Impact of Eucalyptus globulus Labill. (Myrtaceae) plantation on the regeneration of woody species at Entoto Mountain, Addis Ababa, Ethiopia

Abstract

This study was carried out at Entoto mountain Eucalyptus plantation, about 10 km north of the center of Addis Ababa, to assess the impact of Eucalyptus globulus Labill. plantation on the naturally regenerated woody species. Sixty plots of 400 m 2 (20 m X 20 m) size were established along a transect lines at every 300 m distance between them. Transects were laid in north–south directions at 500 m distance from each other. Seedlings, herbaceous species and soil samples were collected from five sub-plots (4 m 2 ) within each major plot. A total of 68 plant species belonging to55 genera and 32 families were identified. Asteraceae (8 species) was the most dominant family. Out of a total of 68 plant species, 41 of them were naturally regenerated woody species recorded in Entoto E. globulus plantation. They represented 33 genera and 25 families. For the analysis of vegetation diversity, woody species density and soil environmental factors, the individual E. globulus plantation stands were used to classify the plots into three categories. These are C1 (plots with less than 154 E. globulus stands), C2 (plots consists of 154 to 199 E. globulus stands) and C3 (plots with greater than 199 E. globulus stands). Twenty plots were identified for each category. There was significance difference (P < 0.05) in the species diversity (H’) between C1 and C2, as well as C1 and C3 while there was no significant difference between C2 and C3. The species richness was also significantly different (P < 0.05) among the three categories of E. globulus plantations. The species diversity and species richness increased with the decrease in E. globulus plantation and vice versa. Sorenson similarity index showed highest similarity between C1 and C2 while C2 and C3 showed relatively weak similarity. The density of naturally regenerated woody species showed a decreasing trend with the increase in the density of E. globulus plantation and vice versa. Therefore, the density of E. globulus plantation was negatively correlated with density of naturally regenerated woody species. The study on vegetation and population structure showed that the density of tree species was high at the lower DBH class levels and there was good regeneration status. Density of naturally regenerated woody species greater than 2.5 cm DBH (cal.932.1 ha-1), height, frequency, basal area and the respective IVI values for naturally regenerated woody species were also calculated. There was no significant difference between the three categories of E. globulus plantations in their major soil nutrient contents.