Dear Authors,
Thank you for your replies to reviewers’ comments. I have now read through reviewers’ comments as well as your replies. Based on my reading of the paper and your replies, I am happy to have you change your manuscript as you suggest in your replies and submit a revised version of the manuscript. However, based on my own reading of the manuscript, I would request you to take into account the following minor comments mainly to improve the clarity of your manuscript and address some minor issues.

1. I don’t think N, B and P in Net Biome Productivity need to be upper case every time you write this term. Similarly for Plant Functional Type.

2. In agreement with reviewer #2, I am confused about how you define the dominant PFT. In my simple mind, a dominant PFT is the one which occupies the largest fraction in a grid cell. Whatever definition you have used, unless I missed it, should be explicitly mentioned in the manuscript. The units of dominant PFT would be fractional coverage. Isn’t it? Also, in Figure 3, having read reviewer # 2’s comment I am now confused if “Dominant PFT” refers to the fractional coverage of the dominant PFT or LAI of the dominant PFT.

3. Please add titles to the four panels in Figure 1.

4. Just to reiterate reviewer #2’s comments it was difficult to read the manuscript with no table explaining the acronyms for PFTs.

5. Page 4, line 24. Replace “species” by ‘PFT”. LPJ doesn’t represent species, it represents PFTs. Correct?

6. Page 4, line 29. Please consider replacing “… including example of all major biomes” with “These regions include all major biomes”.

7. Page 5, line 4. Please consider replacing “a varying time period of 20, 60 and 100 years” with “time periods of 20, 60 and 100 years” here and elsewhere.

8. Page 5, line 14. The manuscript reads, “the sum of all ecosystem-level fluxes, termed Net Biome Productivity (NBP)”. This is a vague definition and may not be correct depending on what fluxes are included. Please reword this properly.

9. Page 5, lines 20-30. Just like reviewer #2, I am lost here. Although Figure A1 helps this section needs to be reworded for an easy read.

10. Page 6, line 3. Please replace “Maps of vegetation and soil C …” with “Maps of simulated vegetation and soil C …”

11. Page 6, lines 22-25. These sentences about pre-condition 1 and 2 are not clear at all to me.

12. Figure 6. It would be really useful to label panels as a), b), c) and d) and refer to the panels in text.

13. Page 6, line 2 reads “Figure 6 shows the maximum differences in recovery times …”. Differences between what and what? Aren’t these just the recovery times? Here and elsewhere you have used the word “difference” and I can’t appreciate what’s the difference between?

14. Page 7, line 7. Shouldn’t the “LU type” be “LU duration” here.

15. Page 7, line 8 reads “While substantial differences occur across the pasture simulations …”. DO you mean differences across P20, P60 and P100.

16. Page 7, line 8 reads “ … and across croplands in boreal forests …”. Do you mean “across cropland simulations (C20, C60 and C100)”.

17. Page 7, lines 11 and 12 read “On the other hand, in our simulations dominant PFT recovery in temperate forests is hardly influenced by the type of former LU, or, conversely, pasture duration has negligible effects on boreal forest recovery”. In the absence of clear definition of “dominant PFT” I can’t appreciate if it’s the LAI or the fractional coverage of dominant PFT that is being talked about.

18. Page 7, lines 14-15 read “Compared to dominant PFT LAI, the starting point of vegetation C recovery averaged over all grid-cells is lower (11-14 % of the reference simulation for vegetation C compared to 39-47 % for dominant PFT) due to higher percentage loss of vegetation C during the period of agriculture and recovery occurs slightly later”. Do you mean starting point after abandonment? I also do not follow what “39-47% for dominant PFT” means. Please reword this sentence.

19. Page 7, lines 18-20 read “Lower standard deviations for the mean differences in recovery times for most biomes (Fig. 6) reflect the more uniform response of post-agricultural vegetation C accumulation across different sites compared to dominant PFT recovery.” Lower compared to what? What does uniform refers to here – uniform in space or across simulations?

