The Pamphlet Collection of Sir Robert Stout: Volume 64
In recapitulating the leading points of my subject, it will be necessary to revert shortly to the general properties of timber referred to at the outset, and consider the peculiarities of our native products in the order then given.
Table No. II. gives the ordinary dimensions, amount of sap-wood, and approximate age of the principal Otago trees. It shows that class for class they are equal in size to those in other countries. The kowhai, rata, manuka, kamai, and black heart birch are on an average as large, if not larger, than oak, ash, elm, and beech, the English timbers for which they are substitutes, and with the exception of yellow pine and cedar, all our pines are considerably larger and more productive than their European and American prototypes. In like manner we show that the growth is more rapid in New Zealand than most other countries that produce ordinary building timber; consequently the reproduction of native trees, if it can be successfully accomplished is more profitable than the introduction of foreign ones.
The proper season for felling timber in New Zealand is not yet fully determined. The late Mr. Balfour said "probably it maybe found that page 171 midsummer is the best;" but Mr. Kirk gives a decided opinion in favour of winter felling. He fixes April to August as the most suitable time in all the forests south of Banks Peninsula. I have no doubt Mr. Kirk is correct in considering this the season in which the trees are freest of sap, for the distinctness of the annual rings in most Otago timbers shows a decided period of repose in the growth. Still it is quite possible that a similar condition exists during the two summer months, December and January, and I would have little hesitation in including them in the felling season. I have instituted a series of experiments with the view of assisting in determining the season when the trees contain the minimum quantity of sap; it consists in observing the strain required to tear off strips of bark in each month of the year. The experiments will not be complete for six months, so I cannot give the results in this paper, but will do so on a future occasion if it is found to be worth publishing. The only well authenticated proof I have obtained of the superiority of winter felling in New Zealand is given in Mr. Horman's fence at Makerewa, already referred to. All the black pine posts erected in the winter of 1861 are still in good preservation, while those felled and erected a few months subsequently were more or less decayed some years ago. Assuming that ripe trees only are felled, and that I none of the sap-wood is used, the time for felling timber is, within certain limits, of secondary importance to its subsequent seasoning and desiccation. The simplest way of obtaining a fair amount of seasoning in New Zealand would he to bark the trees in spring, cut them in the following winter, then slab the logs and let them he in a running stream for a few weeks, or, what is better, let the sawn scantlings be submerged. There is little trouble in doing this when the timber is cut up in the bush as at Catlin River and Southland. After having the sap washed out in this way, the timber should be thoroughly dried under cover in open shed.
Table III., which gives the results of some experiments I made, shows the absolute necessity of seasoning;—it gives the weight of water in a cubic foot of green timber, and the transverse shrinkage in boards twelve inches square and half an inch thick. The results may be accepted as a fair indication of what will be obtained in practice, for the samples were picked heart-wood, cut radially to prevent warping; but they were taken from green logs and subjected to severe drying at a fire, and in the hot air of the Turkish baths. It will be seen that the greatest contraction is in ribbon-wood, next the red birches, and after that the hardwoods generally; the least is in black and white pine. It is worth noticing that English oak and New Zealand red birch, members of the same botanical family, are both given to excessive shrinkage. I should add that the results in Table III. are not higher than would be obtained from European and American timbers of the same class.page 172
|White pine and totara||0.30 of an inch in 20 feet.|
|Red pine||0.23 of an inch in 20 feet.|
|Kauri||0.11 of an inch in 20 feet.|
Of course the kauri was somewhat drier than the others to commence with. There is no record of similar experiments having been made with the timber of other countries, so a comparison cannot be instituted. I believe, however, that our timbers do not shrink more endwise than foreign ones of the same class. The importance of seasoning timber has hitherto been very much overlooked in New Zealand. Instead of using well dried heart-wood from mature trees that are felled at the proper season of the year, we put into our houses wet sap-wood from young trees that are felled when most convenient, probably in their juiciest state; and, to increase the evil, the timber is painted at once, so that all the juices are retained to ferment, and thus breed corruption. It frequently happens that the timber for some of our best buildings is standing in the forest after the work has been commenced. Colonial timbers have fallen into disrepute solely on account of being used in a green state alongside foreign ones that are well seasoned. As a matter of fact, many of the latter are considered worthless in their own country for the same reason. It may therefore be set down as an axiom that no timber is good in the country that produces it.
The late Mr Balfour conducted a series of experiments on the strength of New Zealand woods at the N.Z. Exhibition of 1805. So far as they went these experiments were very satisfactory, but lie himself admitted that they were not exhaustive, and suggested the further investigation of the subject by the General Government. A collection of timber specimens was made for this purpose in 1872, but the experiments have not yet been made. In reporting on the subject Mr Balfour said:—"New Zealand woods compare very fairly with those which we have been accustomed to consider as standards, the absolute strength of very many being above that of British oak, and all being stronger than elm. * * * New Zealand woods are certainly for the most part short in the grain and break with little warning. There are a number of valuable exceptions, but it will be observed that the ratio of safe load to breaking weight is high, which to a great extent compensates for this peculiarity." Mr. Balfour's experiments were made with pieces twelve inches long and one inch square, supported at one end. I observe that Mr. Laslett, who tested the strength of most of the principal woods in the world for the Admiralty, used pieces six feet long and two page 173 inches square, supported at both ends. As his results will probably be the standard in future, any further experiments in New Zealand should be on the same scale. Mr. Brunton, C.E., Invercargill, tested four samples each of black pine and totara on ten feet bearings. One of the former was eight, and all the others four, inches square. The large black pine piece broke with six and three-quarter tons, and the average breaking weight of the smaller pieces was—for black pine, twenty-three and a half hundred-weights; and totara, twenty and three-quarter hundred-weights. When worked out in the same manner, this makes black pine fifty-three per cent, and totara thirty-one per cent, weaker than the mean of Mr Balfour's experiments with small samples. Table No. IV. hereto appended, gives the main results of Mr. Balfour's experiments put into a more popular form than the one he adopts, which is intended for professional men. My table simply gives the "weight," "strength," "elasticity," and "toughness" of the principal Otago timbers, with examples of well-known varieties from other countries.
The fifth and last table that I have prepared is intended as a guide in the selection of native timber for special purposes. It gives an abstract of the properties and uses of the various kinds referred to in the paper.
In conclusion, I claim to have shown that Otago, and New Zealand generally, is well provided with good timber suitable for all the purposes of the constructive and mechanical arts. How then is it that we import £130,000 worth annually from foreign countries? I shall leave the question to be answered by the political economist, for I can see no valid reason for i the anomaly. I can only view the fact as a grave reflection on our enterprise.page 174 page 175 page 176 page 177 page 178 page 179