Timber from rimu has been the main native timber in use since about 1910 when it began to displace kauri, and, as far as one can see, it is likely to remain indefinitely in this position. The quantities available, however, will fall rapidly in the next one or two decades as resources become exhausted. The timber of the rimu is comparatively hard and dense. The tree is a conifer belonging to a group of forest trees, which includes the genus Podocarpus, that is widely represented in highland forests in countries on the west side of the Pacific. In the genus Dacrydium there are about 16 species, of which seven are found in New Zealand, with representatives in Malaysia, New Caledonia, Tasmania, and Chile.
There is disagreement amongst botanists as to the division between the two genera Podocarpus and Dacrydium and, also, to which genus the New Zealand species belong. Rimu grows to heights of about 100 ft and occasionally 150 ft, and the trunk is usually about 3 ft, but can be as much as 6–7 ft, in diameter. The branchlets have a distinctive pendulous character, those on young trees being particularly graceful in appearance. The leaves are small and awl-shaped.
Rimu is the most widespread of all New Zealand forest trees, occurring throughout the North, South, and Stewart Islands from lowland to montane forest. In most places the large, rounded heads of a few to a dozen or so trees per acre emerge well above the general level of the canopy of broadleaf trees below. Such forests have little or no regeneration and seldom contain any trees in the intermediate stages. The large trees can be anything up from 700 to 800 or even 1,000 years old. The facts of age and structure of such forest have given rise to the theory that the rimu is a relic of past climates which have been more favourable to it. It is certainly not replacing itself. However, along the edges of some forests on the pumice plateau of central North Island the rimu is younger, and intermediate age-classes and regeneration do occur. It is also present in secondary “scrub” on clay soils of the north.
On the West Coast of the South Island and on Stewart Island a special type of forest, usually referred to as rimu pole forest, occurs on flat, very wet terraces. In these there is complete representation of age-classes from plentiful regeneration onwards. The older trees seldom exceed 3 ft in diameter but they often occur densely with crowns almost touching. These forests do offer hope of permanent management (and so, in the long run, the only permanent supply of rimu timber) since they grow on difficult soils unsuited to agriculture. Rotations, however, must be long and reckoned in terms of a few hundred years.
The European name for rimu, especially in the South Island, is red pine.
by Alec Lindsay Poole, M.SC., B.FOR.SC., F.R.S.N.Z., Director-General of Forests, Wellington.