20. Page 7, line 27 reads “We interpret this net N flux to the ecosystem as originating from high levels of water stress in these savannas and grasslands …”. Isn’t it more appropriate to say “This net N flux is partly caused by high levels of water stress …”.

21. Page 7, line 21. Just like reviewer #2, I also thought it should have been “boreal forests and grasslands”. You make it clear in your reply, so please make sure to clarify this in your revised manuscript as well.

22. Page 8, line 6 reads “Relative depletion of soil C content under crop and pasture LU is not as large (loss of 0-11 % compared to the reference simulation) as for vegetation C.” This is really low compared to observations (e.g. see Wei, X., Shao, M., Gale, W., and Li, L.: Global pattern of soil carbon losses due to the conversion of forests to agricultural land, Scientific Reports, 4, 4062, doi:10.1038/srep04062, 2014) which report a soil carbon loss of around 40%. This seems to be a limitation of LPJ, as reviewer #2 also points out, and must be noted as such.

23. Page 8, line 1 reads “Upon re-conversion, soil C accumulation is delayed for the pasture simulations …”. Delayed compared to what?

24. Page 8, lines 12-13 read “The general delay for pastures is associated with larger heterotrophic respiration rates (not shown) compared to rates calculated in recovering croplands and low litter input in the early stage of regrowth in forested ecosystems.” But the low litter input as forest regrow would occur regardless of previous LU type (pasture or croplands) so why is this a factor in differing behaviour of pastures versus cropland abandonment.

25. Page 8, lines 17-19 read “Additionally, in the intensive LU simulations (P100, C60, C100), vegetation productivity in the boreal region is further reduced compared to the reference simulation in the first 200 years of regrowth (not shown), reducing litter input to the soil even further.” Why does this happen?

26. Page 9, lines 6-7 read “the sensitivity of grasslands is mainly due to differences between simulations of different LU type”. I think, I know what is meant here but I am not sure. Please reword this part of the sentence.

27. Page 9, lines 11-12 read “The sink capacity of the re-growing vegetation is greatest during the first decades and then gradually goes back to the NBP of the reference simulation.” This sentence is mis-leading because NBP is a measure of whole ecosystem not just vegetation

28. Page 9, lines 12-13 read “P20 and, to a lesser extent, C20, act as a smaller sink than the other simulations”. Act as a smaller sink than what and over what time period?

29. Page 10, line 28 reads “The sequestration rate of above-ground biomass in regenerating tropical forests …”. This sentence reads a bit weird. I think what you mean is “The rate of increase of above-ground biomass …”

30. Page 10, line 31 reads “ … even though in the latter case biomass started to evolve only after around two decades.” What does “evolves” means here – increase or decrease?

31. Page 10, line 32 reads “LPJ-GUESS shows a reduction of vegetation C accumulation with time for both biomes …”. This sentence may be better worded as “ … a reduction in the rate of increase of vegetation C …”

32. Page 12, line 16 reads “ … recovery can occur at similar or even faster speed in the (sub)tropics.” Does “(sub)tropics” means “tropics and sub-tropics”?

33. Please consider using “idealized” in place of “stylized” to refer to your experiments.

34. Page 13, lines 22-23 read “The term recovery is very subjective and, in the absence of a universal definition amongst ecologists, different approaches imply the potential to significantly modify absolute recovery times. By our definition we examine recovery from a C sequestration perspective …”. Please consider modifying this sentence as “The term recovery is subjective and, in the absence of a universal definition amongst ecologists, several definitions currently exist. The definition used in this study examines recovery from a C sequestration perspective …”

35. Page 14, lines7-9. Please rewrite these sentences to make your point more clear.

36. Page 14, line 10. The sentence “Mostly grasslands are affected.” Seems incomplete.

37. Page 14, lines 11-12 read “Patterns are similar for vegetation C but more pronounced, especially for croplands.” What does “pronounced” means here – higher or lower?

38. Page 14, lines 13-15 read “We do not use an upper limit in our primary definition however, because, in the case of C storage, the ecosystem is already operating at a level of service above that which the unmodified ecosystem would have provided.” Upper limit of what? Also, this sentence is not completely clear so please reword it.

