The effect of thinning on Alder (Alnus subcordata) and Persian maple (Acer velutinum) Plantations in Chendella Forest, Mazandaran

The tending operations are essential for the quantitative and qualitative improvement of forests and thinning as the most important step has a significant role in increasing the growth of trees. In this research, the even-aged alder(Alnus subcordata) and Persianmaple (Acer velutinum) stands located in Chendella district in the north of Zirab city in Mazandaran province were investigated to compare the effect of thinning on diameter growth. Three executive rotations were done in these plantations. Close to each plantation, one stand which has received no thinning treatment was selected as the control to compare the effect of thinning treatments on tree characteristics. The D.B.H and other growth parameters of 318 trees were measured. In this investigation 2 or 3 individual trees in each 5cm diameter class (totally 45 trees) were randomly selected to obtain the disk at 20 cm, 130 cm and full length heights for measuring the diameter growth rates. Medium diameter and total height of the tree were measured to calculate the diameter growth of the trees. The Student t-test with SPSS software was used to compare the quantitative characteristics of each of the forest plantations and the control. The results of this study showed that the average DBH and average diameter growth of both species in the thinned stands were higher than the control stand. Also, the mean DBH and average diameter growth in the treated and control stands of alder were more than the treated and control stands of Persian maple. However, the slenderness index of Persian maple trees in both treated and control stands was greater than that of the treated and control alder stands.The results of this study showed that the positive effects of thinning operations on the silvicultural characteristics of alder stands were much more than maple.