Comment on Vickers et al.: Self-correlation between assimilation and respiration resulting from flux partitioning of eddy-covariance CO_2 fluxes

摘要

The paper of Vickers et al. (2009) raises the important issue of self-correlation, also named spurious correlation or artificial correlation, in the context of partitioning measured eddy-covariance (EC) CO_2 fluxes. Vickers et al. argue that there isa spurious correlation between primary production (GPP) and ecosystem respiration (Reco) when these component fluxes are jointly estimated from the measured net ecosystem exchange (NEE) of CO_2. Spurious correlations can arise, for instance, when an independent variable x is compared with a dependent variable z thatis computed fromxasx-y(Kenney, 1982). In this examplexand y are the "original" variables and z is derived from these. The higher the variance of the shared variable x compared to the variance ofy, the higher the spurious correlation between x and z (Kenney, 1982).