This paper presents an overview of paleoenvironmental changes in East Africa during the late Quaternary based on evidence from pollen, diatoms, microscopic charcoal, and lake level records and associated proxies. The paleoenvironmental records derived from different proxies complement each other to provide a more accurate and complete assessment of the paleoenvironmental changes in East Africa. The records show that the period prior to c. 42,000 14C yr BP was characterized by warm climatic conditions similar to the present. This was followed by a change to cold dry conditions from 42,000 to 30,000 14C yr BP, and cold and moist conditions from 30,000 to 21,000 14C yr BP. Temperatures during the latter period leading to the Last Glacial Maximum (LGM) were probably 2 to 4.1°C lower than the present. Between c. 21,000 and 12,500 14C yr BP East Africa's environment was generally cool, punctuated by two significant episodes of prolonged desiccation. Warm and moist conditions punctuated by rapid climatic changes prevailed in the region during the deglacial and middle Holocene period. Ice core records document two significant and abrupt drought events in the region, one at 8300 14C yr BP and the other at 5200 14C yr BP. The onset of a longer and more extensive desiccation period commencing 4000 14C yr BP was registered in nearly all sites. The climate of East Africa was generally drier than present during the Medieval Warm Period (MWP) while fairly wet conditions prevailed during the Little Ice Age (LIA) interrupted by three episodes of aridity, more severe than those of more recent times. Whereas this review advances our understanding of climate and vegetational changes in East Africa beyond the Last Glacial Maximum, it also highlights limitations of the paradigms that explain the forcing mechanisms behind the changes. However, unequivocal interpretation of the multiproxy data from East Africa with respect to paleoenvironmental changes becomes extremely complex and challenging especially when the anthropogenic input is considered.
Soil erosion and land degradation are serious problems in tropical Africa, especially Sub-Saharan Africa, where they are widely recognized as more serious problems than in non-tropical areas. Sub-Saharan Africa experiences deleterious levels of soil erosion, largely due to the interaction between harsh climates of high erosivity, fragile soils of high erodibility, steep slopes, and poor natural resource management. The fundamental challenge is to separate purely background-level soil erosion due to biophysical, geomorphic, topographic, and climatic conditions from what is caused by humans. This review shows that the human-induced causes of soil erosion and land degradation in Sub-Saharan Africa are not fully understood and some of the commonly listed causes may not always stand the test of critical scrutiny. The popular views of human-induced soil erosion and land degradation not only fail to take into consideration the fact that land degradation is primarily a physical process, but also they do injustice to adaptive ecosystem management by the local inhabitants. The review specifically questions the stereotypes of overpopulation, overgrazing, deforestation, overstocking, and general rangeland degradation due to human resource use in Sub-Saharan Africa. Empirical evidence suggests that biophysical factors including soil properties, climatic characteristics, topography, and vegetation can sometimes interact among themselves to yield high soil erosion and degradation rates independent of anthropogenic impacts.
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