Habitat characterizations underestimate the role of edaphic factors controlling the distribution of Entandrophragma

Numerous theories have been developed and tested to explain the high botanical diversity in tropical forests, ranging from nonequilibrium theories emphasizing the importance of chance to equilibrium theories depicting highly specialized species occupying narrow ecological niches. Niche-based theories have most often evaluated species adaptation to different light environments, but some studies have evaluated the importance of edaphic attributes in controlling species distributions. We evaluated the role of edaphic factors in controlling the distribution of African mahogany in the genus Entandrophragma on a 100-ha plot in the Dzanga-Sangha Dense Forest Reserve, Central African Republic. This study went beyond simple characterization of edaphic conditions in topographic or other classes to test for specific associations with chemical and physical soil parameters known to be kimportant to plant growth. Trees greater than or equal to30 cm dbh of the four species of Entandrophragma evaluated were nonrandomly distributed in the forest. Torus translation tests indicated that none of the species exhibited any topographic preferences. However, three of the four species had significant associations with at least two soil chemical attributes. Randomization tests evaluating links between soil chemical and physical properties and topographic position underscored the complexity of the relationship and suggest that inferring edaphic attributes from broadly and simply defined habitat classes may significantly underestimate the importance of soil heterogeneity in contributing to species coexistence.