# Understorey AGB from D30²·H and wood density

Aboveground 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 2, block "All (1≤ diameter <10 cm)", p. 5):

> lnM= a + b × ln(D2 × H) + c × ln(ρ) 1023 -2.554*** 0.880*** 1.100*** 0.158 0.367 0.951 854 0.07 1.10

Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-rho/#equation

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

```
Aboveground biomass = exp(-2.554 + 0.88 * ln(D30^2 * H) + 1.1 * 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(-2.554 + 0.88 * ln(D^2 * H) + 1.1 * ln(rho)), with D in cm, rho in g/cm3, H in m; output in kg.
Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-rho/#canonical

## What it covers

- Output: Aboveground 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-agb-d2h-rho/#where
- Biomes: tropical
- Stand: natural
- Trees measured: 1,023. Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-rho/#n_trees
- Height range: 0.86–15.55 m. Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-rho/#height
- Residual SE: 0.367. Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-rho/#rse
- Method: log-log regression, lnM = a + b ln(X1) + .... Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-rho/#method
- Verification: read in the original source
- Last checked: 2026-11-02. Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-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-agb-d2h-rho/#source

## The facts, in the source's words

**Equation** (Table 2, block "All (1≤ diameter <10 cm)", p. 5):

> lnM= a + b × ln(D2 × H) + c × ln(ρ) 1023 -2.554*** 0.880*** 1.100*** 0.158 0.367 0.951 854 0.07 1.10

Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-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-agb-d2h-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-agb-d2h-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-agb-d2h-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-agb-d2h-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.

## 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 | 0.962 | 0.962 | Computed from the printed form: computed with python3 from the published form (uncorrected, as printed) |
| D30 = 8, H = 9, rho = 0.6 | 11.9 | 11.9 | Computed from the printed form: computed with python3 from the published form (uncorrected, as printed) |

Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d2h-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 AGB from D30²·H and wood density", checked 2026-11-02, https://treeallometry.org/equations/ntonmen-2022-agb-d2h-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-agb-d2h-rho.json
Report a problem: email info@restorationscope.com with the equation id (ntonmen-2022-agb-d2h-rho) and where the right value appears.