Effect of thinning intensity on growth of oriental beech stands based on stand, crop tree and initial diameter classes

The oriental beech (Fagus orientalis Lipsky) is one of the most important broadleaved species in Turkey. It ranks first in terms of distribution area and volume in broadleaved tree species. The aim of this study was to evaluate the effects of thinning on eight-year growth at stand, crop tree and initial tree diameter classes in native and pure oriental beech stands found in three different sites (Sazkoy, Camoluk, and Asar) in Düzce region. Randomized block design with three replication were conducted in each site. Before the thinning, mean stand diameter, top height, basal area and stem number in the experimental sites were 12.9 cm, 18.6 m, 27.86 m2 ha-1 and 2018.0 trees ha-1, respectively. The selective crown thinning treatments were applied as removal of the initial basal area by 0% (control), 21-30% (moderate) and 31-46% (heavy) in each experiment. Compared to control moderate and heavy thinning treatments significantly affected mean stand diameter increment in all experiments and diameter increments increased with increasing thinning intensity. The thinning didn't significantly affect stand basal area increment in all sites. The increasing initial tree diameter classes and thinning intensity significantly increased the mean diameter increments. Thinning had no significant effects on height increment in all experiments. Thinning treatments significantly increased the diameter and basal area increment of crop trees in all sides. Compared to the stand level increments, the crop trees gained 1.41 cm, 1.61 cm and 2.16 cm more diameter increment in control, moderate and heavy treatments, respectively. Results showed that, it will be more accurate to evaluate the effects of thinning treatments on crop trees growth rather than the stand level growth because the effect of the thinning on crop tree growth is much higher than the mean stand growth. Heavy thinning treatments (up to 40-45% of the basal area) can be suggested for young beech stands similar to study stands to get larger crop trees at the end of the management period of the oriental beech stands.