Objective  Forest spatial structure is the result of forest biophysical processes and dynamic succession, and determines the growth process of forests and the function of ecological services. The Xiaoxing’anling Mountains are important ecological function area for diversity protection and water conservation, but their forest degradation is already very serious. In order to provide theoretical support for the structural optimization and adjustment of degraded forests and promote the forest to play their due roles in forest ecological services, it is necessary to analyze the structural characteristics of existing zonal climax communities.

  Method  In this paper, the broadleaved Korean pine forest in the Xilinhe National Nature Reserve was taken as the research object. Based on field survey data, the Voronoi polygons were established using ArcMap software to determine spatial structural units. By the spatial structural units, several spatial structural parameters such as Clark’s clustering index, size differentiation, Hegyi’s competition index, and diversity mingling were calculated. According to them, the spatial structural characteristics were further analyzed.

  Result  The horizontal pattern of broadleaved Korean pine forest stand appeared aggregated distribution, and the results derived from Clark’s clustering index were consistent with those resulted from the standard deviation of Voronoi polygon edge number. The coniferous trees had greater competitive advantages than the broadleaved trees, and the broadleaved trees presented more intense intraspecific competition. However, the trends of Hegyi’s competition index and the size differentiation index were not completely consistent. The species diversity mingling indicated that the forest stand was at a moderate level, and the isolation of conifers was higher than that of broadleaved trees. Furthermore, the extent of isolation was not directly related to the abundance of tree species in the stand.

  Conclusion  The broadleaved Korean pine forest in the Xiaoxing’anling Mountains is characterized by aggregated distribution, moderate mingling, and moderate competition. The structural units of Korean pine and Fabers fir have a high degree of mixing, and the Korean pine and Fabers fir have obvious competitive advantages in their respective structural units; while the structural units of Chinese birch, Manchustripe maple, and Amur lilac are low mixed, respectively. These three species are under great competitive pressure, and more manifested as intra-species competition, among them the Amur lilac is the most representative. These characteristics are not the same as those of the broadleaved Korean pine forest in the Changbai Mountains reported in the literatures. This maybe due to different parameters selected or the result of natural selection of topographic and climatic differences. Further investigation and research are needed.