# Moist tropical zone AGB, quadratic (Eq. 3.2.3)

Aboveground biomass equation for Tropical broadleaf trees (mixed species), Pantropical, from Brown 1997. 170 trees, DBH 5–148 cm. Listed on Tree Allometrics, a free library of tree allometric equations, each quoted from the source that published it.

## Equation

As printed in Brown 1997 (Eq. 3.2.3, Section 3.2.1 table):

> Y = 42.69-12.800(D)+1.242(D2)

Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#equation

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

```
Aboveground biomass = 42.69 - 12.800 * D + 1.242 * D^2
```

Inputs: D = Diameter at breast height (1.3 m) (cm).
The source's own form: 42.69 - 12.800 * D + 1.242 * D^2, with D in cm; output in kg.
Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#canonical

## What it covers

- Output: Aboveground biomass, kg
- Taxon: Tropical broadleaf trees (mixed species) (mixed species); broadleaf
- Where: Tropics, moist zone. Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#where
- Biomes: tropical
- Stand: natural
- Trees measured: 170. Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#n_trees
- DBH range: 5–148 cm. Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#dbh
- R²: 0.84. Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#r2
- Verification: read in the original source
- Last checked: 2026-11-01. Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#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

Brown, S. (1997). Estimating Biomass and Biomass Change of Tropical Forests: a Primer. FAO Forestry Paper 134. Rome: Food and Agriculture Organization of the United Nations. ISBN 92-5-103955-0.

- Link: https://www.fao.org/4/w4095e/w4095e00.htm
- Access: open access
- Copy we read: https://www.fao.org/4/w4095e/w4095e06.htm
- Every equation from this source: https://treeallometry.org/sources/brown-1997/
- Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#source

## The facts, in the source's words

**Equation** (Eq. 3.2.3, Section 3.2.1 table):

> Y = 42.69-12.800(D)+1.242(D2)

Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#equation

**Units** (Section 3.2.1, biomass regression equations table header):

> Y= biomass per tree in kg, D = dbh in cm, and BA = basal area in cm2

Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#quote-published-units

**Trees measured** (Eq. 3.2.3 row: range in dbh (cm), number of trees, adjusted r2):

> 5-148 | 170 | 0,84

Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#quote-fit-n-trees

**Our note:** A. J. R. Gillespie (pers. comm.) revision of the Brown et al. (1989) moist equation. The primer recommends this form for trees with dbh above about 160 cm because it behaves better there than Eq. 3.2.4. r2 is adjusted r². Note: the primer's worked stand-table example says it uses Eq. 3.2.3 but its per-tree values match Eq. 3.2.4. The primer does not say whether a log back-transform correction is included; none applied. Climatic zones per the primer: dry <1500 mm/yr rain with a dry season of several months; moist 1500–4000 mm/yr; wet >4000 mm/yr, lowland conditions 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 |
| --- | --- | --- | --- |
| D = 30 | 776 | 776 | Computed from the printed form: computed with python3 from the published form |
| D = 100 | 11,183 | 11,183 | Computed from the printed form: computed with python3 from the published form |

Cite: https://treeallometry.org/equations/brown-1997-moist-quadratic/#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: Brown, S. (1997). Estimating Biomass and Biomass Change of Tropical Forests: a Primer. FAO Forestry Paper 134. Rome: Food and Agriculture Organization of the United Nations. ISBN 92-5-103955-0.

Cite this page for the record and checks: Tree Allometrics (Restoration Scope), "Moist tropical zone AGB, quadratic (Eq. 3.2.3)", checked 2026-11-01, https://treeallometry.org/equations/brown-1997-moist-quadratic/. 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/brown-1997-moist-quadratic.json
Report a problem: email info@restorationscope.com with the equation id (brown-1997-moist-quadratic) and where the right value appears.