Growth changes of Juglans mandshurica secondary forest with stand age and stand density in Northeast China

Objective To research the suitable stand density for the growth of secondary forest of Juglans mandshurica in different age groups by understanding the growth changes of J. mandshurica with stand age and stand density, in order to provide theoretical support for the subsequent management of secondary forests of J. mandshurica.

Method Survey plots of different stand age and stand density for J. mandshurica were set up in Zhangguangcailing (ZGCL), Laoyeling (LYL), Changbai Mountain (CBS) and Hadaling (HDL) of the eastern part of the three Northeastern Provinces, to analyze the relationship between diameter at breast height (DBH), tree height and accumulation with stand age and stand density.

Result (1) The average DBH, average tree height and accumulation of J. mandshurica were the largest in Changbai Mountain, which were significantly larger than those in other areas (P < 0.05), and the relationship between each index was CBS > LYL > ZGCL > HDL. (2) According to the model fitting, logistic model was the best fitting method for stand age with DBH, tree height and accumulation of J. mandshurica, (R² values of 0.983 2, 0.962 2, and 0.973 1, respectively). The quadratic model was the best fitting method for stand density with DBH, tree height and accumulation of J. mandshurica (R² values of 0.833 6, 0.665 9 and 0.858 7, respectively). (3) The DBH, tree height and accumulation of J. mandshurica were increasing with age in each region, and the increase rate was faster in the early stage. However, the growth rate slowed down after reaching 50 years. (4) The DBH and tree height of J. mandshurica decreased with increase stand density in each region, and the decreasing trend was smaller at low density, but the decreasing speed was higher when the density exceeds a certain level; (5) The growth of J. mandshurica in the four regions showed that the best growth effect was achieved at a moderate stand density of 450-550 tree/ha at < 40 years old, and at a low stand density of 350-450 tree/ha at > 40 years old. That is, the older the J. mandshurica, the higher the requirement for stand density.

Conclusion The results preliminarily revealed the suitable control density for different ages of J. mandshurica stand in different regions, which can be controlled through artificial nurturing and thinning to meet the growth space of J. mandshurica trees. These findings can serve as a basis for the management of J. mandshurica secondary forests.