By the DIRECTOR OF FORESTRY, Union of South Africa
Research into timber seasoning and preservative problems in the Union of South Africa was begun on a very small scale in 1919 by the newly created Timber Investigation Section of the Department of Forestry. The results of this work were so encouraging that in 1926 it was decided to establish a central, self-contained, experimental station. What is now known as the Forest Products Institute came into being in 1928; it is a branch of the Department of Forestry, with the Chief Forest Products Officer in charge of the Institute responsible to the Director of Forestry.
The Institute is perhaps unique in that its original activities included a considerable amount of marketing research and development, with the object of proving the value of local products when correctly handled or designed for large-scale distribution. This policy was well justified, since it had the effect of emphasizing the practical aspect of research and, because of the large volume of products handled, contributed considerable useful experience.
During the last 10 years the functions of the Institute have been purely of an experimental nature; they may be described briefly as research into all problems connected with the conversion, treatment, and utilization of locally grown timbers (indigenous and exotic). Equipment consists of a sawmill, planing mill, and five different types of commercial kilns, to deal with sawing and drying problems and with the evaluation of the physical and working properties of timber; open and pressure tanks to investigate the venous methods of impregnating the numerous timbers with preservatives; numerous testing machines to determine the mechanical properties of squared timber and poles; and facilities for the grading and identification of timber. There is also a chemical laboratory and a large and unique wood museum.
As the Forest Products Institute is the only one of its kind in the African Continent it renders assistance to public and private concerns throughout Africa as well as to local government and private bodies. Courses in kiln seasoning and other subjects are held from time to time. Close contact is maintained with many overseas laboratories of the same type, and reports and publications on the results of the work are interchanged.
Timber Preservation
The State's afforestation of large areas in the Union with exotic softwoods and hardwoods introduced the problem of utilizing the thinnings of young non-durable poles. This problem was partly solved by working out appropriate impregnation schedules and preservative solutions for a wide range of products, including fencing and building poles. The introduction of chemically treated eucalypt telephone and electric transmission-line poles has been particularly useful, since it has enabled scores of small municipalities, which could not have afforded the price of steel poles, to install electric power.
More recently, to combat the activities of the European house borer (Hylotrupes bajulus) and the West Indian dry wood termite (Cryptotermes brevis), appropriate preservatives were found and methods of application-drawn up for imported woods as well as local timbers.
In this connection, the Institute's development of a non-oily, quick-drying, and non-blooming type of pentachlorophenol preservative has had important significance. This preservative, which has high penetrating properties, is used in the form of a soaking treatment for many pine species, and with very low pressures (5 to 20 lb.) for hardwoods.
Sludging, which occurs in some oil creosote mixtures when used as wood preservatives, has been almost entirely eliminated in some cases by the use of an aromatic "bridging agent" or by the use of oil containing highly aromatic properties. This discovery facilitates penetration and enables the use of creosote mixtures with oil, reinforced with pentachlorophenol, copper naphthenate, or other suitable chemicals.
An evaluation of the preservative properties of some eighty different wood; preservatives has been obtained from tests carried out over a number of years. The tests consist not only of observations from actual service throughout the country but also of scientifically planned experiments, based on modern techniques, located in areas where decay hazards as well as combined decay and termite hazards are severe. In all cases the protection offered by the oil preservatives has been found to be far superior to that offered by any water borne salts for outside work.
Work is continuing along these lines in an attempt to extend the use of the available quantities of creosote, which is limited, by appropriate mixtures. Close attention is being given to the use of fish oils in place of dehydrated castor oil in pentachlorophenol solutions; and the termite and decay tests will be extended to include ship-worm and other destructive marine agencies.
Timber Seasoning
From study of the developments in kiln design throughout the world, the Institute has been successful in developing a kiln which combines all recent improvements. This kiln, in addition to the four other types of kilns, has been in operation for the last three years. The design has been widely adopted by the timber trade and has undoubtedly resulted in increased-efficiency in seasoning generally. It includes overhead reversible cross-shaft fans and is suitable for the precise drying of both hard- and softwood timbers.
Kiln seasoning courses held from time to time have been attended by persons resident in the Union, as well as by others resident in adjacent territories. Schedules for most of the important local timbers have been determined, and a standard work on timber seasoning in South Africa has been published in bulletin form.
The Institute has determined the equilibrium moisture content of various timbers in most of the important cities in the Union, and has collected data on the shrinkage and seasoning properties of many woods. A special study of the seasoning of young eucalypt timbers has brought about a reduction in the very high wastage usually associated with their use.- Frame saws and double log-edgers, introduced to deal with the stresses found in these timbers, have proven very successful.
