Browsing by Author "Gashaw, Menassie"

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    Plant Community Studies and Ecological in Vesttgation on the Afro Alpine Vegetation of Sanities Plateau of the mountains ,Ethiopia
    (Addis Ababa University, 1994-06) Gashaw, Menassie; Fetene, Masresha(PhD)
    The vegetation of the afroalpine and subafroalpine regions of Bale Mountains at Sanettie were studied to describe major plant groups and relationships between vegetation and edaphic, climatic and topographic factors. Vegetation composition was studied along an altitudinal gradient extending from 3400 m up to 4300 m above sea level. Vegetation was sampled from 20 m by 20 m quadrats. Frequency and cover of 65 species from a total of 77 quadrats were recorded, human interference was scaled 0 - 5, where 0 stands for insignificant or no interference and 5 for high interference. Soil samples were collected from each quadrat and analyzed for texture, pH, conductivity, organic matter, available phosphorus, total nitrogen, soil moisture content and exchangeable bases (K+ and Na +). Association analysis was performed on the vegetation data using NCLAS: Agglomerative clustering by distance optimization. Seven major plant groups, namely Kniphojia - Euphorbia - Alchemilla scrub, Erica - Philippi belt, Helichrysum citrispinum - Alchemilla abyssinica, Alchemilla hallmanii meadow, Festuca - Carex monostachya swamps, Helichrysllm splendidunl - Lobelia - Festllca - Ellryops and Lobelia - Festuca - Helichrysum gojens plant groups are described. The relative mean annual precipitation and daily fluctuations in temperature were found to be the most important factors determining plant group structure. The gradual changes in altitude associated with changes in atmospheric pressure, moisture, and temperature influenced the distribution of vegetation. Vegetation cover and species diversity decreased with an increase in altitude. Plant cover and diversity decreased with an increase in an estimated degree of human interference. Implications of the findings are discussed and recommendations are given towards the conservation of the biodiversity and the rational utilization of afroalpine ecosystems.
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    Survival Strategies and Ecological Performances of Plants in Regularly Burning Savanna Woodlands and Grasslands of Western Ethiopia, Gambella
    (Addis Ababa Universty, 2000-06) Gashaw, Menassie; Demissew, Sebsebe (Professor)
    The survival mechanisms of plants in response to fire were investigated to understand the ecological freqances of plants in frequently burning plots of savanna woodlands and grasslands. These studies included: strategies of post-fire regeneration and resistance of tree-bark to fire; plant cover, leaf nutrient and condensed tannin concentrations following experimental burning treatments and relationships between fire and seasonal variations in leaf condensed tannin; soil seed bank dynamics; influence of heat on seed germination. Regeneration mechanisms of vegetation were studied along a transect line by quantifying foliar cover and fi'equency of individual plant species regenerating by resprouting, by seedlings or both, during the dry season and the early wet season. Resprouting plants (both facultative and obligate) significantly contributed to post-fire recovery, comprising 98.S % of total vegetation cover. The contribution of seedlings to cover and abundance immediately following fire was negligible, but seedling density increased in the early rainy season, 4 to S months after fire. The vigour of resprouting and seeding among species in different plant growth forms was discussed in relation to fire regimes. The role of tree bark thickness to sUlvival was studied. Results indicated that tree bark resistance to fire varied interspecifically related to bark thickness, other characteristics and age ofthe plant. The effects ofthree treatments: fire, biomass additions and ash fertilisation on plant cover, leaf nutrient (N, P, K) and condensed tannin concentrations were examined prior to experimental burning and after 90 and 210 days. There was a strong effect of fire on the cover of grasses and tree seedlings (P