# Understorey trunk biomass from D30, height and wood density

Stem biomass equation for Understorey trees and saplings, 184 species (stems 1–10 cm diameter), Cameroon, from Yonkeu Ntonmen et al. 2022. 1,023 trees. Listed on Tree Allometrics, a free library of tree allometric equations, each quoted from the source that published it.

## Equation

As printed in Yonkeu Ntonmen et al. 2022 (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

Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#equation

In this library's units, ready to compute (stem biomass in kg):

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

Inputs: D30 = Stem diameter at 30 cm (cm); H = Total tree height (m); rho = Wood density (oven-dry mass / green volume) (g/cm³).
The source's own form: exp(-3.48 + 1.731 * ln(D) + 1.096 * ln(H) + 0.897 * ln(rho)), with D in cm, rho in g/cm3, H in m; output in kg.
Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#canonical

## What it covers

- Output: Stem biomass, kg
- Taxon: Understorey trees and saplings, 184 species (stems 1–10 cm diameter) (mixed species); broadleaf
- Where: Semi-deciduous rainforest, East region, Cameroon. Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#where
- Biomes: tropical
- Stand: natural
- Trees measured: 1,023. Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#n_trees
- Height range: 0.86–15.55 m. Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#height
- Residual SE: 0.438. Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#rse
- Method: log-log regression, lnM = a + b ln(X1) + .... Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#method
- Verification: read in the original source
- Last checked: 2026-11-02. Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#checked_at

A missing fit statistic is one the source doesn't state, or that we haven't recorded; it is never estimated. Outside the stated DBH range or region, the equation is an extrapolation.

## 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: https://doi.org/10.1590/0102-33062020abb0475
- Access: open access
- Copy we read: https://www.scielo.br/j/abb/a/ykhPLqBFcf98nZLQ5nZSKZv/?lang=en&format=pdf
- Every equation from this source: https://treeallometry.org/sources/ntonmen-2022/
- Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#source

## The facts, in the source's words

**Equation** (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

Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#equation

**Units** (Table 3 note, p. 6):

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

Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#quote-published-units

**Trees measured** (Data collection, p. 3):

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

Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#quote-fit-n-trees

**Note** (Data collection, p. 3):

> The diameter was measured at 30 cm aboveground level

Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#quote-notes

**Note** (Data analysis, p. 4):

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

Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#quote-notes-2

**Our note:** 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.

## Checks this equation passes

On every build, the library's form and the source'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 | 0.56 | 0.56 | 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) |

Cite: https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/#checks

The calculator on the page shows carbon as biomass × 0.47 (IPCC 2006 Guidelines, Vol. 4, Ch. 4, Table 4.3) and CO₂e as carbon × 44/12.

## How to cite

Cite the source for the equation: 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. https://doi.org/10.1590/0102-33062020abb0475

Cite this page for the record and checks: Tree Allometrics (Restoration Scope), "Understorey trunk biomass from D30, height and wood density", checked 2026-11-02, https://treeallometry.org/equations/ntonmen-2022-trunk-d-h-rho/. Data CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Quotes are the authors' words.

Data for this equation: https://treeallometry.org/data/equations/ntonmen-2022-trunk-d-h-rho.json
Report a problem: email info@restorationscope.com with the equation id (ntonmen-2022-trunk-d-h-rho) and where the right value appears.