Our unique datasets from undisturbed mature forests support the rationale to assume these forest ecosystems are at steady states. We then calculated τ _e,C, τ _e,Nor τ _e,P in year through dividing the pool size by the corresponding input fluxes. That is

\(\tau_{e,c}=\frac{\sum_{k=1}^{5}C_{k}}{\text{NPP}}\) (4)

\(\tau_{e,X}=\frac{\sum_{k=1}^{5}X_{k}+X_{\text{inorg}}}{F_{X}}\)(5)

where C_k is the amount of C in leaf, wood, root, litter and top 1m depth of soil in g C m^-2, NPP is net primary productivity, X _k is the amount of N or P in leaf, wood, root, litter and top 1m depth of soil in g N or P m^-2, X_inorg is the amount of soil inorganic N or P pool in g N or P m^-2, and F_X is the external input flux of N or P to the ecosystem in g N or P m^-2 yr^-1.