Effect of thinning on Pinus pinea L. development and physico-chemical soil characteristics in northwestern Tunisia: modeling of radial growth under thinning intensity

In this study, the potential beneficial impacts that the thinnings intensity on stand behavior and soil properties are also studied. This study was designed to test the hypothesis that thinning to various stand densities at young age enhance productivity of wood, cones and the physicochemical characteristics of the soil in Pinus pinea stands. We based our study on four thinning intensity (30, 40, 50 and 65%) in comparison with the control plot. The study was supplemented by a haracterization of radial growth of trees under the four thinning intensity. It was based on a complete randomized experimental field installed in 1994 in Tabarka forest, in Tunisia. For the radial growth analysis, three cores were taken from 125 trees at a rate of one tree per plot.The study showed that thinning has a significant effect on all dendrometric parameters. They revealed that a thinning intensity of 65% produces the best wood production (180.710 m3/ha), in annual growth in volume (4.634 m3/ha/year) and cone production (1211 cones/ha) compared to other thinning and control plot. Associated vegetation was also influenced by thinning intensities. The physicochemical characteristics of the soil were improved by thinning compared with the control. Signif- icant radial growth thinning was recorde especially in a thinning of 65% intensity (increases of 3.5 to 6.1 mm/year) compared to the control (1.1 to 2 mm/year). A strong relationship between radial growth and age was recorded at Thinning 4 (R2 = 0.923). These results can be used as an initial basis to refine silvicul- ture of pinion pine in order to improve stand productivity in Tunisia in wood and especially in cones given their importance on the world market.