Eleven-Year Effects of Mechanical Site Preparation on Oaks Planted on Former Agricultural Fields

Round 1

Reviewer 1 Report

 

 

Abstract

Has this site demonstrated compaction issues or presence of a pan?  Consider restating that operational forestry in the region has used mechanical site preparation to improve growth of planted pine unless you can specifically cite soil compaction.  Other benefits are mentioned elsewhere in the paper (eg lines 80-82) so it may be appropriate to be more generic here and elsewhere where compaction seems to be used as a catch all.

Introduction

Have applicable citations from other regions of the world been sought to internationalize the applicability of this paper?

Lines 38-41.  The discussion of planting stock size might fit better into the Discussion section since this was not a treatment

Line 49- Any information on cost comparison regarding fuel or traction needs for each treatment might be included

Lines 74-76 Bedding has also improved tree growth where flooding and soil saturation are not an issue. 

Lines 85-90 Please include the stand age(s)  when differences between treatments were detected in these studies

Lines 105-108 These sentences could be removed

Line 112 Self pruning is referenced here but height to live crown is the variable measured

Lines 118-119     Using wording like “The magnitude of treatment differences have declined over time” would likely be more understandable than “the effects of…. seem to have smoothed” to a reader whose first language is not English

Line 128 More regarding the history agriculture use on the site would be useful, specifically primary crops grown, last crop, and approximate duration of row cropping prior to afforestation.  Given the location of the site on US Army Corps of Engineers land, is conversion a function of marginal status or its ownership/specific use status.

Line 145  Is the Oust XP treatment mentioned here in addition to the post-planting treatments mentioned later?  How much time elapsed between abandonment of row cropping and starting afforestation activities?

Line 172  Please provide a summary of tree survival rates at the time of 11 year measurement.  Might this impact the power of test issues?  You might consider focusing analysis on a subset of the largest trees per treatment (dominant-codominant) to avoid the impact of surviving but highly suppressed individuals that confound studies with planted hardwoods

205         Consider substituting “effects differences have diminished” in place of “effects seem to have evened” and remove the discussion of statistical power in 207-212

211 Meaning of the term “linked” is not clear

245-249                This sentence can be removed

269         Would mortality impact detection of treatment differences?

309 or 320           Can anything be said about pruning feasibility?

322-323                Please consider a more general term, and less mechanistic term, other than compaction to describe site limitations for seedling establishment. 

311-338                This is an excellent summary of the study and its place in an area of forestry that is growing in importance

Author Response

Point 1 -

Abstract

Has this site demonstrated compaction issues or presence of a pan? Consider restating that operational forestry in the region has used mechanical site preparation to improve growth of planted pine unless you can specifically cite soil compaction. Other benefits are mentioned elsewhere in the paper (eg lines 80-82) so it may be appropriate to be more generic here and elsewhere where compaction seems to be used as a catch all.

Response 1 -

In initial site evaluation/assessment, the study site did not possess an inherent natural pan. However, similar to many former agricultural fields across the South, the study site did possess a slight "compacted" traffic pan with slightly elevated bulk density compared to areas outside of the field itself. However, we do not state "compaction" in the abstract, using the term "soil condition problems". Compaction is a specific condition, instead we use the term "soil condition problems" as a catch all. We believe that that serves Reviewer 1's point.

Change - We have toned down the use of the word "compaction" later in the manuscript however. Lines 322 + 323.

 

Point 2 -

Introduction

Have applicable citations from other regions of the world been sought to internationalize the applicability of this paper?

Response 2 -

Very little mechanical site preparation work in afforesting oak species on retired agricultural fields has been performed outside of the southern region of the US. Our literature search did not yield work pertinent to discussion of this study's results. However, we did include multiple citations which draw information from multiple studies of both regional and national level.

 

Point 3 -

Lines 38-41. The discussion of planting stock size might fit better into the Discussion section since this was not a treatment

Response 3 -

These lines refer to expectation of acceptable performance when utilizing "quality seedlings". While seedling size is often a factor of seedling quality, it is not all encompassing. As stated in the text, the studies referenced in these lines tested site condition factors as well as cultural and herbicidal treatments. As such, we feel that this text is appropriate as placed.

