Spatial point patterns and effects of density dependence in secondary poplar-birch forest, Changbai Mountains, China

Taking 5.2 hm~2 secondary poplar-birch forest plot in Changbai Mountains as the research object, the pair-correlation function g(r) of the spatial point pattern analysis and the random label null model and case-control design method were used to discuss the spatial pattern of tree populations and its density dependence effect. The results showed that the L(r) function is more suitable for analyzing whether there is habitat heterogeneity in a research plot. Habitat heterogeneity had a strong impact on mature individuals with different life forms and different tree species on a large scale. This showed that when studying the spatial pattern, the impact of habitat heterogeneity on the research results should be fully considered. After excluding the impact of habitat heterogeneity, 12 of the 14 common tree species showed the significantly spatial aggregation distribution pattern on a small scale. With the increasing of spatial scale, the number of aggregated distribution tree species decreased sharply, and the aggregation rate dropped to 0 on the 18 m scale. The 14 common tree species all exhibited significant density dependence effects, indicating that density dependence was the main mechanism for regulating the spatial structure of temperate forest tree populations. In addition, density dependence was negatively correlated with species abundance and positively correlated with the same species aggregation intensity of sub-forest and shrub layer species. And with the increasing of spatial scale, the percentage of tree species affected by density dependence gradually decreased, and 11 of 14 common tree species reached the maximum density dependence intensity at 0-1 m.