# Subtropical China root biomass from D

Root biomass equation for 8 subtropical forest tree species (23 root systems), China, from Xu et al. 2015. 23 trees. Listed on Tree Allometrics, a free library of tree allometric equations, each quoted from the source that published it.

## Equation

As printed in Xu et al. 2015 (BGB models with diameter, p. 8):

> BGB = exp(−2.80346 + 2.0441ln(D))

Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#equation

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

```
Root biomass = exp(-2.80346 + 2.0441 * ln(D))
```

Inputs: D = Diameter at breast height (1.3 m) (cm).
The source's own form: exp(-2.80346 + 2.0441 * ln(D)), with D in cm; output in kg.
Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#canonical

## What it covers

- Output: Root biomass, kg
- Taxon: 8 subtropical forest tree species (23 root systems) (mixed species); mixed
- Where: Badagongshan National Nature Reserve, Hunan province. Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#where
- Biomes: subtropical, montane
- Stand: natural
- Trees measured: 23. Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#n_trees
- R²: 0.9241. Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#r2
- Residual SE: 0.3437. Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#rse
- Method: Bayesian log-log regression (MCMC). Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#method
- Verification: read in the original source
- Last checked: 2026-11-02. Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#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

Xu, Y., Zhang, J., Franklin, S. B., et al. (2015). Improving allometry models to estimate the above- and belowground biomass of subtropical forest, China. Ecosphere, 6(12), 289.

- DOI: https://doi.org/10.1890/es15-00198.1
- Access: open access
- Copy we read: https://esajournals.onlinelibrary.wiley.com/doi/full/10.1890/ES15-00198.1
- Every equation from this source: https://treeallometry.org/sources/xu-2015/
- Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#source

## The facts, in the source's words

**Equation** (BGB models with diameter, p. 8):

> BGB = exp(−2.80346 + 2.0441ln(D))

Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#equation

**Our note:** Log-log model fitted by Bayesian MCMC; no correction factor is stated, so none is applied. Natural log assumed from the paper's ln notation. Wood density WD is in g cm-3 (Table 2; the running text says g/m3). Whole-tree AGB includes branches, leaves and fruit. Fitted on 23 excavated root systems of eight species (large roots, small roots and stump). The residual standard error given is 0.3437 on the log scale and R² is 0.9241.

## 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 | 6.71 | 6.71 | Computed from the printed form: computed from the printed coefficients |
| D = 30 | 63.4 | 63.4 | Computed from the printed form: computed from the printed coefficients |

Cite: https://treeallometry.org/equations/xu-2015-bgb-d/#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: Xu, Y., Zhang, J., Franklin, S. B., et al. (2015). Improving allometry models to estimate the above- and belowground biomass of subtropical forest, China. Ecosphere, 6(12), 289. https://doi.org/10.1890/es15-00198.1

Cite this page for the record and checks: Tree Allometrics (Restoration Scope), "Subtropical China root biomass from D", checked 2026-11-02, https://treeallometry.org/equations/xu-2015-bgb-d/. 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/xu-2015-bgb-d.json
Report a problem: email info@restorationscope.com with the equation id (xu-2015-bgb-d) and where the right value appears.