Cindy Prescott
Co-editor, Canadian Journal of Forest Research
Dear Dr. Prescott,
Here are the reviewers’ comments (in italics) with our responses detailed. Many of the comments were suggestions for improvement in the presentation, which were nearly all very helpful. We also made some significant changes to the content of the paper. We omitted the results from the formerly agricultural sites, as suggested by the reviewers. We also doubled the sample size for the analysis of the horizontal distribution of roots (relating biomass in the pits to the density of the surrounding trees), which was possible because we have now completed another study of roots excavated from soil pits in similar sites. We now have more confidence in our results. A manuscript describing that study has been submitted to the Soil Science Society of America Journal. That paper compares the pit method with soil coring, which is also a topic our reviewers asked about, and we can now reference it in the Discussion.
Detailed descriptions of all our changes follow.
MS 05-247
The vertical and horizontal distribution of roots in northern hardwood stand of varying age. Ruth D. Yanai, Byung Bae Park, Steven P. Hamburg
Referee #1
This paper reports on the effect of stand age class on root biomass and root biomass horizontal and vertical distribution. The data are definitely valuable to the ecological community and therefore should be published. There are relatively few published data addressing root biomass associated with stand age, and this paper contributes well to what little information there is.
It was especially interesting to reopen the topic of horizontal spatial distribution, which showed that the discussion should not be closed yet.
The manuscript shows many shortcomings though, and should be thoroughly revised by the authors.
What I found to be the main weaknesses, was the inclusion of the mature (former agricultural) stands. There are no hypotheses, very few results and no discussion about these stands. It is not clear why they were included in the study.
I think the real reason they were included in the study is that they were a lot of work to produce and they are not publishable on their own. We did hesitate to include them, and did not hesitate to remove them in this revision.
What I did not like (and cannot accept) was that one of the major findings in this manuscript, was the difference in fine root biomass between the two age classes. But this difference is NOT significant (p = 0.12) and should therefore be interpreted carefully!
We are indeed careful in describing this difference (see under detailed comments, below). There is an 88% probability that the difference is associated with stand age, which seems to make it worthy of mention.
Another thing which was disturbing, was the lack of consistency and correctness in the use of units. Further details are given below.
I overall liked the manuscript, but have many detailed remarks, on where it can be improved:
TITLE:
1/1 Would it be possible to put more emphasis on “varying age”? This is also the emphasis of your paper.
It’s not a very catchy title, but it’s descriptive of the paper. We can’t justify putting more emphasis on stand age, as our results are not very satisfying (as you noted, the p value was 0.12). We couldn’t come up with a better title.
ABSTRACT:
Overall: reflects very well the essentials of methodology and findings.
Detailed:
2/4 soil depth instead of depth
Done.
2/6 When the emphasis of the paper lies on the differences between stand ages, it makes sense to also state the age of the “mature” stands, even in the abstract.
No longer applicable, as the mature stands have been removed from the paper.
2/10 …greater in the old stands… This is not clear: greater than what? (than root biomass in the young stands, in the mature stands…?)
We say “older” now, consistent with the mention of the 55-70 yr-old stands in line 6. Without the mature stands, there should be no possible confusion.
2/11 soil depth instead of depth
Done.
2/23 Two completely different issues should maybe be put in two different sentences
Is this line in the Introduction, not the Abstract? The sentence that starts on 2/23 I didn’t change, as it relates the timing of canopy and root closure. The sentence that ends the abstract relates a conclusion about sampling strategies to the observation of horizontal pattern in root distribution. I didn’t separate those two statements, as the conclusion needs to be limited to that portion of the study; it should not be construed as a conclusion of the whole paper.
INTRODUCTION:
Overall: the introduction is built up in a very clear way: first the emphasis on stand age, then the vertical root distribution, then the horizontal root distribution. Yes, the introduction was limited to the purpose of the paper. I found the paragraph about stand age even a little bit too limited (see 3/8). On some places, I would have been more convinced if more references would have been stated. I was not happy with the last paragraph at all. It was not very clear but more importantly, not complete (see 4/8-15).
Responses follow the detailed comments, below.
Detailed:
2/22 relatively greater? Or: greater than…? This is not clear.
Changed to “additional.”
3/1-2 What is the publication state on this reference at the moment?
It is forthcoming in CJFR and will be cited as such.
3/4 Stands implies ‘within 1 site’. Maybe it’s better to use ‘at different sites’
Done.
3/6 Do you have a reference about this statement on coarse root biomass? (80-100 y)
We added Fahey et al. (2004) as a reference for the pattern of bole biomass accumulation. There are no measurements of coarse root biomass as a function of stand age. We use “presumably” to indicate that no data are available. The sentence in question reads “In contrast, coarse root biomass presumably increases along with bole biomass (Fahey et al. 2005) for 80 to 100 years in northern hardwoods regenerated by clearcutting.”
3/8 Why do you study two different stand age classes to investigate the “root closure” problematic? You say later on that the stands were selected from a 13-stand chronosequence. Wouldn’t it have made more sense to use data from 13 stands with different ages, if the goal was to determine the timing of root closure? Why do you select 3 similar young stands and 3 similar older stands when the intention was to describe the development of roots as a function of stand age? And where do the former agricultural stands come into picture?
The question of root closure makes an appealing introduction to our study, but admittedly, the study was not designed to address this question. We added a sentence to the Methods section, where we describe our stands. “To pinpoint the age of root closure, we would have liked to excavate pits in all thirteen stands, but the expense was prohibitive. We elected to use multiple younger and older sites as replicates of two widely separated age classes.”
3/10-11 I disagree with the statement that excavation is the best way to achieve vertical distribution data. The only reason you give is that soil coring cannot be done below obstructions. You should point out better that excavation is better in the case of soils with a high rock content. (even stone content would not be satisfying – you say later on that you consider stones as particles > 2 mm – this would still be doable with a soil corer)
We say, “..the depth distribution of roots is best measured by excavation, at least in rocky soils…”
[The next 15 pages of the response document are not included here.]