" " 4 12 "
" " 5 14 "
" " 6 6 "
" " 7 0 "
" " 8 1 "
" " 9 0 "
--- 100 "
It may be remarked that, judging by ordinary standards, it was impossible to discriminate between good yielders and others, and if thinning were to be done on the usual lines it is quite possible that some of the best yielding trees would be removed.
Taking the mark No. 5 as the datum line, it will be noted that 79 per cent.
of the trees come below and 21 per cent. above. In the latter proportion the majority lie close to the datum line. It will be seen that there are outstanding yielders even amongst these young trees, and that it would be possible to mark about 10 per cent. of the stand per acre at once for removal in the first round of thinning.
In the case of old trees it is possible that one would encounter greater extremes of yields than those shown in the foregoing table, especially if a certain amount of thinning had been done previously on empirical lines.
Sufficient has been written to show that the only reasonable basis for selection of trees in thinning is that of yields; and it is obvious that if the method be adopted the future yield per acre of any area is bound to be in excess of the same area as thinned on rule-of-thumb lines.
YIELDS PER TREE.--A great feature is made in estate reports of the figure showing the average yield per tree per annum. a.s.suming an area to be yielding at the average high rate of 540 lbs. per acre per annum, with an average stand of ninety trees per acre, the yield per tree per annum averaged over all trees is 6 lbs. Keeping in mind the test-figures on a previous page, it will be obvious that some of these trees may have given very much more than 6 lbs. during the year, and some less. In view of present information it would not be surprising to find that a few might have been yielding upwards of 15 lbs. per annum. Unfortunately this information is only to be obtained by individual tests, and under normal estate conditions the facts escape notice. Cases are known in which out-standing individual trees have been known to yield at the rate of 25 lbs. and more per annum.
[Ill.u.s.tration: WIDELY PLANTED YOUNG AREA, JUST READY TO BE BROUGHT INTO TAPPING.]
[Ill.u.s.tration: FIELD OF OLD RUBBER TREES IN WHICH THINNING HAD BEEN DELAYED TOO LONG.
Note height and comparative lack of girth.]
FUTURE YIELDS PER TREE.--It has been shown that by selective methods based on yields, poor trees can be eliminated. Whether by a process of seed-selection or by means of propagation based on bud-grafting and marcotting, it needs no great stretch of imagination to forecast future conditions under which trees may be bred which will be capable eventually of giving an average yield of 25 lbs. per annum over any given area.
Yields of 1,000 lbs. per acre per annum should be obtained easily.
TREES PER ACRE.--This brings us to the question as to how many trees one should leave to the acre after thinning operations. Figures have been given by various authorities, but it appears to the writer at the present time to be impossible to lay down a general rule. So much depends upon conditions.
In certain cases where the soil is admittedly poor, the average growth below normal, and thinning has been postponed too long, the writer has been forced to the conclusion that it would be most inadvisable, and commercially unsound, to reduce the stand of trees below 120 per acre. In such instances the average yield per tree equalled only 3 lbs. per annum, and although the trees were upwards of nine or ten years old the crowns were small and spa.r.s.e. It is doubtful whether such trees will ever exhibit any further development, and to thin them further would probably lead only to a diminution in the crop per acre.
Under normal conditions of growth an arbitrary figure of eighty trees per acre has been selected as a standard by many estates. In these cases it would probably be correct to state that thinning was undertaken on almost purely empirical lines--_i.e._, that trees were not selected by tests of individual yields. As far as such a method retained the apparently most vigorous trees it was successful; but in view of what has been written it might explain some of the disappointing results which have followed upon such a system of thinning.
It will be clear that any decision regarding the number of trees to be retained must be derived from a study of the detailed results of individual tests. If the large majority of the trees appear to be fairly uniform in yields the first thinning must be confined to comparatively few trees.
Where there is, on the other hand, a good percentage of high-yielding trees the final stand per acre may be appreciably less. Unless and until such information is available, one cannot give any definite opinion as to the requisite number of trees to be retained per acre.
Similarly, intelligence must be displayed in deciding which of several uniformly-yielding trees should be removed. In the average sense of this consideration one must pay no attention to symmetry of s.p.a.cing, but when dealing with trees of fairly uniform yields one needs to study the characteristic development of the trees individually, in order to retain those which would appear to be most favourably situated with regard to surrounding trees.
CHAPTER IV
_TAPPING SYSTEMS_
Broadly there are only two methods employed in obtaining the latex from _Hevea Brasiliensis_. The first is that employed in South America, where incisions are made by means of a light axe. The other is the system of excision, or paring, of the bark practised on plantations in the East.
In the early days of the plantation industry, the South American method seems to have been employed, and the writer has knowledge of trees on one of our best-known estates in Malaya which still exhibit the outward and visible signs of that method. At a comparatively early stage, however, the method of excision was introduced. Curiously enough there appears to be no record of its inception or of the individual who was responsible for the subst.i.tution of this method. We have been so accustomed to regard it as one of the ordinary facts of estate procedure, that this point seems to have escaped notice and enquiry.
As a variant of these two main methods, a slight vogue was for a short while obtained by the operation known as "p.r.i.c.king." This was generally combined with excision of bark, and was then known as the "paring and p.r.i.c.king" method; but the simple operation of p.r.i.c.king alone had its adherents, and various forms of instruments were designed to achieve the object. As a means for obtaining a flow of latex, p.r.i.c.king may have been effective, but the general difficulties attaching to the collection of the latex was such as to put the method out of favour.
