Variation and Determinants of the Shape of Trees With Irregular Trunks in Central Africa

ABSTRACT Trees developing irregularities on their trunks have an influence on the estimation of above‐ground biomass and carbon stocks in the tropics. This study aims to examine the variation and determinants of the shape of trees with irregular trunks in Central Africa. The study used close‐range photogrammetric data and conventional data to analyze 275 trees belonging to 11 species. For each tree, the isoperimetric quotient (Q) at 1.30 m has been estimated from a cross‐sectional disc. Between sites, we observed a significant variation in Q between two forest types, with trees tending to have lower Q values in the semi‐deciduous forest (Semi‐F) than in the evergreen forest (Ever‐F), indicating trees in Semi‐F had more irregular trunk shapes. Similar trends were reported for the three species shared by both forest types, suggesting an environmental control of the shape of trees with irregular trunks. Within sites, the lowest Q value was observed for Triplochiton scleroxylon in Semi‐F and for Pterocarpus soyauxii in Ever‐F, suggesting that these species had more irregular trunks than other species. The determinants of variations in Q were related to tree characteristics and species traits. At the tree level, Q was positively correlated with wood density and negatively correlated with crown volume, suggesting that trees with larger crowns and lower wood density are more likely to develop irregular trunks. At the species level, wind‐dispersed species and deciduous species tended to have more irregular trunks. These results provide insight into the life cycle strategies of tropical tree species.