date: Tue, 28 Aug 2007 15:53:48 UT from: l.griffin@nature.com subject: NATURE: Decision for referees on Nature manuscript 2007-07-07090 to: K.Briffa@uea.ac.uk Content-Disposition: inline Content-Length: 9195 Content-Type: text/plain Dear Professor Briffa Thank you for your help with the manuscript entitled "Climate change and acid deposition reduce long-term tree growth in central Europe" by Professor Xu and colleagues. We have now received all of the referees' reports, which I have attached below for your information. In the light of these various comments, we have declined publication of this study. Thank you again for your help and I hope that we can call upon your advice in the future. Yours sincerely Lisa Griffin Editorial Assistant On behalf of Dr Juliane C. Mossinger Senior Editor - The Macmillan Building, 4-6 Crinan Street, London N1 9XW, UK Tel +44 (0)207 833 4000; Fax +44 (0)207 843 4596; nature@nature.com - 968 National Press Building, 529 14th Street NW, Washington DC 20045, USA Tel +1 202 737 2355; Fax +1 202 628 1609; nature@naturedc.com - 225 Bush Street, Suite 1453, San Francisco CA 94104, USA Tel +1 415 403 9027; Fax +1 415 781 3805; nature@naturesf.com ****************************** Reviewers' comments: Referee #2(Remarks to the Author) I do not intend to provide a very detailed report on this manuscript - it simply does not justify such a use of my time. My overall opinion is that it is a poorly written description of a misconceived investigation, based on limited data. It makes assertions that are not nearly supported by the evidence. The fundamental problem is a lack of rigorous analyses, which amount to little more than computing a series of statistically insignificant correlations between what are often inter-related time series (or at least have various degrees of common trend). What is even more surprising is that the simple or multiple correlations reported are not sufficiently strong to justify the overstated interpretations of cause of tree-growth trends anyway. The paper makes grandiose statements about "the need to unravel the links...tree growth in tropical forests and long-term decreases....in central Europe in response to climate change". It goes no where in this regard. The tree-ring data are insufficient, as is their treatment as regards identifying and accounting for ring growth trends resulting from tree ageing. No attempt is made to investigate interannual ring-width variability (as distinct from 100-year trend) with respect to specific (and relevant) climate variables. The use of data originally in Greenland ice cores as a proxy for local, Belgian atmospheric pollution (let alone specific local soil conditions) is outrageous. Similarly, the use of CO² data only up to the 1970s is clearly limiting. No attempt is made to deal explicitly with interaction effects (such as by using a formal analysis of variance). The paper amounts to little more than exaggerated statements based on insufficient analyses. I firmly reject this submission as being entirely unsuitable for publication in Nature or elsewhere. Referee #3(Remarks to the Author) This paper proposes to sort out effects of temperature, precipitation, acid deposition and [CO2] on growth of oak and beech in northern and central Belgium. I think the ring-width and d13C records the authors derived are potentially important and useful if used in the right way. However, I think the paper suffers from two major problems: 1) the authors are using the Greenland ice core record as a record of acid deposition in Belgium, presumably because of northern hemisphere proximity. One need only look at acid rain maps published for all of Europe over the last 50+ years to see that acid deposition has been far from uniform in Europe, furthermore with evidence of reduction in recent decades. Unlike atmospheric [CO2], which is worldwide, acid deposition is more regional so that the acid deposition trends at each of the Belgium forest sites could be very different from Greenland's records. Aren't there any other records of acid deposition that can be used instead of ice cores? Or at least maybe to establish that the ice cores acidity does represent what is occurring in Belgium? 