Pervasive Negative Effects of Leucaena leucocephala (White-Popinac) Invasion on Regenerating Areas of the Atlantic Forest

Juliano Zardetto , Willian Simioni, Tadeu Siqueira

The use of invasive species in ecological restoration is controversial and has raised recent concerns. In Brazil, some ecosystem restoration and agroforestry projects have proposed that white-popinac (Leucaena leucocephala (Lam.) de Wit), a broadly distributed invasive species, is a promisor species to be used when the soil is severely altered, based on the premise that it might not necessarily disrupt natural regeneration processes, especially in fragmented forests. To address this uncertainty, we investigated its effects on the functional diversity of naturally regenerating forests dominated by invasive grasses within the Atlantic Forest domain. We conducted floristic surveys on the arboreal and herbaceous strata in 29 regenerating areas invaded by white-popinac, each with a unique time-since-invasion, thereby creating a gradient of invasion duration. We estimated the average seed mass of each regenerating area (CWM), as well as species richness and abundance of trees/shrubs and animal dispersed species, and α and β functional metrics. The progression of invasion led to (i) a major decrease in the average seed mass of native species, contrasted by an increase of this metric for invasive species; (ii) an increase in tree abundance, without increasing tree species richness; and (iii) a reduction in the richness of animal-dispersed species. Collectively, these results indicate that the natural regeneration trajectories of Atlantic Forest fragments can be strongly compromised by the advance of white-popinac invasions. Our results highlight the need for early control measures and caution against using white-popinac in restoration, emphasizing the value of functional metrics in monitoring.Therefore, management protocols for the prevention and control of white-popinac must be implemented, and its use in restoration projects should not be advised.