(Dicksonia spp., Cyathea spp.).
The profusion of tree ferns could rightly be said to be the most distinctive feature of New Zealand forest. They occur in all forests and are even more plentiful in cut-over and degraded forests where they obtain more light to regenerate and develop. They also appear in plantations of exotic trees as these grow older and open up.
Some six species go to make up what are commonly known as tree ferns. They are all usually single-stemmed and crowned by a huge rosette of leaves which gradually die from the base of the rosette, leaving the stem scarred and naked. These trunks thicken largely by the growth of a thick mat of aerial roots. The most majestic species is the mamaku, Cyathea medullaris, which grows over 40 ft tall and a foot in diameter. Individual fronds grow up to 15 ft long and 6 ft wide. The main stems of the fronds are stout and black. The species grows in lowland forests throughout New Zealand and in the Chatham and Three Kings Islands, in some Pacific Islands, and in Australia.
C. dealbata or ponga has distinctive whitish under surfaces to the leaves. It grows to 30 ft tall and the fronds to 10 ft long. Distribution is in lowland and montane forests throughout the North and South Islands and the Chatham and Lord Howe Islands. A very beautiful species with pale, brownish-green fronds, and as widely spread as the above two, is C. smithii.
Wheki or Dicksonia squarrosa is probably the commonest tree fern and the most persistent after the removal of forest. It often forms groves by means of spreading underground rhizomes which give rise to several stems. D. fibrosa, kuripaka, is one of the smaller-growing tree ferns and reaches a height of about 15 ft. The stem is very densely covered with a mat of rootlets.
by Alec Lindsay Poole, M.SC., B.FOR.SC., F.R.S.N.Z., Director-General of Forests, Wellington.