IMPACTS OF CLIMATIC FACTORS AND GRAZING ON VEGETATION STRUCTURE, SPECIES DIVERSITY, HERBACEOUS BIOMASS AND SOIL NUTRIENTS IN CASE OF BORANA ZONE, SOUTHERN ETHIOPIA

Abstract

The study was conducted in three districts of Borana Zone, with the objective to determining the impacts of climatic factors and grazing on vegetation structure, herbaceous biomass yield and soil nutrients of Borana rangelands under traditional enclosure and continuous grazing rangeland types during end of growing season. Within both rangeland types of each districts 20 m x 20 m plots were placed at 200 m distances intervals with three replication used to collect woody vegetation and, soil samples from four corners and center of main plots within three depths (0-10 cm, 10-20 cm and 20- 30 cm) to analysis its soil physio-chemical properties. The data of herbaceous plant community was collected from seventeen quadrants (1 m x1 m) that layout in the main plot. The collected data was analyzed by linear regression to determine the impact of climate factors and General Linear Model (GLM) procures and Pearson chi-square statistic for grazing impacts. The herbaceous species richness, diversity and biomass study sites had highly significantly difference (P < 0.001) and positive linear with mean annual precipitation. There is significantly difference (P < 0.05) and negative linear in woody species richness and diversity. Both herbaceous and woody plant species richness and diversity of study areas had a negative linear with mean annual temperature. Due to grazing impact a significance difference (P<0.05) was detected with woody vegetation cover, structure(seedling, sapling and small shrubs and shrubs/trees), richness, evenness, diversity, and density in relation to rangeland types and study sites. The woody plant covers of Arero, Telltale and Yabello continuous grazing were reached about 65.67%, 78.00 % and 78.33 % respectively, which was beyond borderline of encroachment. High relative density and frequency of desirable woody plant species found in the traditional enclosure than continuous grazing rangeland types. Due to grazing and recent drought effect, the herbaceous species was slightly significant showing difference (P<0.05) in their groundcover, richness, evenness, diversity, and dry matter within rangeland types and among study sites. The highest proportion of highly desirable herbaceous species observed in traditional enclosure than continuous grazing rangeland types. The study sites of soil texture class was loam Sandy, sandy loam and silt clay. The soil pH value was significantly different (P > 0.05) among study sites but not significance difference between rangeland types and soil depths. The soil total nitrogen was significantly difference (P > 0.05) between districts, rangeland types and soil depth. Climate factors and continuous grazing have a great impact on rangeland ecosystem. Therefore, rangeland user should be considering both climatic factors and grazing to improve rangeland vegetation status and soil nutrien