 

Point 4 -

Line 49- Any information on cost comparison regarding fuel or traction needs for each treatment might be included

Response 4 - More intensive treatments do indeed usually cost more. However, published costs for treatments used are incredibly generalized and available on a regional basis at best which do not allow for the vast range of localized costs. In addition, all treatments used are not specifically listed in available comparisons in any literature we discuss. Consequently, we do not offer cost comparisons here.

 

Point 5 -

Lines 74-76 Bedding has also improved tree growth where flooding and soil saturation are not an issue.

Response 5 -

Agreed. However, we correctly state simply that bedding is often prescribed to alleviate flooding/saturation problems and that it should provide similar results in low-lying hardwood plantations. Meaning that for this is the primary reasoning for bedding prescription in hardwood plantation efforts. However, it does prove beneficial in some cases where these site conditions are not problematic. 

Change -

We deleted, "on flooded or saturated sites" from the following sentence to include drier sites as well.

 

Point 6 -

Lines 85-90 Please include the stand age(s) when differences between treatments were detected in these studies

Response 6 -

Change -

We added "three-year-old" before the oak species reported.

 

Point 7 -

Lines 105-108 These sentences could be removed

Response 7 -

These sentences refer to a well known problem with hardwood plantations, that of a lack of the natural encroachment of other hardwood species after planting. As stated, this absence has resulted in lower tree densities than original planners expected, leading to issues with poor pruning and stem quality in future forested stands. This is a valid inclusion that sets the stage for the lack of natural pruning discussed afterwards.

 

Point 8 -

Line 112 Self pruning is referenced here but height to live crown is the variable measured

Response 8 -

Change -

OK, we added, "due to absence of live branches" to the end of the sentence.

 

Point 9 -

Lines 118-119     Using wording like “The magnitude of treatment differences have declined over time” would likely be more understandable than “the effects of…. seem to have smoothed” to a reader whose first language is not English

Response 9 -

Agreed.

Change -

We changed, "Over time, trends of effects observed in earlier measurements seem to have smoothed..." to "The magnitude of treatment differences declined over time..." in this sentence.

 

Point 10 -

Line 128 More regarding the history agriculture use on the site would be useful, specifically primary crops grown, last crop, and approximate duration of row cropping prior to afforestation. Given the location of the site on US Army Corps of Engineers land, is conversion a function of marginal status or its ownership/specific use status.

Response 10 -

The next sentence states that the field was in soybean production until a two months prior to mechanical site preparation treatments were installed. A historic record of all crops grown or for how long does not exist according to the local USACE office. The site was/is not of marginal status, but of simple allowance for research purposes.

 

Point 11 -

Line 145 Is the Oust XP treatment mentioned here in addition to the post-planting treatments mentioned later? How much time elapsed between abandonment of row cropping and starting afforestation activities?

Response 11 -

No, the Oust XP treatment is the same as the one mentioned later. The previous paragraph states that row crop production ceased Sept. 2007, the following paragraph states that mechanical site preparation treatments were installed Nov. 2007, the paragraph on seedlings states that seedlings were planted mid-February, and the HWC paragraph states that Oust XP applications went out early March 2008.

 

Point 12 -

Line 172 Please provide a summary of tree survival rates at the time of 11 year measurement. Might this impact the power of test issues? You might consider focusing analysis on a subset of the largest trees per treatment (dominant-codominant) to avoid the impact of surviving but highly suppressed individuals that confound studies with planted hardwoods

Response 12 -

Line 172 does not pertain to tree survival rates at the time of 11-year measurements. However, survival was greater than 97 percent for all species/site preparation combinations at year 11. Survival differences were not detected through analysis, thus we did not feel it warranted to list survival rates in the manuscript. We analyzed all trees because we feel that it gives a more accurate representation of overall treatment effect through inclusion of all crown classes. While crown class differentiation has occurred in this stand, the vast majority of trees are sitting in a codominant position with very few intermediate or dominant stems.

 

Point 13 -

205  Consider substituting “effects differences have diminished” in place of “effects seem to have evened” and remove the discussion of statistical power in 207-212

Response 13 -

Change -

Changed "seem to have evened" to 'differences have diminished" in this sentence.

