Growth of Radiata Pine after Row Thinning Compared with Selective Thinning

SUMMARY In a replicated trial near Canberra, first thinnings of a 16-year-old plantation of radiata pine (Pinus radiata D. Don) were carried out by felling every second row (R2), felling every third row (R3), felling every fifth row plus individually selected trees in intermediate rows (SR), and felling only individually selected trees (S). The trees individually selected for felling were those of poorest vigour or form. At the time of thinning, the stands had, on average, a predominant height of 22.3 m and a basal area of 41.7 m2/ha before thinning and 20.4, 27.9, 24.1 and 24.5 m2/ha after the R2, R3, SR and S thinnings, respectively. There was no significant difference in growth between the R2 and R3 treatments or between the SR and S treatments. During the six years after thinning the overall growth in volume of the row thinned plots (R2 and R3) was estimated to be 17 per cent less than that of the selectively thinned plots (SR and S). This lower growth was due to the retention on the row thinned plots of a larger proportion of small trees which grew less (in per cent of their basal area) than the larger trees. However, the growth of the 250 largest diameter stems per hectare did not vary with treatment. There was no evidence that the form of the trees remaining after thinning was adversely affected by row thinning. The indications are that earlier thinnings would have caused less difference between the growth of row thinned stands and that of selectively thinned stands.