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Title: Impact Assessment of Dam Construction on the Floristic Composition and Diversity: A Case og Gilgel Gibe III Hydro Electric Dam, SouthWestern Ethiopia
Authors: Fisseha, Adugna
Advisors: Sebsebe Demissew(Prof.)
Keywords: Floristic composition
Floristic composition
Plant community
Gibe III dam
Copyright: Nov-2010
Date Added: 12-Jul-2012
Publisher: Addis Ababa University
Abstract: Impact assessment of dam construction on floristic composition and diversity were studied in Gibe III hydroelectric dam project site. The study mainly focuses in identifying and describing the floral species composition and diversity in the upstream, down stream and river bank area, indicating the possible impacts that will occur due to construction and operation phase and to recommend mitigation measures. A total of 62 releves, 20 m x 20 m were laid preferentially by vegetation structure, to collect data on abundance (for shrubs and herbs), DBH and density (for tree species only). Two Indicator Species Analysis (TWINSPAN) was used to classify the vegetation community types. The Shannon-Weiner diversity and evenness indices and density were calculated and the IVI of dominant tree species was finally estimated.A total of 86 plant species belonging to 31 families and 61 genera were identified of which 50% were shrubs, 40.7% were trees, 6.9% were tree/shrubs, 1.2% were herbs and 1.2% were woody climber. The Shannon- Weiner diversity index of the upstream part was the highest and the lowest species diversity was recorded at the down stream. The species diversity and richness was higher at higher altitudes both right and left side of the upstream, H’=3.58, species number (65), H’=3.43 and with species richness (S=68), respectively. The density of woody species with DBH > 2 cm (1228/ha), basal area (0.39m2 /ha), frequency of all tree species (428/ha) and those tree species with higher important value index were Combretum adenogonium, Diospyros mespiliformis, Combretum molle, Ekebergia capensis and Acacia sieberiana. Two Way Indicator Species Analysis classified vegetation of the Gibe III hydroelectric dam site into five community types: (I) Acacia hockii – Harrisonia abyssinica type; (II) Combretum molle – Bridelia scleroneura type; (III) Diospyros mespiliformis – Combretum hereroesen type; (IV) Uvaria leptocladon – Combretum adenogonium type and (V) Croton dichogamus – Terminalia laxiflora type. The Shannon-Weiner diversity and evenness indices showed that community type II was the most diverse and had the highest species richness. The most even distribution of species was at community type I, where as community type V had the least diverse and evenness of species. A total of 53 species belonging to 24 families and 38 genera were recorded in the river banks of the study area, of which 47.17% were shrubs, 45.28% were trees, 5.66% were trees or shrubs and 1.89% was woody climbers.The Shannon-Weiner and evenness indices show that riverine vegetation had higher diversity and even distribution of species. The riverine vegetation density of individual trees with DBH > 2 cm was 1134/ha, frequency of all tree species (69/ha) and riverine vegetation tree species with higher IVI were Combretum molle, Tamarindus indica, Haplocoelum foliolosum, Sterculia setigera and Acacia dolichocephala. Generally, any project implementation in natural ecosystem will cause a negative impact on the vegetation in particular and the ecosystem as a whole. Thus, this study revealed that even though implementing the Gibe III hydroelectric dam has an impact on vegetation composition and diversity, to reduce its impact to a minimum level implementing appropriate mitigation measures is recommended.
Description: A Thesis Submitted to the School of Graduate Studies Addis Ababa University In Partial Fulfillment of the Requirement for the Degree of Master of Science in Environmental Science
URI: http://hdl.handle.net/123456789/3343
Appears in:Thesis - Environmental Sciences

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