Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

In contrast to the northern highlands, southern Ethiopia is within the East African climatic
domain, which is influenced during the larger part of the year by south-easterlies originating over
the Indian Ocean. As in most Ethiopian highlands, the inter-tropical convergence zone (ITCZ),
plus altitudinal and topographic influences all affect the distribution of the precipitation in the Bale
Mountains. Annual rainfall ranges between 600-1500 (2000) mm depending on the relief and altitude
Diurnal variability in temperature in the Bale Mountains is higher than its seasonal variation.
A minimum temperature of -15°C was recorded by Hillman (1986) on the Plateau (3850 m), while
Miehe and Miehe (1994) recorded a night-time minimum temperature of -3°C in the sparsely
vegetated areas of the Ericaceous belt. Solifluction is common in the Afroalpine belt and in the
upper parts of the Ericaceous vegetation.
There is evidence of early settlements in some valleys and plains. Thus, the area has probably
been populated since ancient times, but human land use and barley production in the Ericaceous and
Afroalpine belt has increased tremendously with the construction of an-all-weather road traversing
the plateau. However, the highlands of the Bale Mountains are still less densely populated than
the Semien Mountains in northwestern Ethiopia (population densities are 23.4/km2 and 52.6/km2 ,
respectively). Barley is cultivated in Bale 600-800 m lower than in Semien, and this is due to the
transhumant mode of living in the Bale Mountains.
Vegetation Sampling
The current study covered vegetation in the Ericaceous belt of the Bale Mountains along an altitudinal
gradient ranging from 3000 to 4200 m. Transects were established in homogeneous patches of
vegetation (Mueller-Dombois and Ellenberg 1974). Plots of 15 x 15 m were sampled at intervals
of 20 m lateral distance between the plots. For each plot, one sub-plot of 2 x 2 m was surveyed
for the herbaceous vegetation. All vascular plants in each plot were recorded by estimating their
cover-abundances using the 9-level scale of Braun Blanquet as modified by Van der Maarel (1979).
The size class structure of all tree and shrub species was also assessed in each plot by recording
the height and diameter at breast/stump height (DBH/DSH) of all stems > 2.5 cm were taken. For
multi-stemmed trees, each stem was recorded as individual tree. Species were identified on site with
the help of trained taxonomist and specimens s were collected for identification for using flora of
Ethiopia. Seedlings (below 1.5 m) and saplings (above 1.5 meter but below 2 meter) of juvenile
woody species were counted in a sub plot of 5 x 5 m in each quadrat; the total sample was thus 110
plots and 110 sub plots.
Data Analysis
Vegetation data were analyzed with the software package SYN-TAx 2000, using the hierarchical
clustering by distance optimization (Podani 2000). The Soerensen similarity index was used as the
distance measure and the average linkage as the cluster algorithm. Species diversity was measured
using the Shannon-Weaver index of diversity (Krebs 1989). As a proxy for the age structure of
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 161