Preliminary results of impact of thinning on Norway spruce in Asalem region

Norway spruce (Picea abies (L.) Karst) trees were planted in Asalem region in 1974 in altitude of 1400 m.a.s.l. In order to study the stand response to thinning practice, 1.4 ha of this area was selected and an experiment was conducted by Complete Randomized Block with four treatments and three replications. The thinning treatments included light removal of basal area (10-15%), moderate (15-20%) and heavy (20-25%) and control (with no intervention). Thinning rotation were 3, 5 and 7 years for the treatments, respectively. Diameter at breast height (DBH) of all trees were measured every year. The study began at the age of 23 years and the study period extended between 1996 to 2006 when the trees were 34-years old. The thinning method was positive and from above (Swiss method). Results showed significant difference of stem numbers and diameters among different treatments after 11 years of study (P> 0.05). The lowest and the highest diameter increment was observed in control and light thinning treatments, respectively.