Tree diversity and carbon stocks in the Itombwe Mountains of eastern DR Congo

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.

Automated summary

The study in the Albertine Rift's Itombwe Mountains revealed a negative correlation between tree species richness and elevation, while aboveground biomass was positively correlated with elevation and soil factors. Important tree species are under international conservation concern.