Mixed-Forest Species Establishment in a Monodominant Forest in Central Africa: Implications for Tropical Forest Invasibility.

Background: Traits of non-dominant mixed-forest tree species and their synergies for successful co-occurrence in
monodominant Gilbertiodendron dewevrei forest have not yet been investigated. Here we compared the tree species
diversity of the monodominant forest with its adjacent mixed forest and then determined which fitness proxies and life
history traits of the mixed-forest tree species were most associated with successful co-existence in the monodominant
forest.
Methodology/Principal Findings: We sampled all trees (diameter in breast height [dbh]$10 cm) within 661 ha
topographically homogenous areas of intact central African forest in SE Cameroon, three independent patches of G.
dewevrei-dominated forest and three adjacent areas (450–800 m apart). Monodominant G. dewevrei forest had lower
sample-controlled species richness, species density and population density than its adjacent mixed forest in terms of stems
with dbh$10 cm. Analysis of a suite of population-level characteristics, such as relative abundance and geographical
distribution, and traits such as wood density, height, diameter at breast height, fruit/seed dispersal mechanism and light
requirement–revealed after controlling for phylogeny, species that co-occur with G. dewevrei tend to have higher
abundance in adjacent mixed forest, higher wood density and a lower light requirement.
Conclusions/Significance: Our results suggest that certain traits (wood density and light requirement) and population-level
characteristics (relative abundance) may increase the invasibility of a tree species into a tropical closed-canopy system. Such
knowledge may assist in the pre-emptive identification of invasive tree species.