Abstract: This paper presents a physiological-ecological research on the crown thinning of conifers.It is concluded that suitable crown thinning can speed up the growth of tree trunks:(1)Crown thinning can improve illumination conditions which is advantageous to photosynthesis;(2)It is important to keep the maximum surface area of crown in the process of thin-ning;(3)Gencrally,a thinning intensity of 20—40% can incrcase the growth rate of trees.

Key words: Ecosystem health, Assessment, Health distance, Korean pine and broadleaved mixed forest, Disturbance