Contrasting Conservation Outcomes for Ground-Dwelling and Aerial Insects in Masson Pine Plantations: Reduced Ground-Dwelling Insect Diversity but Comparable Aerial Insect Diversity to Natural Forests

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This is broadly coneived, well executed, and very well written study, targeting a perpetual pain of plantation forestry - that of differences in biodiversity between forest plantations (typically monocultural, even-aged and uniformly managed) and forests with more natural plant species composition, no matter if old-growht or secondary.

Although a general pattern that plantations tend to host lower diversity of species is obvious to most of visitors to such habitats at a first glance, the pattern is relatively little docummented in larger-scale and broadly conceived studies, globally speaking. This also applies to China, where the topic is particularly important given the size of the country, its outstanding biodiversity, and the current "afforestation" activities, which are huge for any standard. So, I much welcommed this study, enjoyed reading it, and look forward seeing it printed.

I have only few rather minor comments. 

Title: I am nor sure with the term "aerial insects", as to a casual reader, aerial insects are those flying high in canopy, or even above it, while you were basically sampling "low flying insects". You might reconsider the title, but I do not insist. 

Level of taxonomic resolution. As I read at lines 217-220, and elsewehre, you sorted and analysed your samples at family level. This is OK, given the sheer diversity of insects intercepeted. Still, your results are probably hugely underestimating the differences between plantations and more natural forests - definitely at ground level (which you indeed had found, and wchich corresponds with the clear differences in ecological variables, descibed at lines 284-294), but quite likely alo at the aerial/flying insect level. This is not downgrading your study, but you should do 2 things, to avoid confusing readers, and help them to interpret your results more clearly
a) - avoid terms "species richness", "species diveristy", atd., and call it what it is - "familial diversity", "familial richness" (or may be "family diversity", "family richness"; use the more used term). 
b) - return to this issue in Discussion, somewhere around 240-555. You are right that your resolution was "sufficient", but state there, that "...more detailed taxonomic resolution, perhaps feasilble only for selected taxa, might bring more detailed insight onto the mechamisms...(etc.)". It would be nice if you cited some of the more detailed studies of yout topic, from across the world. 

line 57-59: For deeer pespective, the origin of monocultures was not "carbon storage", but fear of energetic crisis back in 18th century Europe, before a wide introduction of coal, when wood and charcoal were the only sources for smelting metallic ores. From this paranoia, "economic forestry" expanded globally, with colonial administrations. Dig for some broader, and historically more accurate, citation. 

75-76: mention also geograpic region

197-215 (all the environmental predictors measured) - I only wonder, why to collect so many data, given that many were necessarily, and expectably, intercorrelated. Not necessary to provide a hypothesis for each of them, but may be add a brief hint, what did you expect while taking all the measurements. 

 

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This paper is obviously a revised version of an earlier submission. The authors address an important question (the conservation value of planted forest monocultures). The sampling and study design looks fine, as does the statistical data analysis. One major caveat is the coarse (family level) taxonomic resolution – the authors do discuss that honestly, but this might even be emphasized more strongly, since patterns at species level could look completely different.

While in some contexts the family level may be sufficient as a proxy, there are for sure many situations where species level information reveals patterns that you cannot trace at higher taxonomic levels. For example, among phytophagous insects such as Lepidoptera or beetle families like Chrysomelidar or Curculionidae, many insect species are highly host-plant specific and therefore show very subtle and sensitive responses to change in the species composition of the vegetation. So, completely different species may occur in a plantation, but still these belong to the same family as in natural forest.

Consider the following example. You compare the moth assemblage between a planted pine monoculture and a near-natural oak forest. In the conifer forest you will likely see a fauna consisting of some ‘pests’ that belong to the globally dominant families Geometridae, Noctuidae, Erebidae, Pyralidae, Crambidae, and a few others, whose larvae mostly are conifer specialists. In the oak forest you will likely see again representatives of these same globally dominant families, but completely different species, whose larvae are bound to broad-leaved woody plants. It would be plainly wrong to conclude that the pine monoculture has similar conservation value, even if at the family level the diversity and composition is largely the same. This must be better taken up in the discussion section.

I have a few more suggestions for further improvement.

It must be better described how insect samples were processed. Based on morphology, DNA barcodes, or else? Which literature was used? Were vouchers compared to well curated research collections? Please provide more details about this important step in the workflow! It is also important to give a reference as to what circumscription of families you have adopted, since also at the family level authors may disagree. For example, in many books Erebidae and Noctuidae are treated as two distinct moth families, but occasionally they are all lumped into Noctuidae. Obviously, such discrepancies could affect your analyse on family level.

The Malaise traps need to be described in more detail. How large were they, built from what materials? Were these self-constructed or purchased from a commercial provider?

Since insects were identified only to family level, you technically cannot talk about “species diversity”, but rather have to replace that term by “family diversity”. Please cross-check throughout the paper! This MUST be corrected throughout the text as well as in all tables and especially the figures.

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

Within the limitations of the data (i.e. in the absence of species-level identification of trapped organisms) the authos have done all what was feasible to revise their paper. 

In this present form, this paper will be an interesting contribution to evaluate the ecological value of monocultures built up from non-native trees. These ecosystems are truly dominant in many regions of the world, so studying these systems is topical.