Uneven rate of growth in coniferous timber has not been found to be the cause of excessive warping in any of the species examined when cut to the normal building sizes of 1½" x 4½", 1½" x 6", and 1½" x 9. Sections of 2" x 3" from the center of the stem occasionally show stress, but spiral grain and compression wood are of greater significance in producing warp.
Investigations are now being made of the extent to which the spiral markings, visible on the bark of Pinus longifolia trees, serve as a guide to judging the degree of twist likely to be found in boards sawn from those trees. Spiral grain in P. longifolia appears to have little if anything to do with rate of growth, but is traceable to seed stock. Other stresses in seasoned boards are also being examined to determine the cause of warp, especially in young coniferous timber.
Timber Utilization
Additional and better uses have been found for a number of the indigenous timbers which, owing to the small volume available, should be used to the best advantage. White pear, for example, is admirably suited to printers' cutting sticks; yellow-wood is excellent for battery separators, and Gape ebony is suitable for slide rules.
Such imported species as P. patula and P. radiata, which are now widely planted, have undergone considerable research. Little information could be obtained from outside the country, but the timber from these and numerous other introduced species has now been examined, and a study has been made of the effect of age, rate of growth, and variations which occur within a plantation or a single tree. Some of the generally accepted overseas conceptions have been found inapplicable to these young exotics.- For instance, it has been established that the age of the tree and not the rate of growth influences the wood qualities. In other words, fast rate of growth does not produce light, soft timber unless it has taken place at a very early stage (1 to 10 years) of the tree's growth; in any event, after about ten years, regardless of how fast the trees have been grown, the timber is amply strong for all normal building purposes.
Draft grading rules for local coniferous timber, based on the results of examining many thousands of cubic feet during the course of the experiments, have been prepared by the Institute and, with the co-operation of the Lumber Millers' Association and the South African Bureau of Standards, have also been published for general use.
Early research into the use of wattle, gum, and pine for pulp and paper-making have helped to promote industries which are now well established.
In addition to examining the locally produced timbers, the Institute has prepared and published notes on the properties and uses of a great many hardwoods from adjacent territories. It will continue to work along the lines indicated, and plans to concentrate particularly on research into the production of shingles, diving boards, and sleepers from locally grown timbers.
Timber Mechanics
The Institute works in close co-operation with other laboratories to secure the highest degree of conformity in all routine and other mechanical testing procedures.
From tests of locally grown pine timbers, it has been found that density and strength follow a definite pattern in which there is an increase in strength from the center of the stem outwards, culminating in some instances at about the thirty-fifth year, i.e., when the trees are almost mature or have reached a diameter of about 18 inches, breast height under bark. There is also a decrease in the strength from the base upwards.
No correlation has been found between ring width and strength, other factors being equal, but a distinct correlation between age and unit strength has been observed.
It should be noted that while these facts have been found to hold true for pines' they are not equally applicable to such species as Cryptomeria japonica and some other conifers.
For the testing of transmission poles, special equipment has been installed by which transmission poles up to 48 feet long and 8-inch top diameter can be readily tested for strength. It is largely owing to the results of these tests that the Electric Supply Commission was willing to utilize local wooden poles throughout the country.
Work will continue on determining the factors influencing strength in pine stems; the next species to be investigated will be P. pseudostrobus and P. longifolia. In the latter case the effect of spiral grain on strength will also be determined,
Investigations into Thinning Techniques
Research in the thinning of pure, even-aged coniferous stands, based on O'Connor's method, is being carried out. 1 The basis of this method is that the investigation should not be confined to practical degrees of thinning intensity, but should range by steps from the extreme of complete suppression (in which state the stand can carry no greater number of trees at a given age) to that of free growth (in which state diameter growth cannot be stimulated by further reduction in stocking at a given age). The object is to produce a series of correlated curves from which the experiment takes its name of Correlated Curve Trend or C.C.T. method, expressing the relationship between volume of the mean tree to density of stocking at set intervals throughout the rotation. At the same time other plots are being maintained with the object of estimating the degree of response to various degrees of thinning at various degrees of suppression and at various ages. The degrees of response and suppression are expressed on a relative basis incorporating the degree of thinning, thus reducing the variables to proportions that can be handled on three-variable graphs. The information shown on the graphs is to be applied to the correlated curves to determine the effect of any degree of thinning at any stage, due allowance having been made for the mechanical effect of thinning on the mean D.B.H. of the stand.
