The extent and status of woody treeline species in the Southern slopes of the Bale mountains, Ethiopia
2004
Yoseph Assefa
Study on the distribution and structure of Ericaceous vegetation was made on the southern slopes of Bale mountains, the Harrena escarpment. The vegetation north of Rira village, between 3000 m and 4200 m was sampled after selecting continuous homogenous sites systematically along the altitudinal gradient. Frequency, height and DBH for woody treeline species were taken in 110 quadrates. The environmental parameters along the altitudinal gradient including soil pH, texture, total nitrogen, and soil moisture were measured. Altitude, slope, and aspect were measured for all quadrates. All the environmental and vegetation data were analyzed with Syntax, Canoco, Minitab and Sigma plot statistical softwares. The pattern of distribution of 7 treeline trees and shrubs (Hagenia abyssinica, Hypericum revolutm, Rapanea (Myrsine) melanophloes, Schefflera volkensii, Erica trimera, E. arborae, and Discopodium peninervium) were also documented alitudinally. The height of the tree and shrub species has shown a decreasing tendency with increase in altitude. This trend was very gradual for E. trimera. The species occurs for about a 1.2 km altitudinal range, showing difference in height and habit along the altitudinal gradient. The regression analysis (square r=0.58) has shown a consistent decrease in height along altitude. Among the environmental parameters taken, altitude was the strongest explanatory variable. While incidence of fire is correlated with socioeconomic parameters and relief, soil pH, and texture have shown a stronger correlation with altitude. Percentage total nitrogen showed more significant (p0.01) correlation with microsite factors.
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