Altitudinal filtering of large-tree species explains above-ground biomass variation in an Atlantic Central African rain forest

International audiencePatterns in above-ground biomass of tropical forests over short altitudinal gradients are poorly known. Theaim of this study was to investigate the variation of above-ground biomass with altitude in old-growth forests anddetermine the importance of changes in floristic composition as a cause of this variation. We used a dataset from 151-ha permanent plots established from lowland (200 m asl) to submontane forests (900 m asl) in the NgovayangMassif, south-western Cameroon. We analysed variation over altitude in two specific functional traits, the potentialmaximum tree height and the wood density. Forest above-ground biomass decreased from 500–600 Mg ha−1 inlowland plots to around 260 Mg ha−1 at the highest altitudes. The contribution to above-ground biomass of large-treespecies (dbh ≥ 70 cm) decreased with altitude, while the contribution of smaller trees was constant. Contributionof the Fabaceae subfamily Caesalpinioideae decreased with altitude, while those of Clusiaceae, Phyllanthaceae andBurseraceae increased.While potential maximum tree height significantly decreased, wood specific gravity displayednotrend along the gradient. Finally, the decrease in above-ground biomass along the short altitudinal gradient can be atleast partially explainedbyashift in species composition,withlarge-tree species beingfiltered outat the highestaltitudes.These results suggest that global change could lead to significant shifts in the properties of montane forests over time