Effect of complete abolition of Eucalyptus species on under canopy species diversity in Gullele Botanic Garden, Ethiopia

Abstract

Fast-growing, stress-tolerant tree species belonging to the genus Eucalyptus have historically been introduced in the central highlands of Ethiopia to support various economic and environment-regulating functions. While these non-native tree species are often highly useful, many are simultaneously invasive, generating negative environmental impacts and becoming the greatest global threat to biodiversity. This study is aimed at determining the impacts of the complete removal of the eucalyptus and its replacement by an indigenous species on the undergrowth vegetation of the Gulele Botanic Garden (GBG), Ethiopia. Vegetation data were collected from a total of 60 plots with a dimension of 20 m x 20 m that were laid out and equally distributed among invaded and indigenous species that dominate the landscape. Beside, diversity indices and population structural change parameters were employed for the comparison of changes. Results show that a total of 118 species (103 genera and 57 families) were recorded, and out of those, Eucalyptus camaldulensis was the most dominant species. On the other hand, the richest landscape (Juniperus procera plantation) contained 105 species and 51 families, whereas the poorest landscape (Eucalyptus plantation) was comprised of 66 species and 36 families. Furthermore, the alpha diversity index and vegetation vertical structure of the dominant Eucalyptus plantation differed significantly from those of other landscapes. Regeneration potential was not observed in Eucalyptus-dominant plantations since the inherent physiology of Eucalyptus species repels the regeneration of others. The population structure of the wood species showed an inverse-J curve. The total basal area (BA) of woody species decreased from 64.14 ± 1.54 m2 ha−1, 21.46 ± 0.54 m2 ha−1, and 17.18 m2 ha−1 ± 1.04 for Juniperus procera plantation, mixed plantation, and eucalyptus plantation, respectively. It was concluded that E. camaldulensis was one of the most dominant invasive species that reduced species diversity in the understory. While landscapes replaced after abolition by indigenous plantations demonstrated "fair" to "good" regeneration potential and an alpha diversity index.