At each site, the biomass of different plant components (leaves, woody tissues and roots for both overstory trees, and understory trees, shrubs and grasses) were estimated either using the whole-harvest-method or locally developed allometric equations that relates biomass to field measured tree height and diameter at the breast height (see Text S2 of Tang et al. (2018) ). C, N, and P concentrations (in unit of g C or N or P per g dry matter) of different plant components were measured in laboratory using the biomass samples taken at the sites and used to calculate C, N and P pools in unit of g C or N or P m^-2 at each site (Equation 1). C, N and P pools of the surface litter were estimated from the measured elemental concentrations and the dry weight of litter (Equation 2). For soil, soil core samples were taken from five different depth intervals (0-10cm, 10-20cm, 20-30cm, 30-50cm, 50-100cm). Bulk density, gravel content, and total C, N, and P concentration were measured at each depth to calculate soil C, N and P pools (Equation 3). That is

\(X_{B}={\sum_{i=1}^{3}B_{i}\times x}_{i},\ \ i=1,\ 2,\ 3\) (1)

\(X_{L}=L\times x_{L}\) (2)

\(X_{S}=\ \sum_{j=1}^{5}{\left(1-g_{i}\right)\times\rho_{i}}\times x_{j}\times d_{j}\times 10\)(3)

where B _i is the biomass of component i(leaf, wood or root) in g (dry matter) m^-2, andx _i is C, N or P concentration in biomass component i in g C or N or P g^-1 (dry matter).L is dry weight of litter in g (dry matter) m^-2, and x _L is C, N or P concentration of litter biomass in g C or N or P g^-1(dry matter). g_j represents the volume percentage of gravels with a diameter >2 mm in soil layer j ,ρ_j is bulk density (g cm^-3),x_j is total C, N or P content of soil in g C or N or P per kg soil, and d_j is the thickness in cm of the j ^th layer. A factor 10 is for converting from g 10^-3cm^-2 to g m^-2.