油松树高-胸径非线性混合效应模型的构建

Construction of height-diameter nonlinear mixed effect model for Pinus tabuliformis

为准确预估油松林木树高生长,探究样地间林分状况差异及样地内观测变量的相关性对树高生长预测的影响,以西宁南北山油松针阔混交林为研究对象,采用2013、2016-2021年的固定样地调查数据,从9个备选树高-胸径模型中选择最优基础模型,根据多元逐步回归结果,加入大于对象木的胸高断面积之和(BAL)、Shannon树种多样指数(H_(ba))、林分总断面积(BA)、坡率和坡向的组合项(SLC)构建广义模型,同时考虑样地水平的随机效应再构建广义混合效应模型,分析比较3种模型,确定最优树高预测模型。结果表明:3种模型的拟合效果和预测精度均表现为广义混合效应模型最优,广义模型次之。广义混合效应模型预测结果表明,树高生长与BAL和H_(ba)呈负相关,与BA和SLC呈正相关;BAL、H_(ba)和SLC对树高预测的影响程度随胸径的增加而增加,BA对树高预测的影响程度随胸径的增加而减小;在胸径≤8 cm时树高增速最快,BAL、H_(ba)、BA越小且SLC越大,树高增速越快。本研究构建的油松树高-胸径广义混合效应模型可为西宁地区及相似生态区油松树高生长预估提供参考。

The broadleaf mixed forest dominated by Pinus tabulaeformis in the Nan mountain and Bei mountain of Xining is taken as research object to accurately estimate the height growth of Pinus tabulaeformis,so as to explore the effects of different stand conditions among sample plots and the correlation of the observed variables on tree height growth.The fixed sample survey data from 2013 and 2016—2021 are used for the study.The optimal base model is selected from nine alternative height-diameter models.Based on the results of multiple stepwise regression,the generalized model is constructed by adding the basal area of larger trees(BAL),Shannon species diversity index(H_(ba)),stand basal area(BA),and the combination of slope rate and slope direction(SLC)into the base model.The generalized mixed effect model is constructed after considering the random effects of plot level.Three models are analyzed and compared to determine the optimal height prediction model.The results are as follows:The fitting effect and prediction accuracy of the generalized mixed effect model are the best,followed by the generalized model.The prediction results of the generalized mixed effect model show that height growth is negatively correlated with BAL and H_(ba),and positively correlated with BA and SLC.The effects of BAL,H_(ba)and SLC on the tree height prediction increase with the increase of diameter,while that of BA on the height prediction decreases with the increase of diameter.The height growth rate is the greatest when the diameter is≤8 cm.The height increases with the decreases of BAL,H_(ba),BA and the increase of SLC.The height-diameter generalized mixed effect model of Pinus tabuliformis constructed in the study can provide reference for estimating the height growth of Pinus tabuliformis in Xining and similar ecological areas.