Impacts of rangeland degradation on soil physical, chemical and seed bank properties along a rradient in three rangeland vegetation types in Somali region, eastern Ethiopia

The Somali region of Ethiopia is a typical pastoral area, that occupy >50% of the 0.7 million km2 rangeland in the country. However, all forms of rangeland degradations have become major threats to enhance a sustainable pastoral-livestock production in Ethiopia. But except for very few studies on rangeland condition assessments, no or too little research has been conducted to understand the different impacts of soil degradation on the range bio-physical ecology. As a result, there exists a gap in knowledge to plan present and future rangeland improvement interventions in the country. The purpose of this study is therefore, to understand the impacts of different rangeland degradation conditions on the soil physical, chemical and seed bank properties along a gradient. Three rangeland vegetation types were selected in Erere wereda, Shinille zone in north eastern Somali region of Ethiopia, classified as arid (60%) and arid and semi-arid (40%). The experimental sites included: the Asbuli grassland (9–11.80N and 40–41.80E), the Aydora open savanna (8–10.80N and 40–4180E) and the Hurso closed savanna (4–6.80N and 40–42.80E), with an altitude ranging between 300 and 1200 m.a.s.l,. Each site was laid out in to four sites of degradation condition classes, namely: excellent (benchmark), good, moderate, and poor along the gradients. Accordingly, some important soil physical, chemical and soil seed bank parameters were analyzed using scientific procedures. Based on the results, soil texture showed a shift from clay type to silt clay, while soil erosion and compactions intensities were increased as rangeland conditions declined from excellent in to poor classes along the gradient. Further, increases in conditions of degradation simultaneously increased bulk density while vegetation covers showed a significant (p < 0.05) reduction. This was explained in terms of increased bare ground with inverse proportion of basal cover. On the other hand, soil moisture, organic matter and organic carbon made a significant (p < 0.05) reduction as degradation condition increased from excellent into poor classes. Patterns in soil Nitrogen, available Phosphorus and Potassium also reduced significantly (p < 0.05) as rangeland degradation increased, may be due to higher leaching induced by higher runoff. Nevertheless, Cation exchange capacity, electrical conductivity, pH and percent base saturation (i.e. Ca, mg and Na) highly decreased as degradation was increased. To this end, deteriorations in rangeland condition has an overall negative impact on the soil physical and chemical characteristics, demanding for more efforts to improve the health of range vegetations. Likewise, number and density of regenerated plants declined in the soil seed banks from excellent to poor condition classes. Nevertheless, the soil seed banks still give an opportunity for rangeland improvement using appropriate rehabilitation, conservation and utilization techniques.Keywords: Rangeland ecology, condition classes, soil texture, xchangeable ions, pH, soil nutrients

Disturbances Impact on Longevity of Grass Seeds, Semi-Arid South African Rangeland

The effect of plant and soil disturbances on seed density, species richness, and seed longevity of the soil seed bank was quantified for a semi-arid rangeland, over a 5-yr period (2002/2003-2006/2007 growing seasons). The different soil and plant treatments included fire, tillage (intended as a trampling surrogate), and blocked seed rain (simulating heavy grazing). These three experimental factors were combined in a factorial arrangement. Seed responses were evaluated in the soil seed bank before the new seed set, after the first seed production event, and after the second seed production event. Before disturbance (physical impact on the plant and soil), soil seed bank was dominated by early successional species: conversely, aboveground vegetation was mainly dominated by perennial grasses. After only 4 yr of blocked seed rain, seedling emergence of Decreaser grass species ceased totally both in the field and seed bank, with lower effect on Increaser grass species. Emergence of both Decreaser and Increaser grass species decreased in the seed bank with tillage, whereas the opposite occurred in the field. By contrast, tillage increased the emergence of weeds in the seed bank. The decrease in emergence of Decreaser grass species in both seed bank and field was still evident 4 yr after the rangeland was burnt. The grass species Themeda triandra was the most sensitive to fire in terms of seedling emergence. Blocked seed rain treatment significantly decreased (P<0.05) species richness. Regardless of treatments applied, there was poor similarity between aboveground vegetation and the associated seed bank. Differences in the soil seed bank are likely to reflect manifested properties rather than short-term changes. Several characteristics of seed banks (species composition, seed abundance, and longevity) must be considered in order to understand the dynamics of plant communities following disturbances.The Rangeland Ecology & Management archives are made available by the Society for Range Management and the University of Arizona Libraries. Contact [email protected] for further information.Migrated from OJS platform August 202