Although these formations are essentially distinct and in general readily recognisable, yet in an area of this size there are bound to occur a number of formations which, though possessing distinctive characters, are of comparatively minor importance and these are somewhat arbitrarily classified together with some related group or else omitted from the present discussion to avoid delving into details. Thus, riverbank and watercourse in the warm temperate belt is extended to include cliff and coastal cliff formations. This has particular advantages in dealing with the southern extremity of the Rimutaka Range, where most of the coastal cliff of the area is situated, as the riverbank and coastal cliff associations are very similar. Tussock, herbfield and scree formations, though only listed for the warm subpolar belt, might have been, but for considerations of space, added as well for the cold temperate belt, in the upper part of which they are occasionally important, but these formations are essentially the same in the two belts.

Another problem which only affects the formations of the lowest zones, is that of dealing with the marginal areas where the indigenous communities have been to a greater or less degree altered or destroyed by the action of man. The boundary taken follows approximately the limit of unbroken forest from the Manawatu Gorge down either flank of the range and on the western side touching the coast at Paekakariki, below Mount Wainui, then cutting across the Hutt Valley to the head of the Wainui-o-mata River and following this to the sea. At the northern and western extremities the forest is, at the present day, discontinuous and some of the existing communities are more or less altered so that a certain amount of inference is necessary as to the original associations, the indigenous formation in which certain species occurred and, to a certain extent, the relative frequency of certain species.