ISO 13391-2:2025

Wood and wood-based products — Greenhouse gas dynamics — Part 2: Forest carbon balance

This document provides a methodology for calculating the carbon balance of (a) forest management unit(s) (FMU). This quantification methodology is intended to demonstrate to what extent carbon pools in the FMU represent a net greenhouse gas sink or a net greenhouse gas source. This document provides information that can be used on organizational or aggregated product levels. This calculation methodology considers: — the geographical scale of the FMU; — forest management practices; — land ownership arrangements; — time periods; — the use of forest inventory data and other data sources for determining the forest carbon balance; and — allocation of forest carbon balance to wood that has been sourced in FMU(s). Greenhouse gas emissions from fossil fuels or industrial processes related to forestry operations (e.g. production and distribution of fertilizers, fuels for machinery) are not included in this document. NOTE 1 Greenhouse gas emissions related to forestry operations are covered in ISO 13391-1. The quantity of wood entering the harvested wood products carbon pool is not included in this document. NOTE 2 Material entering the harvested wood products carbon pool is calculated in ISO 13391-1. This document is intended to be used by organizations seeking to understand, commit to or contribute to climate change mitigation. These organizations can be either private or public, regardless of type or size, and located in any jurisdiction or any position within a specific value chain.

Produits en bois et dérivés du bois — Dynamique des gaz à effet de serre — Partie 2: Bilan carbone des forêts

General Information

• Status: Published
• Publication Date: 28-Apr-2025
• ICS: 13.020.40 - Pollution, pollution control and conservation
• ICS: 65.020.01 - Farming and forestry in general
• ICS: 79.020 - Wood technology processes
• Technical Committee: ISO/TC 287 - Sustainable processes for wood and wood-based products
• Drafting Committee: ISO/TC 287 - Sustainable processes for wood and wood-based products
• Current Stage: 6060 - International Standard published
• Start Date: 29-Apr-2025
• Due Date: 16-Feb-2025
• Completion Date: 29-Apr-2025

Standards Content (Sample)

International
Standard
ISO 13391-2
First edition
Wood and wood-based products —
2025-04
Greenhouse gas dynamics —
Part 2:
Forest carbon balance
Produits en bois et dérivés du bois — Dynamique des gaz à effet
de serre —
Partie 2: Bilan carbone des forêts
Reference number
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ii
Contents Page
Foreword .iv
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Methodology for calculating the forest carbon balance . 3
4.1 General requirements .3
4.2 System boundaries . .4
4.3 Characterization of the FMU(s) by the organization .4
4.4 FMUs and land ownership .4
4.5 Geographical scale .5
4.6 Time periods . .5
4.7 Greenhouse gas emissions and removals in the FMU .6
4.7.1 General .6
4.7.2 Tiered approach .8
4.7.3 Tier approach for living biomass above ground .8
4.8 Data sources .8
4.8.1 General .8
4.8.2 Time series data .9
4.9 Data quality .9
4.10 Calculating changes in FMU carbon pools .9
4.10.1 General .9
4.10.2 Stock change methodologies . . . 12
Annex A (informative) Specific guidance for the five carbon pools .13
Bibliography . 14

