[Site index model of Juglans mandshurica natural secondary mixed forest in Changbai Mountain area, Jilin Province, China].

According to slope direction and position of the distribution of Juglans mandshurica natural secondary mixed forest in 12 sites of Changbai Mountain in Jilin Province, and combined with the age structure of J. mandshurica, we set up 109 plots. Based on the age-tree height data, we complied the site index of the forests. We used the three times tree height standard deviation method to eliminate abnormal data, 379 pairs age and tree height data were obtained from the 80 plots. Then, we used seven mathematical models for comparison and got simplex site index-oriented curve equation as H=28.0181(1-e). The coefficient of determination R and the sum of squared residuals were 0.85 and 0.89, respectively, the base age was 50 years, the exponential interval was 2 m, and 7 site index curves of 16-28 m were obtained. According to different site types, polymorphic sites index model was established, and the power function fitting effect was best. Its equation was H=Bt, in which B=10e, B=-0.2139SI+5.6183. Finally, the polymorphic site index model equation was H=10et. The exponential difference method and drop point test were conducted to check the accuracy of the two site index models. The results showed that the polymorphic site index had higher precision and it could accurately reflect the difference in tree height growth under different site types of J. mandshurica. Therefore, it could evaluate the site quality of natural secondary mixed forests of J. mandshurica in Changbai Mountain area of Jilin Province.