A structural analysis of rain forest at Korup and Douala–Edea, Cameroon

Diameter frequency distributions (dfds) of 197 tree species in Korup National Park and 118 tree species in Douala–Edea Forest Reserve (based on c. 41 000 and 25 000 trees ≥ 30 cm gbh in 135 and 104 plots along four transects at each site, respectively) were individually classified into four groups of species according to their maximum diameters (≥99% trees 1% ≥90cm dbh), and separated into two abundance classes (n≥50 and n = 20–49 (or 15–49). A fifth group, from those species in 3 and 4, was defined by a relative lack of small stems and given detailed attention. Dfds were evaluated for all species together on a transect and site basis, and compared for individual species across transects, and between sites for those group 5 species in common. Analysis focussed on three large ectomycorrhizal species in groups 3 and 4, Microberlinia bisulcata, Tetraberlinia bifoliolata and T. moreliana (Caesalpiniaceae), which were restricted to, and dominated, the forest on the nutrient-poor soils of transect P at Korup. M. bisulcata, the most abundant, was markedly group 5 in character, with very few small trees, whilst the Tetraberlinia species had strong replacement potential. Although there were 27 species (42% of groups 3 & 4) at Korup and 19 (48%) at Douala–Edea in group 5, M. bisulcata was unique in its combination of large size, dfd, mycorrhizal habit, spatial distribution and soil association. The potential replacement of this species was contrasted also with a non-ectomycorrhizal caesalp with similar dfd that occurred on nutrient-richer soils, Erythrophleum ivorense. Knowledge of the Caesalpiniaceae-rich la forêt biafriéene of Letouzey (which includes Korup and Douala–Edea) is reviewed, and the distribution, ecology and regeneration of the caesalps discussed. Structure and inferred dynamics of the forest at Korup are discussed with special regard to the ectomycorrhizal species