A Review of Methods to Measure and Monitor Historical Forest Degradation
Martin Herold1, Yasumasa Hirata2, Patrick Van Laake3, Gregory Asner4, Victoria Heymell5, Rosa María Román-Cuesta6
1. Wageningen University. Building 101. Droevendaalsesteeg 3, 6708 PB Wageningen. The Netherlands. Tel. +31 317 481276; Fax: +31 317 419000.
2. Shikoku Research Center, FFPRI. Forestry and Forest Products Research Institute 2-915 Asakuranishi, Kochi, Kochi, 780-8077. Japan. Tel. +81-88-844-1121; begin_of_the_skype_highlightingFax. +81-88-844-1130.
3. UN REDD Vietnam Programme. 172 Ngoc Khanh, #805. Ba Dinh, Ha Noi Vietnam.
4. Carnegie Institution. 260 Panama Street. Stanford, CA 94305. USA. Tel.+1-462-1047 200
5. FAO. Viale delle Terme di Caracalla 15. 00100 Rome, Italy. Tel. +39 06 570 54451 Fax: +39 06 570 55137,
6. UN-REDD Programme. FAO MRV team. Viale delle Terme di Caracalla 15. 00100 Rome. Tel. +39 06 570 52044;Fax: +39 06 570 55137.
Abstract
There are currently more than fifty definitions of forest degradation but none of them is accepted in the international negotiations as a univocal, operational and multipurpose definition (i.e. for the use in national-level reporting. While forest degradation is a broad topic, the review presented here is addressing the degradation issue from a climate change and forest carbon stock change perspective; in particular considering the current discussions on REDD+. The IPCC 4th Assessment Report sustained that the world’s degraded forests reached ca. 100 million of hectares per year. This represents almost 10 times more global area affected by degradation than by deforestation (i.e. ca. 100 million degraded ha.yr-1 versus ca. 13 million deforested ha.yr-1 during 2000-2005). For this reason, forest degradation rates must necessarily be reported together with deforestation rates to guarantee integrated and coherent climate mitigation actions. The REDD+ mechanism addresses the evident role of reducing deforestation and forest degradation as global climate mitigation tools, but it also considers the role of conservation, sustainable management of forests and the enhancement of forest carbon stocks. While the final rules for REDD+ are still under development, non-Annex I countries will have to evaluate their historic rates of deforestation and degradation to estimate their Reference Emission Levels. There is not one method to monitor forest degradation that fits all circumstances and the methodological choice depends on a number of factors including the type of degradation, available data, capacities and resources and the potentials and limitations of various measurement and monitoring approaches. Current degradation rates can be measured through field based data (i.e. Multi-date national forest inventories and permanent sample plot data, commercial forestry datasets, proxy data from domestic markets, etc) and/or remote sensing data (i.e. direct mapping of canopy and forest structural changes or indirect mapping through modelling approaches), with the combination of them both providing the strongest alternative. Historic degradation assessments for non-Annex I countries frequently lack consistent historic field data, forcing countries to rely strongly on remote sensing approaches mixed with current field assessments of carbon stock changes. The current paper describes methodologies for assessing current and historical rates of forest degradation to support developing countries interested in implementing the REDD+ mechanism.
1. Introduction
1.1 Definitions of forest degradation in relation to forest carbon stocks
There are currently more than fifty definitions of forest degradation (Lund 2009, Simula 2009) but none of them is accepted in the international negotiations[1] as a univocal, operational, multipurpose definition.
Forest degradation is generically defined as the reduced capacity of a forest to provide goods and services (FAO 2002). However, this definition is too broad to be operational. In the context of climate change, the IPCC (2003) developed a definition of forest degradation that focuses on human-induced changes in the carbon cycle in the long run:
“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[2]”.
In order to operationalise this definition, i.e. for the use in national-level reporting, it would be necessary to specify an area threshold, as well as time and carbon loss thresholds.
