THE SILVICULTURE OF EXOTIC CONIFERS IN SOUTH AFRICA

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Abstract
This paper was presented to the Fifth British Empire Forestry Conference in London, 1947, and is reprinted here with the kind permission of the Director of Forestry A brief outline of the background to current silvicultural policy in South Africa is given. Methods of afforestation are discussed and recommendations for the amendment, where necessary, of present practice regarding initial espacements and pruning are made. Data upon the effects of growing-space upon mutual competition, upon increment and upon ring width are presented. The data show that under South African conditions suppression of the predominants commences at early ages for a wide range of tree densities and that these ages are not markedly affected by site or species; also that, despite this suppression, ring widths are apt to be large in the predominants during youth, irrespective of tree density. The data show, moreover, that maximum monetary returns from early thinnings are likely to be derived from initial espacements of 9 × 9 to 12 × 12 feet. Data are given which show that the longer thinning to a given density of growing stock is delayed, the greater will be the loss in total volume increment thereafter. Upon the basis of the increments of unthinned stands growing at various densities, extrapolated to maturity, it is shown that the financial returns from relatively heavily thinned stands are likely to be very considerably greater (almost double) those of relatively lightly thinned stands. Reference is made to the remarkable vigour of the Portuguese strain of Pinus pinaster relative to other strains and to the reasons why Portuguese pinaster should, in future, receive the same silvicultural treatment as other medium-fast-growing pines like P.taeda and P.caribaea. The paper concludes with a summary of recommendations made to amend those proposed by the writer in 1939.

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