Abstract: The intraspecific and interspecific competition intensities of rare and endangered tree Parrotia subaequalis in Wanfoshan Nature Reserve, Anhui Province, were quantitatively analyzed with Hegyi singletree competition index model. Meanwhile, for the same tree species from a certain forest community, its competition intensity in two different habitats (hillside and valley) was also discussed. The results showed that the main competitive intensity of the P. subaequalis population came from interspecific competition, and the value was 240.6, which accounted for 69.3% of the total. The competition intensity of intraspecific and interspecific competition with P. subaequalis followed the order of P. subaequalis> Celtis biondii> Cyclobalanopsis glauca> Pistacia chinensis> Celtis sinensis> Liquidambar formosana> Machilus leptophylla. Notably, individual number of P. subaequalis and intensity of intraspecific and interspecific competition were different between the two habitats. The number of trees of P. subaequalis in hillside (178) was more than that in valley (only 65); both intraspecific and interspecific competition intensity in hillside was stronger than in valley. The competition intensity of this species in the small size class (4.0 cm≤DBH＜8.0 cm) was the strongest both in hillside and in valley. There was a significant negative correlation between the whole forest competition intensity and the DBH of objective trees (CI=AD^B). The competition intensity of P. subaequalis declined with increasing DBH, and the stress was more intense for trees with DBH less than 16 cm. In addition, it is suggested that the competition intensity in different habitats may be probably different for a certain tree species in forest communities.

Key words: plant density, winter wheat, ¹⁵N labeled, nitrogen level, nitrate nitrogen content.