Seasonal Dynamics in Botanical Composition, Nutritive Value of Vegetation and Soil Nutrient Status of Gambella Rangelands, Southwestern Ethiopia
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2015-06
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Addis Ababauniversity
Abstract
This study was aimed at undertaking systematic assessment on seasonal dynamics in botanical composition of the vegetation layers; evaluating the seasonal dynamics in nutritive value of the key native grass and browse species; determining the seasonal dynamics in soil nutrient status of the grazing areas; and investigating the perception and traditional ecological knowledge (TEK) of Nuer pastoralists regarding seasonal dynamics in rangelands’ resources. The study was executed in the rangelands of Gambella, on conducting surveys at community and household levels employing a structured questionnaire in a total of 120 respondents. The vegetation and soil surveys were conducted during the consecutive wet and dry seasons of 2013/14. Four representative sites were selected as per district, which include three wet season grazing areas (woodlands, open woodlands and riverine forests) and one dry season grazing areas (savanna grasslands). Vegetation and soil sampling was determined by transect and quadrat methods. Botanical composition of the range was determined. The key native forage species were sampled and analyzed for DM, OM, ash, CP, NDF and ADF. Soil samples were collected and analyzed for OC, OM, TN, available P, CEC, soil pH, and soil texture. The perception and ecological knowledge of the Nuer pastoralists regarding the undergone rangeland resources dynamics has been assessed. Statistical analyses of variance was carried out using Generalized Linear Model of SPSS to test the main and interaction effects of the vegetation and soil parameters.Cross-tabulation and Chi-square tests were used to determine variations in the pastoralists’ perception. There were significant variation between seasons, species and their interaction at P<0.01 of the herbaceous layer in terms of their botanical composition. This indicates seasonal grazing areas dynamism of Gambella rangelands is great, especially of the grass vegetation communities. The woody layer botanical composition did not show significant seasonal
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variations (P>0.05) suggesting evergreen browses playing a vital role as a source of fodder when the herbaceous layer dried up and deteriorated. In the grass species except OM contents all of the parameters showed significant seasonal variations. Among the browse species all the nutritional parameters showed significant seasonal variations (P<0.01). The relatively higher CP value of the grass species during wet season indicates that grass species failed to supply sufficient nutrients for ruminants in dry seasons. Supplementation has been suggested to compensate for the drastic decline in the nutritive values of forage species as the dry season advances. High CP content of the browse species across seasons could justify their wider use as protein supplements for low quality tropical pastures. Except exchangeable cations K+ and Mg2+ all the soil characteristics showed no significant variations (P>0.05) seasonally. A more exhaustive measurement should be conducted over series of years on seasonal basis for a better understanding of the soil chemistry dynamics of the rangeland ecosystem. Nuer pastoralists have an in-depth knowledge and experience regarding the changes that the rangeland ecosystem has undergone. This knowledge and experience is believed to have profound importance for possible integration of scientific principles and practices for future sound rangeland management system in the region.
Key words: ecological knowledge, herbaceous layer, Nuer pastoralists, range ecosystem, soil chemistry, woody layer
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Keywords
ecological knowledge, herbaceous layer, Nuer pastoralists, range ecosystem, soil chemistry, woodylayer