关键词: 无关年龄的差分模型, 胸高断面积, 大于对象木的胸高断面积, 降水量, 太阳辐射, 交互作用

Abstract:

Objective: This study aims to construct an age-independent differential model to simulate the growth dynamics of individual Larix gmelinii (larch) trees' basal area at breast height in larch plantations, analyze the nonlinear regulatory mechanisms of topographic, climatic, stand, and competition factors on growth, and explore the interaction among these factors on tree growth, providing a scientific basis for the formulation of forest management strategies. Method: Larch plantation data from the seventh and eighth national forest resource consecutive inventories in north and northeast China were used to construct an age-independent differential model to simulate the growth process of individual larch trees' basal area at breast height. During the model construction, a dummy variable representing solar radiation based on topographic calculations was introduced, and climate factors (annual precipitation), stand factors (basal area at breast height per hectare), and individual tree competition factors were used as driving variables. Reparameterization analysis was performed to assess the nonlinear impacts of these factors on the growth of basal area at breast height. In addition, sensitivity analysis and interaction effect analysis were conducted on the variables to quantify the contributions of different factors to individual tree growth and to explore the interactive effects among these factors on tree growth. Result: 1) The age-independent differential model had a significant advantage in simulating the growth of individual tree basal area at breast height. The model incorporating climate, stand, and competition factors (Model 4) performed the best, with an R² of 0.956 4 and an RMSE of 0.002 272 m². Compared to the baseline model (Model 2), Model 4 showed an R² increase of 0.51%, and RMSE decrease of 5.18%. 2) Sensitivity analysis showed that competition factors had the most significant impact on individual tree basal area growth, with dominant trees exhibiting higher growth efficiency in resource competition. Secondly, there was a significant positive correlation between the mean annual precipitation and basal area at breast height. Thirdly, the stand basal area per hectare and stand density exhibited an inhibitory effect on individual tree growth. Finally, solar radiation intensity had the least impact, with moderate solar radiation being most favorable for growth, while excessive radiation could lead to heat stress. 3) Interaction effect analysis indicated that climate factors, stand structure, and individual tree competition jointly influenced growth. The promoting effect of precipitation on growth was moderated by competition pressure and stand density, with more pronounced under low competition and low-density conditions. Conclusion: This study simulated the growth process of individual larch trees' basal area at breast height in larch plantations using an age-independent differential model, and evaluated the nonlinear effects of climate, stand, and competition factors. The results show that competition factors have the most significant impact on growth, with dominant trees exhibiting higher growth efficiency in resource competition. Annual mean precipitation, basal area per hectare, and solar radiation also play important roles in growth. Meanwhile, climate factors, stand structure, and individual tree competition jointly influence individual tree growth.

Key words: age-independent difference model, basal area at breast height, basal area of larger trees, precipitation, solar radiation, interactive effect