# BGB Model 6 (DBH and [ln(DBH)]²), peat swamp forest Sarawak

Root biomass equation for Mixed tree species, tropical peat swamp forest, Malaysia, from Monda et al. 2015. 32 trees, DBH 5.2–110.8 cm. Listed on Tree Allometrics, a free library of tree allometric equations, each quoted from the source that published it.

## Equation

As printed in Monda et al. 2015 (Models section, p. 15):

> Model 6: ln(DW)＝a＋b ln(DBH)−e [ln(DBH)]2

Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#equation

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

```
Root biomass = 1.1267 * exp(-6.1049 + 3.9957 * ln(D) - 0.2322 * ln(D)^2)
```

Inputs: D = Diameter at breast height (1.3 m) (cm).
The source's own form: 1.1267 * exp(-6.1049 + 3.9957 * ln(DBH) - 0.2322 * ln(DBH)^2), with DBH in cm; output in kg.
Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#canonical

## What it covers

- Output: Root biomass, kg
- Taxon: Mixed tree species, tropical peat swamp forest (mixed species); broadleaf
- Where: Logged-over peat swamp forest, Sarawak (Alan Batu and other sites, PC1-PC3). Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#where
- Biomes: tropical
- Stand: natural
- Trees measured: 32. Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#n_trees
- DBH range: 5.2–110.8 cm. Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#dbh
- Correction factor: 1.1267 (applied). Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#cf
- Method: log-log regression of dry weight on ln-transformed predictors, back-transformed and multiplied by the correction factor CF = exp(RSE²/2). Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#method
- Verification: read in the original source
- Last checked: 2026-11-02. Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#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

Monda, Y., Kiyono, Y., Melling, L., Damian, C., & Chaddy, A. (2015). Allometric equations considering the influence of hollow trees: A case study for tropical peat swamp forest in Sarawak. TROPICS, 24(1), 11-22.

- DOI: https://doi.org/10.3759/tropics.24.11
- Access: open access
- Copy we read: https://www.jstage.jst.go.jp/article/tropics/24/1/24_11/_pdf
- Every equation from this source: https://treeallometry.org/sources/monda-2015/
- Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#source

## The facts, in the source's words

**Equation** (Models section, p. 15):

> Model 6: ln(DW)＝a＋b ln(DBH)−e [ln(DBH)]2

Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#equation

**Equation** (Table 5, Belowground biomass, p. 19 (columns a, b, c, d, e, adjusted R2, CF, AIC, FI)):

> Model 6 −6.1049 3.9957 *** 0.2322 ns 0.9544 1.1267 49.81 0.02378

Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#quote-expression

**Trees measured** (Table 5):

> Belowground biomass (n＝32)

Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#quote-fit-n-trees

**Largest DBH** (Discussion, p. 20):

> BGB data for trees ranging in DBH from 5.2 to 110.8 cm

Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#quote-fit-dbh-max-cm

**Our note:** Coefficients a-e as printed in Table 5; the e term enters with a minus sign per the model definitions. WD is wood density in Mg m-3, numerically equal to g/cm3. Back-transformed result multiplied by the printed CF. Adjusted R2 0.9544 is not entered as r2. DW is dry mass (kg) of the whole above- or belowground part; hollow cavity volume was measured separately and the models are fitted to the measured biomass of hollow trees.

## 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 |
| --- | --- | --- | --- |
| D = 10 | 7.27 | 7.27 | Computed from the printed form: computed from the published form (coefficients and CF as printed) |
| D = 30 | 137 | 137 | Computed from the printed form: computed from the published form (coefficients and CF as printed) |
| D = 60 | 653 | 653 | Computed from the printed form: computed from the published form (coefficients and CF as printed) |

Cite: https://treeallometry.org/equations/monda-2015-bgb-m6/#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: Monda, Y., Kiyono, Y., Melling, L., Damian, C., & Chaddy, A. (2015). Allometric equations considering the influence of hollow trees: A case study for tropical peat swamp forest in Sarawak. TROPICS, 24(1), 11-22. https://doi.org/10.3759/tropics.24.11

Cite this page for the record and checks: Tree Allometrics (Restoration Scope), "BGB Model 6 (DBH and [ln(DBH)]²), peat swamp forest Sarawak", checked 2026-11-02, https://treeallometry.org/equations/monda-2015-bgb-m6/. 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/monda-2015-bgb-m6.json
Report a problem: email info@restorationscope.com with the equation id (monda-2015-bgb-m6) and where the right value appears.