39. Page 14, line 18 reads “Elements of random fluctuations due to natural variability made a clear identification of recovery period difficult in that case.” Where are these “elements of random natural variability” coming from if you are driving your model offline with climate data that is being repeatedly used.

40. Page 14, lines 28-29 read “This is particularly relevant for flux tower measurements where ongoing regeneration might be overlooked due to large variability of NEE.” What does “regeneration” means here? Do you mean inter-annual variability in NEE makes it difficult to see the underlying long-term trend? If yes, please mention it explicitly.

41. Page 15, line 19. Please replace “climate change and/or atmospheric CO2” with “climate change and/or increasing atmospheric CO2”.


42. The discussion around Figures 4 and 5 will benefit from an additional panel in these figures for the reference simulation.

43. In Figure 6, please replace “TrFo, TeFo and BoFo” by full biome names.

Dear Authors,

Thanks for taking into account reviewers' comments and minor edits suggested by me. The manuscript reads fairly well now. I have read through the revised manuscript again and I am sorry but there are still some minor edits I would like you to address.

Page 2, line 11, please consider removing the word “significantly”

Page 2, line 24, please change “Analyses of the long-term effects of historical LU are often limited by the unavailability of adequate LU information, or the absence of undisturbed ecosystems, and…” to “Analyses of the long-term effects of historical LU are often limited by the availability of adequate LU information, the absence of undisturbed ecosystems, and…”

Page 3, line 23. At the end of the sentence ending with “growth strategies” please include “(see Table A1 for PFT acronyms and names)”. While you did include Table A1 it is never referred to in the main text of the manuscript.

Page 5, line 16-17. The manuscript reads “… and net biome productivity (NBP) (the sum of all ecosystem-level C fluxes including NPP, soil respiration, fire, harvest, land clearing, and decomposition of the product pool).”

Since the above definition of NBP fails to mention the sign convention it is essentially incorrect. Clearly, NBP is not equal to NPP + soil respiration + other terms as your sentence seems to imply. In addition, fire, harvest and land clearing are not fluxes but rather processes. I suggest a more generalized definition below which you may modify to reflect your framework.

Net biome productivity (NBP) is the net atmosphere-land carbon flux after carbon losses associated with respiratory fluxes, fire, harvest, land clearing and decomposition of land use change product pools are subtracted from gross primary productivity.

Page 10, line 21-22. The sentence starting with “For croplands, in their study explicitly represented by a number of managed but unfertilized crop functional types, …” doesn’t read right. Please reword this sentence.

Page 11, line 16. Please include “After abandonment” at the beginning of the sentence so that it reads “After abandonment, croplands accumulate C faster than pastures, and recovery …”. I think, that’s what is implied here.

Page 13, lines 4-5. Please consider modifying this sentence as follows. “Vegetation C shows similar patterns to the dominant PFT, however, the differences BETWEEN SIMULATIONS (P20, P60 AND P100) are more pronounced.”

Page 13, lines 13-14. Please consider modifying this sentence
“NBP differences look similar to soil C but the effects are much smaller”
as follows
“Differences in the recovery times of NBP look similar to soil C but the effects are much smaller.”
This is what is meant here, I presume. Also, what does "effects" refer to here. What kind of effects?

The following sentence after this on Page 13 reads ...
"However, we do not use an upper threshold in the primary definition used in this study because, in the case of C storage, the ecosystem is already operating at a level of service above that which the undisturbed ecosystem would have provided."

In this above sentence the following text "the ecosystem is already operating at a level of service above that which the undisturbed ecosystem would have provided" is somewhat unclear.

Do you mean that if mean + one standard deviation threshold is used for defining recovery then a given variable will have to reach a value higher than it's mean during the undisturbed stage for recovery to occur?

Lastly, please remove bullet number 6 in the conclusions section. This is not an implication based on your study per se but rather a more general statement.

Thank you for making additional minor changes.

Regards,
Vivek.