NEW ZEALAND STATE FOREST SERVICE. LEAFLET No. 26. A. D. McGAVOCK, Director of Forestry. I 2th August, 19 35. THE PROPERTIES AND USES OF KADRI (Agathis australis) . By ALEX R. ENTRICAN, Engineer in Forest Products, N.Z. State Forest Service. SUMMARY. NEW ZEALAND kauri ranks as one of the most generally useful softwoods* in the world and has figured prominently in the inter­ national wood trade for over a century. In yielding flawless timber of exceptionally large size the tree is unsurpassed by any other known species, and although the extensive virgin forests of the early European occupation have been severely depleted the remaining stands are being placed under a system of forest regulations whereby a sustained yield of this valuable softwood will be assured. Owing to its evenness of texture and ease of working, to its small shrinkage and . ability to stay put, to its medium density and excellent strength properties, and to its high durability, the timber is able to meet the most exacting use requirements. Its uses range from all classes of building and general construction to ship-building; car and wagon construction, tank and vat manufacture, military bridging, the production of dairy and agricultural machinery, and to engineering pattern work, &c. * " Softwood " is the commercial term used to distinguish the woods of the needle or scale-leaved trees, such as the true pines (Pinus spp.), rimu, silver-pine, ·&c. (Daorydium spp.), from those of the broad-leaved trees, such as the oaks ( Querous spp.), the eucalypts (Eucalyptus spp.), and the Southern beeches ( N othofagus spp.), known in contra-distinction as " hardwoods." The two terms are of no significance as regards the actual softness or hardness of the woods, and may be applied to the trees as well as to the woods derived therefrom. • 2 THE TREE-ITS FOREST FORM AND HABITS. The kauri is the monarch of the New Zealand forests, dwarfing in stature and magnificence all other indigenous species. The mature tree yields an almost cylindrical bole with considerably less taper than most other species, with the result that, although not attaining the extreme heights of the North American redwoods (Sequoia spp.) and the Australian eucalypts, it ranks amongst the largest timber­ prodµcing species in the world. The taper usually varies between 1 in. :in 4 ft. and 1 in. to 10 ft. The maximum recorded measure­ ments are 150 ft. for ~otal height,, 106 ft. for length of commercial bole, and 24 ft. for diameter. Early botanists and others estimate the maximum dimensions at 200 ft. for total height, 125 ft. for length of commercial bole, and from 28 ft. to 31 ft. for diameter. The largest recorded bole measured 100 ft. in length and 22 ft. in diameter, containing about 30;000 cubic feet of wood, and .capable of yielding about 200,000 ft. board measurement of sawn timber, or sufficient wood to build from ten to fifteen modern six-roomed houses. Veteran trees up to 17 ft. in diameter still exist, but, except for odd specimens, the usual range of diameters in well-stocked stands of mature trees is from 3 ft. to 8 ft. Total heights likewise range between 60 ft. and 100 ft., with odd trees exceeding 130 ft., while the merchantable boles vary from 12 ft. to 60 ft. in length, with an occasional trunk exceed­ ing 80 ft. Generally speaking, the largest-diameter trees seldom yield a bole exceeding 60 ft., many less than 40 ft., while in general the very long-boled trees of from 80 ft. to 100 ft. usually range between 3 ft. and 5 ft. in diameter. The average mature tree pro­ duces a log about 35 ft. in length and 4f ft. in diameter outside bark at mid-length. ·where young-growth classes are represented in the forest the various averages for the stand are, of course, considerably lower. In its immature state the tree grows with a remarkably even­ tapering trunk carrying a short and narrow conical crown formed by a comparatively small number of short, slender branches protruding almost horizontally from the stem. As the result of a natural branch-shedding process by which the lower branches are cast off successively as the young tree increases in height, the trunk is free of the overgrown branch stubs so characteristic of most softwoods. After a prolonged adolescence of 100 years, or considerably more, the height-growth slows down and the branch-shedding process · ceases. A system of large main branches then develops from one common point on the trunk, tp.ese branches radiatiµ.g upwards and outwards until the tree takes on the shape of a feather duster. The widespread nature of the crown of veteran trees in open stands is in striking