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- Kebrom, Tekle, et al.
(författare)
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The role of soil seed banks in the rehabilitation of degraded hill slopes in Southern Wello, Ethiopia
- 2000
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Ingår i: Biotropica. - : Wiley. - 0006-3606 .- 1744-7429. ; 32:1, s. 23-32
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Tidskriftsartikel (refereegranskat)abstract
- The species composition in the soil seed bank of degraded hillslopes in southern Wello, Ethiopia, was assessed using the seedling emergence method and compared with that of the standing vegetation. Surface soils were sampled at 0-to 5-cm depth from 49 plots of four physiognomic vegetation classes (hereafter vegetation classes): forests, shrublands, grasslands, and degraded sites. Soils were spread on sterile sand in a glasshouse and watered. Emerging seedlings were recorded for five months until no new seedlings emerged. A total of 3969 seedlings belonging to 71 species and 30 families germinated. The species composition of the seed bank was dominated by 53 herb species (75%) compared to 2 tree species which accounted for only 3 percent of the total number of species. Seedling density differed significantly among vegetation classes and ranged from 391 to 7807 seeds/m2. Mean species richness also differed significantly among the vegetation classes. Forty-two species were found to be common to the seed banks and the standing vegetation; however, correspondence between species numbers and composition of the seed banks and the standing vegetation was poor. Although most of the species that germinated in the seed banks were herbs and grasses, they can develop a vegetative cover and contribute to reduction of soil erosion. Regeneration of the tree species (some of which have seed viability up to four years) however, requires both time and the presence of mature individuals. Together with hillside closure and soil conservation measures (e.g., terracing), planting of native woody seedlings might help to expedite rehabilitation of degraded hillslopes devoid of trees and shrubs.
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- Tekle, Kebrom
(författare)
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Ecological rehabilitation of degraded hill slopes in southern Wello, Ethiopia
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Clearing of vegetation has left large areas of southern Wello (Ethiopia) at a high risk ofland degradation. In this study, the causes, extent and consequences of land degradationproblems are reviewed. To see land cover changes, aerial photographs from 1958 and1986 were compared with the help of a GIS procedure. By applying multivariateclassification and ordination techniques on the vegetation and environmental datacollected from 65 plots (20x20 m big), the vegetation of the study area was analyzed.Possibilities of ecological rehabilitation were assessed by analyzing results from a soilseed banks experiment and from the study of vegetation dynamics in permanent plots.The land cover changes interpreted from the aerial photographs indicated adeterioration of forests, shrublands and riverine vegetation into open areas andsettlements. This deterioration was manifested in the present vegetation types whichincluded forests, woodlands, shrublands, grasslands, degraded and regenerating sites.The soil seed banks are dominated by herbs with very few tree and shrub seedlings.A low floristic similarity (Sørensen index 26%) was observed between the seed banksand the standing vegetation. Nevertheless, the seed banks' contribution to initial plantcover can not be underestimated.In the permanent plots, an increase in number of individuals and intercept lengthswas recorded. Moreover, there was a strong correlation (r = 0.77) between the interceptlength of the tree/shrub layer and the position of plots on CA - axis 1 of the field layer.Ecological rehabilitation of degraded areas in southern Wello will be successful ifthe goals are geared towards sustainable use of the hill slopes rather than focusing onrecovery of the original vegetation. Measures taken in this line can be helpful inwinning the confidence of the local people without whose participation much can not beaccomplished.
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- Tekle, Kebrom, et al.
(författare)
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Vegetation on hill slopes in southern Wello, Ethiopia : Degradation and regeneration
- 1997
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Ingår i: Nordic Journal of Botany. - : Wiley. - 0107-055X .- 1756-1051. ; 17:5, s. 483-493
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Tidskriftsartikel (refereegranskat)abstract
- A study was made of the vegetation in southern Wello (Ethiopia) in relation to human impact and the environment. 65 sample plots were laid out and analysed with respect to the cover value of vascular plant species. Altitude, slope, aspect and estimates of grazing pressure for each plot were also recorded along with physical and chemical soil properties analysed for samples taken from each plot. The following environmental factors, isolated by forward selection, show correlation with the axes of Canonical Correspondence Analysis (CCA): altitude, grazing, pH, K, Ca, Mg, slope and aspect.Through hierarchical and non-hierarchical clustering methods the vegetation was divided into eight types, from which one was secondary forest characterised by patch dominance of Juniperus procera and Olea europaea ssp. cuspidata. These forest patches are found at high altitude sites and because of their inaccessibility are usually characterised by low livestock density and consequently low grazing pressure. The presence of large boulders and stones in Podocarpus falcatus forest decreases accessibility and creates natural protection for the trees. The other vegetation types, most of which are found at lower altitude and associated with varying intensities of grazing, include grasslands (grazed and protected), regenerating sites dominated by Euclea racemosa and Dodonaea angustifolia, dense and open shrublands and Olea europaea ssp. cuspidata woodlands. Human interference has a major impact on the vegetation of the study area and its recovery will depend on the degree of participation of the local people.
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