YIELD OF ROUND-WOOD FOR PULP AND PAPER PRODUCTION IN STANDS OF Pinus taeda GROWING UNDER DIFFERENT SPACING AND THINNING REGIMES: AN EXPERIMENTAL APPROACH

Abstract

This paper evaluates the statistical effects of five different thinning regimes in combination with five initial plant spacing in loblolly pine plantations on the yield of round-wood for pulp and paper. The data came from an experimental plantation located at Fazenda Lageado, Jaguariaíva, Parana State, in southern Brazil, owned by PISA Pulp and Paper Co. The spicings evaluated were: 2.5 x 1.2 m; 2.5 x 2.0 m; 2.5 x 2.8 m; 2.5 x 3.6 m e 2.5 x 4.4 m. The thinning regimes compared were: a single final cut at age 15 without thinning; a single final cut at age 20 without thinning; systematic thinning along the 6^th planting line at age 9 and final cut at age 20; selective low thinning  of 50% of the trees in the stand at ages 9 and 15 and final cut at age 20; and systematic cut along the 6^th planting line combined with selective low thinning at age 9 for 50% of the trees in the stand, selective low thinning for  50% of the trees in the stand at age 15 and final cut at age 20. The factorial experiment was analyzed by  ANOVA and the test of Tukey. The results revealed significant differences (p< 0,01) among the initial plant spacings and the thinning regimes. The interaction between them was also statistically significant.  The results showed that, for the pulp and paper wood yield, the choice of planting with higher initial density (2.5 x 1.2 or 2.5 x 2.0 m) is recommendable. When selective thininngs are conducted, the higher density treatment results in greater pulp and paper wood yield. In addition, no significant difference could be noticed as compared to the 2.5 x 2.0 m spacing, when no thinning or a single systematic thinning was carried out. It was concluded from the analysis that the no thinning regime is more favorable to the pulp and paper wood yield in a 20-year rotation. Nonetheless, shorter rotation (15 years for instance) is not recommendable because of the low yield, which corroborated the practice adopted by various forest companies nowadays. The best combination of initial density with thinning regime was 2.5 x 1.2 m and a single final cut at age 20. However, for this stand density, the adoption of the 2.5 x 2.0 m spacing did not affect the pulp and paper wood yield. There is no significant difference between the thinning regime without thinning and  that using a single systematic thinning and a final cut at age 20, if the highest initial spacing is chosen.