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Peer review report 1 On “Gross and aboveground net primary production at Canadian forest carbon flux sites”
Agricultural and Forest Meteorology 201S (2015) 521
Contents lists available at ScienceDirect
Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet
Peer review report
Peer review report 1 On “Gross and aboveground net primary production at Canadian forest carbon flux sites”
Original Submission Recommendation Minor Revision Comments to Author This paper makes a very valuable synthesis of carbon uptake and sequestration of a large set of forest ecosystems growing in Canada under various environmental conditions. Another strength of this work is to include data obtained in chronosequences of several tree species, therefore taking into account the age effects. I do not find major flaws in this manuscript, which is acceptable for publication in this journal. However, some minor corrections are required. I also propose some suggestions aiming atimproving data analysis and interpretation. The fact that ANPP/GPP ratio seems constant with age and with environmental factors isclearly shown in this work. May be some discussion about ecosystem respiration (Reco), both autotrophic and heterotrophic would help to interpret this finding: a lot of papers report that factors increasing GPP also increase Reco. On the contrary, for instance, drought reduces both GPP and Reco. As a result, GPP and ANPP vary roughly in parallel. A minor point, about statistical significance, for instance lines 240-242, when p < 0.10, differences are not significant. The effect of both LAI and soil N is also clearly demonstrated. Do the ANPP and GPPdependence to LAI, not to stand age, means that LAI does not change with age, except may be in the youngest stages? This LAI-age dependence would be worth to be mentioned.
DOI of original article: http://dx.doi.org/10.1016/j.agrformet.2013.02.004. 0168-1923/$ – see front matter http://dx.doi.org/10.1016/j.agrformet.2015.07.193
Another finding to be discussed is that better correlations are obtained with GPP than with ANPP. Is it because GPP is a primary mechanism, while ANPP is buffered and influenced byother mechanisms or factors? 4. About ANPP and GPP dependence to precipitation, I am a bit disappointed, as I feel that the authors could go further in this analysis. We know that mechanisms such as carbon uptake or evapotranspiration are not linearly related to water supply. Therefore, annual precipitatin, even if it significantly explains ANPP and GPP, may be better correlations would be obtained with seasonal precipitation (defined for instance with temperature thresholds). Miscellaneous - Jack pine and white pine forests ANPP values (lines 252-255) are at the lower range oftemperate pine stands. Canadian climate is probably not typically temperate, even at thesouthern part, with a shorter growing season. - Table 2: “tree biomass” is probably aerial tree biomass - Fig. 1: is it an explanation for the strong peak of GPP and ANPP for stand yw? - A paper from our group (Granier et al., 2008), dealing with carbon balance and tree growth of a broad-leaved stand could be cited. We found a NPP/GPP ratio of 0.48 and interannual variations of NPP and GPP are also reported. Andre Granier Available online 6 August 2015
Contents lists available at ScienceDirect
Agricultural and Forest Meteorology journal homepage: www.elsevier.com/locate/agrformet
Peer review report
Peer review report 1 On “Gross and aboveground net primary production at Canadian forest carbon flux sites”
Original Submission Recommendation Minor Revision Comments to Author This paper makes a very valuable synthesis of carbon uptake and sequestration of a large set of forest ecosystems growing in Canada under various environmental conditions. Another strength of this work is to include data obtained in chronosequences of several tree species, therefore taking into account the age effects. I do not find major flaws in this manuscript, which is acceptable for publication in this journal. However, some minor corrections are required. I also propose some suggestions aiming atimproving data analysis and interpretation. The fact that ANPP/GPP ratio seems constant with age and with environmental factors isclearly shown in this work. May be some discussion about ecosystem respiration (Reco), both autotrophic and heterotrophic would help to interpret this finding: a lot of papers report that factors increasing GPP also increase Reco. On the contrary, for instance, drought reduces both GPP and Reco. As a result, GPP and ANPP vary roughly in parallel. A minor point, about statistical significance, for instance lines 240-242, when p < 0.10, differences are not significant. The effect of both LAI and soil N is also clearly demonstrated. Do the ANPP and GPPdependence to LAI, not to stand age, means that LAI does not change with age, except may be in the youngest stages? This LAI-age dependence would be worth to be mentioned.
DOI of original article: http://dx.doi.org/10.1016/j.agrformet.2013.02.004. 0168-1923/$ – see front matter http://dx.doi.org/10.1016/j.agrformet.2015.07.193
Another finding to be discussed is that better correlations are obtained with GPP than with ANPP. Is it because GPP is a primary mechanism, while ANPP is buffered and influenced byother mechanisms or factors? 4. About ANPP and GPP dependence to precipitation, I am a bit disappointed, as I feel that the authors could go further in this analysis. We know that mechanisms such as carbon uptake or evapotranspiration are not linearly related to water supply. Therefore, annual precipitatin, even if it significantly explains ANPP and GPP, may be better correlations would be obtained with seasonal precipitation (defined for instance with temperature thresholds). Miscellaneous - Jack pine and white pine forests ANPP values (lines 252-255) are at the lower range oftemperate pine stands. Canadian climate is probably not typically temperate, even at thesouthern part, with a shorter growing season. - Table 2: “tree biomass” is probably aerial tree biomass - Fig. 1: is it an explanation for the strong peak of GPP and ANPP for stand yw? - A paper from our group (Granier et al., 2008), dealing with carbon balance and tree growth of a broad-leaved stand could be cited. We found a NPP/GPP ratio of 0.48 and interannual variations of NPP and GPP are also reported. Andre Granier Available online 6 August 2015