Sensitivity of Green-Up Date to Meteorological Indicators in Hulun Buir Grasslands of China

Round 1

Reviewer 1 Report

The study focuses meteorological effects on GUD with remote sensing method, being quite interesting. However, only comparing partial correlations and sensitivities is insufficient as proof. Further analyses are required. 

1. The authors must update the data to the present, because the limited number of data (only 15 years) is clearly the restriction.
2. The sensitivity has no meaning in the points where the partial correlation coefficient is not significant. The authors must exclude the points from the sensitivity analysis. 
3. When comparing the factors comprehensively, p = 0.1 should be considered as no significance based on the principle of multiple comparisons. 
4. Strong positive partial correlation between GUD and daily maximum temperature and strong negative partial correlation between GUD and daily minimum temperature in the same area is quite strange in Figure 8. Exceptional data may have the effect. Scatter plots is required. 
5. Do the temporal trends in Figure 3-7 mean the difference between 2001 and 2015? Regression analysis against years is required. 
6. Temporal trend of GUD is required. 

Author Response

Please check the word file.

Author Response File: Author Response.docx

Reviewer 2 Report

Dear authors

my comments are grouped as "Generic", applying to all or most of the paper, and "Specific", mostly referring to specific text. 

My comments are usually formatted as

22 the cat is green -> the cat is black

meaning that on line 22 I suggest that "the cat is green" should become "the cat is black"

A. Generic

Comments 4 and 5 are substantial.

1. The language of this publication is well understandable but still needs editing. I have not, generally, attempted to correct the language, except where the meaning is unclear because of the wording or grammar. The paper frequently uses the conditional “could” instead of the present tense. I have mentioned this for lines 30, 31, 36, 78, but the authors are requested to scan the text and change could with the present tense.

2. You use the word "green-up" at least 50 times in this paper, and "greening" once. The next time you write on the subject, use "greening" which is a much nicer word to say exactly the same thing.

3. This paper often uses “temperature/precipitation”. Does the Journal have some recommendation as to the use of “/” which can be read as “and” or “or” or “and and or” . I suggest to replace it with “and”

4. The methodological section, in particular the processing of climatic data is insufficiently detailed. See, for instance, my comment to line 142 and “201 and 211”.

It is also rather surprising that the whole publication is about explaining the factors behind the beginning of greening, but there is no map of greening which, I think is an essential component of this work. A reader like myself will tend to distrust your work because you say so little about greening. I have some experience with the agrometeorological analysis of "greening" and in the real world, I frequently find two or even more greenings in a year? I can also have have weak or strong greening, and a lot of inter-annual variability of greening. I request you to add a section about the green-up in the Hulun Buir grassland area, including at least one map showing the "average green-up date" and possibly another showing the variability of the green-up dates.

5. Your section of results

240-372 (Partial correlation analysis between green-up date and meteorological factors) and 373-490 (Sensitivity analysis of green-up date to meteorological factors) are two very long and very boring sections, without any summary. This is just the description of some tables, which I suggest you include in the paper rather than the endless text. The tables will immediately show any patterns. 

 B. Specific

22 Sensitivity of green-up date to temperature/precipitation → Sensitivity to temperature and precipitation

Comment: really, this is just one of many factors. Even without going to the detail of the sensitivity of a number of physiological processes to temperature and water availability, at the macro-level I could argue that the duration of the vegetative cycle from germination or regreening to maturity, or biomass accumulation are equally sensitive to temperature and precipitation. I am also very surprised that you do not mention photoperiodism as a factor. I have often observed that vegetation is some areas starts greening ahead of the rain... because of photoperiodism. I am not suggesting that NE China vegetation is photoperiodic, but can you rule it out?

