# Wet tropical zone AGB, quadratic (Brown 1997 Eq. 3.2.5)

Aboveground biomass equation for Tropical broadleaf trees (mixed species), Pantropical, from Brown & Iverson 1992. 169 trees, DBH 4–112 cm. Listed on Tree Allometrics, a free library of tree allometric equations, each quoted from the source that published it.

**From a secondary source, not the original:** we could only read this equation in https://www.fao.org/4/w4095e/w4095e06.htm (another paper, brief or compilation). Check it against the original before relying on it.

## Equation

As printed in Brown & Iverson 1992 (Eq. 3.2.5, Section 3.2.1 table):

> Y = 21.297-6.953(D)+0.740(D2)

Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#equation

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

```
Aboveground biomass = 21.297 - 6.953 * D + 0.740 * D^2
```

Inputs: D = Diameter at breast height (1.3 m) (cm).
The source's own form: 21.297 - 6.953 * D + 0.740 * D^2, with D in cm; output in kg.
Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#canonical

## What it covers

- Output: Aboveground biomass, kg
- Taxon: Tropical broadleaf trees (mixed species) (mixed species); broadleaf
- Where: Tropics, wet zone. Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#where
- Biomes: tropical
- Stand: natural
- Trees measured: 169. Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#n_trees
- DBH range: 4–112 cm. Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#dbh
- R²: 0.92. Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#r2
- Verification: from a secondary source (https://www.fao.org/4/w4095e/w4095e06.htm)
- Last checked: 2026-11-01. Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#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., & Iverson, L. R. (1992). Biomass estimates for tropical forests. World Resources Review, 4, 366–384.

- Link: https://www.fao.org/4/w4095e/w4095e0b.htm
- Access: paywalled
- Every equation from this source: https://treeallometry.org/sources/brown-iverson-1992/
- Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#source

## The facts, in the source's words

**Equation** (Eq. 3.2.5, Section 3.2.1 table):

> Y = 21.297-6.953(D)+0.740(D2)

Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#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-iverson-1992-wet/#quote-published-units

**Note** (Brown 1997, Section 3.2.1 table, footnote c):

> c From Brown and Iverson (1992)

Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#quote-notes

**Trees measured** (Brown 1997, Eq. 3.2.5 row: range in dbh (cm), number of trees, adjusted r2):

> 4-112 | 169 | 0.92

Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#quote-fit-n-trees

**Our note:** Commonly cited as Brown (1997) Eq. 3.2.5, but the primer's footnote c attributes it to Brown and Iverson (1992), which could not be read; taken from Brown (1997). r2 is adjusted r². 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 | 479 | 479 | Computed from the printed form: computed with python3 from the published form |

Cite: https://treeallometry.org/equations/brown-iverson-1992-wet/#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., & Iverson, L. R. (1992). Biomass estimates for tropical forests. World Resources Review, 4, 366–384.

Cite this page for the record and checks: Tree Allometrics (Restoration Scope), "Wet tropical zone AGB, quadratic (Brown 1997 Eq. 3.2.5)", checked 2026-11-01, https://treeallometry.org/equations/brown-iverson-1992-wet/. 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-iverson-1992-wet.json
Report a problem: email info@restorationscope.com with the equation id (brown-iverson-1992-wet) and where the right value appears.