RADIAL GROWTH AND STEM TAPERING IN THINNED PLANTATIONS OF Pinus patula SCHIEDE ex SCHLECHTENDAL & CHAMISSO

Abstract

Pinus patula Schiede ex Schlechtendal & Chamisso is an endemic species of Mexico, with significant economic relevance due to its high productive potential in forest plantations and natural forests. The intensity and frequency of thinning cuts generally influence the thickness of the annual growth rings, the proportion of latewood, and the tapering of the stem. This study evaluated the radial growth and thickness of the growth rings and their earlywood and latewood components at different stem heights, as well as the stem taper index of young Pinus patula plantations with thinning cuts applied at nine and 13 years of age. Ten trees were selected and cut in each of two thinned plots with a diameter at breast height similar to that of the plot mean to obtain three 3 cm thick cross sections (slices) at different heights of each sampled tree. Thinning cuts reduced the impact on the thickness of the annual rings and their earlywood and latewood components at the basal section. The effect of the cut was only observable the year after the thinnings, with an increase in basal area and earlywood thickness; afterwards, the radial growth rate returned to its original pattern. The thickness of the rings and their earlywood and latewood components was higher at the middle and upper stem sections, causing a gradual reduction in stem tapering. This results confirmed that thinning cuts were performed late, when the crown had already concentrated at the top of the tree, due to high competition for growth space.