Shashie Ayele, Lisanework Nigatu, Tamado Tana* and Steve W. Adkins
An invasive weed (Parthenium hysterophorus) is widely spread in the rangelands of Jijiga zone, Southeast Ethiopia. However, its impact on the diversity and composition of the standing vegetation and the soil seed bank of rangelands has not been determined. Thus, this study was undertaken to assess the impact of parthenium weed infestation on the above-ground and on the soil seed bank of herbaceous communities. On assessment of the above-ground vegetation, a total of 56 taxa belonging to 17 plant families were recorded with the most frequent families being Poaceae (20) and Asteraceae (9). The cover percentage of grasses was decreased from 62.7% at the no parthenium weed infested sites to 16.6% at the highest infested sites. Similarly, the dry biomass of Poaceae was significantly decreased from 428.1 g m-2 to 30.0 g m-2 from no to high parthenium weed infestation. In the soil seed bank, a total of 51 species belonging to 16 plant families were recorded with the most frequent families being Poaceae (16) and Asteraceae (7). Out of the 56 taxa recorded on the above-ground vegetation, 38 taxa were present in the seed bank with the lowest coefficient of similarity of 0.14 at the high parthenium weed infested sites. The germinable soil seed bank varied from 300.8 m-2 at very low to 1878.6 m-2 at high parthenium weed infestation. Parthenium weed in the seed bank accounted for 0.1% under no to 84.2% under its high infestation while that of grasses was decreased from 81.7% to 6.1%. Species richness and evenness indices of both the above ground vegetation and of the soil seed bank were significantly decreased at the high parthenium weed infestation. Hence, it can be concluded that the infestation of parthenium weed has significantly reduced the amount and composition of both the above ground and the seed bank of herbaceous vegetation especially the palatable grass species in the rangelands of south-eastern Ethiopia.
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