Riparian-zone vegetation increasingly is seen as critically important ecologically in landscapes. While generally of limited relative area, its roles as biodiversity haven and in mediating landwater exchanges are vital. Therefore, identifying boundaries of such vegetation is important and has clear management significance. We measured 20 sites from first to fourth order streams, with vegetation sampled at 10 m intervals for 100 m transects running perpendicularly to the streams. We identified locations of sharp transitions by using Bayesian model-selection. There did not appear to be a clear relationship between the width of riparian-zone vegetation and stream order and other factors such as local topography. These outcomes suggest that the delineation of widths of riparian vegetation zones needs to be established on a stream-by-stream, if not locality-by-locality basis, and that strict operational management prescriptions (e.g., set distances from streams within which logging or other disturbances are prohibited) for safeguarding potentially sensitive areas, such as many riparian rainforest areas, often will be inappropriate.