The spatial propagation and increasing dominance of Gilbertiodendron dewevrei (Fabaceae) in the eastern Congo basin

Abstract

Though substantial research has been conducted on possible historical, physiological, and symbiotic mechanisms that permit monodominance to occur within tropical lowland rainforests, less is known about the successional rates at which monodominance exerts itself on surrounding forest structures. Here we extend efforts to evaluate the longitudinal dynamics ofGilbertiodendron dewevrei-dominated forest in Central Africa by considering this species’ spatial dynamics. Using three 10-ha censused field plots measured across three time periods, we present the first quantitative estimates of the spatial propagation ofGilbertiodendroninto adjacent mixed species forest. Using three analytical strategies, we demonstrate thatGilbertiodendronis increasing in dominance and that monodominant forest patches are expanding into the surrounding forest at a statistically significant rate. The rates of successional advance vary by patch and direction, but average 0.31 m year−1, with speeds greatest in the direction of the prevailing winds. We show that the advancement ofGilbertiodendronis significantly slower than documented rates from other forest ecotones across Central Africa. When paired with stress tolerance traits and ectomycorrhizal associations, these findings help to clarify the means by whichGilbertiodendron dewevreigains dominance in otherwise species-diverse regions.