INFLUENCE OF THINNINGS ON THE ECCENTRICITY OF THE STEM OF PINUS-KESIYA IN THE MANGORO REGION (MADAGASCAR)

The eccentricity of the section perpendicular to the stem axis (SPSA) presents technological drawbacks. The aim of this work is to explore whether and how much this phenomenon is influenced by thinnings; the basic hypothesis is that the release of competition associated with thinning leads to an asymmetrical development of the crown which. induces an increased cambial activity in the direction of felled trees. Fifteen 20-year-old trees from a CCT-Plots trial that had been thinned 5 times and five 14-year-old trees belonging to stands that had been thinned once have been analyzed; disks were taken every meter from 0.3 m to 5.3 m and every 2 m up to a 15 cm top-end overbark diameter The eccentricity was quantified by measuring 16 radii on each disk. Ten release-of-competition indexes were constructed including the distance, the size and the direction of the trees removed. The results suggest that: (1) the evolution of SPSA eccentricity is independent of the spatial distribution of thinned competitors; (2) the variation of SPSA form is consistent along the bole; (3) the initial (ie before thinning) SPSA form is a good indicator of the evolution of the eccentricity after thinning; and (4) in most cases the final SPSA form may be predicted from a very early SPSA form (ie when cambial age is about 5 yr).