CORRELATIONS BETWEEN VEGETATION AND LANDFORMS IN SOUTHWEST UGANDA

Abstract

In a subhumid to semiarid equatorial area of southwest Uganda landscape development proceeded in phases dictated by differential upwarp within a major continental uparching and by differential lithology. A phase of considerable upwarp and deformation followed by a prolonged pause caused the dissection of the initial (pre-Terliary?) planed Rwampara Surface and the differentiation of a lower planed Cayaza Surface in the proto-Katonga basin throughout most of the area. Presumption of continuous moderate tilting resulted in the differentiation of a third Sanga surface which in its turn was dissected mainly through lithological differentiation by the last erosional phase of lowland expansion. The landscape consequently consists of upland formed of resistant lithology and preserving on its crests remnants of three consecutive levels and of lowland developed upon incompetent lithology. The relatively rapid development of a planed lowland surface allowed for relatively early deceleration of geomorphic process deep weathering and retardation of pedogenesis while upland was being constantly dissected. Active dissection of the upland prevented the preservation of extensive remnants of ancient laterite duricrusts upon crests and enabled constant active pedogenesis. As a result soils of the older upland surfaces are of a more youthfull character than those of the younger lowland surface. The former are relatively unstable actively forming soils which reflect the current climatic environment. The latter are sedentary developed on pro-weathered material and preserve properties of a former mere humid climate. In the lowland periphery where soils are relatively younger and accretion of material from eroding upland slopes occurs these qualities are notified and lowland soils are more similar to upland soil.