1 A. J. O'Connor, Forest Research with Special Reference to Planting Distances and Thinning, Government Printer, Pretoria, 1935.
Experiments of this nature are being conducted for all the main exotic conifers (i.e., Pinus patula, P. radiata, P. taeda, P. caribaea, P. pinaster and P. roxburghii) on all types of site on which they are of commercial importance. The oldest experiments have now been in progress for 12 years and show the following preliminary results:
1. Neither species nor site quality markedly influences the age at which mutual competition between the components of a stand of given density commences.2. Mutual competition between the components of stand commences in 1,200 trees per acre in the fourth year, in 600 trees per acre in the fifth year, in 400 trees per acre in the sixth year, in 300 trees per acre in the seventh year, in 200 trees per acre in the eighth year, in 150 trees per acre in the ninth year, and in 100 trees per acre in the tenth year.
3. A stand when thinned will tend to assume the same rate of growth (volume increment) as the rate that is normal (on the same site quality and at the same age) for the density to which it has been reduced by the thinning. The relevant data is still somewhat meager, but it appears that this statement holds good for all stands up to the twentieth year, irrespective of the degree of suppression in operation prior to thinning or of the intensity of the thinning. Expressed in O'Connor's terminology, it may be said that the coefficient of response is unity for all coefficients of suppression.
4. The response to thinning takes 6-10 years to find full expression. The current annual increment of the thinned stand gradually increases and equals that of a stand at the density to which it has been thinned after 3-5 years. Thereafter it surpasses the increment of such a stand and falls again to equal it at 6-10 years remaining level with it thereafter. The periodic mean annual increment of the two stands is the same over the full period of 6-10 years.
Pruning Investigations
Pruning in South Africa is based on the conclusion that the knotty core must be restricted to a diameter of 4 inches. The effects of removing live branches, necessitated by such a restriction, have been closely studied.
Experiments on pines show the following results:
1. The effects of pruning are more marked and more lasting when selected stems only are pruned than when all the trees in the stand are pruned.2. Live pruning retards diameter increment more than height increment.
3. Pruning 25 percent of the living crown has no significant effect on either diameter or height increment.
4. Pruning 50 percent of the living crown has a significant effect on diameter increment but not on height increment.
5. Pruning 75 percent of the living crown affects both diameter and height increment to a significant extent.
6. Recovery of normal increment after 75 percent of the living crown has been pruned takes 2 years if all the trees in the stand are pruned and 3-5 years if selected stems only are pruned.
7. Between the ages of 4 and 8 years the effect of selective live pruning on growth is inversely proportional to the age at which pruning takes place, the older stands being less severely affected.
8. The ability to withstand severe selective live pruning varies inversely with the site quality, the depression of increment being least and the rate of recovery greatest on poor sites.
9. The taper of the stem is decreased in the region 10 feet above and 10 feet below the lowest whorl of branches.
10. The mean branch diameter of the remaining branches is not increased by live pruning.
The present practice in South Africa is to prune to a height of 22 feet. Further experiments are being undertaken to determine whether it is economical to prune to greater heights.
Genetic Research
Research of this nature is still in its initial stages. Efforts are being made to improve the form and rate of growth of the main coniferous species by the collection of seed from elite trees and by controlled pollination. In addition, the possibilities of producing useful hybrids are being examined.
An investigation into spiral grain in Pinus roxoburghii (Syn. P. longifolia) has confirmed conclusions that the main factors concerned in the production of spiral grain are hereditary. Steps are being taken, therefore, to establish future sources of seed in suitably isolated stands from which all excessively twisted stems have been removed.
Statistics
Stem volume alignment charts and percentage utilization tables have already been produced for the main coniferous species. Similar tables are in the course of production for the main eucalypt species. Statistical plots are also maintained for all exotic species of commercial importance not covered by the C.C.T. method.
In view of the importance of the forest lands owned by the Union Department of Forestry for Water Conservation, comprehensive research to determine the effects of afforestation and other forms of veld management on water resources has been undertaken.
Two research stations have been established, one at Jonkershoek, in the winter rainfall region, about 35 miles from Cape Town and 6 miles from Stellenbosch and one at Cathedral Peak, in the summer-rainfall region, about 26 miles from Winterton in the Bergville district of Natal. The investigations at these centers are analytical and experimental, and some of the results obtained have already been described in Unasylva. ²
² Vol. IV, No. 1 (January-March 1950).
