Effect of thinning intensity on the growth of oriental beech (Fagus orientalis Lipsky) stands in Duzce

This study was carry out in even-aged, natural and pure oriental beech (Fagus orientalis Lipsky) dominated stands in Düzce, Turkey and evaluated the 3rd-4th year results of thinning effect on growth, in terms of the stands, initial diameter class and crop trees. Thinning experiments in five different sites (Asar, Çamoluk, Sazköy, Düverdüzü and Kurtsuyu) were conducted in a randomized block design with three replications. Prior to thinning, mean stand diameter, top height, stem number and basal area in the experimental sites were 14,1 cm; 19,7 m; 2337 trees ha-1 and 29,25 m2 ha-1, respectively. Three thinning intensities (control, moderate and heavy) were applied in all sites. The selective thinning intensities included removal of initial basal area by 0% (control), 21-30% (moderate) and 31-46% (heavy). Thinning affected stand diameter increment in all sites. Generally absolute and relative diameter increments increased with increasing thinning intensity. Thinning intensity didn't significantly affect stand basal area increment in all sites, but significantly influenced relative stand basal area increment which was the highest in heavy treatment and the lowest in the control. Thinning substantially increased stand volume increment in Çamoluk, yet decreased in Asar. On other sites, thinning intensity didn't significantly affect stand volume increment. Also, thinning intensity significantly affected on relative stand volume increment, which was the highest in heavy treatment and the lowest in the control. Relative to initial diameter classes, the greatest diameter increments occurred in the thickest diameter class. Height growth didn't vary significantly according to thinning intensity. Diameter, basal area and volume increments of crop trees were increased by thinning in Asar, Çamoluk and Sazköy, but in other sites they didn't demonstrate significant change. Mean diameter, basal area and volume increments of crop trees were 2,0; 2,5 and 2,7 times greater than those of the whole stand, respectively following thinning. Before thinning, estimated of leaf area index in all sites ranged between 3,37-5,14 m2 m-2. Compare to the initial values, leaf area index significantly decreased on the heavy-thinned plots, yet expanded back to the initial values 3-4 years after thinning. The leaf area index had a strong and positive relationship with relative diameter, basal area and volume increment. In conclusion, the diameter increment gain of crop trees was greater when compared to that of the stand level as a result of thinning. Therefore, focus should be on crop trees for thinning operations. In addition, heavy thinning should be recommended for an enhanced wood quality as well as thick diameters.