Efeitos biológicos e econômicos de tratamentos silviculturais em plantios de Pinus taeda L. no Nordeste Argentino

Abstract

The aim of this thesis was to study the effect of pre-commercial thinning and pruning on growth, yield, wood quality and economic results, on a 15th year old stand of Pinus taeda L. in the Argentinean northeast. The study was established in a deep red clay soil, with a systematic design of blocks for thinning intensity and sub-blocks for pruning intensity. The thinning treatments, performed at 3 year old were: 1666 (without thinning); 833; 416 and 208 trees ha-1. The pruning were done annually, starting at 3 year old, and applied by 2, 3 or 4 consecutive years removing 30, 50 and 70 % of the living crown respectively. The general model obtained by linear regression allowed to estimate, with good precision (e%=5,9), the quadratic mean diameter (dg) in function of age. The variable remnants trees, remnant crown, and number of prunings were considered to estimate the general function coefficients. At 15 year old, the dg varied from 25,6 to 41,5 cm to 1666 and 208 trees ha-1 respectively without pruning. The dg was negatively affected by pruning and positively affected by thinning. The height was not affected by pruning and thinning. The height of the stand was 23,8 m. The normal distribution represented the dg data in a best way. With 1666 trees ha-1 the number of live trees began to decline at age 6. The SDI was 1181 trees ha-1. The trees showed more taper when thinning were more intensive. The basal area varied from 56,3 and 27 m2 trees ha-1 for 1666 and 208 trees ha-1 respectively, without punning. The volumes were higher in the higher densities varying between 679,9 and 327,4 m3 ha-1 with 833 and 208 trees ha-1 respectively. When the trees were pruned the volume ha-1 decreased between 1,6 and 10,4 % depending on the density. The production with more value was showed by 416 trees ha-1. The crown ratio was negatively affected by pruning and positively affected by thinning; estimated values of 59,1 and 22,7 % were obtained with 208 and 1666 trees ha-1 respectively. Wood density was affected by thinning showing highest estimated values when thinning were more intensive; varying between 404 and 342,8 Kg m-3 for 208 and 1100 trees ha-1 respectively. The latewood % showed the same behavior than wood density the estimated values varied between 40,2 and 29,3 % for 208 and 1200 trees ha-1 respectively. In general terms, the n° of rings by inch near the pith was lower than 2 and higher than 4 near the bark. The maximum values of NPV; IRR; B/C and AEV were 1055,6 US$ ha-1; 11,9 %; 1,43; e 123,3 US$ ha-1 planting 833 trees ha-1 thinning to 416 trees ha-1 and pruning, in a15 years rotation. The best economical results were obtained with treatments of pruning and thinning.