 

Point 14 -

211 Meaning of the term “linked” is not clear

Response 14 -

Ha, I guess "linked" is older terminology now. Sorry. The term just means that ANOVA showed a statistically significant F-test but multiple comparison didn't show a difference.

Change -

Deleted "linked and" from the sentence because the meaning and result is ultimately the same.

 

Point 15 -

245-249  This sentence can be removed

Response 15 -

Agreed.

Change -

Removed "It is possible that the added elevation of soil beds better positioned Shumard oak root systems for resisting soil moisture damage compared to those growing in control or subsoiled plots. Although species were analyzed separately, Shumard oak and swamp chestnut oak DBH averages were appreciably less than average DBH of Nuttall oak grown in comparable mechanical treatments."

 

Point 16 -

269         Would mortality impact detection of treatment differences?

Response 16 -

In this case, at greater than 97 percent survival, we do not feel that survival (or lack thereof) played a major role in treatment effect detection.

 

Point 17 -

309 or 320           Can anything be said about pruning feasibility?

Response 17 -

Both logistical and economic feasibility of pruning hardwood plantations is really outside the scope of our manuscript due to a lack of available information on the effects of the treatment as a commercial venture in hardwoods. We are sure that a vendor could perform the treatment, but have no base to pull from on what the end result would be on impacts to future wood growth/quality or financial returns.

 

Point 18 -

322-323   Please consider a more general term, and less mechanistic term, other than compaction to describe site limitations for seedling establishment.

Response 18 -

Done.

Change - We changed "compaction" to "soil related problems" in one instance and deleted the term in another.

 

Point 19 -

311-338                This is an excellent summary of the study and its place in an area of forestry that is growing in importance

Response 19 -

Thank you and we appreciate your time in reviewing this manuscript.

Reviewer 2 Report

Review of 11 year effects of mechanical site prep

Line 88, 89, 90, careful with syntax. The sentence could be made more clear by substituting a descriptive subject into the sentence instead of “other work” – what exactly did this other work test? Was it the effect of bedding on growth and survival? If so, please say so explicitly.

Sentence at 121 – 123 is unclear.  How can early treatment effects be tools?  I can see how they might be indicators.  Please revise.

Were controls considered ‘treatments’ or was a separate analysis comparing treatments to controls performed?  The latter is often preferred – or at least it is in some circles.

Line 202 – 204, please rephrase – absence of statistical differences based on ANOVA has already been described, but the sentence seems to want to focus on the range of values observed (useful to know) the authors should state what treatments resulted in the highest and lowest observed values, even if these differences were not significant based on a P value.  Those types of statistical tests are not the only way to describe what they observed and what it means.

Line 205, For the benefit of those who have not read your previous manuscript, please add detail to the statement “effects seem to have evened” – what effects increased or decreased?

 

Line 211, explain what you mean by “mechanical treatment averages…were linked..”

Line 233 – an important observation and conclusion by the authors. For the benefit of those not familiar with your growing conditions, why would intraspecific competition decrease the likelihood that soil treatments would produce differential results?  I could imagine that competition would increase the advantage of trees on favorable soil treatments. Is your conclusion based on the likely distribution of root zones in an 11 year old tree (I.e., that roots are well below any soil layer affected by mechanical treatment)?

Line 254, the authors state “..SCO possessed a p-vale….”. Well, I guess I understand what is being said, but this is not a good way to say it.  SCO, as a species, does not possess anything.  It is better to be precise in your language and to say something like “There were differences in SCO HT among mechanical treatments (p< XXX)” etc.  As part of the discussion, the authors should tell the reader whether observed differences (whether at P<0.05 or not) appeared to be biologically meaningful. Were trees on one type of treatment healthier or in any way noticeably different?  Do you believe the extra 5 – 10 % more height at this stage reflects more competitiveness or long-term vigor?  Again, please explain what you mean by “treatment means were linked” – I am not familiar with that terminology and am not sure I can interpret it as the authors intend.

