Effects of thinning intensities on Loblolly pine (Pinus taeda L.) plantation in Guilan province (Iran)

In an 18-year-old Pinus taeda plantation in Pylambra region (Guilan province, north of Iran), 1.5 ha of well stocked stand at 3x2 meter spacing in 4 replications and 2 treatments, a: light thinning with 15% removing of basal area at 3 years rotation, b: heavy thinning with 30% removing of basal area at 5 years rotation and c: control, were selected and the effects of thinning operations on remained tree growth were studied during 15years. d.b.h, hieght and stem volume,were annually measured and all data were analyzed with SPSS. The results show that the age of 8-10 is suitable for precommercial thinning. The mean d.b.h., hieght and basal area of trees in thinned plots are greater than unthinned plots. Mean d.b.h. increased of %68 and %72 in light and heavy thinned plots and the stem quality obviously improved. Mean tree volume increased from 0.29 to 1.3 m 3 stem-1, respectively during 15 years. Equations for volume estimation of trees in 10-25 cm and 20-40 cm d.b.h. are presented for the region. It is concluded that the d.b.h, height and volume per stem of Loblolly pine increased with thinning. Heavily and lightly thinned plots produced higher total stem volume compared with the controlled plots and differences were significant at 5%. Mean annual volume increment are estimated up to 18.7 m3ha-1 hectare. Therefore, Loblolly pine is introduced as an adapted and resistante with high volume growth species in the coastal plain of Guilan province