Format: ORAL

Ellen Heimpel1,2, Antie Ahrends1, Kyle G. Dexter2, Jefferson S. Hall3, Josrald Mamboueni4, Vincent P. Medjibe5, David Morgan6, Crickette Sanz7,8, David J. Harris1

1 Royal Botanic Garden Edinburgh, Edinburgh, UK 2 School of Geosciences, University of Edinburgh, Edinburgh, UK 3 Smithsonian Tropical Research Institute, Balboa, Ancon, Panama 4 Institut National de Recherche Forestière, Brazzaville, Congo 5 Gabon National Parks Agency, Libreville, Gabon 6 Lester E. Fisher Center for the Study and Conservation of Apes, Lincoln Park Zoo, Chicago, USA 7 Department of Anthropology, Washington University in St. Louis, St. Louis, USA 8 Congo Program, Wildlife Conservation Society, Brazzaville, Congo

Within the tropical lowland rainforests of central Africa, there is a tree species, Gilbertiodendron dewevrei, that forms stands in which up to 90% of the trees belong to just this one species, overturning every stereotype of plant diversity in the tropics. Monodominant Gilbertiodendron dewevrei forest covers large areas of the Congo Basin, but it is currently unclear whether it is sufficiently distinct from adjacent mixed terre firme forest to warrant separate treatment for conservation planning and carbon calculations. This study aimed to compare the structure and diversity of monodominant and mixed forest, and ask whether there is a unique vascular plant community associated with G. dewevrei forest. We utilised a combination of plot data and herbarium specimens collected in the Sangha Trinational (a network of protected areas in Cameroon, Central African Republic, and the Republic of Congo). Plot inventories were used to compare G. dewevrei forest and mixed forest for stem density, basal area, above ground biomass, stem size distribution, species diversity, and species composition. In addition, a database of 3,557 herbarium specimens was used to identify species of vascular plants that are associated with G. dewevrei forest. We found that Gilbertiodendron dewevrei forest is distinct in both structure and species composition from mixed forest. G. dewevrei forest has a lower stem number (of trees 10 cm), but a greater proportion of larger trees ( 70 cm), suggesting higher carbon stocks. The species composition is distinct from mixed forest, with 56 species of vascular plant significantly associated with G. dewevrei forest. Monodominant G. dewevrei forest in the Sangha Trinational is both compositionally and structurally distinct from mixed forest. We therefore recommend this forest type be considered separately from mixed forest for conservation planning and carbon stock calculations.