Effects of Environmental Factors on Distribution of Vegetation on the Eastern Slopes of South Welo Highlands
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Date
1998-05
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Addis Ababa University
Abstract
The vegetation of the eastern parts of South Welo was studied in three sites at altitudes of
1,200m-1,500m , 1,700111-2,200111 and 2,400111-2,800111 using stratified random sal1lpling.
From each zone, 18 stands (quadrats) with 20 m x 20 m were selected randomly and totally
54 sample stands were analyzed in which 144 species of plants were recorded and laler
identified in the National Herbarium (Science Faculty). For each stand, composite soil
samples were taken from depths of 0-25cm and analyzed for pH. conductivity, texture,
organic carbon, total nitrogen, and available phosphonls. Exchangeable cations (Ca, lvlg,
K, Na) were analyzed for 5 samples from each zone. Measurement of altitude, slope and soil
colour were taken in the field fi'om eadi stana
The classificatioll of the 54 stands was conducted by cluster analysis using the computer
package SYNTAX. The resemblance index employed was similarity ratio. To analyze species
diversity, ShamlOn-Wiever diversity index was employed Using this technique, three major
clusters (plant communities): Juniperus-Erica type (cluster A), Euclea schimperi type
(cluster B), Acacia asak type (cluster C) in descending altitudinal order and nine subclusters
designnted as a, b, c, d, e, j g, hand i were identified (where a and b are in cluster A; c, d
and e in eluster B andjg,h and i in cluster C). To compare different clusters and subclusters
mean values and one-way ANOVA, followed by Duncan'sINeuman-Keuls mUltiple
comparisons were computed
The results of the multiple comparison show that the highest number of significant contrasts
among the three major clusters were observed fi'om variations in altitudes and related
moisture change. Moreover, the three major clusters Significantly vOlY in their texture,
organiC carbon, and organiC matter. There is no significant variation in environmental
factors between pair of the subclusters within each zone. The analysis of species diversity
show that with decreasing altin/de, the richness of vegetatioll in species composition also
decrease.
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Keywords
Effects of Environmental