Woody Species Diversity and Structure of Sagi tagata Natural Forest Ilu Aba Bor Zone, of Oromia National Regional state, South West Ethiopia

Abstract

This study was carried out on Sagi Tagata Natural Forest, Ilu Aba Bor Zone, Southwest Ethiopia, with the objectives of assessing the woody species diversity and structure of the vegetation. Sagi Tagata forest is one of the very few remnant moist evergreen afromontane forests in Ethiopia. To identify woody species diversity, community structure and the disturbance level of Sagi Tagata forest, five lines transects having 500m distance between each other were laid down from bottom to top of the mountain. Data were collected from 40 quadrants, each with 20m × 20m (400 m 2 ) laid at the intrvalof 20m in elevation along the transects using GPS. Altitudes and geographic coordinates were recorded for each quadrant, and cover/abundance value was estimated for all woody species. Height and diameter at breast height of all woody species taller than 2m and wider than 2.5cm was measured. Specimens were collected, pressed, dried and taken to Jimma University Herbarium for identification. Community class analysis was done using PC_ORD for Windows version 5.3 and six plant community types were identified. Shannon-Wiener Diversity index for each community type was determined using Past Computer Software version 1.34. Sorensen’s similarity index was used to determine the similarity between Sagi Tagata and other forests in Ethiopia in woody species richness. The most dominant tree species relatively with the highest importance value index were Pouteria adolfi–friederici (11.38%), Deinbollia kilimandscharica (9.0%), Albizia gummifera (7.33%), Chionanthus milddbraedii (6.63%), Millettia ferruginea (6.32%) and Croton macrostachyus (4.26%). Analysis of population structure for majority of species revealed normal distribution patterns.The total basal area 0f the Sagi Tagata forest was 31.01m 2 /ha. Woody species comparisons with other similar forests in the country were showed that Sagi Tagata Natural Forest has more similarity to the moist evergreen Afromontane forests.