Abstract: In this study,a 1 hm² sample plot of Picea crassifolia forest was delimited to analyze the intraspecific competition of Picea crassifolia population in the subalpine zone of the Qilian Mountains using the method of gradually expanding the scope and Duan Renyan’s improved individual tree competition index model.The results were as follows:(1) In the Picea crassifolia population,the competition intensity decreased gradually with the increase of circularity radius,and the circularity radius affecting the competition of Picea crassifolia trees was 6 m; (2) The competition intensity of Picea crassifolia decreased with the increase of diameter at breast height (DBH),especially it decreased sharply in the DBH ranges of 5-10 cm and 25-30 cm,and the inflection point occurred at DBH range of 25-30 cm.With the increase of DBH,the competitive pressure of Picea crassifolia changed gently,and the competition occurred mainly in DBH range less than 25-30 cm; (3) The intraspecific competition and diameter of Picea crassifolia trees followed a power function ofCI = AD^-B,and the level was significant.The experimental data showed that the model could be used to predict the intraspecific competition of [WTBX]Picea crassifolia[WTBZ] population well.The analyzed results could provide a theoretical basis and reference for tending and managing Picea crassifolia forests in the Qilian Mountains.

Key words: Picea crassifolia, intraspecific competition, competition index, Qilian Mountains