Uganda

UGANDA IS SITUATED in the interlacustrine highlands of central Africa; these highlands are generally characterized by a high plateau that is associated with the Great Rift Valley that dominates Uganda. The plateau generally lies between 3,280 to 6,562 ft. (1,000–2,000 m.). One characteristic feature of the Great Rift Valley is the development of numerous lakes; these include Tanganyika and Kivu, while in the Albertine Rift region in the north, the lakes include George, Edward, and Albert. Uplift along the shoulders of the Western Rift Valley resulted in the reversal of the previously west-flowing rivers and the creation of the basin now occupied by Lake Victoria. The Nile River, which forms the eastern boundary of the interlacustrine highlands, is the major outlet of Lake Victoria, flowing northward from Lake Victoria. Farther to the west, Uganda is dominated by the Ruwenzori mountain range—the infamous mountains of the moon—that straddle the border with the Democratic Republic of Congo.

The climate of Uganda varies from humid through seasonally arid conditions. Precipitation is dependent largely on the Intertropical Convergence Zone (ITCZ); the movement of the ITCZ follows the position of maximum surface heating associated with the overhead position of the sun. Climate is further modified by topography and by the proximity of the large lakes. The distribution of vegetation is mainly dependent on altitude, levels of precipitation, and human activities. Because of human pressure, cultivated and grazed land occupies much of Uganda. Much of the interlacustrine highlands lie within a phytogeographical zone known as the Lake Victoria Regional Mosaic, where five distinct floras meet; namely, the Afromontane, Guineo-Congolian, Somalia-Masai, Sudanian, and Zambazian Regional Centers of Endemism. Above 6,562 ft. (2,000 m.) there are three distinct vegetation belts; namely, Afroalpine, Ericaceous, and Montane forest belts. The Afroalpine Belt occurs mainly above 11,810 ft. (3,600 m.) in the high mountains of the region, which include Mount Elgon, the Virunga volcanic mountains, and the Rwenzori.

Environmental histories of Uganda have been reconstructed via a long history of palaeoecological research from the numerous lakes and swamps. Recent interest in other proxy records, such as archaeology, historical linguistics, oral traditions, and meteorological data have provided a detailed understanding of the environmental history of Uganda and the associations between environmental and human histories in the region. Under the cool and dry climate conditions of the last glacial [Page 994]maximum, vegetation from higher altitudes extended to lower elevations. From around 15,000 years before present (yr. BP), as global climates warmed, montane forest types retreated back to mountainous areas, reaching the minimal extent around 6,000 yr. BP under the warm and wet conditions of the mid-Holocene.

The climate history from 5,000 yr. BP to the present is more complex, as ecosystems have been increasingly influenced by human activity. A period of relatively drier climate between 5,000 and 2,000 yr. BP is marked by relatively low lake water levels. Vegetation also reflected this climate change, experiencing a marked transition to drier forest types from about 3,500 yr. BP. Uganda experienced a return to relatively moist environmental conditions after about 2,000 yr. BP; during this same period, areas around Lake Victoria experienced a decrease in evergreen forest, with it being replaced by semideciduous forest. The introduction of agriculture to Uganda is commonly associated with Bantu-speaking people, who are reported to have spread throughout much of central Africa after about 3,000 yr. BP.

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