In recent years, the term "carbon-emitting forests" has been reacurring a lot. This term refers to forests that have gone from being carbon sinks to being sources of CO2 emissions. In other words, they release more carbon into the atmosphere than they can absorb.
We have written this article to help you better understand the concept of carbon-emitting forests. Where are they in the world? Do they really contribute to global warming? Is this phenomenon reversible? This article reviews the causes, problems and solutions that can be brought to forests that become carbon emitters.
In summary:
- Forests are natural carbon sinks that store CO2 absorbed through photosynthesis, emphasizing the importance of maintaining healthy forests over the long term in order to reduce the impact of CO2 in the atmosphere.
- Increased tree mortality in weakened forests, due to factors linked to human intervention and global warming, is disrupting the flow of carbon into and out of forests. As a result, forest ecosystems sequester less and less carbon, and can become net sources of carbon. Today, some forests in tropical and subtropical regions are already carbon emitters.
- Although the size of the world's forests has increased over the last 20 years, almost half of these new forests are plantations, often monocultures. They are less beneficial for biodiversity and long-term carbon storage than natural forests, underlining the importance of forest integrity. It is crucial to rebuild dense native ecosystem forests on a large scale in order to counteract the phenomenon of forest carbon emissions.
How do forests capture carbon?
To interpret CO2 fluxes into and out of forests, it is first important to understand how forests function.
A carbon sink is a natural system that sequesters and stores carbon from the atmosphere. It can be a forest, but also oceans, grasslands, etc.
Today, forests cover 31% of the earth's surface. They are the second largest carbon sink in the world, after the oceans, which absorb 40% of all the CO2 produced on Earth. By absorbing carbon from CO2 molecules in the air through photosynthesis, plants and trees store this CO2 in the form of wood and organic matter, while releasing twice as much oxygen into the atmosphere. It should be noted that the older the forest ecosystem, the greater its capacity to absorb carbon and the more carbon it has stored. It is therefore essential to maintain healthy forests over the long term.
What factors can cause forests to emit carbon?
Although they absorb more CO2 than they release, forests have always naturally emitted carbon.
At night, for example, since photosynthesis is no longer possible due to lack of light, plants breathe like any other living thing, inhaling oxygen and exhaling carbon dioxide. The decomposition of dead wood also releases CO2, which is stored in the plant's organic matter.
Therefore, we quickly understand that, while a healthy forest will contribute to reduce carbon in the atmosphere, a weakened forest will, on the contrary, contribute to global warming.
And these weakened forests are more and more numerous. The increase in tree mortality is a reality. It is due to factors such as global warming as a whole, fires, droughts, diseases, parasites, ecosystem degradation. It is also explained by deforestation, on the one hand, and the fragility of young trees planted in monoculture on the other hand. Deforestation alone releases nearly 1.8 billion tons of CO2 into the atmosphere each year.
This increase in mortality disrupts the flow of carbon into and out of forests. Forest ecosystems are sequestering less and less carbon, and consequently releasing more and more. As a result, some forests can now become net sources of carbon, accelerating climate change.
Which forests emit carbon today?
The map below shows global forestry greenhouse gas flows between 2001 and 2021. It shows that some forests are already emitting carbon. In violet, in Central and Latin America, Africa and South-East Asia. In other words, they are concentrated in the tropical and subtropical biome, in countries such as Brazil, Congo, Malaysia, Indonesia and elsewhere. In these areas, destructive human activities are causing the disappearance of the high natural carbon sequestration capacity of these tropical forests. Other carbon-emitting forests exist in parts of Russia, Canada, Central America and Madagascar.
How to limit forest carbon emissions?
In order to rebalance carbon flows in forests, priority must be given to protecting existing forest ecosystems. Older forests have the capacity to sequester greater quantities of carbon from the atmosphere, much more rapidly than younger forests.
Large-scale reforestation is necessary to reverse deforestation and forest degradation. But it is even more crucial to recreate the degraded native ecosystem, i.e., a high integrity forest, as closely as possible.
Forest integrity and the need for high biodiversity forests
The forest is of interest to many economic and social actors, looking for carbon offsets. According to the World Resources Institute, between 2000 and 2020, the size of the world's forests increased by 1.3 million square kilometers, an area larger than Peru, led by China and India. But, as Elizabeth Pennisi explains in an article in Science, about 45% of these new forests are plantations, in other words, dense aggregations dominated by a single species that are less beneficial for biodiversity and long-term carbon storage than natural forests. Indeed, it is not enough to plant trees to recreate a forest.
In a 2019 study published in the journal Nature, Lewis and colleagues estimated that if the world's 350 million hectares of degraded forests were allowed to regenerate naturally, these lands would sequester around 42 billion metric tons of carbon by 2100. In contrast, if the land were filled with commercial single-tree plantations, carbon storage would drop to around 1 billion metric tons.
What is at stake here is forest integrity, which is defined in terms of how much the structure, composition and function of a forest have been altered by humans. High integrity forests are more effective at slowing the rate of climate change by sequestering and storing carbon.
Declining biodiversity levels attack forest integrity, resulting in other problems linked to soil fertility and stability, water abundance, productivity, local population, and finally carbon storage. As it does not promote local biodiversity, reforestation by planting a single species is an impediment to a carbon-sequestering forest. This article explains in more detail the advantages of ecosystem restoration over single-species reforestation.
There is an urgent need to act and reverse the phenomenon of carbon-emitting forests, by rebuilding native ecosystems in tropical areas, enabling us to sequester as much carbon as possible and accelerate the fight against global warming as quickly as possible.
This type of reconstitution of biodiverse ecosystems is the method favored by various actors, including MORFO. Discover MORFO by clicking here.
