Dynamic changing rule in leaf mass of Larix kaempferi plantations and its relationship with quantitative maturity age

Objective Through growth equations, this paper investigates the dynamics of leaf mass (leaf dry mass), stand volume, and stand density in Larix kaempferi, with a focus on examining the relationship between stand leaf mass and quantitative maturity age.

Method This study focused on Larix kaempferi plantations in the Changlinggang Forest Farm, Jianshi County, Hubei Province of central China. Based on data from 90 sample trees across 30 sample plots, we developed individual tree leaf mass stand density, stand leaf mass, and stand volume models. The aim was to investigate the dynamic patterns of leaf mass at both individual tree and stand levels, as well as the relationship between peak stand leaf mass timing and quantitative maturity age.

Result (1) The optimal model for individual tree leaf mass was a heteroscedasticity-adjusted Logistic equation incorporating dummy variables (dominant, intermediate, and suppressed trees) with a power function (R² = 0.620, rRMSE = 0.554, RMSE = 2.821 kg, MAE = 1.756 kg). The optimal model for stand density was a Logistic equation ( R² = 0.708, rRMSE = 0.190, RMSE = 187.975 plant/ha, MAE = 168.045 plant/ha). The optimal model for stand volume was a Korf equation (R² = 0.703, rRMSE = 0.337, RMSE = 59.681 m³/ha, MAE = 48.705 m³/ha). (2) The leaf mass of a single tree increased with forest age, while the leaf mass of stand showed a unimodal trend, reaching its peak at 24 years and then decreasing. The leaf mass of different forest layers showed obvious stratification characteristics with the increase of forest age. (3) The trend of changes in annual average growth of forest leaves and stock volume were consistent, and the time when the forest leaves reaching their peak was highly consistent with the quantity maturity age (24 years).

Conclusion The tree-class-based leaf mass prediction model developed in this study accurately captures the differences in leaf dynamics at both individual tree and stand scales. It is also found that the peak stand leaf mass coincides closely with quantitative maturity age. These findings provide a theoretical basis and practical guidance for accurate leaf mass estimation, scientific forest management planning, and optimal rotation age determination for Larix kaempferi plantations in Hubei Province of central China.