Résumé
The natural regeneration of tree species depends on seed and pollen
dispersal. To assess if limited dispersal could be critical for the
sustainability of selective logging practices, we performed parentage
analyses in two Central African legume canopy species displaying
contrasted floral and fruit traits: Distemonanthus benthamianus and
Erythrophleum suaveolens. We also developed new tools linking forward
dispersal kernels with backward migration rates to better characterize
long-distance dispersal. Much longer pollen dispersal in D. benthamianus
(mean distance dp=700m, mp=52% immigration rate in 6 km2 plot, s=7%
selfing rate) than in E. suaveolens (dp=294m, mp=22% in 2 km2 plot, s=20%)
might reflect different insect pollinators. At a local scale, secondary
seed dispersal by vertebrates led to larger seed dispersal distances in
the barochorous E. suaveolens (ds=175m) than in the wind-dispersed D.
benthamianus (ds=71m). Yet, seed dispersal appeared much more fat-tailed
in the latter species (15-25% seeds dispersing >500m), putatively
due to storm winds (papery pods). The reproductive success was correlated
to trunk diameter in E. suaveolens and crown dominance in D. benthamianus.
Contrary to D. benthamianus, E. suaveolens underwent significant
assortative mating, increasing further the already high inbreeding of its
juveniles due to selfing, which seems offset by strong inbreeding
depression. To achieve sustainable exploitation, seed and pollen dispersal
distances did not appear limiting, but the natural regeneration of E.
suaveolens might become insufficient if all trees above the minimum legal
cutting diameter were exploited. This highlights the importance of
assessing the diameter structure of reproductive trees for logged species.