contrast to the narrow crowns in dense stands. Almost invariably all branches below the main branching system have been cleanly shed, and the subsequent growth of the trunk is such that · ultimately it appears almost free of taper. The main branches themselves take on enormous proportions, attaining a diameter of .3 ft. and more in veteran trees. Al~hough the leaves are of a glossy olive-green, the trees are sparsely-foliaged, and the ash-grey colour of the bark gives to the general appearance of the kauri forest a peculiar haziness. For a softwood the leaves are of peculiar shape and size, 3 those of the young tree being as much as 4 in. in length by ! in. in width, with acute apices, while in the mature trees the leaves are much shorter and almost egg-shaped, usually under 1i in. in length, although still from i in. to i in. in width. Both types of leaves carry distinctive parallel markings. Unlike the softwoods of the Northern Temperate Zone, kauri appears to grow almost the whole year round, the only rest period being any exceptionally dry season during the early summer months between December and February, and it is at the conclusion of this period that a second growth of leaves occurs, the normal formation taking place in the very early spring. It flowers from as early as June to as late as October, but August is the peak flowering month. The cones ripen about eighteen months later, becoming almost spherical jn shape at maturity and from 2 in. to 3 in. in diameter. The cones break up still attached to the tree, but leave no permanent axis as do the true firs, for instance. There is a good deal of popular misapprehension about cone and 'seed. In most years green cones of all sizes may litter the ground beneath the trees, and it is often stated that the cones disintegrate on the ground to shed the seed. No authenticated case is known where these fallen cones have produced ripe and viable seed; and it is certain that many of the failures to germinate kauri-seed artificially are due to collection of immature seed from such fallen cones. The true matured seed collected from ripe cones in a good seed-year germinates readily; but good seed-years are not frequent (probably the cycle is five-year to seven-year), and even in such a year the season for collecting seed from the very fugacious cones is extremely short, and the task of collecting from branch-tips on the massive head perched above, say, 60 ft. of bare cylindrical bole is no light one. The seed itself is of the usual shape of pinaceous seeds, although decidedly flat and thin, and the seed-wing (about 1 in. by "i in.) is not detachable from the seed, a factor very adverse to the preparation of a clean seed-sample according to ordinary commercial standards for seed. Even in veteran trees the bark is extremely thin, usually only from i in. to Ji in. in thickness. That of young trees is smooth and prominently marked with white bandings. Its structure is characterized by a multiplicity of resin-cells, which are the source of the "kauri-gum" of commerce. They secrete a resinous substance when the bark is c.ut or otherwise injured, thus functioning as a protection to the growing wood beneath. The freshly bled gum is referred to as " candle gum." With undue exposure of the cambium or sapwood, however, the protection is insufficient to prevent attack by the kauri platypus (Platyptts apicalis), the borings of which are fortunately strictly localized. The bark, which scales off the mature tree in large flakes as much as several square feet in area, keeps the bole free of the climbing plants so common to other New Zealand tree species. The flakes leave a characteristic ripple or wave mark on the trunk, and form· at the base of the trunk a heap of decaying matter which may attain a height of 5 ft. or more. Resin also tends to collect in the forks of the main branches, and such gum, forming in the kauri forests o::f geological times, was probably the source of the fossil gum now being recovered from old swamps which have replaced previous forests. · Resin also occurs in the ray cells, but is essentially different from the ordinary "kauri-gum" of commerce. The wobd tends to become infiltrated with such resin only when damaged, either internally by the formation of heart shakes or externally by wounds to the trunk. The tops and stumps likewise become charged with this resin when healthy trees are felled. The kauri is a shallow-:rooting species. The young tree develops a thick tap root several feet in length, but ultimately this tends to decay and the mature tree is dependent upon a system of main and secondary laterals.