Line 300, please use past tense consistently when reporting results

A photo would be nice. If these trees were not thinned (I didn’t see that they were), then these trees are packed pretty tight at age 11 aren’t they?  It will be easier to understand their growth dynamics and the importance of HLC differences by looking at a photo.

The authors may have mentioned it, but since this is a single site study, I would like their evaluation of how representative these results might be. Is the site typical of afforestation sites for oak in the Mississippi valley? Was growth typical? Was weed competition (woody and otherwise) typical?

I like the conclusions, but would appreciate even a little more. Given the cost of mechanical treatment and the main advantage related to survival, do we know where the tradeoff occurs? Is it cheaper to just plant a few more trees on non-pretreated ground? Alternatively, since Nuttall doesn’t self prune anyway, is it worth the effort to ensure that species has high early survival (assuming the main advantage of denser stands is better stem quality)? 

 

I agree that the economics and silvics of planted oaks is still a very dark black box. I appreciate the author’s work.  No doubt seedling quality matters a lot. Has anyone looked at genetic quality?  On quality sites I would be surprised if sources didn’t vary by 20% in growth by age 11 – a predictable 20% difference in growth based on soil treatments would be considered important news. We found that in some cases genetic differences were more important than seedling quality in determining 5 year growth.

Thank you for this contribution to our understanding of oak afforestation.

Author Response

Point 1 -

Line 88, 89, 90, careful with syntax. The sentence could be made more clear by substituting a descriptive subject into the sentence instead of “other work” – what exactly did this other work test? Was it the effect of bedding on growth and survival? If so, please say so explicitly.

Response 1 -

Changed "other work" to "two bedding studies in" to clarify.

 

Point 2 -

Sentence at 121 – 123 is unclear. How can early treatment effects be tools? I can see how they might be indicators. Please revise.

Response 2 -

All treatments can serve as tools to achieve an end goal. They are viewed by land managers simply a way to produce something. However, since Reviewer 2 does not like the term we have replaced it with "indicators".

 

Point 3 -

Were controls considered ‘treatments’ or was a separate analysis comparing treatments to controls performed? The latter is often preferred – or at least it is in some circles.

Response 3 -

We compared the control with the other mechanical treatments (subsoiling, bedding, combination plowing) in the Tukey’s multiple comparison test. This method was selected because it is generally considered the most conservative post-hoc test (limiting Type 1 errors) when equal sample sizes exist.

 

Point 4 -

Line 202 – 204, please rephrase – absence of statistical differences based on ANOVA has already been described, but the sentence seems to want to focus on the range of values observed (useful to know) the authors should state what treatments resulted in the highest and lowest observed values, even if these differences were not significant based on a P value. Those types of statistical tests are not the only way to describe what they observed and what it means.

Response 4 -

We feel that this is a stylistic request and that our presentation is not incorrect. The addition of these averages into the body of the manuscript simply adds unnecessary text. All mentioned values are listed, as stated in the text, in Table 1 which immediately follows the mentioned sentence.

 

Point 5 -

Line 205, For the benefit of those who have not read your previous manuscript, please add detail to the statement “effects seem to have evened” – what effects increased or decreased?

Response 5 -

Good point. We changed "effects seem to have evened" to "effect differences have diminished" in the sentence.

 

Point 6 -

Line 211, explain what you mean by “mechanical treatment averages…were linked..”

Response 6 -

It seems like "linked" is older terminology now. Sorry. The term just means that ANOVA showed a statistically significant F-test but multiple comparison didn't detect a difference. We changed this by deleting "linked and" from the sentence because the meaning/result is ultimately the same.

 

Point 7 -

Line 233 – an important observation and conclusion by the authors. For the benefit of those not familiar with your growing conditions, why would intraspecific competition decrease the likelihood that soil treatments would produce differential results? I could imagine that competition would increase the advantage of trees on favorable soil treatments. Is your conclusion based on the likely distribution of root zones in an 11 year old tree (I.e., that roots are well below any soil layer affected by mechanical treatment)?

Response 7 -

Our conclusion is based on the well known tendency of increasing difficulty in detecting differences in biological studies over time. Variation increases in these datasets as the trees get older, thus decreasing the likelihood of being able to detect differences in treatment effects as time/variability increases.

