Secondary forests play an important part in carbon capture because they tend to absorb a larger amount of carbon than they lose to the atmosphere. However, the size and average age of these often abandoned areas where vegetation grows back were unknown until now. In a study recently published in the journal Scientific Data, a group led by two researchers at Brazil’s National Institute for Space Research (INPE) quantified these variables and found that the estimated carbon uptake by secondary forests throughout Brazil offset 12% of the carbon emissions due to deforestation in the Brazilian Amazon alone in a 33-year period.
The study was supported by FAPESP via two projects. The first project began in 2017 and is led by Luciana Vanni Gatti. The second began in 2019 and is led by Luiz Eduardo Oliveira e Cruz de Aragão.
“The capacity of secondary forests to absorb carbon is known from studies that involve monitoring of areas in the field. Their average net carbon uptake rate in Neotropical regions is 11 times that of old-growth forests. However, the long-term dynamics of secondary forests in Brazil and worldwide is poorly understood,” said Aragão, one of the authors of the study, which was conducted at INPE as part of Celso H. L Silva Júnior’s Ph.D. research.
This knowledge is fundamental to enable Brazil to achieve its Nationally Determined Contribution targets under the 2015 Paris Agreement. These include the restoration and reforestation of 12 million hectares of forest by 2030, he noted.
Age and size of secondary forests in each biome
The study calculated the increment in secondary forests that previously had anthropic cover (plantation, pasture, urban infrastructure, or mining) and their age, biome by biome. According to Aragão, secondary forest growth is not linear and correlates with age, so that it is important to establish the age of a forest in order to estimate its carbon uptake.
The data showed that a total of 262,791 square kilometers (km²) of secondary forests were recovered in Brazil between 1986 and 2018. This corresponds to 59% of the old-growth forest area cleared in the Brazilian Amazon between 1988 and 2019.
“The restored forests were located all over Brazil with the smallest proportion in the Pantanal [wetlands in the Center-West], accounting for 0.43% [1,120 km²] of the total mapped area. The largest proportion was in the Amazon, with 56.61% [148,764 km²]. The Caatinga [the semi-arid biome in the Northeast] accounted for 2.32% [6,106 km²] of the total area and had the youngest secondary forests—over 50% were between one and six years old,” Aragão said.
The Atlantic Rainforest ranked second by size of restored areas, with 70,218 km² (or 26.72% of the total), and had the oldest—over half were