Browsing by Author "Woldu, Zerihun (PhD)"
Now showing 1 - 9 of 9
Results Per Page
Sort Options
Item Comparative Study of the Vegetation Composition of Mt. Alutu and Mt. Chubbi along Altitudinal Gradient(Addis Ababa University, 1999-06) Shibru, Simon; Woldu, Zerihun (PhD)Comparative study of the vegetation composition of Mt. Alutu and Mt. Chubbi along altitudinal gradient was performed. Seventy-one, 20m x 20m stands, thirty-seven from Mt. Alutu and thirty-four from Mt Chubbi were selected systematically and all plants in the stands were recorded as present. Cover abundance value for trees, slU'ubs, and herbs was estimated. In addition trees and shrubs were counted. Enviromnental factors (altitude, slopes degree and slope aspect) were measured. The vegetation data from both mountains were merged and analyzed using the program SYNTAX. The utility program was employed to analyze species diversity. Eight homogenous clusters of stands were recognized. The resulting clusters were intelpreted as conUllunity types and given provisional names after two or three dominant species. The clusters of the stands were compared for their averaged environmental factors using Tukey's family error rate test. The clusters of stands were found to show the highest degree of contrast due to variation in altitude, i.e. in Mt. Alutu and Mt. Chubbi the main vegetation gradient is caused by differences in altitude. The altitude gradient is associated with changes in slope degree. In the present study sites altitude to larger extent, and slope degree to a lesser extent were found to be the major determinants of vegetational variation, whereas, slope aspect was less important.Item Ecological Investigations on the Potential of three Woodland Tree Species for Agrofrestry Practices(Addis Ababa University, 1994-06) Abate Asferachew; Woldu, Zerihun (PhD)Three indigenous tree species namely Acacia tortilis (Forssk.) Hayne, Acacia senegal (L.) Willd. and Balanites aegyptiaca (L.) Del. were studied to explore their potential for agroforestry practices. Studies on the ecology and growth characteristics of the three tree species and their influence on environment were conducted at three different sites; Adamitulu, Awash and Abajata Shalla National Parks in the rift valley. A total of 15 releves (50 x 50 m), five releves in each of the sites were established. In each of the releves presence and abscence and frequency of all tree species was recorded. From each site a total of 15 trees, five for each study tree, were randomly selected for detailed investigation. Tree characteristics which included tree height, diameter at breast height (DBH), canopy depth, canopy radius and canopy diameter of each of the study trees were measured. Cover of undercanopy vegetation was estimated for each of the study trees to assess the influence of trees on undercanopy species diversity. To investigate the influence of trees on undercanopy soil, samples were collected from 50, 250, and 450 cm distances at 02.5, 5.0 - 8.0, and 20 - 23 cm depths along the transect radiating from tree boles. Texture, pH, conductivity, organic carbon, total nitrogen, available phosphorus and exchangeable potassium of the soil samples were analyzed. For comparison purposes cover of vegetation outside tree canopies and soil physical and chemical properties beyond the canopies of trees were also investigated. Of the three sites, Abijata Shalla area was characterized by high tree density (61/ 2500 m2 ), followed by Awash National Park (36/ 2500 m2 ) and Adamitulu area (17/ 2500 m2 ). Acacia torti/is had the highest DBH (0.42 ± 0.12 m), canopy diameter (13.64 ± 2.25 m) and canopy radius (6.91 ± 0.79 m) whereas the highest tree height (5.18 ± 0.77 m) and canopy depth (2.14 ± 0.73 m) were recorded for B. aegyptiaca. Undercanopy vegetation diversity of A. tortilis was highest (2.13) foIlowed by A. senegal (1.92) and B. aegyptiaca (1.78). In all sites undercanopy species diversity was significantly higher than vegetation diversity outside of tree canopies. Texture and pH did not vary between under and outside canopy soils implying that tree canopies did not affect these soil properties. Surface soil conductivity, organic carbon, total nitrogen, available phosphorus and exchangeable potassium were significantly higher under tree canopies for all the study trees compared with outside canopy soils. Comparison of the study trees top soil nutrient contents indicated that under canopy soils of A. tonilis had higher values foIlowed by A. senegal and B. aegyptiaca, respectively. Acacia tortilis and A. senegal had comparable seedling growth rates whereas the former had a higher seedling emergence vigor. The results showed that the study trees significantly enriched soil under their canopies and created a suitable environment for the growth of undercanopy vegetation. Over all A.tortilis had better growth characteristics and improVed most undercanopy soil. The significance of the findings for agroforestry are discussed.Item An Ecological Study o,f The Grassland Vegetation in Some Parts of Gojam.