RIVER TYPES, SITE EVOLUTION AND SUCCESSIONAL VEGETATION PATTERNS IN PERUVIAN AMAZONIA

Lateral migration of Amazonian lowland rivers causes a vegetation succ ession on recently deposited fluvial sediments. The forest ground is f ormed gradually in sequence, giving rise to age-zonation of the succes sional stages. Using Landsat MSS maps and field observations, we studi ed variations in fluvial landform evolution and river character. The w idely used characterizations of the rivers according to their suspensi on-load character and channel pattern were evaluated in relation to th e vegetation succession. Sequential successional forests appear extens ively along meandering white-water rivers, which are rich in suspended sediments and are characterized by mobile channels. Conversely, veget ation zonation is less pronounced at the margins of slowly eroding sus pension-poor rivers. Line transects were established to document meand er development along eight different rivers. The chemical composition of the recently deposited alluvium differs markedly both among rivers and along the transects. Concentrations of organic carbon and nitrogen increase toward the meander neck along with the acid reaction of the soil. The rate of riverine forest regeneration in Peruvian lowland Ama zonia was extrapolated on the basis of erosion data from four differen t rivers. and suggests that approximately 130 km2 of forest is annuall y eroded and replaced by successional vegetation, the equivalent of 0. 2% of the present floodplain area of this region.