# Understorey AGB from D30 (1-10 cm stems)

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 (Data analysis, p. 3):

> The correction factor (CF) calculated by the formula CF= RSE²/2 (5); was used to correct the systematic bias due to the log transformation applied to the models

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

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

```
Aboveground biomass = exp(-2.811 + 0.11 + 2.474 * ln(D30))
```

Inputs: D30 = Stem diameter at 30 cm (cm).
The source's own form: exp(-2.811 + 0.11 + 2.474 * ln(D)), with D in cm; output in kg.
Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d/#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-d/#where
- Biomes: tropical
- Stand: natural
- Trees measured: 1,023. Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d/#n_trees
- Residual SE: 0.475. Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d/#rse
- Method: log-log regression, lnM = a + b ln(X1) + .... Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d/#method
- Verification: read in the original source
- Last checked: 2026-11-03. Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d/#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-d/#source

## The facts, in the source's words

**Equation** (Data analysis, p. 3):

> The correction factor (CF) calculated by the formula CF= RSE²/2 (5); was used to correct the systematic bias due to the log transformation applied to the models

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

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

> lnM= a + b × ln(D) 1023 -2.811*** 2.474*** 0.199 0.475 0.918 1384 0.11 0.11

Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d/#quote-expression

**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-d/#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-d/#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-d/#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-d/#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). The back-transform adds the paper’s CF column (0.11, = RSE²/2, an additive term on the log scale) to the intercept, as its Data analysis says the CF was used to correct the log-transformation bias. 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 | 1.02 | 1.02 | Computed from the printed form: computed with python3 from the published form (CF added to the intercept) |
| D30 = 8 | 11.5 | 11.5 | Computed from the printed form: computed with python3 from the published form (CF added to the intercept) |

Cite: https://treeallometry.org/equations/ntonmen-2022-agb-d/#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 D30 (1-10 cm stems)", checked 2026-11-03, https://treeallometry.org/equations/ntonmen-2022-agb-d/. 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-d.json
Report a problem: email info@restorationscope.com with the equation id (ntonmen-2022-agb-d) and where the right value appears.