The assessment of NPP/GPP ratio

Abstract

In 1998, we obtained a close linear relationship between gross primary biomass production (GPP), the total mass of carbon fixed annually by photosynthesis, and net primary biomass production, designated (NPP) (Waring et al. 1998).Collalti and Prentice (2019) (henceforth denoted C&P) recently asserted that Waring, in that 1998 paper, hypothesised that this constant NPP/GPP ratio was "universal across biomes, tree species and stand ages".This is not correct.We said, in the abstract of that paper: "To search for possible common relationships (between GPP and respiration), we assembled annual carbon budgets from 12 forest sites analysis indicated that the total NPP/GPP ratio was conservative (0.470.04).This finding supports the possibility of greatly simplifying forest models".We wereand are well aware that the ratio we obtained is an empirical approximation, which is likely to vary in different stands and under different conditions.We did not postulate that it might be universal across biomes, tree species and ages; that would have been a legitimate, testable hypothesis, but we are not aware that anyone has stated it in that way.However, the fact that the constant ratio was subsequently questioned and tested by a number of authors (Medlyn and Dewar 1999, Mkel & Valentine 2001, Litton et al. 2007, DeLucia et al. 2007, among others) in relation to a range of forests and conditions, suggests that they considered the hypothesis of its universal application to be implicit.The various investigations have yielded a range of values, mostly between 0.4 and 0.6.C&P examined data from more than 200 stands, from which they obtained an average NPP/GPP ratio 1 Joe Landsberg [

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