Understanding the processes that allow phylogenetically related plant species coexist is important to understand the ecological and evolutionary processes that structure biological communities. In this study, we investigated how the species Erythroxylum simonis, Erythroxylum pauferrense and Erythroxylum citrifolium share ecological niche dimensions according to the abiotic characteristics of their environments of occurrence. To this end, in ten pre-established plots in an Atlantic Forest remnant in northeastern Brazil, we carried out a population survey of the three species and characterised their abiotic niche by measuring light availability, humidity and the physical–chemical properties of the soil. We used generalised linear models to test whether abiotic variables influence species abundance. Our results indicate that the three species coexist along the different environmental gradients, with some level of niche overlap. The species E. simonis is the best competitor, showing generalist behaviour and the highest abundance in all environmental gradients. We emphasise that the adult populations of the species have adapted to various environmental and ecological challenges. Thus, the results reported are influenced by their ability to perform well in terms of physiology, growth and survival in their early-life stages.

Most studies aiming to quantify carbon stocks in tropical forests have focused on aboveground biomass, omitting carbon in soils and woody debris. Here, we quantified carbon stocks in soils up to 3 m depth, woody debris, and aboveground and belowground tree biomass for the 25-ha Amacayacu Forests Dynamics plot in the northwestern Amazon. Including soils to 3 m depth, total carbon stocks averaged 358.9 ± 24.2 Mg C ha−1, of which soils contributed 53%, biomass 44.2%, and woody debris 2.7%. When only including soils to 0.5 m depth, carbon stocks diminished to 222.1 Mg C ha−1 and biomass became the largest contributor. Among 1-ha subplots, total carbon stocks were correlated with soil carbon stocks at ≥0.5 m depth, belowground biomass of all trees, and aboveground biomass of trees ≥60 cm DBH. Our results support the assumption of biomass as the likely largest carbon source associated with land use change in northwestern Amazonia. However, mining and erosion following land use change could also promote a significant release of carbon from soil, the largest carbon stock. To improve the global carbon balance, we need to better quantify total carbon stocks and dynamics in tropical forests beyond aboveground biomass.