Abstract:Spatial pattern and spatial association analysis are important methods to study the population characteristics and community structure underlying ecological processes. In this study, spatial point pattern analysis was conducted to examine the spatial distribution pattern of and the spatial associations between the different developmental stages of the Quercus variabilis and Pinus tabulaeformis populations in a mountainous area of Beijing. Only 11 tree populations were observed in the community, in which Q. variabilis and P. tabulaeformis were the dominantspecies. Intermediate-diameter individuals of both species were most prevalent. The populations lacked regenerative saplings, indicating that the populations are in decline. At the study scale, all Q. variabilis and P. tabuliformis individuals were significantly clustered, and as the scale increased, the distribution became more random and regular. The distribution pattern of Q. variabilis populations varied with the spatial scale; they were mainly aggregated at the small scale(0-39 m) and randomly distributed at the large scale(39-50m).The distribution pattern of P. tabuliformis populations was mainly aggregated at the small scale(0-34m) and randomly distributed at the large scale(34-50m).The spatial association between Q. variabilis and P. tabuliformis was significantly negative. The distribution patterns of Q. variabilis and P. tabulaeformis populations at different developmental stages were closely related to the scale. The spatial distribution patterns of young and middle-aged Q. variabilis individuals were significantly clustered, where as those of older trees were random. The spatial distribution pattern of P.tabuliformis was significantly random at all scales. Spatial association of Q. variabilis and P. tabulaeformis at different developmental stages was primarily observed at the small scale. The association between middle-aged and young trees was significantly positive at the medium and small scales. However, the spatial association between young, middle-aged, and old trees was negative, and gradually disappeared as the scale increased. These data suggest that the spatial distribution and spatial associations of Q. variabilis and P. tabulaeformis populations were mainly affected by environmental heterogeneity, the biological properties of the populations(especially the seed dispersion mechanism, intraspecific relationships, and interspecific relationships), the differing developmental stages, and changes in spatial scale.