Soil seed bank evaluation along a degradation gradient in arid rangelands of the Somali region, eastern Ethiopia

The potential and regeneration capacity of soil seed banks in three eastern Ethiopian rangeland ecosystems (Asbuli grassland or arid grassland, Aydora open savanna or arid bush/grassland and Hurso closed savanna or arid bush land) were determined over a degradation gradient. Soil samples from 0.09m² blocks (100mm deep) were spread evenly in plastic containers in the greenhouse and studied over a 1-year period. The aboveground species composition was also compared. Sampling was from rangelands in excellent, good, moderate and poor conditions for each ecosystem. A total of 122 plant species were identified in the soil seed banks, with 32% in the Asbuli grassland, 35% in the Aydora open savanna and 33% in the Hurso closed savanna. Seedlings emerging from soil samples were in the order of decreasing number, grasses, forbs, woody plants, weeds and legumes. Seedling density decreased (P <0.05) in the soil seed bank with rangeland degradation in all ecosystems. Grass species richness was poorer in the degraded Asbuli grassland ecosystems, but increased in the Aydora open savanna and Hurso closed savanna. The grass species Tragus berteronianus and woody plant Crotolaria albicaulis dominated the botanical composition of the seed bank for all ecosystems with rangeland degradation. Eragrostis cilianensis and Eriochloa nubica were the dominant grass species in the soil seed bank of all ecosystems, regardless of rangeland degradation. There is no adequate evidence to prove that severe degraded rangelands in eastern Ethiopia maintain adequate soil seed banks that would improve the condition of it through restoration. Application of efficient management systems and long-term conservation planning in future is therefore important for sustainable use of the natural recourse and livestock production systems in arid ecosystems.