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Deforestation in the tropics is often followed by the creation of anthropogenic savannas used for animal husbandry. By discontinuing burning regimes, forests may recolonize the savanna and carbon stocks may recover. However, little is known about the success and speed of tropical forest recovery, while such information is vital for a better quantification of efforts to r educe e missions from d eforestation and forest d egradation (REDD+) as well as supporting Forest Landscape Restoration (FLR) practices. Therefore, we designed a forest regeneration experiment within a savanna patch in the Mayombe hills (Democratic Republic of Congo), by discontinuing the annual burning regime in an 88 ha exclosure since 2005. 101 permanent inventory plots (40.4 ha) were installed in 2010 and remeasured in 2014. Tree species were classified as savanna or forest specialists. We estimate a forest specialist encroachment rate of 9 stems ha−1 yr−1 and a savanna specialist disappearance rate of 16 stems ha−1 yr−1. Average diameter of forest specialists did not change due to an increasing influx of recruits, while average diameter of savanna trees increased due to decreasing recruitment. Carbon stored by forest specialists increased from 3.12 to 5.60 Mg C ha−1, suggesting a forest carbon recovery rate of 0.62 Mg C ha−1 yr−1. Using the average carbon stock of 19 nearby mature rainforest plots as a reference, we estimate a total forest carbon recovery time of at least 150 years. The Manzonzi exclosure may potentially become an important reference experiment to quantify REDD+ schemes in Central Africa. Furthermore, this natural regeneration experiment demonstrates how carbon sequestration and biodiversity conservation can go hand-in-hand. However, more censuses are needed to better quantify the long-term carbon recovery trajectory within the protected area. • Forest recovery on anthropogenic savannas is quantifiable after 9 years of fire exclusion. • Forest specialist stem density is increasing at a rate of 9 stems ha−1 yr−1. • Savanna specialist stem density is decreasing at a rate of 16 stems ha−1 yr−1. • Observed forest carbon recovery rate is 0.62 MgC ha−1 yr−1. • Estimated total forest carbon recovery time is 150 years. [ABSTRACT FROM AUTHOR]

Trees structure the Earth's most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations 1-6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth's 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories 7 , we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world's most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees., (© 2024. The Author(s).)

Tropical forests store 40-50 per cent of terrestrial vegetation carbon 1 . However, spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests 2 . Owing to climatic and soil changes with increasing elevation 3 , AGC stocks are lower in tropical montane forests compared with lowland forests 2 . Here we assemble and analyse a dataset of structurally intact old-growth forests (AfriMont) spanning 44 montane sites in 12 African countries. We find that montane sites in the AfriMont plot network have a mean AGC stock of 149.4 megagrams of carbon per hectare (95% confidence interval 137.1-164.2), which is comparable to lowland forests in the African Tropical Rainforest Observation Network 4 and about 70 per cent and 32 per cent higher than averages from plot networks in montane 2,5,6 and lowland 7 forests in the Neotropics, respectively. Notably, our results are two-thirds higher than the Intergovernmental Panel on Climate Change default values for these forests in Africa 8 . We find that the low stem density and high abundance of large trees of African lowland forests 4 is mirrored in the montane forests sampled. This carbon store is endangered: we estimate that 0.8 million hectares of old-growth African montane forest have been lost since 2000. We provide country-specific montane forest AGC stock estimates modelled from our plot network to help to guide forest conservation and reforestation interventions. Our findings highlight the need for conserving these biodiverse 9,10 and carbon-rich ecosystems., (© 2021. The Author(s), under exclusive licence to Springer Nature Limited.)

Structurally intact tropical forests sequestered about half of the global terrestrial carbon uptake over the 1990s and early 2000s, removing about 15 per cent of anthropogenic carbon dioxide emissions 1-3 . Climate-driven vegetation models typically predict that this tropical forest 'carbon sink' will continue for decades 4,5 . Here we assess trends in the carbon sink using 244 structurally intact African tropical forests spanning 11 countries, compare them with 321 published plots from Amazonia and investigate the underlying drivers of the trends. The carbon sink in live aboveground biomass in intact African tropical forests has been stable for the three decades to 2015, at 0.66 tonnes of carbon per hectare per year (95 per cent confidence interval 0.53-0.79), in contrast to the long-term decline in Amazonian forests 6 . Therefore the carbon sink responses of Earth's two largest expanses of tropical forest have diverged. The difference is largely driven by carbon losses from tree mortality, with no detectable multi-decadal trend in Africa and a long-term increase in Amazonia. Both continents show increasing tree growth, consistent with the expected net effect of rising atmospheric carbon dioxide and air temperature 7-9 . Despite the past stability of the African carbon sink, our most intensively monitored plots suggest a post-2010 increase in carbon losses, delayed compared to Amazonia, indicating asynchronous carbon sink saturation on the two continents. A statistical model including carbon dioxide, temperature, drought and forest dynamics accounts for the observed trends and indicates a long-term future decline in the African sink, whereas the Amazonian sink continues to weaken rapidly. Overall, the uptake of carbon into Earth's intact tropical forests peaked in the 1990s. Given that the global terrestrial carbon sink is increasing in size, independent observations indicating greater recent carbon uptake into the Northern Hemisphere landmass 10 reinforce our conclusion that the intact tropical forest carbon sink has already peaked. This saturation and ongoing decline of the tropical forest carbon sink has consequences for policies intended to stabilize Earth's climate.