Table 4. Possible links between vegetation zones and flow categories in southern African rivers (modified from Boucher 2002). Vegetation zone Type of vegetation Correlations with flow categories Aquatic Algae and submerged macrophytes Perennials maintained by dry-season low flows Lower wetbank Mosses, ferns, sedges Wet-season low flows Upper wetbank Sedges, reeds, herbs, grasses Class 1, 2, and 3 intra-annual floods Lower dynamic Pioneer communities, annuals, young trees and occasional older ones Reached by Class 3 and 4 intra-annual floods; too high for wetbank vegetation, floods too regularly for trees to establish Tree and shrub Trees and shrubs Tree line maintained by 1:2 yr floods; whole tree and shrub zone reached by 1:2 up to 1:20 yr floods Back dynamic Outer limit of riparian species, semi-terrestrial Reached by >1:20 yr flood