The role of habitat specialization in the regeneration of Entandrophragma spp: Implications for the maintenance of species diversity and forest management in Central Africa

Significant ecological research has focused on how tropical forests maintain diversity and researchers agree that this issue it critical to forest management. Entandrophragma spp. represent some of the most valuable timber species harvested in Central Africa. This dissertation describes a study designed to test hypotheses that emphasize the importance of resource heterogeneity and the regeneration niche in maintaining diversity with an emphasis on Entandrophragma spp.; Four co-occurring Entandrophragma species were tested at the mesoscale landscape for randomness and relationships with belowground resources. All individuals of each of the four species ≥10 cm dbh were mapped on a 100-ha plot with a survey laser that also generated a topographic map. Soil samples were collected from the upper 15 cm of the mineral soil on a sampling grid of 126 evenly spaced points on the plot as well as under up to 25 randomly selected trees of each Entandrophragma species.; Torus translation tests showed that species were not associated with topography but three of the four species were associated with one or more plant macronutrients as well as other soil chemical properties important to plant growth. All four species were grown together in a randomized complete block design in a shade house experiment under different moisture and nutrient conditions. Seedling performance matched what would be expected from the distribution of these species on the 100-ha plot. Entandrophragma cylindricum, the species dominating regional timber export lists, was significantly associated with microsites with high levels of exchangeable calcium and magnesium, including termite mounds. This species doubled its relative growth rate between highly infertile and moderately fertile forest soils in nursery trials.; Results of an experiment comparing seedling growth under varied light conditions suggest a possible explanation to the consistently reported rarity of E. utile.; The results of this research suggest that resource levels are indeed important in determining the distribution and thus maintaining Entandrophragma spp. within the forest. This research also shows that “habitat” is much more complicated than topographic position with respect to soil nutrients. Further, plants adapted to infertile soils can respond dramatically to apparently insignificant increases in macronutrients. The results are discussed in relation to forest management.