2) a bigger problem is that the authors have confused d13C with water-use efficiency (WUE), and they assume that because d13C declines, then WUE declines (for example, the statement on p. 8 "The decrease in long-term tree water use efficiency, as reflected in tree ring δ13C"). This would be true if neither atmospheric δ13C nor [CO2] change, but in fact both of them are changing, so it is possible that a downward tree-ring δ13C trend might actually represent an increase in WUE when calculated. I believe both the Duquesney et al. (1998) and Saurer et al. (2004) papers properly calculate WUE from their data. The authors need to properly calculate intrinsic WUE before their analysis, because based on the δ13C declines in Fig. 2, I estimate that at worst WUE is constant, but more likely it is increasing (certainly for beech), so many of their stated observations involving decreasing WUE are just wrong. Once WUE is calculated, the authors may find it is counteracting the effect of reduced precipitation to some degree. Other comments 3) why is there δ15N methodology in the Methods section when no d15N is reported in this paper? 4) many statements throughout the manuscript, such as "with the temperature increase resulting from rising [CO2]" on page 9, and "due to [CO2]-induced warming" in the abstract, are wrong. The authors cannot demonstrate that [CO2] is causing rising temperature, only that they are correlated (not necessarily cause-effect related), furthermore that is not the purpose of the paper. Additionally it is wrong because the authors have not (nor has anyone) separated out the proportion of temperature rise coming from [CO2] versus other greenhouse gases, nor the fraction of global warming that is currently related to anthropogenic causes versus natural warming (THAT, would be a Nature cover story!). I suggest the authors drop all reference to "[CO2] caused warming" and simply discuss response of trees to warming, [CO2], acid deposition, etc. (this comment is also related to the statement on p. 7 "The [CO2] is not directly related to annual rainfall, summer rainfall and growing season rainfall, but is positively related to winter rainfall", and to "[CO2]-induced warming" both on p. 9 and in the Abstract) 5) at the beginning the authors refer to experiments looking at the effects of single environmental parameters on growth. Of course the purpose of these experiments is to isolate the influence of these individual factors, which is not a bad thing but a good thing. Furthermore, the authors' system with multiple influences may be too complex to sort everything out. The biggest omission I can see is the effect of ozone (O3), which undoubtedly has also been increasing in the region and also has strong deleterious effects on plant growth. For all we know, everything the authors have presented in regard to reduced growth is a consequence of ozone pollution, and slightly different responses of oak and beech to ozone pollution. 6) The first sentence of the abstract "Climate change, particularly rising atmospheric carbon dioxide concentration [CO2]" implies that rising [CO2] is a climate change, which it is not. Perhaps it should be written "Global environmental change, particularly rising atmospheric carbon dioxide concentration [CO2]...". This also applies to "may be used to reconstruct past, long-term climate change (particularly atmospheric [CO2]" on p. 2. 7) on p. 3, the goal of "to examine the relationships between rising [CO2] and local temperature" appears to me beyond the limits of the paper and what can be done with the data. 8) what does "and decreasing source of atmospheric δ13C from increasing CO2 emissions" mean on p. 4? Do authors mean "decreasing atmospheric d13C from increasing CO2 emissions"? 9) on page 4, the statement "Plant water use efficiency and growth can be increased by elevated [CO2]" repeats what was just said 4 lines above. 10) on page 5 the statement "due to the fact that central Belgium with higher mean temperature and lower mean annual rainfall has a more water limiting environment, compared with high Belgium" (also on p. 8 "central Belgium with lower rainfall"), seems opposed to the later statement on p. 6 that "Hence, it is reasonable to use the rainfall and temperature data in central Belgium as estimates of those for high Belgium due to their longer period". The authors need to reconcile these: either they are climatically different or they are climatically the same. 11) on p. 8 "compared with the significant decrease in oak tree ring δ13C from rising [CO2] (Fig. 1)", but there is not d13C in Fig. 1 (only Fig. 2). 12) what does "were corrected to coincide with the 5-year periodicity of individual tree Rings" on p. 10? * Please see NPG's author and referees' website (www.nature.com/authors) for information about and links to policies, services and author benefits. See also http://blogs.nature.com/nautilus, our blog for authors, and http://blogs.nature.com/peer-to-peer, our blog about peer-review. This email has been sent through the NPG Manuscript Tracking System NY-610A-NPG&MTS