Protecting existing forests and reforesting suitable areas could bind around 226 billion tons of carbon and thus contribute to climate protection. This is the conclusion reached by a research group of around 200 people led by Lidong Mo from ETH Zurich in the specialist journal Nature.
As long as forests remain intact, they can absorb carbon dioxide from the air and thus offset greenhouse gas emissions. However, half of the Earth’s forested area has already been lost due to human activities, such as deforestation for settlements or pastures.
Using satellite data and on-site measurements of the biomass of trees, roots, dead wood and soil, Mo’s team first determined the previous loss of carbon due to deforestation: The scientists estimate that forests today store 328 gigatons less carbon than without it the influence of humans would be the case.
The effect would only become apparent in 100 years at the earliest
But how much of it can be restored? After all, people live in some of these deforested regions today. Significantly more area is needed to grow food crops and animal feed or to graze animals. However, there are also large areas largely without settlements or agriculture, emphasize the authors of the study. Restoring forests on such “low human footprint” land alone could remove 226 billion tons of carbon from the atmosphere. This corresponds to 829 billion tonnes of CO₂, around 20 times the global annual emissions of the greenhouse gas.
Around 60 percent of this potential could be realized by better protecting existing forests that are currently in poor condition, the researchers say. Primeval forests store a particularly large amount of carbon, for example because they have a particularly high level of biodiversity. If more forests were to approach this condition again, they could store significantly more CO₂ than they currently do and thus have a greater effect on climate protection. The remaining 40 percent of the potential could be achieved by reforesting suitable but previously underused deforested areas. This is not about “mass tree plantations,” emphasizes ETH Professor Thomas Crowther in a statement. Rather, local communities and farmers need to be supported in order to increase the species richness in forests. “Only then will we get long-term carbon storage as a byproduct.”
At the same time, restoring forests should not be a substitute for reducing fossil CO₂ emissions, the researchers emphasize. If emissions continue to rise, prolonged droughts, fires and extreme temperatures could threaten the forests themselves and reduce their ability to absorb carbon.
“Reforestation of fallow, forestable land is ecologically absolutely desirable,” says Christian Körner, emeritus professor of botany at the University of Basel, who was not involved in the current work. “The effect as a carbon store is very delayed.” The magnitudes mentioned in the study would probably only be achievable in 100 to 200 years, “if we started immediately everywhere at the same time,” said Körner. Preventing the deforestation of old forests, however, “has an immediate effect”.
With material from the Science Media Center