The Victoria Basin forest-grassland mosaic is an ecoregion that lies mostly in Uganda and extends into neighboring countries. The ecoregion is centered north and west of Lake Victoria, with an outlier on the border of Ethiopia and South Sudan.
The ecoregion's climate is tropical. Annual maximum mean temperatures range from 24º to 27º, and mean minimum temperatures range from 15 °C to 18 °C. Rainfall generally ranges from 1000 to 1400 mm annually, but exceeds 2000 mm on the Ssese Islands in Lake Victoria, and in the northern enclave on the South Sudan-Ethiopia border, and is only 700 mm around Lake Edward in the Western Rift. Most rain falls in the two rainy seasons, from March to May and from August to November.
Flora and Fauna
The predominant vegetation includes extensive areas of savanna and woodland, interspersed with smaller areas of forest. Papyrus swamps are common in river lowlands.
Plant communities
The principal plant communities include Lake Victoria drier peripheral semi-evergreen Guineo-Congolian rain forest, Lake Victoria transitional rain forest, moist Combretum wooded grassland, dry combretum wooded grassland, Evergreen and semi-evergreen bushland and thicket, Edaphic wooded grassland on drainage-impeded or seasonally flooded soils, and swamp forest. Semi-evergreen rainforest. Semi-evergreen rainforest was the predominant vegetation type on the north shore of Lake Victoria and southeast of Lake Albert. Botanist Frank White designated it as "Lake Victoria drier peripheral semi-evergreen Guineo-Congolian rain forest", a floristically-impoverished variant of the species-rich Guineo-Congolian forests found further to the east in the Congo basin. Characteristic trees include large-leaved albizia ', cheesewood ', false mvule ', African ita ', white stinkwood', bastard white stinkwood ', red-fruited white stinkwood ', Celtis philippensis, Celtis zenkeri, white star apple', Uganda ironwood ', Budongo mahogany ', Sapelli mahogany ', Budongo heavy mahogany ', orange-barked terminalia ', smooth-barked mahogany ', big-leaf mahogany', umbrella tree ', Mildbraediodendron excelsum, mvule ', Uganda mulberry ', African greenheart ', aningeria ', and African nutmeg '. This vegetation type covers an area of 48,223 km², of which 4.6% is in protected areas explicitly designated for biodiversity, species or landscape protection, and another 4.9% is in areas designated for both protection and sustainable use. Human activity has transformed most of the original rainforest area to various types of savanna, or to agriculture and tree plantations. Mabira Forest is the largest remaining block of semi-evergreen forest. The reserve is secondary forest, and has been subject to long-term human influence, including logging since the early 20th century and encroachment by banana and coffee plantations in the 1970s and 80s. Lake Victoria transitional rain forest. Transitional rainforests are evergreen rain forests found at the eastern and western ends of the ecoregion. They are transitional between lowland forests which are mostly made up of Guineo-Congolian species, and higher-elevation Afromontane forests, and the transitional forests include both characteristic lowland and highland species. The Kakamega and South Nandi forests in western Kenya occur 1520 to 1680 meters elevation, west of the highlands that bound the Eastern Rift. Characteristic trees of the Kakamega and South Nandi forests include Alangium ', peacock flower ', pear wood ', Bastard white stinkwood ', Chrysophyllum gorungosanum, Drum tree ', Ehretia cymosa, Budongo mahogany ', Orange-milk tree ', River macaranga ', Umbrella tree', Calabash nutmeg ', Neoboutonia macrocalyx, East African newtonia ', Aningeria ', Red stinkwood ', Jumping seed tree ', Strombosia scheffleri, Guinea waterberry ', Turraea holstii, and lemonwood '. Swamp forest.' A distinctive swamp forest community is found along the lower reaches of the Kagera River west of Lake Victoria, on the border of Tanzania and Uganda. The Tanzanian portion is known as the Minziro Forest, and the Ugandan portion as the Sango Bay forests. Baikieaea insignis subsp. minor and Afrocarpus dawei'' are the dominant canopy trees.
