Dahomey Gap is a special zone where coastal West African rainforest is missing, creating a broad area of savanna. This savanna area is characterized by a strong rainfall gradient from south to north towards Sahara Desert, recurrent human firing. Competition for light has been designated to be a regulatory factor affecting stem and crown growth in rainforest. In open savanna environment where light is not main limited factor, twelve plots 1-ha each have been setup in two sites to check how tree architecture changes along the vegetation gradient. After the site- level analysis, species-level analysis had been undertaken by allometric relationships to test how species invest in DBH and crown size.
Significant differences were detected in the intercept in allometric relationships for height-DBH and height-crown width between north and south, and among species. DBH tended to be consistently larger in south than north for most species. DBH and crown allometry were not consistent in the same site except for species, which had small leaf size. Allometric properties were different among tall-, medium- and short- statured trees. Allometric relationships were consistent for DBH and crown architecture for tall trees (trees with wider crown indicated ticker stem) but not for medium and short trees. We therefore hypothesize that the differences in trunk size and crown width allometry are related to the trade-off between vertical growth to escape fire and allocation resources for crown expansion. Species were not able to invest in DBH and crown width due to arid conditions.