Impact of Initial Planting Density on the Optimal Economic Rotation of Chinese Fir (Cunninghamia lanceolata (Lamb.) Hook) in an Experimental Forest Plantation

Round 1

Reviewer 1 Report

This paper builds on a large body of forest economics research evaluating optimal rotation ages. The authors apply their analysis to the context of establishing a Chinese fir plantation, and focus on how the initial planting density influences land expected value (LEV) and the optimal rotation age. Sensitivity analysis further explores how changes in the discount rate influence optimal planting and harvesting decisions. The contributions are not significant, but the authors do a nice job of positioning this work within the existing literature and describing the marginal addition to the knowledge base.

I have mostly minor concerns and suggestions for improvement. 

Abstract: here and elsewhere, define "quality effect." I assume you mean the shift in diameter class to higher value, but this could be clearer

Lines 71-72: Here and elsewhere you describe this study as capturing the dynamics of optimal rotation periods under different economic and technological conditions. But your analysis assumes constant discount rates, constant stumpage prices, and constant harvesting costs. Please clarify and bound the scope of what your analysis is actually doing.

Line 116-118: Please provide citations to support assertion that thinning is not conducted on Chinese fir plantations

Lines 145-231: 

Please make sure to clearly introduce all variables, for instance LEV(e) versus LEV (c), or p with the subscript T.

Why are equations 6-8 necessary? They seem to have only minor changers and are effectively redundant with equations 1-3. Especially since p and Q, not V, are used again in equations 9-10.

Equation 9, please explain the new subscripts on variables p and Q.

line 200: that the initial planting density determines the proportional distribution of standing timber volume for different diameter classes isn't actually demonstrated until Section 3 and Figure 1

line 204: does this modeling formulation or the analysis actually consider simultaneous changes in the stumpage price or discount rate? I thought they were held constant for the analysis.

please expand on derivation of equation 10

Figure 1: please label the panels so readers can clearly know which image corresponds to 5, 10, 15, or 20 years

Line 296: Please change the sentence "Accordingly, the selected initial planting density should be between the two extremes of low-density or high-density planting." This would only be true if stumpage value was the criterion, which it is not. LEV is.

Table3: Please clarify how the opportunity cost of land and opportunity cost of harvest were calculated. I do not believe this is presented in the Methods

Table 4: I recommend adding LEV so readers can see how much economic bottom line is impacted, not just the rotation age

Line 370: The sentence "Therefore, we favor a low initial planting density..." seems inappropriate and overly general. Instead consider, "A low initial planting density generates the highest LEV for Chinese fir plantations, given the assumptions in this analysis."

Figure 2: I recommend moving this figure to the Methods when the functional forms for the Weibull curves are introduced. 

Figure 2: Please make the figure larger so the differences between the planting densities are more easy to see.

Line 449: "discount rate at that time." Again, I thought discount rates were held constant in this analysis. Please clarify.

Line 449: Again, please define "quality effect"

Lines 471-475: Good caveats. Which is why I think the authors may want to avoid making broad recommendations earlier in the paper given the limitations of the current study.

Author Response

Please see the attachment

Author Response File: Author Response.docx

Reviewer 2 Report

General information

The authors examined the relationship between the initial planting density and optimal rotation period in the absence of thinning. To assess the impact of the initial planting density on optimal rotation, the authors explicitly included the distribution of stand diameter classes and price differences representing the quality of stumpage in a model of forest land expected value. When the discount rate was low, the optimal rotation lengths for the varying initial planting densities exhibited minimal differences. However, LEVs increased with increasing planting density, that is, the low cost of planting production and the high profitability of timber production converged in low-density forest plantations. When the discount rate was higher, a lower initial planting density corresponded to a shorter rotation period, implying a faster turnover of the investment and a low optional risk. Optimal rotation lengths were shortest for an initial plantation density of 3,000–5,000 seedlings/ha when the discount rate was at a median value, resulting in the fastest turnover of the investment.

