The following figures must not be taken as typical. They represent the average results from several tasks in a young field from which all ill-grown and deformed trees had been removed. It is immaterial what the units represent, as they are purely arbitrary and were selected for the purpose of obtaining a fairly wide range.
Any trees which failed to yield sufficient latex to reach the first mark were registered at zero. The following percentages were obtained:
| Zero | 3 | per cent. | |||
| Above | mark | 1 | 6 | „ | |
| „ | „ | 2 | 16 | „ | |
| „ | „ | 3 | 42 | „ | |
| „ | „ | 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. Assuming 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.
