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Our ecological understanding of tropical montane forests in Africa is still limited, particularly in the Albertine Rift. Because of a greater role of environmental filtering at higher elevations, tree species' richness and aboveground biomass (AGB) is expected to decrease with increasing elevation. However, broader scale patterns are complex and different patterns have also been observed in different mountains. We established eight permanent 1-ha plots in Itombwe Mountains and sampled all trees >= 10 cm diameter following standard RAINFOR protocols to investigate tree species' richness, forest structure, and estimated AGB. We also collected and analyzed soil samples to establish how these affected AGB. We identified over 120 tree species, 12 of which were of international conservation concern according to IUCN criteria. Species richness was significantly negatively correlated with elevation. AGB ranged from 268 Mg/ha (submontane) to 396 Mg/ha (middle montane forests), and it was significantly positively correlated with elevation, soil organic matter, and soil organic C and N. We compare Itombwe with other montane forests in the Albertine Rift, to demonstrate their high floristic diversity, high abundance of large stems, and high AGB, insights which are crucial for the future management of these unique forests. Abstract in French is available with online material.

Mountain environments experience more rapid changes in temperature than lower elevations. However, little is known about the climatic changes already observed in African mountains, or the adaptation strategies used by hunter-gatherer communities. Semi-structured interviews were administered to 100 Twa hunter-gatherers living around Mt Kahuzi in eastern Democratic Republic of the Congo (DR Congo). We also organized 10 focus-group discussions with Tembo farmers living in the same area and we gathered historical data from Kamembe meteorological station. Twa respondents perceived reduced rainfall and fog, and increased temperatures. They also reported several impacts including reduced crop yields and abundance of forest products (caterpillars, mushrooms, honey). Tembo perceptions of climatic changes and impacts agreed with the Twa. Meteorological data available shows reduced rainfall and increased temperatures - but there are no records on fog. Despite being aware of climatic changes and impacts, Twa are not using any adaptation strategy, while Tembo farmers are using some (as they own land for farming or animal rearing, and are more business minded). For the Twa, their socioeconomic condition create high sensitivity to climate change and constrain adaptive capacity. For the Twa, we recommend the use of 'science with society' (SWS) participatory approach

The forests of the Albertine Rift are known for their high biodiversity and the important ecosystem services they provide to millions of inhabitants. However, their conservation and the maintenance of ecosystem service delivery is a challenge, particularly in the Democratic Republic of the Congo. Our research investigates how livelihood strategy and ethnicity affects local perceptions of forest ecosystem services. We collected data through 25 focus-group discussions in villages from distinct ethnic groups, including farmers (Tembo, Shi, and Nyindu) and hunter-gatherers (Twa). Twa identify more food-provisioning services and rank bush meat and honey as the most important. They also show stronger place attachment to the forest than the farmers, who value other ecosystem services, but all rank microclimate regulation as the most important. Our findings help assess ecosystem services trade-offs, highlight the important impacts of restricted access to forests resources for Twa, and point to the need for developing alternative livelihood strategies for these communities.

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.