By using totally locating method and single tree competition index model, this paper studied the competition intensity of Mongolian pine forests in Hulun Buir sand region of Inner Mongolia, with the fire-disturbed Mongolian pine forest as a case.

Based on the growth theory of Von Bertalanffy, this paper built the single tree growth model for Cryptomeria fortunei stands by using simple competition index, By means of general rule that density affects stem shape, analysed the relationship between simple competition index and shape index,and established shape index model, so as to provide a new way for volume measurement of standing trees.

Then,with a plot size of 100 m × 100 m,Hegyi s competition index model for individual trees was used to determine competition within dominant tree populations in an evergreen broad-leaved forest of National Nature Reserve of Mount Tianmu.

mongolica natural forest in Honghuaerji Nature Reserve of Inner Mongolia were analyzed by the Hegyi s single tree competition index.

Analyzed the intraspecific and interspecific relationship of Bruguiera gymnorrhiza and Rhizophora stylosa with commonly used niche calculation formula and Hegyi single-tree competition index mode, the results showed that they had extreme similar niche breadth and high value of the niche overlap index.