Figure 2. Variation in tree diameter distribution among the 176 genera across the SRI.

Projection of the genera and the 10-cm-wide diameter classes in the ordination space defined by the first two axes of a correspondence analysis of the abundance matrix, as defined by 176 genera and 13 diameter classes. The size of the circles is proportional to the square root of the genus abundance. The color of the symbol corresponds to the two groups identified with a clustering analysis (based on Euclidean distances and an average agglomeration method) on the species score on the first factorial axis. Genera that showed a reverse-J diameter distribution (n = 134) are indicated in gray and those genera that showed a deviation from the reverse-J distribution (n = 42) in black (e.g., Baillonella). Black filled circles indicate the four genera that are monospecific in the SRI and used for the age estimations. Diameter distribution of the 10 most abundant genera is shown in addition to that of the four selected genera: Celtis (gray), Polyalthia (gray), Strombosia (gray), Petersianthus (gray), Manilkara (gray), Entandrophragma (black), Terminalia (black), Anonidium (gray), Staudtia (gray), and Macaranga (gray). Statistics: R (https://www.r-project.org/), CAD: Illustrator CS4 (https://www.adobe.com).

DOI: http://dx.doi.org/10.7554/eLife.20343.004

Figure 2—figure supplement 1. Distribution of diameters of the four study species in the 22 study sites (black).

The solid lines on the average diameter distributions (gray) correspond to the fitted parametric diameter distribution (Weibull), which was used to estimate the mode and corresponding age. Ages and dates (AD) in the Sangha River Interval were estimated using the mean annual increment of diameter of (a) 367 Erythrophleum suaveolens, (b) 199 Pericopsis elata, (c) 152 Terminalia superba and (d) 265 Triplochiton scleroxylon. Age estimations were validated with published tree-ring data for these four species in natural forests in Cameroon (C), the Democratic Republic of Congo (DRC) and the Ivory Coast (IC) (Supplementary file 3). Maps: QGIS 2.14 (http://www.qgis.org), CAD: Illustrator CS4 (https://www.adobe.com).

DOI: http://dx.doi.org/10.7554/eLife.20343.005

Figure 2—figure supplement 2. Growth models (a, c, e and g) and growth trajectories (b, d, f and h) for the four study species based on tree-ring data.

Eight growth models (i.e., Canham, Gompertz, Verhulst, Power, Power mult, Lognormal, Linear and Mean) were fitted to the data. Age estimations were obtained with numerical solutions to ordinary differential equations (ODE). Solid lines correspond to the model prediction on the observed range of diameters. Dashed lines correspond to the predictions for small trees (below the inventory threshold of ≤10 cm). For growth models, the color of symbols indicates access to light (light gray = emergent and dominant trees, Dawkins 5; gray = canopy and codominant trees, Dawkins 4; black = lower canopy and understory dominated trees, Dawkins ≤3). For growth trajectories, age/diameter values based on published tree-ring data are indicated in light gray. Statistics: R (https://www.r-project.org/), CAD: Illustrator CS4 (https://www.adobe.com).

DOI: http://dx.doi.org/10.7554/eLife.20343.006