The impacts of invasive trees on the structure and composition of tropical forests show some consistent patterns but many are context dependent

Tropical forests harbour significant proportion of global biodiversity. Recent studies are, however, reporting an increase in plant invasion and its effect on these forests. We surveyed three forest reserves in Ghana to determine how differences in invasion levels influence plant community structure. Species diversity and species richness, particularly pioneer and non-pioneer light demanders, decrease with increasing invasion level. There was no consistent pattern regarding the impact of different levels of invasion on the diversity of the different tree functional groups. Stand density of native trees were the same in two of the reserves whilst the basal area of the highly invaded sites was higher than that of the lightly invaded sites in two of the three reserves. Generally, while there are some patterns in diversity indices and functional groups that are broadly maintained across the three reserves, site-specificity was also important, with the direction of impact influenced by the type of species and habitats. The study adds to the growing body of evidence that ecological impacts of invasive species do not always increase proportionally with invader density but are complex and context-dependent. It also provides insights into silviculture and other forest management decision-making and interventions, with respect to invasive tree species in forest reserves.