In the employment of "paring and p.r.i.c.king," a thin shaving of bark was excised on one occasion. At the next tapping no bark was excised, but a p.r.i.c.king instrument was used along the previously cut surface. It was not proved that any advantage was gained by this method, which was more commonly employed in Ceylon than elsewhere, and it would be surprising to find it in use at the present day.
In the ordinary way the method of excision is practised in such a manner that the "cut" gradually descends to the base of the tree.
Planters with original views, and of an enquiring nature, often query the common practice; and it has been suggested that "as the latex descends by the force of gravity," one"s paring should be done in an upward direction, thus obtaining a greater pressure of latex--and hence a greater flow. It will be obvious that it would be no simple matter to collect effectively the latex thus obtained from the under edge of a sloping cut, but apart from this the argument would appear to be founded upon what is now accepted to be a fallacy--viz., that the latex _per se_ is manufactured in the leaves and gravitates down the tree.
FORMER SYSTEMS OF TAPPING.--To hark back ten years in the plantation rubber industry is equivalent to delving into history, since development has been so rapid. It was then thought necessary to place upon the trees a number of simultaneous cuts which the modern planter would judge to be inconceivably excessive. Were it not for evidence in the shape of photographs extant, it would be difficult to convince a young planter that such systems were employed.
It was not uncommon for trees to have from six to ten cuts, sometimes all placed on one half of the tree in a herring-bone fashion, and sometimes divided into two portions, each of which tapped the opposite quarter panel of the tree"s circ.u.mference. Such superimposed cuts were s.p.a.ced from 1 foot to 18 inches apart.
On other occasions, a spiral cut was employed, commencing at a height of, say, 5 feet, and gradually descending to the cup at the base of the tree.
Later systems varied from several cuts on a half-circ.u.mference, or on a quarter of the tree, tapped either daily, or on alternate days, to cases in which one-third or one-fifth of the tree was employed. Also popular were the systems of the [V] and half-spiral cuts on half the circ.u.mference.
It did not take long to be recognised that with all these systems demanding a number of simultaneous parings from the same panel of bark, the rate of excision was so heavy that the period available for the renewal of bark was insufficient for continuous tapping.
As a result most of the systems specified have fallen into desuetude, and the tendency has since been to reduce the number of cuts, or the periodicity of tapping, so as to allow for increasing periods of bark renewal.
In the earlier days, a period of four years was thought to be an extremely generous allowance, whereas six years is now becoming recognised as a minimum necessity. Eight years is not regarded as extravagant, while with older bark on some estates periods of ten and twelve years have to be allowed for full renewal. Even so no finality has been reached, and no general rule can be laid down. Local conditions of planting and growth exercise great influence, and the writers have in mind instances in which a period of eight years has proved to be insufficient even for a first renewal after the excision of virgin bark.
In the main the most popular systems of tapping are:
(_a_) One cut on a quarter of the tree, tapped daily.
(_b_) One cut on a third of the tree, tapped daily.
(_c_) One cut on half the circ.u.mference, tapped on alternate days.
(_d_) A [V] cut on half the circ.u.mference, tapped on alternate days.
Variants and extremes are:
(1) One cut on a quarter, tapped on alternate days.
(2) One cut on a half, tapped daily.
Superficially viewed the latter is four times as strenuous as the former, and the relative position seems to be inexplicable. It may be explained that as a rule the former system is practised on old trees with poorly renewed bark, in order to allow for adequate bark renewal; and the latter is employed in opening young trees just brought into tapping, when the rate of bark renewal is at a maximum.
[Ill.u.s.tration: TWO CUTS ON A QUARTER CIRc.u.mFERENCE, ON AN OLD TREE.]
A few estates in this country still continue to tap trees by means of two superimposed cuts on a quarter of the tree. This was a very popular system some four or five years ago, but it has come to be recognised by practical experience that any system employing superimposed cuts leads to a high consumption of bark without proportionate increase in yield. For instance, if one compares the system of two cuts on a quarter tapped daily with a similar system employing only one cut, one finds that the major quant.i.ty of latex is yielded by the lower cut, and that the single-cut system which excises approximately half the amount of bark gives about 80 per cent. of the yield obtained by the tapping of two superimposed cuts.
Of experiments to test the relative values of different systems of tapping there have been many. Most of them suffered from the initial handicap that they dealt with systems which were then popular. In order to obtain any valid result they had to be undertaken over a long period. Meantime there was a progressive movement in actual estate practice towards a greater conservatism in bark removal, and hence the experiments as originally planned lost value.
Moreover, in Malaya it was difficult for experimenters to obtain practical support in the form of areas of trees suitable for experiment. As a result experiments were often confined to small blocks of trees, and a small number of blocks, from which any conclusions derived were subject to considerable errors of experiment. Often comparisons were made between only two blocks, and no allowance was made for varying factors, such as initial differences in yielding capacities of the trees, soil conditions, or the personal equation of the tappers. As a general rule, therefore, the results were vitiated to a very appreciable extent.
All these factors were later taken into consideration in an experiment undertaken on behalf of the Rubber Growers" a.s.sociation. In this instance unique facilities were provided by the London Asiatic Rubber Company on their property at s.e.m.e.nyih Estate, and it is only fitting that the company should receive the recognition which its enterprise deserves.
It would have been a great advantage to have included in that experiment other features which have since come into prominence, but the original scope of the experiment had to be confined to the point of comparing yields obtained in making comparative tests based on one system of tapping with different frequencies. Such data were required as a check upon a Ceylon tapping experiment which had attracted much attention. In that experiment trees were tapped at intervals ranging from one day to seven days; and it was concluded that after a period of three and a half years trees tapped with greater intervals gave yields equalling or exceeding those obtained from trees tapped with shorter intervals.