Equations / Stem biomass

Understorey trunk biomass from D30, height and wood density

Stem biomassUnderstorey trees and saplings, 184 species (stems 1–10 cm diameter)CameroonnaturalRead from the original paper

Many species, no single photo

Equation

As printed (Table 3, block "Trunk", p. 6)

lnM= a + b × ln(D)+c × ln(H) + d × ln (ρ) 1023 -3.480*** 1.731*** 1.096*** 0.897*** 1.318 0.438 0.939 1220 0.10 2.44

In this library's units, ready to compute (kg)

Stem biomass = exp(-3.48 + 1.731 * ln(D30) + 1.096 * ln(H) + 0.897 * ln(rho))

D30: Stem diameter at 30 cm, cm
H: Total tree height, m
rho: Wood density (oven-dry mass / green volume), g/cm³

Selected from Table 2/3 "All" (1 ≤ diameter < 10 cm, n = 1023) block; the paper also gives separate seedling (1-5 cm) and sapling (5-10 cm) fits and crown-diameter models (not included: crown diameter unit is ambiguous, Table 1 header says cm but values are 0.19-7.55). D is the stem diameter at 30 cm above ground (D30), not DBH, so no DBH range is stored; Table 1 gives D 1.00-9.99 cm and H 0.86-15.55 m for the whole data set. Wood density is the mean of base, trunk and branch samples (dry weight / fresh volume). Published as the plain exp() back-transform: the paper lists a CF column (= RSE²/2, an additive term on the log scale) but does not print the corrected equation, so no correction factor is applied or stored. Total AGB = trunk + branches + leaves (dry mass, oven-dried at 105/70 °C). Recommended by the authors: the models with more predictors fit better (Adj.R² up to 0.956 with four predictors); the D-only model is the simplest. Stem (trunk) component only.

Source

Yonkeu Ntonmen, A. F., Zapfack, L., Djomo Chimi, C., et al. (2022). Complementary allometric model of understory tree biomass in the semi-deciduous rainforest of Cameroon. Acta Botanica Brasilica, 36, e2020abb0475.

doi:10.1590/0102-33062020abb0475 · Open access · copy we read

H: tree height; ρ: wood density; C: crown diameter; N: sample size; a, b, c and d are the model’s fitted parameters

Units · Table 3 note, p. 6

AGB and several measurement variables (diameter, height, crown diameter, and wood density) were measured on 1023 understorey stems belonging to 184 species

Trees measured · Data collection, p. 3

The diameter was measured at 30 cm aboveground level

Note · Data collection, p. 3

The correction factor (CF) calculated by the formula CF= RSE²/2 (5)

Note · Data analysis, p. 4

Trees measured: 1,023
Height range: 0.86–15.55 m
Residual SE: 0.438
Method: log-log regression, lnM = a + b ln(X1) + ...
Where: Semi-deciduous rainforest, East region, Cameroon
Last checked: 2026-11-02

Calculate

D30 (cm)Height (m)Wood density (g/cm³)

Height from

0.56

Stem biomass (kg)

0.263

Carbon (kg), ×0.47

0.966

CO₂e (kg), ×44/12

Checks this equation passes

On every build, the library's form and the paper's own form (in its units) must both give these values within 1%.

Inputs	Expected	We get	From
D30 = 3, H = 4, rho = 0.56	0.560	0.560	Computed from the printed form computed with python3 from the published form (uncorrected, as printed)
D30 = 8, H = 9, rho = 0.6	7.92	7.92	Computed from the printed form computed with python3 from the published form (uncorrected, as printed)

Report a problem with this equation · JSON

Understorey AGB from D30 and height · same paper · Aboveground biomass
Understorey AGB from D30 and wood density · same paper · Aboveground biomass
Understorey AGB from D30 (1-10 cm stems) · same paper · Aboveground biomass
Understorey AGB from D30²·H and wood density · same paper · Aboveground biomass

Understorey trunk biomass from D30, height and wood density

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