(Addis Ababa University, 1991-01) Asgedom, Yemane; Woldu, Zerihun (PhD)A study of the grassland vegetation in Gojam was made in October, 1989. 148 stands from 30 sites, were systematically sampled. A total of 115 species of vascular plants were recorded and cover-abundance for each species was estimated. The most commonly encountered species are members of the families Poaceae, Asteraceae, Cyperaceae and Fabaceae in that order. The vegetation data matrix was summarized by minimum variance and complete-linkage clustering techniques. Two major groups were identified by minimum variance clustering, i.e., one containing most of the quadrats from the wet sites and the other consisting most quadrats from the drier sites. Nine groups were identified by complete-linkage. These groups show some variations in management and drainage conditions and also show variability in species composition and diversity. In the protected and enclosed sites for afforestation, the dominant grasses are Andropogon abyss in icus R.Br ex Fresen and Hyparrhenia spp. while in the grazed sites Pennisetum sphacelatum Th. Dar and Schinz, Eleusfne floccifolia (Forsk.) Spreng., Plantago lanceolata L., Eragrostis tenuifolia A. Rich and Cynodon dactylon (L.) Pers. are the species which have higher cover abundance values. In the wet sites which are protected during the rainy season Andropogon chrysostachys Steud, Pennisetum glabrum Steud., Eragrostis botryodes Clayton., Uebelinia sp. Pycreus atronervatus (BoCk) C.B.Cl and P. flavesence L. are the dominant species. In the wet and grazed sites the common species are Echinocloa haploclada Stapf. , Arthraxon micans (Nees) Hochst, Paspallum commersonii Lam. and Hygrophilla auriculata (Schum) Heine. The clusters obtained were compared based on the mean values of the environmental factors using analysis of variance and t-test. The intensively grazed and protected sites show differences in the mean values of per cent organic carbon and total nitrogen content. PH, conduct i v ity and cat i on content of the so il showed positive correlation between them selves.Item An Ecological Study of the Lowland Vegetation of Key Afer-Shala Luqa and Southwest of Lake Chamo, Southern Ethiopia(Addis Ababa University, 1997-11) Soromessa, Teshome; Derilissew, Sebsebe (PhD); Woldu, Zerihun (PhD)Studies in the vegetation of Key Afer-Shala Luqa ailG SouthWest of take Chaino Southern Ethiopia were conducted from Nov. 21, 1996 to February 27, 1997. The data on aboveground herbaceous phytomass was collected using 1m2 quadrat from 13 selected sites. To determine the different plant communities, data from 71 quadrats (400 m2) was collected following a 1-9 modified Braun Blanquet scale (van der Maarel, 1979). The environmental data collected consists of soil, altitude, slope and aspect. The average aboveground herbaceous phytomass ranged between 35.9 gm-2 in Shala plain to 1016.8 gm-2 in Southwest of Lake Chamo. Multivariate methods were employed to summarise the vegetation data. Seven community types and an outliers were identified. Statistical test (post-hoc comparison of means) among the community types showed significant variation in altitude indicating that altitude is the most important factor. Analysis of diversity among community types showed that the Hyparrhenia jilipendula- Combretl/Ill moUe dominated community is richer in species than others, while the Commiplwra cyclophylla-Actilliopteris radiata-Sallsevieria ehrenbergii dominated community is the least species rich community. The low aboveground herbaceous phytomass in sites like Shala might be attributed to ecological incompatibility with prevailing stocking rate. To ameliorate the interrelated causes of resource degradation, destocking should be taken into consideration.Item The Effect Of mineral Nutrition on the Growth of Three Ethiopian Grass Species(Addis Ababa University, 1989-06) Abera, Saba; Woldu, Zerihun (PhD)The effe,',ts of n'Jtrient gru.dients on the growth and chemlc8.1 compositions of three grass specief1 (Arilll:ll.];LQ®ll /lbyItem Forage Diversity and Impact of Grazing Management System on Rangeland Ecosystems in Mbeere District, Kenya(Addis Ababa Universty, 2003-06) Kamau, Peris; Woldu, Zerihun (PhD)Plant species composition, biomass, frequency and density of Mbeere rangeland has been described to compare open and enclosed sites. A total of 245 plallf species were identified. Clipping and preference unit technique were used to estimate herbaceous alld trees and shrub biomass respectively. Density and callopy cover were done through counting and visual estimation for three growth forms while forage preference was through direct obsen'ation. Soil samples were analysed for soil moisture, pH, total nitrogen, organic matter, exchangeable cations, percent carbon, available phosphorus, bulk density, soil colour and textural class (sand, clay and silt content). The species sampled were classified illfo twenty community types (ten each for herbaceous and all vascular plant species) using Syntax. The effect of grazing and management system in this rangeland was studied both on the vegetation and on the soil properties. Grazing reduces above ground biomass in communal