iii
Foreword
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vi
Introduction
The carbon balance of land-based systems is crucial for climate change mitigation. The Intergovernmental
[5]
Panel on Climate Change (IPCC) estimated in its sixth assessment report that land-based systems are a
net sink of carbon that counteracts 17 % of the emissions from fossil fuels and industrial processes. Most of
this contribution is attributed to managed forests, whereas areas subject to deforestation lead to emissions.
It is made clear that active forest management can make significant contributions towards climate goals.
This document provides a methodology for calculating the carbon balance for forest management units
(FMUs) where wood is sourced for wood-based products. It is part of the ISO 13391 series for calculation of
the overall greenhouse gas dynamics of wood and wood-based products.
The forest carbon balance is generally determined as the difference between:
— sequestration (gains) of carbon in the forest through primary production of biomass by photosynthesis; and
— losses of carbon through:
a) natural processes, such as decomposition or wildfire; and
b) harvesting of wood for wood-based products.
The methodology presented in this document defines the forest carbon balance as changes in carbon
reservoirs (carbon pools) of living biomass, dead biomass and soil organic matter. The ISO 13391 series
considers seven carbon pools, as outlined in ISO 13391-1, of which five are addressed in this document. Non-
CO greenhouse gases are also considered.
The management of a forest landscape can lead to an increase of carbon stocks. This increase includes
wood harvested from the area entering the harvested wood products carbon pool, which is covered in
ISO 13391-1. Changes in dead biomass, soil organic matter and exceptional events such as uncontrollable
wildfires, storms, droughts, floods or pests, often linked to climate change, and others such as earthquakes
and volcanic eruptions, also need to be accounted for. Due to climate change, forests are increasingly at risk
from such hazards which contribute to the loss of useful wood material and the release of greenhouse gases,
harming the goals of sustainable forestry. In response to these risks, this document makes it possible to
gather data to monitor forest carbon balance which can support evaluation of the climate resilience, climate
adaptation, and mitigation of climate change over time.
When calculating the carbon balance for FMUs, it is necessary to allow for distinct assessment of forests
under different land ownership arrangements, different geographical scales, and different forest
management practices. The methodology in this document is intended to assist organizations and other
aggregations of forest managers (e.g. cooperatives, regional authorities, etc.) to calculate carbon balance.
Until now, calculations by different organizations have been carried out using different methods and system
boundaries. This has generated highly varied results, making comparisons impossible. Additionally, absent
or inconsistent site-specific data on forest carbon can make any such comparisons meaningless. Therefore,
in providing a consistent approach to the collection and assessment of site-specific data, the methodology
presented in this document can be of importance for the wood and wood-based industry and for society as
a whole.
vii
International Standard ISO 13391-2:2025(en)
Wood and wood-based products — Greenhouse gas
dynamics —
Part 2:
Forest carbon balance
1 Scope
This document provides a methodology for calculating the carbon balance of (a) forest management unit(s)
(FMU). This quantification methodology is intended to demonstrate to what extent carbon pools in the FMU
represent a net greenhouse gas sink or a net greenhouse gas source. This document provides information
that can be used on organizational or aggregated product levels.
This calculation methodology considers:
— the geographical scale of the FMU;
— forest management practices;
— land ownership arrangements;
— time periods;
— the use of forest inventory data and other data sources for determining the forest carbon balance; and
— allocation of forest carbon balance to wood that has been sourced in FMU(s).
Greenhouse gas emissions from fossil fuels or industrial processes related to forestry operations (e.g.
production and distribution of fertilizers, fuels for machinery) are not included in this document.
NOTE 1 Greenhouse gas emissions related to forestry operations are covered in ISO 13391-1.
The quantity of wood entering the harvested wood products carbon pool is not included in this document.
NOTE 2 Material entering the harvested wood products carbon pool is calculated in ISO 13391-1.
This document is intended to be used by organizations seeking to understand, commit to or contribute to
climate change mitigation. These organizations can be either private or public, regardless of type or size,
and located in any jurisdiction or any position within a specific value chain.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 13391-1:2025, Wood and wood-based products — Greenhouse gas dynamics — Part 1: Framework for value
chain calculations
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13391-1 and the following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
set-aside area
land excluded from wood production
Note 1 to entry: This is usually for regional development or environmental purposes.
Note 2 to entry: “Wood” is defined in ISO 13391-1:2025, 3.14.
3.2
biological growth
quantitative increase in above-ground biomass (including standing timber or other woody materials) and
below ground biomass within the forest management unit during a specified time period
Note 1 to entry: “Biomass” and “forest management unit” are defined in ISO 13391-1:2025, 3.15 and 3.20.
3.3
land ownership
legal right to freely and exclusively use, control, transfer, or otherwise benefit from a forest
Note 1 to entry: Land ownership can vary and includes ownership by states, companies, communities, organizations
or individuals.
Note 2 to entry: “Forest” is defined in ISO 13391-1:2025, 3.19.
[12]
[SOURCE: FAO, modified — information has been reorganized to fit the structure of an International
Standard. Notes 1 and 2 to entry have been added.]
3.4
concession
system of awarding harvesting (3.6) rights to individuals, private companies or communities who assume
the risk and responsibility of forest resources exploitation or management
Note 1 to entry: “Forest” is defined in ISO 13391-1:2025, 3.19.
[13]
[SOURCE: FSC, modified — “and/” has been removed in two places and Note 1 to entry has been added.]
3.5
harvest,noun
raw material or other biomass from trees that is removed from the forest
Note 1 to entry: The quantity removed is expressed as a unit of mass or volume.
Note 2 to entry: “Forest” and ”biomass” are defined in ISO 13391-1:2025, 3.19 and 3.15.
3.6
harvesting
set of consecutive operations to convert standing trees to desired products for further processing at
manufacturing facilities
[SOURCE: ISO 8965:2022, 3.1.1, modified — preferred term "logging" and Note 1 to entry have been
removed.]
3.7
thinning
selective felling in immature stands to promote the growth or condition of the remaining trees
Note 1 to entry: The concept of "felling" is defined in ISO 8965:2022, 3.3.12.

