Abstract: The relationship between shrub species diversity and stand spatial structure was examined in Chinese fir public welfare forests with different stand ages (young forests, middle aged forests and near matured forests) in Fushou Forest Farm of Pingjiang County, Hunan Province of China, based on the measurements of 18 permanent plots. Five indices (mingling index, competition index, stand layer index, uniform angle scale and open degree of stand) were used to describe the spatial structure of Chinese fir stands, and four indices (Simpson diversity, Shannon diversity, Pielou evenness, and Margalef richness) were employed to characterize shrub species diversity. The most important spatial structure index impacting shrub species diversity was estimated by using grey integrated connection grade method. The results showed that: (1) There were significant differences in competition index, stand layer index, uniform angle scale, and open degree of stand (P<0.05), but no significant difference in mingling degree among the different aged stands (P>0.05). (2) There was no significant difference in Simpson diversity, Shannon diversity and Pielou evenness indices among different stands (P>0.05), but significant differences in Margalef richness index (P<0.05). (3) The uniform angle scale was a common factor affecting shrub species diversity of different aged stands. The competition index was the important factor affecting shrub species diversity in young and middle-aged forests, while open degree was the important factor affecting that in young and near matured forests. To improve species diversity of understory shrubs, the spatial structure optimization scheme could be adopted by mainly arranging the horizontal distribution of trees and complementally adjusting understory light condition and the competition among individual trees.

Key words: Chinese fir, spatial structure index, diversity index, grey integrated connection grade.