Ecological Study of the Natural Regeneration of the Woody Species In Enclosed Areas In Raya Azebo Woreda, Southern Zone, Tigray

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Addis Ababa University


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.



Natural Regeneration, Ordination, Area Closures, Anthropogenic Activities, Species Diversity, Soil Texture