Ecological Study of the Natural Regeneration of the Woody Species In Enclosed Areas In Raya Azebo Woreda, Southern Zone, Tigray
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Date
2018-12-04
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Addis Ababa University
Abstract
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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Keywords
Natural Regeneration, Ordination, Area Closures, Anthropogenic Activities, Species Diversity, Soil Texture