Forest degradation, from the point of view of climate change policy and the IPCC national estimation and reporting guidelines, refers to a loss of carbon stock within forests that remain forests (IPCC 2003). More specifically, degradation represents a human-induced negative impact on carbon stocks, with measured forest variables (i.e. canopy cover) remaining above the threshold for the definition of a forest. Moreover, to be distinguished from (sustainable) forestry activities, the decrease should be persistent. The IPCC 2003 definition faces several challenges if used for monitoring purposes: i) it lacks a clear definition of a temporal threshold considered as “long term”; ii) it lacks a suggestion or identification of minimum thresholds of carbon stock change associated with degradation to distinguish it from natural forest disturbances; and iii) it is challenged by the identification and isolation of human-induced degradation from other degradation factors, which may well be interlinked. The persistence could be evaluated by monitoring carbon stock changes either over time (i.e. a net decrease during a given period, e.g. 20 years) or along space (e.g. a net decrease over a large area where all the successional stages of a managed forest are present) (GOFC-GOLD 2009).
Considering that, at national level, sustainable forest management may lead to national gross losses of carbon stocks (e.g. through harvesting) which are lower than (or equal to) national gross gains (in particular through forest growth), consequently a net decrease of forest carbon stocks at national level during a reporting period would be due to forest degradation within the country. Conversely, a net increase of forest carbon stocks at national level would correspond to forest enhancement. Therefore, it is also possible that no specific definition is needed, and that any net emission will be reported simply as a net decrease of carbon stock in the category “Forest land remaining forest land” (GOFC-GOLD 2009) – a perspective that is also shared by an expert group convened by the UNFCCC SBSTA[3] (UNFCCC 2008).
For the purpose of this paper, which is aims to provide a review of different assessment methods, the above mentioned assumption will be used. However, under other circumstances, a specific definition may be required. In this case, Simula (2009) summarizes the elements that an operational definition of forest degradation should provide: 1) identification of forest goods and services, 2) a spatial context of assessment, 3) a reference point, 4) coverage of both the process and state (degradation/degraded forests), 5) relevant threshold values, 6) specification of reasons for degradation (human induced/natural), 7) an agreed set of variables, and 8) indicators to measure the change of a forest. Additional elements could be added or singled out, depending on the particular interests related to the purpose of the definition.
While forest degradation is broad topic, the review presented here is addressing the degradation issue from a climate change, carbon and REDD+ perspective. The authors have collated and critically reviewed case studies, articles, guidelines, manuals and other documents describing methodologies for assessing current and historical rates of forest degradation to support developing countries interested in implementing the REDD+ mechanism.
1.2 Main causes of forest degradation affecting changes in forest carbon stocks
Forest degradation can have any number of causes, dependent on resource condition, environmental factors, socio-economic and demographic pressure and “incidents” – e.g. pests, disease, fire, natural disasters. The understanding and separation of different degradation processes is important for the definition of suitable methods for measuring and monitoring. Various types of degradation will have different effects on the forest (carbon) and result in different types of indicators that can be used for monitoring degradation using in situ and remote methods (i.e. trees being removed, canopy damaged etc.).
For the purpose of this review the emphasis is on those forms of forest degradation that are caused by direct human impacts on the forests (i.e wood removal) or indirect human impacts (i.e. long term forest management that favours fire presence and impacts) on the forest. The reduction of forest degradation by human influenced causes is eligible under the REDD+ mechanism (4/CP.15[4]; Draft Decision/CP.16[5]).
1.2.1. Extraction of forest products for subsistence
Privately or communally managed forests are often subject to extraction of forest products for immediate use by local households. Extractions are for such uses as fuelwood for cooking, collection of fruits, roots and other edible tree organs, collection of fodder for livestock, and harvesting of timber and thatch for construction. In more established and stable cultures and communities such extractions can be sustainable (e.g. tribal groups in Papua New Guinea and elsewhere, community managed forests in Nepal and India, the ejido system in Mexico), but in many other cases the increasing population of the last few decades has put so much pressure on the forest that the extraction is no longer sustainable.
The following sub-sections describe activities causing forest degradation and reductions in carbon stocks in forests that are not under other land uses; reflecting the requirements of the definition used for FAO’s global forest resources assessments. It should be noted that expansion of agriculture into forests (i.e. forest grazing, shifting cultivation, agroforestry) also cause losses in forest carbon stocks and should also be considered and monitored, and depending on the forest definition reported as either emissions on forest or non-forest land.