5-26 Then examining the partial correlation and sensitivity of green-up date to T max , T min , and precipitation → We then examined the partial correlation and sensitivity of green-up date to T max , T min , and precipitation

30, 31, 36, 78

Comment: the use of the “conditional could” is is very ambiguous, as if you doubted your results. I suggest to replace this by the present tense:

30 T min in winter promotes green-up

31 precipitation in April also promotes green-up

36 The results of this study reveal that the response of vegetation

78 the increase of T min can significantly

 

32

Comment: define GUD on the first occurrence of the abbreviation on this line

38

Comment: add “greening” to the keywords

43-44 Phenology is the study of the periodic growth and development of plant and animal behavior throughout the year → Phenology is the study of the development of plants and animals

Comment: phenology addresses qualitative changes over time. As such, it does not cover growth (i.e. biomass increase). The word “periodic” is not necessary, even if most development is indeed periodic in nature.

48 productivity → production

Comment: productivity is an economic concept, not biological

48-53

Comment: you realise that this concept of “per unit variation” is largely arbitrary and potentially meaningless for temperature, because it depends on the unit. Take this situation: a certain variable is 20 days at 0°C and 30 days at 10°C. You say that the “sensitivity” (30-20)/(10-0), i.e. 1 day/°C. If I express the temperature is degrees Fahrenheit, the sensitivity becomes (30-20)/(50-32) i.e. 0.55 day/°F. The same applies to statements such as (line 53, rephrased) “the average temperature of the land surface increased 1.4 times faster than the minimum temperature”. If I express the temperature in some other unit (Fahrenheit, of absolute temperature) , the result is different.

59 understanding the temperature sensitivity to GUD → understanding the sensitivity of GUD to temperature

Comment: the current sentence is meaningless

62-63 Temperature is considered to be the main factor controlling temperate and cold zone vegetation in the Northern Hemisphere → Temperature is considered to be a convenient descriptor of temperate and cold zone vegetation distribution

Comment: the main factor is solar radiation, followed by rainfall, which defines to what extent the available solar radiation can be used by plants. Temperature is not really a “factor” here but a proxy for radiation. This is exactly the approach of the main vegetation classifications and mapping such as those by Köppen and subsequent ones. It applies to the northern and the southern hemisphere alike. I would also like to stress that Tmin and Tmax have very different drivers. Tmax largely depends on solar radiation, but Tmin is to a large extent controlled by moisture, when moisture is present, i.e. probably more so in the east of the region than in the west. When temperature cools overnight, it will opften happen that dew starts condensing, and temperature will not decrease any further as long as there is air moisture that condenses.

69 temperature differences

Comment: the “temperature difference” is often referred to as “thermal amplitude”

69-70 T max may be more effective than T min to meet the heat accumulation required for leaf development → T max is more relevant than T min for leaf development

Comment: consider (1) Tmin=10°C and Tmax=30°C. The difference is 20°C. If (2) I take Tmin=0°C and Tmax=25°C, the difference is 25°C. Which is more favourable, (1) or (2)? (1), of course. The minimum temperature is rather irrelevant if we stay above freezing.

73: ground-based fixed observations → ground-based observations

90 but soil moisture → because soil moisture

91 It is widely believed that vegetation activity → It is often observed that vegetation activity

Comment: This is not a general observation, and does not apply to many tropical highlands where high elevations are wet and temperate, e.g. in Ethiopia and much of esatern African Highlands.

99: the occurrence dates → the dates

106 effects on GUD, further research → effects on GUD, for which additional research

124: productivity → biomass

Comment: refer to previous comment to line 48

142

Comment: this whole section is insufficiently detailed. For instance, you never define “spring” and “winter”. Which periods are covered? You say you used nearest-neigbour interpolation, because the method is easily available and simple. It is also one of the most elementary, unsophisticated and error prone methods available, that does not even achieve the acuracy of Thiessen polygons with exponent n=2. Which exponent did you use? The fact that the maps so closely follow the hydrography seems to indicate sone altitude correction, was done, but how? Did you do also do a horizontal (lon-lat) gradient correction in addition to the vertical (altitude) one?

