# Dry tropical zone AGB from DBH (Eq. 3.2.1)

Aboveground biomass equation for Tropical broadleaf trees (mixed species), Pantropical, from Brown 1997. 28 trees, DBH 5–40 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. 3.2.1, Section 3.2.1 table):

> Y = exp{-1.996+2.32*ln(D)}

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

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

```
Aboveground biomass = exp(-1.996 + 2.32 * ln(D))
```

Inputs: D = Diameter at breast height (1.3 m) (cm).
The source's own form: exp(-1.996 + 2.32 * ln(D)), with D in cm; output in kg.
Cite: https://treeallometry.org/equations/brown-1997-dry/#canonical

## What it covers

- Output: Aboveground biomass, kg
- Taxon: Tropical broadleaf trees (mixed species) (mixed species); broadleaf
- Where: Tropics, dry zone. Cite: https://treeallometry.org/equations/brown-1997-dry/#where
- Biomes: tropical, dryland
- Stand: natural
- Trees measured: 28. Cite: https://treeallometry.org/equations/brown-1997-dry/#n_trees
- DBH range: 5–40 cm. Cite: https://treeallometry.org/equations/brown-1997-dry/#dbh
- R²: 0.89. Cite: https://treeallometry.org/equations/brown-1997-dry/#r2
- Verification: read in the original source
- Last checked: 2026-11-01. Cite: https://treeallometry.org/equations/brown-1997-dry/#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-dry/#source

## The facts, in the source's words

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

> Y = exp{-1.996+2.32*ln(D)}

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

**Trees measured** (Eq. 3.2.1 row: range in dbh (cm), number of trees, adjusted r2):

> 5-40 | 28 | 0.89

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

**Our note:** Revised from Brown et al. (1989) for dry forest in India. The primer recommends it for dry zones with rainfall > 900 mm/yr (Eq. 3.2.2, Martinez-Yrizar et al. 1992, for < 900 mm/yr). r2 is the adjusted r² printed in the table. 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 = 20 | 142 | 142 | Computed from the printed form: computed with python3 from the published form |

Cite: https://treeallometry.org/equations/brown-1997-dry/#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), "Dry tropical zone AGB from DBH (Eq. 3.2.1)", checked 2026-11-01, https://treeallometry.org/equations/brown-1997-dry/. 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-dry.json
Report a problem: email info@restorationscope.com with the equation id (brown-1997-dry) and where the right value appears.