As for root distribution in root zones, we do not think that differences in soil compaction/bulk density/etc resulting from mechanical treatment 11 years previous exist. Ancillary use of a soil probe did not indicate that differences still exist.

 

Point 8 -

Line 254, the authors state “..SCO possessed a p-vale….”. Well, I guess I understand what is being said, but this is not a good way to say it. SCO, as a species, does not possess anything. It is better to be precise in your language and to say something like “There were differences in SCO HT among mechanical treatments (p< XXX)” etc. As part of the discussion, the authors should tell the reader whether observed differences (whether at P<0.05 or not) appeared to be biologically meaningful. Were trees on one type of treatment healthier or in any way noticeably different? Do you believe the extra 5 – 10 % more height at this stage reflects more competitiveness or long-term vigor? Again, please explain what you mean by “treatment means were linked” – I am not familiar with that terminology and am not sure I can interpret it as the authors intend.

Response 8 -

Differences that Reviewer 2 would like to see discussed are not supported by literature and would be of a purely suppositional nature based on personal observations. This type of research in hardwood plantations is its infancy. Treatment effects and general physiology in these stands is very different from that of natural stands with projects being established to answer some of these questions.

We changed "possessed" to "analysis yielded" and "linked due to the low statistical power of the test" to " not significant".

 

Point 9 -

Line 300, please use past tense consistently when reporting results

Response 9 - We did not use past tense in reporting results in line 300. Present tense was used in discussion of species inherencies regarding general growth trends in that sentence. The following sentence supports this typical trend and uses past tense to refer to table values for swamp chestnut oak.

 

Point 10 -

A photo would be nice. If these trees were not thinned (I didn’t see that they were), then these trees are packed pretty tight at age 11 aren’t they? It will be easier to understand their growth dynamics and the importance of HLC differences by looking at a photo.

Response 10 - We do not possess photos of this stand at age 11. Yes, similar to the vast majority of oak plantation at that age, trees were "getting tight". This is typical of the stand type and is a factor that will be present in pretty much any future work  in these stands.

 

Point 11 -

The authors may have mentioned it, but since this is a single site study, I would like their evaluation of how representative these results might be. Is the site typical of afforestation sites for oak in the Mississippi valley? Was growth typical? Was weed competition (woody and otherwise) typical?

Response 11 - Again, as stated in the manuscript and in response above, published information on silvicultural research in LMAV oak plantations is incredibly limited. Any inferences as to the representative status of this study to the "norm" for tree growth across the region would be purely observational. Personally, we feel that it does, but are remiss to state it as such.

 

Point 12 -

I like the conclusions, but would appreciate even a little more. Given the cost of mechanical treatment and the main advantage related to survival, do we know where the tradeoff occurs? Is it cheaper to just plant a few more trees on non-pretreated ground? Alternatively, since Nuttall doesn’t self prune anyway, is it worth the effort to ensure that species has high early survival (assuming the main advantage of denser stands is better stem quality)?

Response 12 -

All good questions, and some of this research is being done, but answers do not currently exist due to the extremely limited knowledge available for these systems. We simply do not possess the data with which to make solid assessments of this right now. Of note however, Nuttall oak does prune, just not as quickly or cleanly as some of the other oak species.

 

Point 13 -

I agree that the economics and silvics of planted oaks is still a very dark black box. I appreciate the author’s work. No doubt seedling quality matters a lot. Has anyone looked at genetic quality? On quality sites I would be surprised if sources didn’t vary by 20% in growth by age 11 – a predictable 20% difference in growth based on soil treatments would be considered important news. We found that in some cases genetic differences were more important than seedling quality in determining 5 year growth.

Response 13 -

At the point that this study was implemented, "genetically improved" hardwood stock was not available. There are a couple of producers of a few oak species now, but supply is very limited. Genetic improvement stands to open a new era in hardwoods just as it did in pine plantation silviculture. However, consideration of genetically improved stock is outside the scope of this manuscript.

 

Point 14 -

Thank you for this contribution to our understanding of oak afforestation.

Response 14 -

Thank you and we appreciate the time you spent in reviewing this manuscript.