Abstract: The authors studied the influence of a thinning intensity on uniform angle index in Larix principis Plantation in Saihanba mechanicalforest farm of Chengde.The four different treatments of thinning intensities are 225 trees/hm², 600 trees/hm², 900 trees/hm² and 1350 trees/hm² respectively. The higher frequency distribution of uniform angle index was 0.25 in very heavy thinning group(A), heavy thinning group(B) and mid-thinning intensity group(C). Their average uniform angle index was less than 0.475. The result showed that they were equality distribution in the three different treatments of thinning intensities of Larix principis Plantation. The higher frequency distribution of uniform angle index was 0.75 in light thinning group(D) and control area(E) and their average uniform angle index was 0.477 and 0.5.The result showed that the forest trees were in random distribution in light thinning group (D)and control area (E).The average uniform angle indexes were 0.3929 and 0.25in mixed wood and coniferous mixed forest.It showed that forest trees were distributed uniformly in mixed forests.

Key words: thinning, Larix principis, uniform angle index