Objective To provide a typical reference in the aspect of height-to-diameter ratio of broad-leaved trees for the sustainable management of artificial broad-leaved forest, semi-natural broad-leaved forest and natural broad-leaved forest in mid-subtropical zone, the relationship between tree height-to-diameter ratio and DBH and tree height were revealed in each stratum of typical natural broad-leaved forests.

Method In Jian’ou Wanmulin Provincial Nature Reserve, 50 m × 50 m plots were set up in 5 most typical natural broad-leaved forest in mid-subtropical zone respectively. Spearman rank correlation coefficient was used to analyze the correlation between tree height-to-diameter ratio and DBH and tree height in each stratum, and exponential function and hyperbola equation were chosen to fit the relationship between height-to-diameter ratio and DBH in each stratum.

ResultsThe variation range of the average value of the height-to-diameter ratio in each stratum was not large. The average height-to-diameter ratio of the stand in the 5 sample plots was 103.1. The mean height-to-diameter ratio in stratum Ⅲ(112.7) was the largest, followed by stratum Ⅱ (89.0) and stratum Ⅰ(66.9), as well as in the minimum and maximum values. The height-to-diameter ratio of each stratum showed a significant negative correlation with DHB and the correlation coefficient was high. The absolute value of correlation coefficient was the highest in stratum Ⅰ(0.896～0.961) and stratum Ⅱ(0.912～0.971), the middle in the stand(0.613～0.749), and the lowest in stratum Ⅲ(0.415～0.596).The relationship between tree height-to-diameter ratio and tree height in each stratum was complex and the absolute value of correlation coefficient was low (< 0.480). The stand showed extremely negative correlation, but the absolute value of correlation coefficient was low (0.283～0.458). The R² of the tree height-to-diameter ratio and DBH in stratum Ⅰ and stratum Ⅱ fitted by exponential function were 0.852～0.906 and 0.830～0.914, respectively, while the R² of the stand and stratum Ⅲ were 0.465～0.575 and 0.202～0.399, respectively. The R² of the height-to-diameter ratio and DBH in stratum Ⅰ and stratum Ⅱ fitted by hyperbolic curve were 0.874～0.937 and 0.856～0.968, respectively, while the R² of the stand and stratum Ⅲ were 0.387～0.536 and 0.186～0.350, respectively. Exponential function fitting stand and stratum Ⅰ relationship of DBH than height-to-diameter ratio of R² was relatively high, and RMSE and AMR was relatively small. hyperbola from fitting relationship of DBH than height-to-diameter ratio stratum Ⅰ and stratum Ⅱ fitted by hyperbola equation had relatively high R² and small RMSE and AMR was values.

Conclusion The tree height/diameter ratio of typical natural broad-leaved forest in mid-subtropical zone varies with the stratum. The tree height/diameter ratio in the same stratum also varies with DBH. The height-to-diameter ratio and DBH in each stratum shows a very significant negative correlation and the correlation coefficient is high, and the curve fitting of the relationship is significant. Hyperbolic function can well describe the relationship between height-to-diameter ratio and DBH in the stratum Ⅰ and stratum Ⅱ, while exponential function is more suitable to describe the relationship between height-to-diameter ratio and DBH in the stand and the stratum Ⅲ. The relationship between tree height-to-diameter ratio and tree height in each stratum is complex and the correlation coefficient is low. In the typical natural broad-leaved forest of the mid-subtropical zone, the characteristics of tree height/diameter ratio can be expressed by the relationship curve between tree height to diameter and DBH of each stratum.