lands mainly through overgrazing and elimination of palatable species. Forage productivity on the other hand largely depends on availability of rainfall and disturbance. In the dry season the biomass accumulated was relatively low but substantially increased during the wet season. Grazing management systems used in this particular rangeland have a direct impact on forage diversity. T-test results sholVS that total species ric/lIless and herbaceous richness in the open site were significantly differellf (pItem Plant Communities and Diversity along Altitudinal Gradients from Lake Abaya to Chencha Higlands(Addis Ababa University, 2002-06) Wana, Desalegn; Woldu, Zerihun (PhD)Vegetation-environment relationships have been investigated in the study. Community transition and species diversity are affected among others by environmental heterogeneity. Multivariate numerical techniques were adopted to identify communities. The resemblance function for the identification of communities was similarity ratio, while correlation coefficient was used to identify species groups. Shannon-Wiener diversity index and Jaccard’s community coefficient were computed to measure species diversity in a community and community transitions respectively. One-way analysis of Variance (ANOVA) was used to test the differentiation of communities due to environmental factors such as soil properties, slope and aspect. The results helped to identify five plant communities and seven species groups. Statistical analysis indicates that the differentiation of communities might partly be explained by the variation of soil properties and topographic features at p<0.05 level of significance, excepting Cation exchange capacity. Community’s grade gradually along altitudinal gradients as indicated by the high community coefficients 0.52, 0.53 and 0.16 (Table 1 and 2) in between adjacent communities. Shannon- Wiener diversity index revealed that species diversity and richness is high in communities 1, 2 and 3 at 1250-1800m altitudinal ranges. The high species diversity and richness could be due to environmental heterogeneity, which are associated with the effect of altitude. These communities are found in steep slopes and in areas of human settlement nearby where disturbance of the vegetation is observed. Therefore, conservation of these vegetation types should be given priority concern for the conservation of biodiversity in the study areaItem Root Growth Patterns and Plant Adaptability in Three Acacia Species(Addis Ababa University, 1999-06) Haileselassie, Teklehaimanot; Woldu, Zerihun (PhD); Fetene, Masresha(PhD)Trees and shmbs screened for desirable properties can play an important role in the rehabilitation of degraded lands. Indigenous species adapted to harsh conditions of degraded sites can reverse degradation processes by stabilizing soils, increasing organic matter and improvements of nutrient status etc. Studies have shown that Acacia species have a potential for use in agroforestry systems and rehabilitation of degraded lands. For proper evaluation of the use of Acacia species in rehabilitation schemes and for agroforestry systems, studies in the root growth patterns and adaptability are essential. The main objective of this study was, therefore, to assess the root growth patterns of some Acacia species namely, A.seyaf Del., A.senegal (L.) Willd. and A.tortilis (Forrsk) Hayne and see the relevance of the results in adaptation to aridity. The study was conducted in Abernosa Ranch and Abiyata Shalla National Park. To investigate rooting patterns of the selected Acacia species, young trees were carefully excavated exposing a representative portion of the root system and quantitative data taken on depth at which the first lateral root starts, radial spreading of lateral roots and the zone of most intense lateral roots. Saplings were completely uprooted and separated for shoot and root palis, and oven-dried for the determination of shoot-root ratio. To see the effect of the Acacia trees on their undergrowth, comparison of herbaceous root biomass was carried out with adjacent open grassland in Abernosa. There was some difference in root growth patterns between species, A.seyal characterized by few but very big lateral root in close proximity to the surface, A.senegal with very dense lateral roots near to the surface and A. tortilis with less prominent lateral roots as compared to the others. The length of the taproots and shootroot ratio of the saplings uprooted indicated that A.tortilis has greater depth penetration. There was no significant difference within species between the two sites for depth of first lateral root, zone of most intense lateral roots and for radius of lateral spread. Depth penetration and ramification of lateral roots seem to be a function of soil and bedrock conditions. The herbaceous root biomass under A.seyal was significantly higher than the adjacent open grassland indicating the influence in increasing productivity.Item Root Growth Patterns and Plant Adaptability in three Acacia Species(Addis Ababa Universty, 1998-06) Haileselassie, Teklehaimanot; Woldu, Zerihun (PhD)