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Forest degradation

Aware of potential difficulties, SBSTA in Decision 11/CP7 invited IPCC, inter alia, “to develop definitions for direct human-induced “degradation” (sic) of forests … and methodological options to inventory and report on emissions resulting from these activities….”

Box 3 lists different definitions of forest degradation; they are compared in Table 4.

Box 3: Definitions of Forest Degradation

FAO, 2000: a reduction of canopy cover or stocking within the forest.

Explanatory note:
For the purpose of having a harmonized set of forest and forest change definitions, that also is measurable with conventional techniques, forest degradation is assumed to be indicated by the reduction of canopy cover and/or stocking of the forest through logging, fire, windfelling or other events, provided that the canopy cover stays above 10% (cf. definition of forest). In a more general sense, forest degradation is the long-term reduction of the overall supply of benefits from forest, which includes wood, biodiversity and other products or service.

FAO 2001, 2006: Changes within the forest which negatively affect the structure or function of the stand or site, and thereby lower the capacity to supply products and/or services.

Explanatory note:
Takes different forms particularly in open forest formations deriving mainly from human activities such as overgrazing, overexploitation (for fuelwood or timber), repeated fires, or due to attacks by insects, diseases, plant parasites or other natural sources such as cyclones. In most cases, degradation does not show as a decrease in the area of woody vegetation but rather as a gradual reduction of biomass, changes in species composition and soil degradation. Unsustainable logging practices can contribute to degradation if the extraction of mature trees is not accompanied with their regeneration or if the use of heavy machinery causes soil compaction or loss of productive forest area.

FAO, 2003: the long-term reduction of the overall potential supply of benefits from the forest, which includes carbon, wood, biodiversity and other goods and services.

UNEP/CBD, 2001: A degraded forest is a secondary forest that has lost, through human activities, the structure, function, species composition or productivity normally associated with a natural forest type expected on that site. Hence, a degraded forest delivers a reduced supply of goods and services from the given site and maintains only limited biological diversity. Biological diversity of degraded forests includes many non-tree components, which may dominate in the under-canopy vegetation.

ITTO, 2002: Long-term reduction of the overall potential supply of benefits from the forest, including wood, biodiversity and other products or services.

ITTO 2005: a direct human-induced loss of forest values (particularly carbon), likely to be characterized by a reduction of tree crown cover. Routine management from which crown cover will recover within the normal cycle of forest management operations is not included.

IPCC 2003a: a direct human-induced loss of forest values (particularly carbon), likely to be characterized by a reduction of tree cover. Routine management from which crown cover will recover within the normal cycle of forest management operations is not included.

IPCC, 2003b: a direct human-induced activity that leads to a long-term reduction in forest carbon stocks.

IPCC, 2003c: the overuse or poor management of forests that leads to long-term reduced biomass density (carbon stocks).

IPCC, 2003d: a direct human-induced long-term loss (persisting for X years or more) of at least Y % of forest carbon stocks (and forest values) since time T and not qualifying as deforestation or an elected activity under Article 3.4 of the Kyoto Protocol.

Table 4: Parameters of forest degradation


FAO 2000

FAO 2001, 2006


CBD 2001

ITTO15 2002

ITTO 2005

IPCC 2003d

IPCC 2003a

IPCC 2003b


Forest type


secondary forest


Change within the forest




crown cover



species composition




Reduction of capacity to provide:








carbon stocks


> y %


other functions


Time scale











specified duration


X years




human- induced




Reference state


natural forest




carbon stock at initial date






forest management under Art.3.4


A comparison of attributes addressed (Table 4) illustrates considerable amplitude. Nevertheless, most globally established definitions allude to the basic notion of a human-induced, long-term, negative change in the forest’s structure, function and capacity to provide goods and services in general. Degradation has thus the clearly negative connotation of a long-term impairment of a forest.

Such a long-term impairment, however, can realistically only be assessed ex post, after a given observation period. This violates one criterion for a set of useful definitions listed above, in that degradation in this sense is not measurable during a short assessment period.

Moreover, a useful definition should also serve the purpose, namely a strong link to greenhouse gas emissions resulting from an activity. Again, the traditional notion of forest degradation does not meet this criterion: Certain forms of degradation, such as very slowly reversible soil compaction, impacts of acid rain or felling damages to residual trees, may not result in carbon emissions over long time spans. Vice versa, reductions in crown cover or growing stock that do cause short-term carbon emissions, i.e. in sustainable selective harvesting, thinning or shelter-wood cuttings, do not degrade a forest. On the contrary, these measures may improve it.

Overall, forest “degradation” appears as an unfortunate term for the purpose of addressing emissions from “forests remaining forests” (IPCC, 2003, 2007). Significantly, the IPCC task force established under 11/CP7 (s. above) could not agree on any definition of forest degradation for this purpose. The Second Expert Meeting on Harmonizing Forest-related Definitions (FAO, 2003) also recommended using another term than “degradation”, such as “stock reduction” in the context of carbon monitoring in forests remaining forests.

Supporting terms

At the management unit, landscape or national level, forest degradation may take the form of forest fragmentation, with or without reaching the threshold for deforestation within a spatial assessment unit. Forest fragmentation is particularly pronounced in the tropics, where affected areas may exceed the area of deforestation. A drastic increase in the length of exposed forest edges induces tree mortality and disturbances and decreases biomass. Carbon emissions arising from these edges are clearly human induced, would not have happened without fragmentation, and are not negligible (Laurance, 2005).

Other directly human –induced processes, such as forest rehabilitation, forest restoration and forest improvement may lead to possible carbon stock accretion within the forests. .

Moreover, there is evidence for indirectly human-induced carbon stock increases through enhanced biomass growth in many tropical forests as consequences of higher temperatures, nitrogen deposition, altered disturbance- and competition regimes, and raised CO2 levels in the ambient air. This sequestration with an estimated magnitude of 0.05 to roughly 0.5 t C/ha yr-1 (Laurance 2005; Baker et al., 2005), is not negligible for net emissions.

Finally, growing stocks and carbon stocks may accrue within many logged-over or secondary tropical forests as a result of the natural biomass growth through ageing.

Issues and choices

Parties may have to decide

• which processes leading to carbon stock reductions and greenhouse gas emissions in forests, without qualifying as deforestation, should be covered by an agreement;

• whether to continue using the term forest degradation

• how to address forest fragmentation;

• if there should be quantitative thresholds and spatial assessment units;

• whether and how to address direct or indirect human impact;

• whether and how to address and separate human-induced and natural carbon stock changes.

15 in FAO 2003

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