High aboveground carbon stock of African tropical montane forests

Abstract

Tropical forests store 40-50 per cent of terrestrial vegetation carbon¹. However, spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests². Owing to climatic and soil changes with increasing elevation³, AGC stocks are lower in tropical montane forests compared with lowland forests². 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 Network⁴ and about 70 per cent and 32 per cent higher than averages from plot networks in montane^2,5,6 and lowland⁷ 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 Africa⁸. We find that the low stem density and high abundance of large trees of African lowland forests⁴ 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.