Abstract: 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. The results showed that within the same sampling plots, dead trees had the similar competition intensity, while the accompanying species in living and whole stems had two or three times higher competition intensity than Mongolian pine. The competition stress of Mongolian pine mainly came from intra-specific, and that of accompanying species mainly came from inter-specific. The competition intensity of living Mongolian pine was significantly lower in fire-disturbed than in undisturbed plot, and the competition intensity (CI) of living stems had a power functional relationship with their diameter at breast height (D), i.e., CI=AD-B. It was concluded that surface fire could significantly decrease the competition intensity among the stems, which would benefit the growth and development of living stems and the culture of the stems with larger diameter of breast height.

Key words: tree hole, Populus euphratica, Tarim River., hollow-bearing tree