The ecological significance of the central North Island ash showers: The vegetation

[First paragraph(s)...]
The soil-forming ash-showers of the central North Island as now defined cover, sometimes disjointedly, over 20 per cent. of the area of New Zealand. This size in itself is of great importance ecologically.
The remarks that follow are based upon a general knowledge only of some of the vegetation growing on these showers, and upon one or two detailed studies. Much of the natural vegeta- tions has been destroyed and is difficult to re- construct in theory, but on the young showers the pattern of the primitive vegetation often remains. It is to this pattern that the following remarks apply.
Attention will be confined to the younger showers, more particularly the Taupo shower, because their influence on the vegetation is obvious even from a superficial examination. Older showers have become mostly covered with forest.