Résumé
Due to the reduction of population density and/or the environmental
changes it induces, selective logging could affect the demography,
reproductive biology and evolutionary potential of forest trees. This is
particularly relevant in tropical forests where natural population
densities can be low and isolated trees may be subject to outcross pollen
limitation and/or produce low quality selfed seeds that exhibit inbreeding
depression. Comparing reproductive biology processes and genetic diversity
of populations at different densities can provide indirect evidence of the
potential impacts of logging. Here, we analysed patterns of genetic
diversity, mating system and gene flow in three Central African
populations of the self-compatible legume timber species Erythrophleum
suaveolens with contrasting densities (0.11, 0.68 and 1.72 adults per ha).
The comparison of inbreeding levels among cohorts suggests that selfing is
detrimental as inbred individuals are eliminated between seedling and
adult stages. Levels of genetic diversity, selfing rates (about 16%) and
patterns of spatial genetic structure (Sp about 0.006) were similar in all
three populations. However, the extent of gene dispersal differed markedly
among populations: the average distance of pollen dispersal increased with
decreasing density (from 200 m in the high-density population to 1000 m in
the low-density one). Overall, our results suggest that the reproductive
biology and genetic diversity of the species are not be affected by
current logging practices. However, further investigations need to be
conducted in low-density populations to evaluate (i) if pollen limitation
may reduce seed production and (ii) the regeneration potential of the
species.