基于抚育间伐效应的长白落叶松人工林单木直径生长模型

【目的】分析抚育间伐对长白落叶松人工林单木胸径(D)生长的影响规律并对其进行模拟。【方法】基于黑龙江省孟家岗林场与江山娇林场10块固定样地复测数据,建立了基于抚育间伐效应的与树木距离无关的长白落叶松单木胸径5年生长量预估模型,量化了抚育间伐对林木直径生长的影响。长白落叶松单木直径生长模型为基于样地效应的单水平线性混合效应模型,根据赤池信息准则(AIC)和贝叶斯信息准则(BIC)等统计指标和似然比检验对模型进行比较和筛选,并采用独立样本数据对模型进行检验。【结果】当地位指数一定且林分年龄较小时,抚育间伐强度越大,林木直径生长量越大; 当林分年龄较大时,抚育间伐对林木直径生长影响不明显。同一林分中,林木直径生长量随林木径阶增大呈增大趋势。长白落叶松单木直径生长模型中显著自变量为:林木前期胸径的二次方(D²)、胸径的自然对数(ln D)、林分中大于对象木的所有林木断面积之和(B)、地位指数(I)、抚育间伐年龄(T_i)和间伐强度(P_i)。落叶松单木直径生长最优混合效应模型的AIC、BIC和均方根误差均小于一般线性模型。独立样本数据检验最优线性混合效应模型和一般线性模型的拟合效率分别为0.678 和0.624。【结论】基于抚育间伐效应的落叶松直径生长的最优线性混合效应模型优于一般线性模型。模型能够较好地量化抚育间伐对落叶松人工林单木直径生长的影响。

Modelling individual tree diameter growth for Larix olgensis based on thinning effects

【Objective】The objectives of the paper were to analyze and simulate the effects of thinning on the individual tree diameter growth of Larix olgensis in plantation.【Methods】Based on the remeasured data of 10 permanent plots in Mengjiagang Forest Farm and Jiangshanjiao Forest Farm of Heilongjiang Province, a distance-independent individual tree diameter growth model based on thinning effects for Larix olgensis was developed to quantify the effects of thinning. The diameter growth model for Larix olgensis was defined as a single-level linear mixed-effects model with a random plot effect. The AIC and BIC statistics and Likelihood ratio test were used for model comparison and selection, and the models were tested by using independent sample data. 【Results】The individual tree diameter growth increased with the increasing thinning intensities for young stands under the same site index, but the thinning effects for individual tree diameter growth was not significant for stands of greater age. The individual tree growth increased with diameter classes for smaller trees. The significant independent variables of the individual tree diameter growth models were the square of diameter at breast height(DBH), the natural logarithm of DBH, the basal area of trees larger than the subject tree, site index, thinning age, and thinning intensity. The AIC and BIC statistics and root mean square error(RMSE)of the best individual tree diameter growth mixed-effects model were less than those of the general linear model for Larix olgensis. The best linear mixed-effects model and general linear model of individual tree diameter growth for Larix olgensis achieved an efficiency of 0.678 and 0.624, respectively, when tested by using independent sample data. 【Conclusion】The fitting and testing results showed that the best linear mixed-effects model was better than the general linear model for individual diameter growth for Larix olgensis. The best linear mixed-effects model can quantify the effects of thinning on the individual tree diameter growth of Larix olgensis.