Human impact on the environment in the Ethiopian and Eritrean highlands—a state of the art

Nyssen, Jan; Poesen, Jean; Moeyersons, J; Deckers, Jozef; Haile, Mitiku; Lang, Andreas

doi:10.1016/s0012-8252(03)00078-3

Cited by 528 publications

(406 citation statements)

References 101 publications

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“…These highlands extend between the lowlands at the southwestern shore of the Red Sea in the north, the Danakil depression and the Ethiopian Rift Valley in the east and the valley of the Upper Nile in the west. Nyssen et al (2004; provided an extensive overview of the environment of the Ethiopian highlands. The climate varies with elevation, but on the plateaus rainfall is generally bimodal, with a short and erratic February-April rainy season and a long and intensive June-September rainy season.…”

Section: Study Areamentioning

confidence: 99%

“…In the southwest of the country, shade coffee cultivation has, until now, guaranteed that more or less natural forest remained an important land cover (Tadesse et al 2014), despite the clear trade-off between coffee productivity and forest ecological quality (Senbeta and Denich 2006;Schmitt et al 2010;Aerts et al 2011;Hundera et al 2013). In the central and northern Ethiopian highlands, however, high historical land use pressure has resulted in widespread deforestation and land degradation (Darbyshire et al 2003;Nyssen et al 2004). Crop land and degraded grazing land are the dominant land covers, with only very few patches of forest remaining and these are almost entirely confined to the vicinity of churches, monasteries and other holy sites such as springs.…”

Section: Introductionmentioning

confidence: 99%

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Conservation of the Ethiopian church forests: Threats, opportunities and implications for their management

Aerts

Overtveld

November

et al. 2016

Science of The Total Environment

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117

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In the central and northern highlands of Ethiopia, native forest and forest biodiversity is almost confined to sacred groves associated with churches. Local communities rely on these 'church forests' for essential ecosystem services including shade and fresh water but little is known about their region-wide distribution and conservation value. We (1) performed the first large-scale spatially-explicit assessment of church forests, combining remote-sensing and field data, to assess the number of forests, their size, shape, isolation and woody plant species composition, (2) determined their plant communities and related these to environmental variables and potential natural vegetation, (3) identified the main challenges to biodiversity conservation in view of plant population dynamics and anthropogenic disturbances, and (4) present guidelines for management and policy. The 394 forests identified in satellite images were on average ~2 ha in size and generally separated by ~2 km from the nearest neighboring forest. Shape complexity, not size, decreased from the northern to the central highlands. Overall, 148 indigenous tree, shrub and liana species were recorded across the 78 surveyed forests. Patch α-diversity increased with mean annual precipitation, but typically only 25 woody species occurred per patch. The combined results showed that >50% of tree species present in tropical northeast Africa were still present in the 78 studied church forests, even though individual forests were small and relatively species-poor. Tree species composition of church forests varied with elevation and precipitation, and resembled the potential natural vegetation. With a wide distribution over the landscape, these church forests have high conservation value. However, long-term conservation of biodiversity of individual patches and evolutionary potential of species may be threatened by isolation, small sizes of tree species populations and disturbance, especially when considering climate change. Forest management interventions are essential and should be supported by environmental education and other forms of public engagement.

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Section: Study Areamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Conservation of the Ethiopian church forests: Threats, opportunities and implications for their management

Aerts

Overtveld

November

et al. 2016

Science of The Total Environment

Self Cite

117

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“…During the last decades, important efforts in land use management and soil and water conservation have been made (Nyssen et al 2004). Repeated photo surveys indicate that sheet and rill erosion rates have decreased over the decades due to an improved vegetation cover .…”

