Abstract: A number of statistic methods (variance ratio method, χ² test, Pearson’s correlation coefficient test and Spearman’s rank correlation coefficient test) were used to characterize interspecific associations of 13 overstory tree species, 14 shrub species and 16 herbaceous species in a secondary natural forest of Choerospondias axillaris in mid-subtropical region at Qingyanghu National Forest Park, Hunan Province. The overall interspecific associations were non-significantly negative, significantly negative and non-significantly positive correlations among dominant plant populations in overstory, shrub and herbaceous layers, respectively. The χ² test showed that the speciespairs of negative correlation were dominant in the three layers, accounting for 80.77%, 80.22% and 83.33% of the total speciespairs in overstory, shrub and herbaceous layers, respectively; followed by speciespairs of positive correlation, which accounted for 16.67%, 18.68% and 16.67% in the three layers, respectively. There were few speciespairs of no correlations in the plant community. The Pearson’s correlation coefficient test showed that the number of speciespairs in positive association was 41, the number of speciespairs in negative association was 37, and the association ratio was 1.11 in overstory layer; the corresponding values were 34, 57 and 0.60, and 43, 77 and 0.56 in shrub and herbaceous layers, respectively. The Spearman’s rank correlation coefficient test showed that the number of species pairs in positive association was 40, the number of species pairs in negative association was 37, the number of species pairs in non-association was 1, and the association ratio was 1.08 in overstory layer; the corresponding values were 35, 55, 1 and 0.64, and 45, 74, 1 and 0.61 in shrub and herbaceous layers, respectively.

Key words: fate of ¹⁵N, fulvic acid, ¹⁵N-urea, yield, apple