Browsing by Author "Woldu, Zerihun (Professer)"

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    Ecological Study of the Natural Regeneration of the Woody Species In Enclosed Areas In Raya Azebo Woreda, Southern Zone, Tigray
    (Addis Ababa University, 2018-12-04) Woldu, Habtu; Demissew, Sebsebe (Professer); Woldu, Zerihun (Professer)
    The study was conducted in Raya Azebo Woreda, Southern Tigray at about 662 km from Addis Ababa. It is under severe pressure due to grazing, anthropogenic activities and rainfall fluctuations. Floristic composition, natural regneration and soil analysis were assessed. Data were collected from three area closures and their adjacent grazed lands using preferential and systematic sampling procedures. Vegetation data were collected from a total of 90 sampling plots and each field site comprised of 30 plots. In each of the study sites, sample plots having an equal size of 20 m x 20 m were designated as the main plots used to investigate the densities and distribution of woody species. Moreover, each main plot was divided into five smaller sub-plots of sizes 5 m x 5 m for regeneration counts (seedlings and saplings) and sizes of 2 m x 2 m for measuring cover abundance of herbaceous layers (grasses and forbs) in the woodland. In each sampling plot diameters of each woody species and environmental variables were recorded. From each plot, soil samples were collected to analyze the following edaphic parameters: soil pH, soil texture, available phosphorus, total nitrogen, cation exchange capacity, exchangeable bases and soil conductivity. A total of 133 species representing 45 families were recorded. Fabaceae followed by Poaceae, Asteracae and Euphorbiaceae were the most dominant families in the study area. Five plant community types were identified from the hierarchical cluster analysis and named after two dominant species in each cluster. The density of all seedlings were 410 individuals/ha while the total sapling density was about 212 individuals/ha. The overall regeneration status of the study area was found to be good regeneration (5.56%), fair regeneration (55.56%), poor regeneration (22.22%) and no regeneration (16.67%). The major factors affecting the regeneration of species in the woodland are frequent rainfall fluctuations, anthropogenic distrubances and grazing pressures. The influential environmental variables of the study area were altitude, pH, EC, Na, K, Ca, Mg, CEC, TN, OM, P, Sand%, Silt% and Clay%. The proportion of sand, silt and clay contents of the study area was 66.58%, 21.66% and 11.78% respectively which impliess the soils in the area was sand dominated. The five textural classes of soil identified in the study areas were sandy loam followed by sandy clay loam, clay loam, loamy sand and loam. The soil pH in the area ranges from neutral (7.0 - 7.3) to strongly alkaline (8.5 - 9.0) because the pH of dryland soils could be affected by the deposition of unleached exchangeable cations on the soil surface due to insufficient rainfall, hence, keeping the soil pH high.
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    Vegetation, Land Use Pattern and Soil Seed Bank Composition Along Altitudinal Gradient From Lake Tana to Mount Guna, South Gondar, Northern Ethiopia.
    (Addis Ababa University, 2018-04-03) Belay, Birhanu; Demissew, Sebsebe (Professer); Woldu, Zerihun (Professer); Evangelista, Paul (PhD)
    Vegetation distribution, Land use pattern and soil seed bank composition along altitudinal gradients from Lake Tana to Mount Guna, South Gondar, Northern Ethiopia. Birhanu Belay Telake, PhD Dissertation Addis Ababa University, 2018 The study area covers two watersheds (Rib and Gumara) occurring between Lake Tana and Mount Guna with elevation ranges between 1781 (near Lake Tana), and 4102 m asl (at Guna Mt.) which harbors different habitats. The study was conducted with the objectives of (i) investigating floristic composition, community types and vegetation structure, (ii) identifying the most important environmental predictors used to build habitat suitability Model for prioritized invasive species, (iii) evaluating soil seed bank composition, density and its implication for restoration, and (iv) determining the trend, rate and extent of LU/LC change for the period 1984-2017. Preferential sampling technique was used to establish 98 plots, 20 x 20 m each. The data was analyzed using Rx64 3.4.2 software packages. In aboveground vegetation, a total of 342 plant species were identified, of which 97.53% were angiosperms, 5.84% endemic, 3.51% invasive and 52.05% were herbs. Asteraceae was the most dominant family with 47 (13.74%) species. Five community types were identified, of which Cynodon dactylon and Eleusine indica Community type I harbors 30.31% of the species. About 22.08% of the total IVI value calculated for Chionanthus mildbraedii (6.63%), Juniperus procera (5.89%), Maytenus arbutifolia (4.87%), and Syzygium guineense (4.69%). Maximum entropy (Maxent) indicates that the highest contribution to predict the spatial distribution of Senna didymobotrya was recorded from Classified Map (41%), and elevation (33.2%). Among 17 environmental parameters, only nine were significant at p≤0.05. In the soil seed bank, 12,896 individuals were extracted from 392 soil samples laid on 15 x 15 cm are represented by 140 species, 103 genera and 44 families. Poaceae was the most dominant family with 32 (22.86%) species. Seven LU/LC types were identified using ArcMap 10.3.1: Cropland, Forest, Grassland, Settlement, Shrubland, Water, and Wetlands. Cropland, Water and Settlement show an increasing pattern while Grassland, Shrubland and Wetlands continuously decrease with time series. But Forest showed an irregular pattern. It is hoped that this study will provide information for decision-makers and academicians on the vegetation status, long-term LU/LC changes, drivers and impacts of Rib and Gumara catchments in order to take appropriate measures.