Latitudinal variation in the woody species diversity of Afzelia africana Sm. habitats in West Africa

This study assessed the woody flora composition of Afzelia africana Sm. habitats along a latitudinal gradient, from the northern limit of the species distribution to the Guinean littoral forest. Data were collected from 201 sample units located in different vegetation types that span four bioclimatic zones: Guinean, Sudano-Guinean, Sudanian and Sahelo-Sudanian zones. The woody flora diversity was described by computing the estimated species richness and the Shannon diversity index within EstimateS 9.1, based on the observed species richness. A sample-based randomization procedure with 95 % confidence intervals was used to compare the patterns of plant richness between vegetation stands. A Non Metric Multidimensional Scaling was performed on presence-absence data matrix to explore the patterns of woody species composition in natural stands. A Canonical Correspondence Analysis was further applied to correlate the patterns of habitat differentiation with climatic variables (temperature, precipitation) and altitude. A total of 165 woody species were recorded, with the highest species richness in Sahelo Sudanian zone. There was no significant difference in richness between samples from Guinean, Sudano-Guinean and Sudanian zones. Plots in the Sudanian and Sudano-Guinean zones were similar but distinct from those of Guinean and Sahelo-Sudanian zones, a pattern that is supported by precipitation and temperature distributions. Results also suggest important cooccurring species characteristic of each habitat as inferred from the Important Value Index (IVI). It is recommended that habitats of A. africana in Sudanian and Sudano-Guinean zones receive similar management and conservation plans while the Guinean and the Sahelo Sudanian zones can be treated separately.