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

it was absent from the central subzone. Hypericum revolutum and Myrsine melanophloeos showed
a similar distribution. General density of tree species showed a similar trend as the frequency and
cover. Hagenia abyssinica attained its highest density (i.e. no. of stems / ha) in the lower subzone,
while M. melanophloeos had its peak in the central subzone.
Table 2. Height, DBH , and total number of stems for five treeline species at the lower (1), central
(2), and upper (3) subzones of the Ericaceous belt in the Harenna escarpment, Bale Mountains (for
DBH and height mean ± 1 standard deviation).
Species Subzones DBH Height n (no. of stems)
D. penninervum 1 2.23 ±1.90 119
2 1.75 ±1.28
3 -- -- -
E. arborea 1 - 1.62 ±1.20 106
2 4.04 1.12 ±0.80
3 -- 0.95 -
E. trimera 1 23.34 ± 7.44 10.19 ±2.20 255
2 12.32 ±12.38 5.30 ±4.53
3 10.00 ±8.20 2.08 ±1.98
H. revolutum 1 26.75 ±8.83 13.60 ±3.37 96
2 16.74 ±10.11 7.37 ±5.86
3 -- --
M. melanophloeos 1 25.02 ±9.49 16.50 ± 6.87 91
2 14.34 ±7.81 8.96 ±6.60
3 -- --
Population structure of trees/shrubs
The height of treeline species decreased with increasing altitude (Table 2). The most notable change
was observed for E. trimera. The regression analysis showed a strong inverse relation between
altitude and plant height (R2 = 0.60). This could be attributed to increase in the environmental struss
such as decrease in temperature (8. Height=54.81-1.42E-0.2altitude).
Although E. trimera is found in all three subzones, it shows variation along the altitudinal gradient.
In the lower (Fig. 1a) and central (Fig. 1b) subzones the size class 7 and 8 are not represented,
while classes 4, 7, 8, 9 are absent in the upper subzones. There might be various reasons for their
absence. A socio-economic study in the area (IBC pers. comm.) has revealed that fuel wood is the
main source of energy for the local communities. Erica trimera and E. arborea are the third most
preferred species only surpassed by M. melanophloeos and Schefflera volkensii. The small twigs of
Erica are the most preferred species for cooking staple foods that require a medium but steady heat
source. Logs are used for constructing huts and fences around farm yards. In addition, Erica spp. are
also highly preferred species for cattle fodder, and construction of bee hives.
Hagenia abyssinica has a more or less ‘J’ shaped-distribution in the lower subzone. However,
it was totally absent in the first, second, fifth, seventh, eighth, and ninth diameter class (Fig. 1d).
Those diameter classes are economically needed both for logging and timber production. The species
is known to be the preferred species for timber production due to its durability and resistance to
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 165