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2. Processes causing carbon stock changes and greenhouse gas emissions from forests

Figure 1 illustrates forest change dynamics linked to greenhouse gas emissions and/or removals.

Figure1: Forest change dynamics

Source: FAO, 20063

More specifically, carbon stock changes in, or greenhouse gas emissions and removals by, forests may occur or be affected in the following ways:

♦ Natural processes in the forest ecosystem (growth, ageing, mortality, forest fires or other disturbances);

♦ Indirect human influences, such as climate change, CO2- fertilization, industrial emissions and their interactions;

♦ Sustainable management practices, e.g. regeneration, tending and harvesting in forests;

♦ Conversions of forests to other forest types;

♦ Unsustainable use, such as over-harvesting;

♦ Conversion of forests to cropland, grassland, wetlands, settlements, or other lands as used by the Intergovernmental Panel on Climate Change (IPCC, 2003a).

A transition matrix (Table 1) illustrates the spectrum and scale of transitions that occurred in the pan-tropics between 1990-2000. It compares area changes for the categories used between 1990 (last two columns) with the corresponding totals in 2000 (last two rows)4. Cells of the matrix reflect specific transitions5. As per the FAO definition of forest, agro-forests and urban forests6 are classified under the category “other land cover” in this matrix. If certain urban- and agro-forests are also considered as forests, e.g. in the Marrakech Accords (MA) to the Kyoto Protocol, transition processes will multiply and monitoring could become even more demanding.

Table1: Area transition matrix for the period 1900-2000 at pan-tropical level in Mha (FAO, 2001)

The table illustrates area changes only. Changes within forests, e.g. growing stock attritions or accretions, may also affect net greenhouse gas emissions or removals. In their submissions to UNFCCC, some countries suggest including even devegetation as an activity to be covered by an eventual agreement. Parties will have to decide to which of these land-cover categories, area transitions and other change processes an eventual agreement will apply, and if gross or net carbon stock changes, emissions and/or removals should be considered.

The following analyzes definitional options for the terms forest, deforestation and forest degradation in order to facilitate informed choices. For this analysis, definitions may be compared by referring to their exact wording (Boxes 1, 2, 3) or schematically, via comparative matrices, where shaded cells indicate that the definition covers the item, a blank cell that it does not. Any quantitative parameters given are provided in the cells (Tables 2, 3, 4).

In addition, the paper highlights some terms employed by the IPCC in its guidelines for transforming forest change processes into emissions and removals of greenhouse gases (IPCC, 2007).


Definitions for the term forest have been discussed at length during the First and Second Expert Consultations on Harmonizing Forest–related Definitions by Various Stakeholders, which were organized by FAO and IPCC jointly with other partners in Rome in 2002 (FAO, 2003). Three globally established forest definitions emerged. They are provided in Box 1, and compared schematically in Table 2.

Box 1: Definitions of Forest

UNFCCC, 2001: “Forest is a minimum area of land of 0.05-1.0 hectares with tree crown cover (or equivalent stocking level) of more than 10-30 per cent with trees having the potential to reach a minimum height of 2-5 metres at maturity in situ. A forest may consist either of closed forest formations, where trees of various storeys and undergrowth cover a high proportion of the ground, or open forest. Young natural stands and all plantations which have yet to reach a crown density of 10-30 per cent or tree height of 2-5 metres are included under forest, as are areas normally forming part of the forest area which are temporarily unstocked as a result of human intervention such as harvesting or natural causes but which are expected to revert to forest.

UNEP/CBD, 2001: Forest is a land area of more than 0.5 ha, with a tree canopy cover of more than 10 percent, which is not primarily under agriculture or other specific non-forest land use. In the case of young forest or regions where tree growth is climatically suppressed, the trees should be capable of reaching a height of 5 m in situ, and of meeting the canopy cover requirement.

FAO, 2006: Land spanning more than 0.5 hectares with trees higher than 5 metres and a canopy cover of more than 10 percent, or trees able to reach these thresholds in situ. It does not include land that is predominantly under agriculture or urban use.

Explanatory note:
Forest is determined both by the presence of trees and the absence of other predominant land uses. The trees should be able to reach a minimum height of 5 m in situ. Areas under reforestation that have not yet reached but are expected to reach a canopy cover of 10 percent and tree height of 5 m are included, as are temporarily unstocked areas, resulting from human intervention or natural causes, which are expected to regenerate.

It includes areas with bamboo and palms provided that height and canopy cover criteria are met.

It includes forest roads, firebreaks and other small open areas; forest in national parks, nature reserves and other protected areas, such as those of specific scientific, historical, cultural or spiritual interest.

It includes windbreaks, shelterbelts and corridors of trees with an area of more than 0.5 ha and width of more than 20 m.

It includes plantations primarily used for forestry and protection purposes, such as rubberwood plantations and cork oak stands.

It excludes tree stands in agricultural production systems, for example fruit plantations and agroforestry systems. The term also excludes trees in urban parks and gardens.

Table 27: Attributes and thresholds of ”forest”





    Young stands


    Temporarily unstocked areas


    Forestry land use


    Min. area (ha)




    Min. height (m)




    Crown cover (%)




    Strip width (m)



Major differences between these globally applied forest definitions are

Quantitative thresholds

Under MA, only industrial (Annex I countries-AI) are obliged to define forests, by selecting parameter values within the ranges allowed and indicated in the matrix above. These values should be “consistent with the information that has historically been reported to the FAO or other international bodies”.

Historically, a full set of parameter values has been reported to FAO only for the Forest Resources Assessment (FRA) 2000 and FRA 2005. Most countries reported data which they themselves had adjusted to FAO standards; some reported based on unadjusted national parameters which, for the year 2000, FAO then adjusted to the globally agreed parameter values with the consent of countries. AI countries should therefore choose parameter values within the allowable ranges, consistent with their “historical” reporting to FAO in 2000, 2005 or both.

Non-Annex I countries (NAI) must currently only define forest if they intend to participate in the CDM, selecting from the same set of parameters values as AI countries (Neef et al., 2006).

Under these new negotiations, many more NAI countries might have to define forests. Their existing national forest definitions reflect specific biomes, biophysical and social conditions; they are anchored in history, law and forestry practice. Applying such a national definition to the current process might appear simple, consistent, and match existing national datasets. However, most countries’ definitions do not quantify at least some parameters. Unfortunately, national definitions cannot therefore be simply transposed to the current process11. Therefore, all participating developing countries might have to define a complete set of parameters and values which could be common, biome- or country-specific, or may even vary within a country.

3 “reforestation” and “other lands” as defined by FAO, 2001.
4 Thus, net loss of closed forests between 1990 to 2000 was 1205.1-1135.2, or 70 Mha; Complete conversion of closed forests to another land cover occurred on 43 Mha.
5 For example, between 1990 and 2000 1.2 Mha of closed forests underwent a transition to open forests
6 see Appendix 1.
7 for interpretation see text above.
8 Marrakech Accord.
9 Convention on Biological Diversity.
10 Global Forest Resources Assessment of FAO.
11 Of the 122 NAI countries which reported to FAO, 44 countries employ merely functional definitions; forty countries used at least one quantified parameter to define forest; twenty-one countries applied the FAO definition with 3 parameters; seventeen countries did not provide national definitions.

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