Also: I assume you have a map of GUD? Why do you not show it? The whole area you studied has rather different types of growing seasons between E and W, and between N and S. Your whole exercise is meaningless if you do not show a map of GUD. I would also imagine that in many places you have motre tha one greening. Hpow have you handled this?

171: SOS

Comment: first occurrence of SOS. Define it here.

194: TS-MK

Comment: first occurrence of TS-MK. Define it here.

194-195: spring

Comment: you have not defined spring and winter. You should do so under section 2.3, as I mentioned above. I am also surprised to read that (221-222) we suggest 3 months in the spring is needed for more fine-scale analysis. Your spring is not 3 months?

201 and 211

Comment: Both figures show trends, i.e. changes over time. Fig. 3 shows winter Tx (a) and winter Tn (b). Fig. 4 shows winter Tx (a) and spring Tn (b). What is the difference between 3(a) and 4 (a) which are both winter Tx? In addition, you write that (fig. 3) trends are non significant in 85.7% and 88.4% of the areas, which means that it is significant in 14.3% and 11.6%, respectively. Therefore, I would expect the insets in fig. 3(a) and 3(b) to show some colour to tell me where the trends are significant. I see only white. The same applies to figure 4.

I am also very surprised that pixel size is much larger in the west of the study area than in the east in figure 3 to 7. Figures from 8 onwards show the same pixel size everywhere. Why is this so? This is not explained in the methodology.

234-235 The trend of winter precipitation in southwest China is weak accounting for 27.7% of the whole region with a trend of 0 mm/decade.

Comment: this may be so, but we are in NE China. Correct or provide a reference!

240-372 (Partial correlation analysis between green-up date and meteorological factors) and 373-490 (Sensitivity analysis of green-up date to meteorological factors)

Comment: this sections are just long and repetitive enumeration of results. I think they could and should be summarised with many less words in a set of tables, maybe one for for TS, one for TM, LM and one for UM. This would have the added advantage of directly showing differences and patterms, which are currently lost in the endless text. The tables could also be arranged by period: winter, spring, April, May...

522-523 carbohydrate absorption

Comment: what is “carbohydrate absorption”? I assume you don’t mean CO2 absorption because we are during the night. Are you referring to carbohydrate synthesis? Polymerisation of short-chained sugars into starch or cellulose?

524-525 nighttime also negatively affects plant photosynthesis by increasing autotrophic respiration

Comment: night-time respiration may use up some synthetates produced during the day, but night-time conditions do not affect photosynthesis itself.

527: nitrogen salinity and availability

Comment: what is “nitrogen salinity”? The concentration of inorganic nitrates? If this is so, please use “inorganic nitrogen” and say “availability of inorganic nitrogen nutrients”

528: and spring phenology → shifts in phenology during spring

533: less → low

534: promote vegetation green-up

Comment: do you mean “triggers earlier vegetation green-up” or “more intense green-up”?

548: T min could improve the biomass in arid temperate grassland areas of China

Comment: yes, but this could also be an artefact in the sense that Tmin stays higher in the moister regions (see comments to lines 62-63)

559: were mainly decrease trend in winter → tended to decrease during winter over the period studied.

563: other types

Comment: this is not clear. What are “other types”?

577 References

Comment: most references are old. There are only one for each 2021 and 2020 and about 50% are older than 10 years.

Author Response

Please check the word file.

Author Response File: Author Response.docx

Reviewer 3 Report

Please find the attachment for my comments. Thank you. 

Comments for author File: Comments.pdf

Author Response

Please check the word file.

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The reviewer agrees that the revision has been properly made. Following revision will improve the manuscript more. 

1. List of abbreviations may help the readers.
2. The font size in figures seems to be small. Please check it in printed version. 
3. The reviewer still considers that some scatter plots are effective for the reader to understand and check the relationship. The representative relationships such as described in the abstract should be shown in scatter plots. 

 

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

Thank you for taking into account my comments.

Best wishes and congratulations for an interesting paper!

Author Response

Thank you very much for your suggestion.

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.