The Amazon is the largest expanse of tropical rainforest in the world. Although deforestation continues to reduce overall forest cover, frequent land abandonment is enabling the expansion of secondary forests, which rapidly sequester large quantities of carbon. It has been suggested that this regeneration could be a fundamental resource in mitigating climate change. However, a lack of spatially explicit, high-resolution information on their extent, age and temporal dynamics mean it is not clear how much secondary forests are currently contributing. We address this gap using the 30m-resolution MapBiomas 3.1 dataset to provide the first estimate of carbon sequestration by secondary forests across the Brazilian Amazon. We harness this impressive new dataset to produce novel insight into the local, landscape and climate context of secondary forests on an unprecedented spatial scale and explore the implications these factors may have on carbon sequestration rate.
Results/Conclusions
There are 5.6 million secondary forest patches in the Brazilian Amazon, covering 129,361 km2. Using age-derived sequestration rates, we estimate they may be storing as much as 0.69±0.1 billion Mg C, equivalent to 2.55 billion Mg of CO2. The dynamic nature of tropical agriculture means secondary forest patches are often short lived. This is reflected in the skewed age distribution which is dominated by young forests (<20 years; 85.8%). Therefore, secondary forests are currently only storing a fraction of their total carbon capacity and have a high future sequestration potential. However, most secondary forests are growing in regions where rainfall is lower than the biome average (SF: 1945mm, Amazon: 2224mm) and where climatic water deficit (SF: -375.5 mm yr-1, Amazon: -259 mm yr-1) and seasonality (SF: 70%, Amazon: 57%) are greater, conditions known to reduce carbon sequestration rate. Additionally, just 29 % of secondary forest is situated in landscapes where more than half of the surrounding area (1 km radius) is old growth forest, which could limit recovery due to reduced access to varied seed sources. This work is an important first step in understanding secondary forest carbon sequestration and their climate change mitigation potential.