A STUDY ON CHANGES OF WOODY VEGETATION COMPOSITION ALONG ALTITUDINAL GRADIENT FROM LAKE ABAYA TO IIlLLSOF DORZE, GAMO GOFA ZONE, SOUTHWEST ETHIOPIA

Abstract

This study was conducted on the forest between Lake Abaya and hills of Dorie. Gama Gofa zone. SNNPR. Southwest Ethiopia. The objective of the study was to determine woody species composition and structure of the vegetation. assess the correlation of plan! species with environmental parameters, determin e regeneration status of the forest and analyze the variation in species richness and dominance patte rns along attitudinal gradient. Systematic sampling method was used to collect th e vegetation data. Accordingly, 60 quadrats, each with 20mx20m were laid to sample the woody species. In addition, seedlings and saplings were taken fro m the main plots. Altitude. slope and aspect were also measured for each quadtat . Following modified Braun­ Blanquet scale, cover abundance values of trees and shrubs were estimated. While data on Height and DBH of frees and shrubs were collected t o determine vegetation structure. Shannon-Wiener diversity index, species richness, evenness and Sorensen similarity i ndex were determined for assessing the diversity and similarity of the vegetation along the attitudinal gradient. In addition, Cluster analysis ,vas performed using PC-ORD5 10 c lassi fy the vegetation i1110 communities. Fif t y three plant species belonging 45 genera and 30 families were identified in this study. Fabaceaefoliowed b y Anacaridiaceae were found to be the most abundant families. Structural data analysis of the vegetation provided a density of 1026. 2/ha and a total basal area of 15. 61111 2 /lw. I n the three altitudinal zones of the study area (Lower. Middle, Upper), small sized individuals shown 10 be prevalent. The 111os1 dominant tree species which scored the highest importance values were Terminalia brownii, Ficus sur, Euclea divinorum, and Dodonaea angustifolia. The cluster analysis yielded four plant / community types that are named after one or two dominant species. The study 011 the regeneration status of the woody species indicated poor regeneration status i 11 th e forest. Generally, the forest is dominated b y small sized trees and shrubs indicating that i i i s in the secondary stage of development. Besides low regeneration potential, the vegetation is exposed to human-induced degradations and therefore, taking appropriate conservation measures and also conducting a more detailed study i s recommended