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

B. Rocky slopes with Alchemilla haumannii and heather
Gentle slopes vegetated by Alchemilla haumannii and varying densities of Erica, with scattered
rocks or scree.
C. Grazed sparse heather slopes and short sedge swamps
A mixed class, representing both clumped Erica and shallow wetlands with short sedges. Sample
size was too low to accurately describe the plant species composition.
D. Lava slopes: rock formations with interspersed heather
Shaded slopes dominated by bare rock and boulders, with interstitial Erica. An example of this class
is the spectacular lava formations at Rafu.
E. Lava flows: boulders interspersed with shrubby grassland
The flatter tops of the lava flows with a preponderance of bare rock, although less so than class D
(Table 5). Euryops prostratus is highly prevalent, with Erica and Helichrysum splendidum bushes
scattered through sparse grassland.
F. Bare rock and Helichrysum citrispinum/Alchemilla haumannii
Vegetated mainly by A. haumannii and H. citrispinum (characteristic of rocky ground, (Hedberg
1957)), or short H. splendidum, bare bedrock dominates the spectral signature. It has the highest
proportion of rock along with class T, the highest cover of A. haumannii and the second highest
cover of H. citrispinum after class G. The ground cover is dominated by A. abyssinica rather than
grasses.
G. Sparse mixed Helichrysum with Alchemilla abyssinica
Helichrysum sp. dominate this class; it has by far the highest cover of Helichrysum gofense, and
also the highest cover of H. citrispinum. Grass cover is low, and there is more bare soil, pebbles
and scattered small rocks and fewer expanses of bare rock than its closest relative, class F. As with
classes I and J, solifluction (churning of the soil through diurnal freeze-thaw cycles) is likely to
contribute to the low vegetation cover at the high altitude characteristic of this class,
Table 2.
h. Dense Helichrysum splendidum with scattered giant lobelia
Representing the high-altitude Helichrysum pastures characteristic of the Bale Mountains plateaux,
this class has by far the highest density of H. splendidum, and the highest occurrence of giant lobelia
Lobelia rhynchopetalum. It is the most widespread vegetation type in the northwestern reaches of
Sanetti, south of the Rafu lava flows. The uniform H. splendidum cover is interrupted by occasional
lichen-covered rocks and Lobelia stands, and grasses dominate the ground cover.
I. Sparse Helichrysum gofense/Euryops prostratus
With very low cover dominated by creeping shrubs such as H. gofense and Euryops prostratus, this
class has short vegetation and large expanses of bare soil. It is part of the nival zone (cold desert
belt), found at a median altitude of 4079 m. Solifluction is likely to be a major cause of the low
vegetation cover in this class and its closest relative, class J. Fairly high densities of Haplocarpha
rueppellii support this conclusion, as this species is often found on solifluction soil as well as
favouring wetlands and stream edges (Hedberg 1957).
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 106