreal forest
Abstract. Forest disturbances can cause shifts in boreal vegetation cover from predominantly evergreen to deciduous trees or non-forest dominance. This, in turn, impacts land surface properties and, potentially, regional climate. Accurately considering such shifts in future projections of vegetation dynamics under climate change is crucial but hindered e.g. uncertainties in future disturbance regimes. In this study, we investigate how sensitive future projections of boreal forest dynamics are to additional changes in disturbance regimes. We use the dynamic vegetation model LPJ-GUESS to investigate and disentangle the impacts of climate change and intensifying disturbance regimes in future projections of boreal vegetation cover as well as changes in land surface properties such as albedo and evapotranspiration. Our simulations find that warming alone drives shifts towards more densely forested landscapes, and more intense disturbances reduce tree cover in favor of shrubs and grasses, while the interaction between climate and disturbances leads to an expansion of deciduous trees. Our results additionally indicate that warming decreases albedo and increases evapotranspiration, while more intense disturbances have the opposite effect, potentially offsetting climate impacts. Warming and disturbances are thus comparably important agents of change in boreal forests. Our findings highlight future disturbance regimes as a key source of model uncertainty and underscore the necessity of accounting for disturbances-induced effects on vegetation composition and land surface-atmosphere feedback.
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RC1: 'Comment on egusphere-2024-1028', Anonymous Referee #1, 20 Jun 2024
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Review of Layritz et al. Biogeosciences
General comments:
In this paper, the authors used the LPJ-GUESS model to investigate and disentangle the impacts of climate change, intensifying disturbances frequency and their interactive effect in future projections of boreal vegetation cover. They also explore impacts of abrupt changes in vegetation area and composition on the land-surface properties albedo and evapotranspiration. And finally, they investigate the level of resilience of the boreal vegetation.
They found that climate is the primary factor driving the increase in total vegetation cover and carbon (denser and more forested vegetation). However, changes in vegetation composition (from needleleaf evergreen and tundra to broadleaf summergreen dominance) are influenced by a complex interplay between climate, disturbances, and their interactions. They also found that warming climate reduces albedo and increases evapotranspiration, whereas more intense disturbances have the opposite effect, potentially counteracting the impacts of climate change. Consequently, both warming and disturbances are significant agents of change in boreal forests. While albedo and evapotranspiration recovered on a decadal timescale, disturbance-induced effects on vegetation are long-lasting but recover on a centennial time scale.
First of all, I enjoyed reading of this manuscript. This paper shed new lights on the impacts of future climate change and changing disturbances regimes on boreal forests. Some improvements to the paper should be made and these are listed below. However, once assessed, I don't think these issues would prevent the publication of the manuscript in Biogeosciences.
I didn’t review the English language because I’m not an Anglophone.
Principal criteria
Scientific significance:
Does the manuscript represent a substantial contribution to scientific progress within the scope of Biogeosciences (substantial new concepts, ideas, methods, or data)?Good
Scientific quality:
Are the scientific approach and applied methods valid? Are the results discussed in an appropriate and balanced way (consideration of related work, including appropriate references)?Good
Presentation quality:
Are the scientific results and conclusions presented in a clear, concise, and well-structured way (number and quality of figures/tables, appropriate use of English language)?Excellent
Specific comments:
P3 – Line 74: “has been validated in previous studies “. Without going into too much detail, it would still be interesting to explain here how these validations were carried out, in order to ensure from the outset that the reader is confident about the validity of using this model.
P4 – Line 92: Where is Appendix A1 for a detailed description?
P4 – Line 93: Add a capital letter at the beginning of a sentence
P4 – Line 100: “From within the ISIMIP ensemble, data of the MRIESM2.0 Earth system model was chosen, as its response best represents the ensemble average.” Based on what? In my opinion, taking just one climate model does not allow us to correctly determine the uncertainties of simulations. It would have been better to use two or three. What temporal resolution?
Page 4 – Line 103: “Figure 1a shows the CO2 concentration, and Fig. A1 the climate data used. » Please explain a little bit more the projected changes in climate variables.
Page 4 – Line 109: In table 1, you need to add more details here about the projected changes in climate variables, not only for temperature and not only for one period.
Page 4 – line 110: “on disturbance probability ». It is more appropriate to use “frequency” instead of probability.
Page 6 – Line 141: For what year? What area? And how?
Page 9 – Line 185: “The range of total AGC compares well to satellite-derived data (Fig. B2), however, observed values are slightly lower and feature a pronounced peak around 3 kg/m2 not present in the modeled data.” The peaks around three still represent a good proportion of the pixels... Can you show a map of anomalies between simulated and observed data to see where the model is simulating correctly?
Page 12 – Line 253: Add space between “October” and “(Fig. 4a)”
Page 12 – Line 272: Remove space after Fig. 4a
Page 12 – Line 274: Remove capital letter to Fig. 4a and B.
Page 14 – Line 313: “previous modeling studies performed with LPJ-GUESS”. What about other modeling studies performed with other models?
Page 14 – Line 314: “and the range of total AGC corresponds to observations (Fig. B2). » I’m not sure if you sum up all the ABC shows on Fig. B2.
Page 14 – Line 315: Scandinavia
Page 19 – Line 415 : « It should be noted that ecophysiological control on ET is relatively weak in the current version of LPJ-GUESS. » I agree so why study it if we can't really distinguish causes of changes?
Page 20 – Line 438: “This means that regeneration failure - eroding of seed banks through too frequent disturbances (Turner et al. (2019); Hansen et al. (2018)) - cannot occur by model design. Here, different reproductive strategies, e.g. serotony or resprouting, would also be important to consider”. The fact that regeneration accidents are not included is an important limitation that needs to be taken into account in order to strongly balance the results of this study. See studies on this subject in Quebec (e.g. Girard et al. 2008)
Page 20 – Line 443: “However, it is important to keep in mind that specific disturbances can have additional effects we are not considering here.” Yes additional effect and to go further, you need to discuss about amplifying effects between disturbances.
Page 20 – Line 445: “Further, our disturbance dynamics are neither linked to climate nor to vegetation type, as, for example, a detailed fire disturbance module would be.” SPITIFIRE is already implemented in LPJ so why you didn’t used it?
Citation: https://doi.org/10.5194/egusphere-2024-1028-RC1
Model code and software
LPJ-GUESS Release v4.1.1 model code J. Nord et al. https://zenodo.org/records/8065737
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