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

among seasons are usually only a few °C. While thermal seasons are thus weakly pronounced, wet
season are often clear because most tropical mountains lie outside the permanently moist tropics
(Smith 1980; Rundel 1994).
Soil temperatures of 5.9 - 7.3°C are often described to coincide with the treeline position
(Rundel 1994; Miehe and Miehe 1994); this goes back to an earlier proposal of a threshold at 7°C
mean soil temperature (Walter and Medina 1969). There is a wide range of divergent opinions on
the interactions between plant life form and microclimate. Koerner (1999, 2003) argues that the tree
life-form is disadvantageous on high mountains because the vertical stature results in close coupling
to the ambient climate and thus in more severe stress in the free air than near the ground. However,
ecophysiological research on the giant rosette plant Lobelia rhynchopetalum, which builds tree-like
life-forms in the Bale Mountains, showed that plants escape the pronounced diurnal fluctuations and
the harsh environmental stress near the ground by having an arborescent habit (Masresha Fetene et
al. 1998). A similar observation has been made on Mt. Elgon (Wesche 2002), and this has also been
noted by O. Hedberg decades ago: “When camping in the alpine belt an explorer soon discovers that
it pays better to put a sheep skin below the sleeping bag than on top of it – the cold comes from the
surface of the ground” (p. 23, Hedberg 1964).
Centuries of human land use have fundamentally altered tropical-alpine landscapes
particularly in Africa (Miehe 2000). The lower Afroalpine belt has been severely affected by fires
(Hedberg 1964), which are responsible for the patchy vegetation structure (Wesche et al. 2000).
Fires are mostly man-made, and caused a depression of the actual treeline in most mountain ranges
(Miehe and Miehe 1994; Wesche et al. 2000).
Regions above 3000 m a.s.l. including the treeline ecotone in eastern Africa are characterized
by Ericaceous vegetation (Miehe and Miehe 1994), which comprises a number of taxa with small
sclerophyllous leaves. The most prominent family is the Ericaceae, which is distributed throughout
the world. The sub-family Ericoideae is restricted to Africa, the Mediterranean and northern Europe
(Beentje 1994); Erica itself is a macrogenus with a largely artificial taxonomy. The Bale Mountains
have the most extensive Ericaceous vegetation in east Africa and the largest Afroalpine environment
of all (Hedberg 1986; Miehe and Miehe 1994). The mountains host a unique mixture of various
biogeographical elements. Important endemic mammals in the area include the giant mole rat
(Tachyoryctes macrocephalus), but also the endangered Ethiopian wolf (Canis simensis), which has
its most important habitat there (Sillero-Zubiri et al. 1995). The flora is still not completely known,
but there are a number of endemic and / or endangered species (Hedberg 1975; Miehe and Miehe
1994).
Although the Ericaceous vegetation of the Bale Mountains is claimed to be relatively intact
(Miehe and Miehe 1994) and more spatially extensive than in other regions of eastern Africa, it
is frequently cleared by local communities to create new pastures and arable land. The growing
concern for the destruction of mountain ecosystems in general, and the importance of this particular
mountain region as a refuge for the endemic fauna and flora (Brown 1973), calls for rapid action in
conservation and management. This in turn requires baseline data on the ecology of the prominent
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 159