Degradation refers to a direct decline in forest carbon stocks that do not result in deforestation, which is defined as when the tree cover in an area is reduced below 10 to 30 percent and involves the conversion of land into other uses, such as for agriculture. Human-driven causes include timber harvesting, wood fuel collection, and fires. When the levels of wood harvesting for heating or cooking exceed regrowth of the forest, it is unsustainable because it leads to an overall reduction in woody biomass, thereby resulting in carbon emissions.
Wildfires can also contribute to degradation, because the damage they cause does not necessarily result in a change in the use of land, and so it cannot be classified as deforestation. While deforestation is easy to quantify through the use of remote sensing satellites, degradation is much more difficult, mainly because it involves subtle changes in the forest canopy, which require higher-resolution imagery to detect.
Using previous studies and databases, Pearson and his team estimated carbon dioxide emissions from timber harvesting, wood fuel harvests, and wildfires during 2005 to 2010 from tropical forests covering an area of 2.2 billion hectares (about 5.4 billion acres) and spanning 74 countries.
Their estimates included both uncollected above-ground biomass and underground root biomass. In order to make a comparison with their estimate of degradation, they also calculated emissions from deforestation in those same countries, which included dead wood, litter, and soil carbon (peat and non-peat) in addition to both above-ground and below-ground biomass. As a result, they account for all five carbon pools in forests as outlined by the Intergovernmental Panel for Climate Change (IPCC).
Most deforestation estimates only consider above-ground biomass, but there is at least 20 percent as much biomass under the ground as above it, the researchers write. In addition, deforestation of tropical peat swamps has been a major source of emissions in Indonesia and Malaysia.
They found that emissions from forest degradation amounted to 2.1 billion tons of carbon dioxide annually, of which half were from timber harvesting, a third from wood fuel harvesting, and a fifth from forest fires.
The top five countries in order of the highest emissions from forest degradation are Indonesia, Brazil, India, Malaysia, and the Philippines. But the sources of emissions differed according to region: While selective logging for timber was the main driver in South America (Brazil, Mexico) and Southeast Asia (Indonesia, Malaysia), wood fuel harvesting was overwhelmingly confined to South Asia (India, Pakistan) and East Africa (Ethiopia, Kenya), while fires were prominent in Central Africa (Democratic Republic of Congo and Angola) and South America (Brazil and Bolivia).
Bubble charts illustrate total forest degradation and the breakdown by region. The size of the bubbles indicates the relative magnitude of annual emissions (Pearson, Brown, Murray, & Sidman 2017).
Comparing the emissions from degradation as a percentage of deforestation reveals valuable information. Some countries that typically have low emissions from deforestation, such as those in South Asia and East Africa, exhibit high emissions from forest degradation, primarily due to their high levels of wood fuel harvesting, where it is often used for cooking. Strikingly, in 28 countries — a third of those studied — emissions from forest degradation exceeded those from deforestation.
A. Total forest degradation emissions for each region, B. Forest degradation emissions as a percent of total forest emissions for each region (Pearson, Brown, Murray, & Sidman 2017).
The World Bank established a Carbon Fund that provides funding for the UN’s program for reducing emissions from deforestation and forest degradation, known as REDD+, in which developing countries are rewarded financially for lowering emissions from human activities that drive emissions from the destruction of forests.
The REDD+ framework (Indicator 3.3) states that if a country’s emissions from forest degradation are over 10 percent, then they should be included in that country’s count of total forest-related emissions. Under this definition, 85 percent of the 74 countries studied qualify as needing to account for forest degradation in their forest-related emissions totals.
But forest degradation comprises a range of activities, and so far there is no method to account for each separately, Pearson explains. He gives the example of Peru, where total degradation emissions are 11 percent and so exceed the minimum required to be included. Of this, eight percent came from timber harvesting, and the remaining three percent from both fire and wood fuel harvesting. In contrast, Columbia’s total degradation emissions were nine percent, which means it wouldn’t need to account for forest degradation, almost all of which came from timber harvesting. On the other hand, Peru would need to account for fire and wood fuel harvesting even though they represent just three percent of emissions.
Climate change mitigation strategies must take into consideration that the livelihoods of much of the world’s impoverished communities is directly tied to forests, and we all rely on resources derived from forests, Pearson added. “We cannot put a fence around forests and instead must plan for sustainable use of forests which benefits both the global climate and development,” he said.
Demonstrating the significance of emissions from forest degradation, this study can be used as a starting point to guide mitigation efforts. Pearson would like to see a greater focus on forest degradation in post-2020 climate agreements. He suggests policy makers should include the individual sources of forest degradation rather than the total amount and to consider forest degradation when planning for land uses under development funding.
“The results of this study clearly demonstrate the importance of accounting greenhouse gases from forest degradation by human activities,” Pearson and his co-authors write. “The scale of emissions presented indicates that the exclusion of forest degradation from national and international [greenhouse gas] accounting is distorting.”
Small forest fire near Nawnghkio, Shan state, Myanmar. Photo by Yoav David / Wikimedia Commons.
- Pearson, R.H.T., Brown, S., Murray, L., Sidman, G. (2017). Greenhouse gas emissions from tropical forest degradation: an underestimated source. Carbon Balance and Management, 12(3). doi:10.1186/s13021-017-0072-2