Dacrycarpus dacrydioides forests in South Westland between the Waitangitaona and Saltwater rivers occur on low terraces of alluvial silt. Their relationship to other river flat and swamp communities on post-glacial surfaces is described. Recently abandoned river beds are colonised by pioneer species, which give way to vegetation dominated by grasses, sedges and rushes, which in turn are invaded by woody plants, especially Coprosma propinqua and Podocarpus totara var. waihoensis.
Forest vegetation patterns alongside the Poerua River, south Westland, were studied to determine whether a distinct riparian community could be defined either immediately adjacent to the river, or out to the limit of overbank flooding. Ten randomly located 100 m transects were established perpendicular to the river at each of two sites. Ground cover of alluvial sediment indicated that annual overbank flooding occurred up to 20 m into the forest (the flood zone).