1.2.2. Extraction of forest products for local markets
Most developing countries have seen rapid urbanization in recent decades and this has created a market for forest-based products which, in some cases, has resulted in forest degradation. Particularly the production of charcoal has led to forest degradation, in dry forest ecosystems such as the miombo of southern Africa. Other products that are harvested include timber, bamboo and rattan for construction and furniture making and minor products such as raffia, vines and leaves for making household utensils and rope.
Serving local and national markets for forest-based products has been facilitated by the expansion of road infrastructure in most developing countries. Better infrastructure has decreased the cost and expanded the options of transportation of forest products. Since the cost of forest products – e.g. charcoal – is often far lower than “urban” alternatives – e.g. kerosene – the cost of transportation is easily recouped.
1.2.3. Industrial extraction of forest products
International scrutiny of harvesting operations in developing countries has led to the development of alternative harvesting schemes to replace the total removal of commercially interesting tree species of specimens above a minimal girth and with little or no consideration for the remaining stock during harvesting. While the management is fostering regeneration of the forest – this is an explicit requirement under all international certification schemes for selective harvesting – the forest will have noticeably lower carbon stocks for many years.
1.2.4. Natural disturbances such as wildfire
All forms of excessive forest product extraction leading to degradation, as described in this section, impact the resilience of the forest to withstand external impacts, such as fire, pests and drought. These impacts can be positive, although most are negative. Most impacts are driven by changes in the local hydrology: through extraction of trees or tree products more solar radiation is transferred to the soil which leads to drying of the soil and ultimately stress for the trees. For forests out of human influence, natural fires and degradation due to insect outbreaks are not reported under the Convention (i.e. remote Siberian boreal forests ignited by lightning). However, very few developing countries have non-human influenced forest, so fires as well as insect outbreaks and any other forest disturbances, must be reported and will reduce a country’s REDD+ emission gains.
Different degradation processes are usually active within the same country. Some may affect large areas, some not, and it is common that they are not equally distributed among the country’s territory. Thus, forest degradation activities are often focused in specific areas and this should be considered in national measurement and monitoring efforts.
1.3 Forest degradation as key source category in the context of REDD+
Disturbances that lead to degradation such as forest fires, pests (insects and diseases) and climatic events including drought, wind, snow, ice, and floods have been reported to roughly affect 100 million of hectares globally per year (FAO 2006a, in the IPCC 4th Assessment Report (Nabuurs et al. 2007)). Globally, this value represents almost 10 times more area affected by forest degradation than by deforestation (i.e. 12.9 million ha.yr-1 (2000-2005), FAO (2006b); MEA (2005), indicating the scale and importance of global forest disturbances that lead to degradation. While these values are a compilation of areas affected by forest disturbances around the world, tropical regions are well known for large scale disturbances that lead to forest degradation: fire activity has been repeatedly reported to affect the tropic and subtropical region more than other latitudes (Dwyer et al. 1999, Giglio et al. 2006) and severe storms and wind blows are also well known large scale degradation factors in tropical South America (Negrón-Juárez et al. 2010). For this reason, in the context of REDD+, forest degradation rates must necessarily be reported together with deforestation rates to guarantee integrated and coherent climate mitigation actions.
Forest degradation often has different driving forces than deforestation. The emission levels of degradation are lower than for deforestation (per unit area); but cumulative and secondary effects result in significant carbon emission and degradation is often a precursor to deforestation. Addressing deforestation does not automatically reduce rates of degradation. Failing to include degradation in a REDD+ agreement could leave considerable amounts of forest-based emissions unaccounted for (Murdiyarso et al. 2009). In case reducing deforestation measures are taken, monitoring forest degradation is important to avoid displacement of emissions from reduced deforestation. The evident role of reducing deforestation and forest degradation as global mitigation tools led to the petition by the Coalition for Rainforest Nations in Montreal 2005, at COP11, to reinforce Article 2 of the Kyoto Protocol regarding the protection and enhancement of sinks and reservoirs of greenhouse gases not controlled by the Montreal Protocol.