Table 2 Formulas of regression models used in the study

Site-specific tree-level models

(1) Y = a × D^b

(2) Y = a + b × D²

(3) Y = a + b × log(D)

(4) Y = a + (b/D)

(5) Y = a × (D²H)^b

(6) Y = a × D^b × H^c

(7) Y = a + b × log(D²H)

(8) Y = a + b × D² + c × H

(9) Y = a + b × (D²H)

(10) Y = a + b × D² + c × H²

Biomass (dry weight) of the tree component (kg)

D—diameter (cm),

H—height (m),

D²H—pseudovolume (m³).

(Jagodziński et al., 2018a, b)

General tree-level models

(11) log(W) = a + b × log(D) + u_j

(12) log(W) = a + b × log(D²H) + u_j

(13) log(W) = a + b × log(D) + c × log(H) + u_j

Biomass (dry weight) of the tree component (kg)

D—diameter (cm),

H—height (m),

D²H—pseudovolume (m³),

u_j—random intercept for plot j.

(Forrester et al. 2017)

Stand-level models

(14) Y = a × z^b

(15) Y = a + b × e^{−z × c}

(16) Y = a + b/z

(17) Y = a + b/z^c

Biomass (Mg ha⁻¹)

BCEF (Mg m⁻³)

z—tree stand characteristics (stand density, height, volume or age)

(Teobaldelli et al. 2009; Wojtan et al. 2011; Jagodziński et al. 2018b)