The manuscript, although prepared well, is not free from mistakes that sometimes lead to confusion. Authors should pay special attention to used abbreviation. In addition, the beginning of the introduction requires shortening and removing “nothing that adds” fragments. In abstract you should remove subtitles, I do not see them in this journal. Generally, the manuscript is very long! Try to reduce its length by paying attention to the repetition and sentence slightly related to the main thought of the publication. In addition, the editorial site publication of the requires major reorganization (I suggest joining the second and third chapter). Conclusions should be such a home message and not such a long chapter, full of repetitions. Correct assumptions for calculations and modeling have been prepared. Moreover, much work should be done to improve figures legend, because they are illegible on black and white print. The above and the following comments are only indications for improving the editorial side of the manuscript and do not diminish the value of the discussed results. Generally, the manuscript is very interesting (theme and content) and I think it should be published.

L49

Add Latin name.

L62-64

An example of a sentence that nothing adds in the context of your article.

L76 and 79

How do you understand “timber quality”? This is key here. In Poland, a large starting density of trees is used to make the timber of good quality (e.g. 8000-10000 per ha).

L126

Move to the next paragraph.

L149

How do you understand “P” Maybe “p”?

L258

Parameter A or a?

L310

seedlings; Opportunity x2

L323

Quoting in results? I have not met this yet ...

L385

How do you understand “s” in “T*s”?

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

Reviewer comments

General

The manuscript is dealing with an important and interesting topic of plantation silviculture. It is written clearly and comprehensively and provides essential help to the management of Chinese fir plantations. The English language is clear and the reader can clearly understand the basic idea of the manuscript.

Nevertheless, it should be stressed more clearly in the paper that the authors are dealing only with optimal rotation in economical sense (economic rotation). Also, the authors confess that they do not include other important factors (ecological, risk factors such as accidental events, climate changes, etc.) which can strongly influence discussed economic rotation. Also, the point the authors do not mention is that initial spacing influence greatly „general stability" (vitality, resistance to stressful factors) so the risk of achieving optimal rotation is questionable for monocultures. Thus, the strong recommendation to authors is that they stress this point even in the title and more clearly in the manuscript (especially in conclusions). Presenting only economical aspect as the only factor affecting setting optimal rotation in plantation silviculture could be misleading especially in time when the multifunctionality of plantation silviculture is discussed globally. Even when financial gain is the most important goal, it is known that site production capacity is decreasing already after the second rotation and calculations based only on financial gain are not complete.

Furthermore, some scholars propose longer rotation age for Chinese fir then currently used or discussed in the manuscript highlighting other important aspects when determining real rotation age (e.g. Selvalakshmi Selvaraj, Vasu Duraisamy, Zhijun Huang, Futao Guo, Xiangqing Ma 2017). This raises a question: what is the amount of financial loss or gain at longer rotation ages, which reconcile the ecological aspects, biodiversity, and social functions? Recommendation to authors would be to state this issue in the manuscript, or even provide some calculations for other rotations (e.g. for spacings included in the experiment predicted calculations for rotations of 20, 25, 30 yrs.). This way this theoretical paper would be more valuable and useful.

Given the predicted climate changes, a decrease of site production capacity already after second rotation and other predicted circumstances authors are strongly advised not to give any predictions for the long run (e.g. 200 yrs.), not even as a mere example.

Specific comments

Abstract

The abstract should be rewritten and should poresent the content of the paper more clearly.

L 16 Objectives of the paper are missing. Strong recommendation to include them.

L 17-18 The explanation on how the authors have conducted research is missing (data acquiring and processing, statistical analyses, etc.)

L 21 „the direction of the impact of initial planting density" should be clarified

Introduction

L 79 Can you support this statement with scientific research ?: „A decrease in the initial planting density corresponds to ... and, consequently, to better timber quality"

Material and methods

L 273 Authors are recommended to explain more clearly how did they include calculations for different assortments which could be obtained from different diameter classes.

Author Response

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Author Response File: Author Response.docx