Impact Assessment Of Dam Construction On The Floristic Cmposition And Diversity A Case Of Gilgel Iii Hydroelectric Damsouthwe Stern Ethiopia

Impact assessment of dam construction on floristic composition and diversity werernstudied in Gibe III hydroelectric dam project site. The study mainly focuses in identifyingrnand describing the floral species composition and diversity in the upstream, down streamrnand river bank area, indicating the possible impacts that will occur due to constructionrnand operation phase and to recommend mitigation measures. A total of 62 releves, 20 mrnx 20 m were laid preferentially by vegetation structure, to collect data on abundance (forrnshrubs and herbs), DBH and density (for tree species only). Two Indicator SpeciesrnAnalysis (TWINSPAN) was used to classify the vegetation community types. ThernShannon-Weiner diversity and evenness indices and density were calculated and the IVIrnof dominant tree species was finally estimated.A total of 86 plant species belonging to 31rnfamilies and 61 genera were identified of which 50% were shrubs, 40.7% were trees,rn6.9% were tree/shrubs, 1.2% were herbs and 1.2% were woody climber. The Shannon-rnWeiner diversity index of the upstream part was the highest and the lowest speciesrndiversity was recorded at the down stream. The species diversity and richness was higherrnat higher altitudes both right and left side of the upstream, H’=3.58, species numberrn(65), H’=3.43 and with species richness (S=68), respectively. The density of woodyrnspecies with DBH > 2 cm (1228/ha), basal area (0.39m2 /ha), frequency of all treernspecies (428/ha) and those tree species with higher important value index werernCombretum adenogonium, Diospyros mespiliformis, Combretum molle, Ekebergiarncapensis and Acacia sieberiana. Two Way Indicator Species Analysis classifiedrnvegetation of the Gibe III hydroelectric dam site into five community types: (I) Acaciarnhockii – Harrisonia abyssinica type; (II) Combretum molle – Bridelia scleroneura type;rn(III) Diospyros mespiliformis – Combretum hereroesen type; (IV) Uvaria leptocladon –rnCombretum adenogonium type and (V) Croton dichogamus – Terminalia laxiflora type.rnThe Shannon-Weiner diversity and evenness indices showed that community type II wasrnthe most diverse and had the highest species richness. The most even distribution ofrnspecies was at community type I, where as community type V had the least diverse andrnevenness of species. A total of 53 species belonging to 24 families and 38 genera werernrecorded in the river banks of the study area, of which 47.17% were shrubs, 45.28% wererntrees, 5.66% were trees or shrubs and 1.89% was woody climbers.The Shannon-Weinerrnand evenness indices show that riverine vegetation had higher diversity and evenrndistribution of species. The riverine vegetation density of individual trees with DBH > 2rncm was 1134/ha, frequency of all tree species (69/ha) and riverine vegetation tree speciesrnwith higher IVI were Combretum molle, Tamarindus indica, Haplocoelum foliolosum,rnSterculia setigera and Acacia dolichocephala. Generally, any project implementation inrnnatural ecosystem will cause a negative impact on the vegetation in particular and thernecosystem as a whole. Thus, this study revealed that even though implementing the GibernIII hydroelectric dam has an impact on vegetation composition and diversity, to reducernits impact to a minimum level implementing appropriate mitigation measures isrnrecommended.rnKey words: Floristic composition, Species diversity, Plant community, Gibe III dam

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