Isolated Trees in Two Tibetan Plateau Treelines Reveal Growth Plasticity to Harsh Conditions of the Little Ice Age

Round 1

Reviewer 1 Report

 

General comments

The manuscript “Isolated trees in two Tibetan Plateau treelines reveal growth plasticity to harsh conditions of the Little Ice Age” by Zheng et al. is an ordinary description of growth differences between older and younger trees. Mostly those differences are not confirmed by the corresponded statistical analysis. I do not understand a mix of parametrical (e.g. t-test) and non-parametrical (e.g. kernel estimations, GLK) analysis through the MS. I do not understand why the authors indicated the older trees as ‘isolated’. The criteria which is based on ‘before and after 1850’(see lines 107-121) looks strange. One of the principal results ‘The results showed that age-related exponential growth trend was not obvious in ring-width sequences of the isolated trees’ (see lines 13-14) also applies to ‘non-isolated trees’ for both habitats (see Figure 3). Moreover, ‘The coefficient of variation in ring widths of the isolated trees was significantly greater than that of the treeline trees growing after the Little Ice Age’ (see lines 15-17) is not obvious based on high dispersion of the coefficient of variation (see Fig. 6).

Specific comments

Lines 82-83: Which fitted curves and what an approach (software) were used?

Lines 83-85: Standardization technique should be described in details with corresponded references!

Lines 90: ‘Kernel probability density’ as a non-parametric estimation should be described in details with corresponded density!

Lines 94-95: Why was a parametric test (t-test) applied?

Lines 102-105: How were those lengths (11 and 51 years) of window selected taking into account other possible values, e.g. 15, 21, 25, etc? What was a criterion to select the certain length? It is well known that sliding window significantly affects on spectrum of time series!

Lines 107-121: This is not a result. This section should be moved to the Materials and Methods.

Line 132: What does ‘young age’ mean? I know a term ‘juvenile period of tree growth’. This sentence should be clarified.

Lines 135-137: The Gaussian distribution (as well as abnormality) should be confirmed by the appropriated statistical testing.

Line 144: By the definition, the ‘highest concentration’ means the estimated average of the statistical sample!

Figure 6: The capture should clarify all the characters on the figure

Line 161: The term ‘'obvious' should be confirmed by the appropriated spectrum analysis taking into account a colored noise in the time series!

Lines 220-229: This section should be moved to the Results.

Lines 228-229: The statement is not correct! It is easily to check by the spectrum analysis (e.g. MTM).

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

Dear authors, I found your study very interesting, especially in context of your previous research in the southern Tibetan Plateau. The tree growth investigation under the LIA cold environmental conditions in the highest treeline of the Northern Hemisphere is important for a better understanding of canopy surviving processes. Please, find some minor remarks below.

 

1.     The map (fig. 1) contains the unreadable part (in the top right corner): perhaps authors want to zoom into the specific region, but it does not show a big difference between the map in the big box and the zoomed area. Besides, I suggest naming (or to put numbers) the sites on the map to make it recognizable (for those who did not read your previous study).

2.     Fig. 2. Please bring the axes to the same values for temperature and precipitation for both graphs: figures do not show an important difference between the two sites, as you mentioned under lines 63-66.

3.     The section 2.2 needs to add some information about the sites and trees conditions. Slope exposition might influence the tree growth as well as inclination. Are there any specific scars on trees related to the rockfalls, debris flow or other geomorphic processes? If yes, please specify the trees numbers. Please add the information about the slope and inclination to the section 2.2.

4.     Please specify the mean distance between isolated trees. Does the altitude differ for trees of the location?

5.     I suggest adding some photos of the two forest stands to visualize the growth conditions of these trees.

6.     Line 130. Do different climatic conditions or slope direction play a role in the growth diversity in the two locations?

7.     Line 131. Please specify the name of the trees that showed a decreasing trend.

8.     Trees in the Basu treeline grow higher than in the Longkazi treeline by 150 meters, it is not a huge elevation difference, but the number of isolated trees and their growth patterns differs significantly. Probably, the reason of this difference is due to the climatic conditions as you mentioned in the section 2.1. It has to be discussed because trees on the lower elevation have a growth decreasing trend at a young age in comparison with trees growth higher, but in the colder environment.

9.     Fig. 7. What does “51yr serial-coefficients” (axis y) mean?

10.  Line 182. Please, provide the reconstructed temperatures rate before and after 1850 from the studies you cited in the manuscript: “Meanwhile, the independent climatic  reconstructions on the Tibetan Plateau showed average low temperature (///) before 1850 and average high temperature (///) after 1850”

11.  Lines 221-228. Authors show some common and different growth variations in Bosu and Langkazi treeline driven by single or different environmental factors. I suggest comparing these periods for both locations to find similar patterns and reasons why they are different. Are there any similarities in the growth dynamics for both treelines?

 

Author Response

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Author Response File: Author Response.pdf

Reviewer 3 Report

Dear authors,

Thank you for the opportunity to read the research results.

In my opinion, in order to increase the value of the manuscript, improvements should be made to the introductory chapter. I believe that the conceptualization part should be extended with a series of newer, and more current works, and from many other regions of the globe that have been affected by the Pleistocene glaciation.

For figure 1 (Fig.1 Location of the study site on the southeastern Tibetan Plateau), I suggest changing the color of the text "Tibet Plateau", as it is not legible.

I suggest introducing a workflow to the methodology chapter, in order to follow the methodological steps more easily.

Do you write more clearly what this study brings compared to previous studies? The answer to this question should be incorporated into the discussion chapter.

What were the limitations of the study? The answer to this question should be incorporated into the discussion chapter.

Who uses this study? The answer to this question should be incorporated in the chapter on conclusions. Please develop more and more clearly.

Sincerely,

Author Response

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Author Response File: Author Response.pdf