基于地形与竞争因子的青冈栎次生林树高哑变量模型研究

考虑不同地形和林木竞争对青冈栎树高与胸径关系的影响，构建青冈栎树高与胸径的哑变量模型，为青冈栎次生林的树高预测和可持续经营提供理论依据。以16个青冈栎次生林固定样地为研究对象，通过确定系数（R²）、赤池信息量准则（AIC）、均方根误差（RMSE）和平均预估误差（MPE）4个评价指标，从11个基础模型中筛选出最优的基础模型。利用F统计检验分析了不同坡向和坡度对青冈栎树高与胸径关系的影响，同时对Hegyi简单竞争指标进行了改进。基于坡向、坡度和竞争强度3个哑变量，构建青冈栎树高与胸径的哑变量模型。结果表明，对数模型M2为最优基础模型，其确定系数（R²=0.686）最大，均方根误差（RMSE=1.380）和平均预估误差（MPE=1.242）最小；不同坡向和坡度下，模型的F统计值均大于F临界值；Hegyi改进指标与树高、胸径的相关系数达到-0.452、-0.418，相比Hegyi简单竞争指标有明显提高；基础模型中引入坡向、坡度和竞争强度哑变量后，模型的拟合精度均显著提高，R²提高了0.035，RMSE减少了0.077，MPE减少了0.070%。从林木的水平和垂直空间上构建青冈栎林木竞争指标更加准确，坡向、坡度和林木竞争对青冈栎树高与胸径关系存在显著影响。综合考虑地形与林木竞争的哑变量模型拟合精度更高，能为青冈栎树高生长的预测提供参考。

Establishment of the Height Dummy Variable Model of Cyclobalanopsis glauca Secondary Forest Based on Terrain and Competition Factors

Considering the influence of different site conditions and forest competition on the relationship between tree height and diameter of Cyclobalanopsis glauca,the dummy variable model of tree height and diameter was established to provide theoretical basis for tree height prediction and sustainable management of C.glauca secondary forest.Sixteen fixed sample plots were selected as research objects.The optimal basic model was selected from 11 basic models by determining four evaluation indexes,including the coefficient of determination(R^2),the Akaike information criterion(AIC),the root mean square error(RMSE) and the mean prediction error(MPE).The influences of different slope directions and slope gradients on the relationship between height and diameter of C.glauca tree were analyzed by F-test.The simple competition index of Hegyi was improved.The dummy variable model of the height and diameter was constructed based on slope direction,slope gradient and competition index.The results showed that the logarithmic model M2 was the optimal basic model with the maximum determination coefficient(R^2=0.686),the minimum root mean square error(RMSE=1.380) and the mean prediction error(MPE=1.242).The statistical value(F) of the model was greater than the critical value(F) under different slope directions and slope gradients.The correlation coefficients between the improvement index of Hegyi and tree height and diameter were-0.452 and-0.418,respectively,which were significantly higher than the simple competition index of Hegyi.The fitting accuracy of the model was significantly improved because R^2 increased by 0.035,RMSE decreased by 0.077,and MPE decreased by 0.070% after adding dummy variables into the foundation model.Considering the horizontal and vertical space of trees,the competition index was more accurate.The relationship between the height and diameter was significantly affected by different slope directions,slope gradients and competition.The dummy variable model with topography and competition had higher fitting accuracy,it could provide references for the tree height prediction of C.glauca.