Section: Ii2 the Catchment Response To Disturbances In Land Use Andmentioning

confidence: 99%

Sediment yield as a desertification risk indicator

Vanmaercke

Poesen

Maetens

et al. 2011

Science of The Total Environment

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Soil erosion is often regarded as one of the main processes of desertification. This has lead to the use of various desertification indicators that are related to soil erosion. Most of these indicators focus, however, on small spatial units, while little attention has been given to the amount of sediment exported at the catchment scale. Such a small spatial unit approach neglects the transfer of sediment through catchments as well as the scale-dependency of erosion processes. Furthermore, this approach does not consider important off-site impacts of soil erosion, such as sediment deposition in reservoirs, flooding as well as ecological impacts.This study aims to illustrate the importance of also considering catchment sediment yield (SY, t km -2 y -1 ) in desertification assessment studies. Based on recently established databases of SY and soil loss rates in Europe and examples from previous studies, we illustrate that soil erosion rates at the plot scale are not representative for catchment SY, as they are often several orders of magnitude smaller. Also, the erosion response of catchments to changes in land use or climate often differs strongly from responses to those changes at the plot scale.We further discuss several of the impacts of SY and their link with desertification: i.e. the sedimentation of reservoirs, problems related to flooding, catchment hydrology, export of nutrients and ecological implications.Using earlier established criteria we evaluate the potential for using catchment SY as a desertification indicator and conclude that this could give an important added value to desertification studies. SY, used in combination with other indicators, allows the identification of other sediment sources than those considered at the plot scale and can reflect the results of desertification processes over longer time periods than periods over which assessments at the plot scale have been made. We argue therefore, that SY is a strong complementary indicator of desertification providing valuable information on the catchment response to changes in drivers of desertification.

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“…Food production in Ethiopia is not able to support the increasing population due to the erratic rainfall and the fragile environment in combination with extreme poverty, stagnating technology, and high population and livestock densities (Ramakrishna and Demeke 2002;Nyssen et al 2004a). Agriculture remains mainly rain-fed (Belete 2007) and, although the country is referred to as the 'water tower' of northeast Africa, it has one of the lowest reservoir storage capacities in the world (WCD 2000) and one of the lowest levels of electricity consumption per capita in the world, exploiting only 1-3% of its estimated 30,000 MW hydropower potential (Solomon 1998;Feibel 2003).…”

Section: Introductionmentioning

confidence: 99%

“…However, wellconsidered implementation of reservoirs is often impossible due to a lack of reliable sediment yield data, leading to reservoir sedimentation problems (Haregeweyn et al 2008). Nyssen et al (2004a) indicated that very few sediment yield data exist for medium-sized catchments (100-10,000 km²) in the Ethiopian highlands.…”

Section: Introductionmentioning

confidence: 99%

Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia

et al. 2010

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Purpose The Ethiopian highlands are a fragile environment, characterized by steep slopes, intense rainfall, a sparse vegetation cover and the occurrence of flash floods. Although important efforts have been made to mitigate the ongoing soil erosion and land degradation problems, the sediment dynamics at medium-sized catchment scale (100-10,000 km²)are not fully understood. Therefore, this study aims to provide a better of sediment export processes and the importance of flash flood events in semi-arid tropical catchments. 2Methods Measuring campaigns were conducted in 10 subcatchments of the Geba, a tributary of the Tekeze, representative of the northern Ethiopian highlands. During 2 to 4 rainy seasons, the rivers were sampled for their suspended sediment concentration (SSC) and runoff discharge.Results and discussion Variations in SSC and sediment grain-size distribution indicate changes in sediment supply during the rainy season, due to the depletion of readily available sediments and the development of a vegetation cover.Also during flood events, changes in sediment supply are observed. Sediment yields (i.e. 497-6,543 t km -2 yr -1 ) are higher than suggested by previous studies and correlate with rainfall depth. The majority of sediment export occurs during a few short but intense flash floods. No clear effect of implemented soil and water conservation measures could be detected in the sediment yields of the catchments.Conclusions Sediment export rates in the Ethiopian highlands are high, are characterized by important changes in sediment supply and are mainly controlled by the occurrence and magnitude of flash flood events. Mitigation measures to reduce sediment yield at the catchment scale should therefore not only focus on the reduction of hillslope erosion rates, but also on the magnitude of these floods.

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Human impact on the environment in the Ethiopian and Eritrean highlands—a state of the art

Cited by 528 publications

References 101 publications

Conservation of the Ethiopian church forests: Threats, opportunities and implications for their management

Conservation of the Ethiopian church forests: Threats, opportunities and implications for their management

Sediment yield as a desertification risk indicator

Sediment dynamics and the role of flash floods in sediment export from medium-sized catchments: a case study from the semi-arid tropical highlands in northern Ethiopia

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