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

Ericaceous vegetation. The present study attempts to provide a description of plant communities and
an analysis of the structure of woody species in Ericaceous vegetation along the southern slopes of
the Bale Mountains.
Description of the Study Area
Floristic background
The botanical exploration of the Bale Mountains started in 1906 by Neuman and Ellenbeck (cited in
Miehe and Miehe 1994), followed by Smeds (1959), and Mooney (1963). In a series of publications
Hedberg (1951, 1964, 1975, 1986) made important analyses of the vegetation and ecology of
Afroalpine regions in Ethiopia. Weinert (1981), Weinert and Mazurek (1984) and Uhlig (1988)
also published ecological studies on the vegetation of the Bale Mountains. Research on the floristic
composition and physiognomy of the montane vegetation was conducted by Mesfin Tadesse (1986),
Friis (1986), Lisanework Negatu and Mesfin Tadesse (1989), and Uhlig (1988, 1991). However,
except for Hedberg (1986), Menassie Gashaw and Masresha Fetene (1996), and Miehe and Miehe
(1994), most of these studies were confined to the montane forest belt.
Based on its physiognomy, Friis (1986) recognized the zone between 3200 m and 3500 m
as the uppermost forest zone. This vegetation zone is relatively little disturbed by humans (Miehe
and Miehe 1994). The main constituent of this zone, Erica trimera, forms trees up to 15 m in
height. The vegetation differs considerably in physiognomy from that of higher elevations. Friis
(1986) recognizes fire as the primary reason for this physiognomic change, and altitude as a possible
additional factor.
More detailed data on the Ericaceous vegetation of Bale were provided by Miehe and Miehe
(1994), who compared and contrasted their findings globally and regionally. The giant heathers on
the southern slopes of the mountains harbor epiphytic communities that are crucial in buffering
water deifiet between montane and Afroalpine vegetation. These epiphytic mosses gradually release
the absorbed moisture; it was estimated that up to 50,000 litters per ha are absorbed in another east
African cloud forest (Pocs 1976). The cryptograms also serve as bio-indicators of environmental
conditions.
Geology and climate
The study area is located at the southern slope of the Bale Mountains, at the Harenna escarpment
between 6°45′ and 7°N and 39°45′ and 39°40′ E. The rocks are of volcanic origin. They are
predominantly trachytes but also include rhyolites, basalts and associated agglomerates and tuffs
(Weinert and Mazurek 1984). Although detailed information about glaciations is still lacking, the
current land forms in the mountains appear to have resulted from tectonic activity and glaciations. At
least two glacial periods (18,000 BP and 2,000 BP) are documented from the mountains (Bonnefille
1993).
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 160