Environmental and Social Impact Assessment - Gibe III

Gibe III – Environmental and Social Impact Assessment 300 ENV R CS 002 C - A9003099
The biomass of the woodland on the hill slopes at Terraces II and III was estimated in 20m x 20m (400 m 2 )
at three different sites. Biomass of the forest vegetation in terrace IV was estimated at two different sites.
The geographical coordinate of each stop is recorded as degree decimal and UTM using a Garmin GPS.
The presence of terrestrial and aquatic animals species i.e. insects, lizards, birds, primates, ungulates,
warthogs, forest hogs, porcupines, various ungulates and their predators and aquatic animal species such as
fish, crocodiles and hippos as well as birds were noted and their food web speculated.
Omo Valley is part of the Broad-leaved deciduous woodland of Western Ethiopia described in Pichi-Sermoli
1957. The vegetation on the hill slopes of the valley is characterized by deciduous phenology of the
woodland species which shed their leaves during the dry season and regain them during the wet season as an
adaptive mechanism for the prolonged dry season. Important species include Boswellia pirote, Lannea
schimperi, Anogeissus leiocarpus, Terminallia browni, Combretum molle, Tamarindus indica,
Stereospermum kunthianum and Gardenia ternifolia. There is also a distinct narrow zone of riparian
vegetation along river and stream banks owing to the relatively moist conditions Pichi-Sermoli (1957). The
species composition of the riparian vegetation is similar to that of the hill slopes except that the individual
trees are larger in size.
The altitudinal ranges, temperature, humidity and the floristic and physiognomy composition of the
vegetation in the Omo river basin along with the system in Gibe Basin provide ideal conditions for Tsetse fly
infestation (Getachew, 1983; NMSA, 1996; Reid, R., et al. 1997, Reid et al., 2000).
5.2.2.1 Forest and Vegetation Resources
The existing vegetation in the project area is broadly classified into two parts, namely the woodland and the
riparian. However, the proposed reservoir area is neither contiguous with, nor in close proximity with any of
the nationally or regionally protected forest areas.
The landscape on either side of the valley had four distinct terraces, terrace I on the plateau (above 2300 m
asl), Terrace II at 1600 m asl, Terrace III at 1000 and Terrace IV at the river bank.
The dry woodland landscape can be partitioned into three distinct types (Pichi-Semoli, 1957) namely:
• the highland vegetation which is remnant of the vegetation of the plateau referred to as the dry
evergreen mountain forest and the associated grasslands at Terrace I;
• the broadleaved deciduous woodland of the low-lying altitude at terrace II and III; and
• the riparian vegetation at Terrace IV.
The Highland Vegetation: The highland vegetation could be encountered on the plateau at 2300 m asl and
above at Wolayita, Waka and the vicinity before the dissent to the valley as part of the agroforestry system.
The species include Erythrina brucei, Prunus africana, Podocarpus gracilior, Juniperus procera, Croton
macrostachyus and Arunidnaria alpina interspaced in with enset and Eucalyptus plantations.
The Lowland Broadleaved Deciduous Woodland: The plant species of the Omo Valley have over time
developed adaptive mechanisms and traits that allow them either to survive fire, to germinate after the heat
shock or to regenerate after a fire episode. The selective pressure of fire on the plant communities has
produced plant species, which are fire resistant, or pyrophytes (Kuhnholtz-Lordat, 1938). In the Omo valley,
the bush fires occur between late February and early April. The combination of climatic factors such as
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