Environment & Ecosystem Science (EES)

This study comparatively assessed the regeneration and diversity of indigenous woody species under three exotic tree plantations (Eucalyptus camaldulensis, Cupressus lusitanica, and Grevillea robusta) and adjacent natural forests in Gomma District, southwestern Ethiopia. We hypothesized that exotic plantations vary in their capacity to support native species, with higher canopy openness favoring greater richness and diversity. Systematic sampling was conducted in 48 plots to evaluate species composition, diversity indices, regeneration status, and stand structure. Natural forests exhibited the highest diversity (H’ = 3.29; R = 8.36), while Cupressus plantations showed the lowest (H’ = 2.05; R = 2.13). Among plantations, Eucalyptus camaldulensis supported higher richness and diversity than Grevillea and Cupressus. Inverse J- shaped DBH distributions indicated generally good regeneration, yet valuable timber species such as Podocarpus falcatus were absent, suggesting dispersal and microsite limitations. Low compositional similarity (<40%) between plantations and natural forests underscores ecological disconnection. Beyond species counts, our findings reveal functional and management implications: exotic plantations partially support native regeneration but cannot substitute for natural forests. Integrated plantation design—enrichment planting, mixed-species stands, and assisted regeneration—offers pathways to balance production forestry with biodiversity conservation in Ethiopia’s highlands.