Effect of thinning on growth of Acer velutinum Boiss. in northern forests of Iran

It has become necessary to develop stands of fast growing endemic species in the Caspian forests because of their reduction in area and the domestic demand of timber processing industries in Iran. Acer velutinum, an endemic species in Iran, is often planted in monocultures or in a mixture with other endemic species. Our study was conducted on A. velutinum planted in Berenjestanak (control plots) and Chaibagh (thinned plots) in northern Iran in 1991. A randomized sampling method with circular sampling plots of 100 m² was used to measure diameter and height of trees. The results show that the diameter of trees in thinned stands was 19.98 cm and in the control stands 13.84 cm, while the mean heights were 18.33 and 17.46 m, respectively. The mean basal area in thinned stands was 30.74 m² and in the control 15.70 m² per ha. The results of Student's t tests indicate that there are significant differences at a probability level of 99.9% between the two variously treated stands in diameter (d), height (h), basal area, volume growth and the stability coefficient. We conclude that tending operations with suitable intensity in different time periods are recommended to obtain stable stands.