# Knightia excelsa, NZ, total aboveground biomass from RCD (Table 3)

Aboveground biomass equation for Knightia excelsa, New Zealand, from Marden et al. 2025. Listed on Tree Allometrics, a free library of tree allometric equations, each quoted from the source that published it.

## Equation

As printed in Marden et al. 2025 (Table 3, Total above-ground biomass, Knightia excelsa):

> y = 63.7e0.0526x

Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#equation

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

```
Aboveground biomass = 0.0637 * exp(0.526 * DRC)
```

Inputs: DRC = Root collar / stem base diameter (cm).
The source's own form: 63.7 * exp(0.0526 * RCD), with RCD in mm; output in g.
Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#canonical

## What it covers

- Output: Aboveground biomass, kg
- Taxon: Knightia excelsa (species), family Proteaceae; broadleaf
- Where: Taruheru River terrace, Gisborne, New Zealand. Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#where
- Biomes: temperate
- Stand: plantation
- R²: 0.799. Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#r2
- Method: nonlinear least squares, exponential (y = a e^(bx)). Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#method
- Verification: read in the original source
- Last checked: 2026-11-02. Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#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

Marden, M., Mason, N. W. H., Lambie, S., & Rowan, D. (2025). Total plant biomass, carbon stock, and species- and age-specific allometry for 12 of New Zealand's early-colonising indigenous shrub and tree species to 5 years of age. New Zealand Journal of Forestry Science, 55, 3.

- DOI: https://doi.org/10.33494/nzjfs552025x387x
- Access: open access
- Copy we read: https://nzjforestryscience.nz/index.php/nzjfs/article/view/387/122
- Every equation from this source: https://treeallometry.org/sources/marden-2025/
- Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#source

## The facts, in the source's words

**Equation** (Table 3, Total above-ground biomass, Knightia excelsa):

> y = 63.7e0.0526x

Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#equation

**R²** (Table 3, Total above-ground biomass, Knightia excelsa, r² column):

> 0.799

Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#quote-fit-r2

**Our note:** Open-spaced juvenile plants (2-year-old containerised plants on-grown for 3 years, sampled up to 5 years). The tables are headed 'at age 5 years' but the appendix figures show points from all harvest years, and the paper gives no n or RCD range for these fits, so none is recorded. x is root collar diameter in mm; biomass in g and height in m (units inferred from Table 2 and Appendix 1 means, which the equations reproduce; the paper does not print units beside the equations). r² for exponential fits is a pseudo r².

## 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 |
| --- | --- | --- | --- |
| DRC = 2 | 0.182 | 0.182 | Computed from the printed form: hand-computed from the published form (RCD in mm, mass in g, converted) |
| DRC = 6 | 1.5 | 1.5 | Computed from the printed form: hand-computed from the published form (RCD in mm, mass in g, converted) |
| DRC = 15 | 170 | 170 | Computed from the printed form: hand-computed from the published form (RCD in mm, mass in g, converted) |

Cite: https://treeallometry.org/equations/marden-2025-knightia-agb/#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: Marden, M., Mason, N. W. H., Lambie, S., & Rowan, D. (2025). Total plant biomass, carbon stock, and species- and age-specific allometry for 12 of New Zealand's early-colonising indigenous shrub and tree species to 5 years of age. New Zealand Journal of Forestry Science, 55, 3. https://doi.org/10.33494/nzjfs552025x387x

Cite this page for the record and checks: Tree Allometrics (Restoration Scope), "Knightia excelsa, NZ, total aboveground biomass from RCD (Table 3)", checked 2026-11-02, https://treeallometry.org/equations/marden-2025-knightia-agb/. 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/marden-2025-knightia-agb.json
Report a problem: email info@restorationscope.com with the equation id (marden-2025-knightia-agb) and where the right value appears.