Growth variation and early selection ofBetula platyphylla in natural stands

The stem analysis ofBetula platyphylla in natural forest at the Maoershan Forest Experimental Station of Northeast Forestry University, showed that the growth variation of the trees, including height and diameter breast height, decreases with the increase of the age. There is the turning point for the growth variation of the tree from acute change to relative stability when the trees are in eighteen years old. There are significant differences among the height, diameter and volume growth of the trees at that time. Therefore, the optimal age for early selection of this species in natural stands is eighteen years old (18 a). Diameter is used as main index for selection and height growth as auxiliary one.