利用随机效应模型模拟东北三省胡桃楸地位指数

通过精确模拟东北三省胡桃楸多形地位指数混合效应模型,为胡桃楸立地质量评价提供科学依据,本研究在辽宁、吉林和黑龙江三省23个典型区域内,采用样圆法布设样地197块,测定样地内胡桃楸树高-年龄数据,共得到数据1537组,同时将立地因子进行划分和赋值,应用方差分析和模型拟合进行计算。结果表明: 坡位是影响胡桃楸优势木生长最显著的因素,其次为土壤深度、坡度和坡向等;对8种常见基础模型进行拟合与分析,发现逻辑斯蒂模型H=a/1+exp(b+cA)]为最优基础模型(R²=0.70),平均绝对误差(MAE)为2.52;对4种主要影响因素进行随机组合,得到随机组合因素最优地位指数模型M_8.15,其R²=0.90,提高了基础模型的拟合精度;采用K均值聚类分组法进一步将初始的立地类型划分为6个立地类型组,按6个立地类型组建立的非线性混合效应模型M_final,即H=(20.1837+u_i)/1+exp (1.7352-0.0961A)]+ε_ij,其R²=0.92,AIC=912.65,模型的拟合度和精确度显著提高,可以用于东北三省复杂立地类型下胡桃楸立地质量的准确评价。

Simulating site index of Juglans mandshurica using a random effect model in three provinces of Northeast China

To evaluate site quality and provide scientific evidence, the mixed effect model of polymorphic site index of Juglans mandshurica was accurately simulated in the three provinces of Northeast China. A total of 197 plots in the 23 typical regions of Liaoning, Jilin and Heilongjiang provinces were set by the sample circle method, from which we got 1537 height-age data of J. mandshurica. The site factors were divided, assigned and calculated using variance analysis and model fitting. The results showed that slope position was the dominant factor affecting the growth of dominant wood of J. mandshurica, followed by soil depth, slope and aspect. After fitting and analyzing eight common basic models, we found that the logistic model H=a/1+exp(b+cA)] was the optimal one (R²=0.70), with a mean absolute error (MAE) of 2.52. When the four main influen-cing factors were randomly combined, the optimal site index model of the stochastic combination (M_8.15) was obtained with R² of 0.90, which improved the fitting accuracy of the base model. The K-means clustering method was used to further divide the initial groups of site types into six groups. We established the nonlinear mixed effect model M_final, H=(20.1837+u_i)/1+exp (1.7352-0.0961A)]+ε_ij, with R² and Akaike's information criterion (AIC) being 0.92 and 912.65, respectively, which could significantly improve the fitting and accuracy of the model. The equation could be used for the accurate evaluation of site quality of J. mandshurica under the complex site types in the three provinces of Northeast China.