Note 2 to entry: Forest biomass removed by thinning can be used for products.
Note 3 to entry: “Forest” and ”biomass” are defined in ISO 13391-1:2015, 3.19 and 3.15.
[SOURCE: ISO 6814: 2009, 2.2.19, modified — Notes 1 – 3 to entry have been added.]
3.8
forest inventory
description of the quantity and quality of trees and other biological and biophysical features of the forest
and the characteristics of the land on which the forest grows
Note 1 to entry: Data recorded within inventories can include wood volumes, growth rates, size distribution pattern,
species composition, stand conditions, soil carbon and location of stands.
Note 2 to entry: “Forest” is defined in ISO 13391-1:2025, 3.19.
3.9
anthropogenic process
process directly caused by human management actions
EXAMPLE Planting, removals of woody materials, thinning, harvesting.
3.10
non-anthropogenic process
process not directly caused by human management actions
EXAMPLE Pests, decay, windthrow, wildfire.
4 Methodology for calculating the forest carbon balance
4.1 General requirements
The requirements in ISO 13391-1:2025, Clause 4 and 5.1 shall be followed.
Calculation of the forest carbon balance shall include information on net changes over time of greenhouse
gas sources and greenhouse gas sinks in the following five forest carbon pools:
1) living biomass above ground;
2) living biomass below ground;
3) deadwood;
4) litter;
5) soil organic matter (SOM).
Emissions of nitrous oxide and methane, if any, shall be included in the calculation, expressed in CO e. This
includes emissions from drained organic soils, as well as nitrous oxide emissions from soils fertilized with
(nitrogen) fertilizers, and non-CO greenhouse gases emitted from controlled burning.
NOTE Other nitrous oxide and methane emissions (such as from fertilizer manufacture and other value chain
greenhouse gas emissions) are addressed in ISO 13391-1. It is only the emissions arising from interaction of the fertilizer
with the soil that are considered within the forest carbon balance, as they relate to changes in the soil carbon pools.
Information on carbon pool changes should be representative of the FMU. Information on carbon pool
changes can be derived from forest inventories, forest growth and yield projections, soil surveys, or remote
sensing monitoring. When sufficient information is not available for one or several carbon pools for the FMU,
secondary data together with documented assumptions may be used and reported. In this case, the data
quality requirements of ISO 13391-1:2025, 5.1.5 shall apply. When more than one FMU is defined by the
organization, the forest carbon balances of these may be aggregated.

4.2 System boundaries
The system boundary for the calculation shall be one or several FMUs, corresponding to the total wood
volume handled by the organization or area of study. All parts of each FMU shall be included.
The organization shall decide the scope of the FMU(s) following the requirements and guidelines given by
this document. See 4.3 for more information.
The calculation shall cover the difference between increase of carbon in standing stock and soil carbon
due to biological growth, and losses of carbon due to extraction through thinning and harvesting as well as
losses due to pests, wildfires, storms and decomposition, for example. Losses due to exceptional events, such
as from pests and diseases, uncontrollable wildfires, storms, droughts, floods, earthquakes and volcanic
eruptions, shall be included, but may be reported separately along with documentation of the event(s). The
calculated forest carbon balance shall cover a defined time period.
The carbon balance of an FMU shall include all changes in carbon pools within the defined time period,
covering both anthropogenic and non-anthropogenic processes.
Land use change shall be included in describing system boundaries; in particular, how greenhouse gas
sources and greenhouse gas sinks are accounted for in the case of deforestation and afforestation.
Greenhouse gas emissions from fossil fuels and industrial processes related to forestry operations are not
included in this document, they are covered in ISO 13391-1.
4.3 Characterization of the FMU(s) by the organization
The organization shall define the FMU(s) based on a set of characteristics of their choosing. Characteristics
that can be relevant for the forest carbon balance calculation include:
— boundaries (including land ownership);
— location and ecology;
— legal arrangements; and
— forest managem
...