Spatial distribution patterns and associations of main tree species in spruce-fir forest in Changbai Mountains, northeastern China.

To reveal the mechanisms for species coexistence of spruce-fir forest communities in Changbai Mountains, northeastern China, the population structure, spatial distribution patterns and spatial associations of Abies nephrolepis and Picea jezoensis were analyzed by g(r) function based on Ripley's K- function in a 5.2 hm2 spruce-fir forest community plot. The results showed that the two species had a total of 8 730 individuals, and accounting for 68.1% of the total individuals. The basal areas of two species accounted for 51.9%, and may suggest dominant status of two species in the plot. The DBH-class structures of the two species exhibited inverse "J" type distributions each. Spatial pattern analysis showed that the small-sized individuals of A. nephrolepis and P. jezoensis displayed an aggregated distribution, especially at small scales. The individuals were randomly distributed as the increase of DBH-class, and the aggregated intensity became lower with the increase of scales. The A. nephrolepis showed negative correlations between small-sized individuals and large-sized individuals at 0-50 m scales, and could suggest intense intraspecific competition between the two groups. The P. jezoensis species exhibited negative correlations or no significant correlations among different DBH-classes at small scales, indicating that the intraspecific competition was relatively weak. It showed positively correlations between the small -sized A. nephrolepis and all DBH-classes P. jezoensis, as well as between small-sized P. jezoensis and all DBH-classes A. nephrolepis; it may indicate those two species could survive below the canopy of each other. The middle-sized and large-sized individuals of A. nephrolepis and P. jezoensis were negatively correlated and not significantly correlated from one to another, and suggesting the existence of intense intraspecies and interspecies competitions between the two species as the increase of DBH-class. The spatial distribution patterns of the two species were mainly affected by seed dispersal limitations and the negative density-dependent effect, while similar biological characteristics (shade tolerance) made them coexist in this forest community.