Objective To analyze the second-order characteristics of broadleaved Korean pine (Pinus koraiensis) forest in order to provide references for their protection, restoration and structural optimization.

Method Taking four types of broadleaved Korean pine forests in Jiaohe of Jilin Province as examples, the single variable double correlation function and second-order characteristic functions of mark double correlation function, mark variation function, mark differentiation, mark mingling were used to analyze the tree species and size differentiation characteristics.

Result The distribution patterns of these broadleaved Korean pine forests were significantly different. The distribution patterns of Juglans mandshurica-Abies holophylla-Pinus koraiensis forest (plot A), Fraxinus koraiensis-Pinus koraiensis forest (plot C) and Juglans mandshurica-Acer koraiensis-Pinus koraiensis forest (plot D) showed a significant cluster distribution on a certain scale, while those of Juglans mandshurica- Fraxinus koraiensis-Pinus koraiensis forest (plot B) followed the random distribution. Within the range of r, the DBH of tree mark tended to be smaller than the average DBH and the spatial autocorrelation was positive, especially in the scale of r = 0~8 m and r = 13~33 m. The mark DBH of plot B and plot D showed significant aggregation characteristics of similar size trees on the scale of r = 4~6 m and r = 0~12 m, respectively, while the plot C showed different sizes trees aggregation distribution on the scale of r = 0~5 m. The tree species distribution of the four types of broadleaved Korean pine forests belonged to completely random distribution, but there was the phenomenon of the same species aggregation on a certain scale. The scale ranges of the same species aggregation of plot A, plot B, plot C and plot D were r = 0~10 m, r = 0~25 m, r = 0~12 m and r = 0~8 m respectively.

Conclusion The mark second-order characteristics of different types of broadleaved Korean pine forests showed significant difference, which is related to different development stages and degree of broadleaved Korean pine forest. The mark second-order characteristics further refine the differentiation characteristics of tree species and tree size on different scales, which has certain significance for broadleaved Korean pine forest management.