将乐地区马尾松最优冠幅模型研究
Optimal Crown Diameter Models for Pinus massoniana in Jiangle, Fujian Province

树冠是树木进行光合作用和呼吸作用的重要场所，冠幅作为树冠的重要因子，直接影响树木的生活力和生产力，同时也是反映树木的长期竞争水平的重要指标。该文使用福建省将乐国有林场980株马尾松调查数据，基于11种常用树冠直径模型，利用R软件的nls模块对马尾松冠幅与胸径关系进行拟合，选取精度最高的作为基础模型，通过对基础模型添加变量改进模型，并用调整后的决定系数adj-R2、偏差Bias、剩余均方根误差RMSE对模型精度进行检验。结果表明:模型11在添加了样地优势木平均高（Ht）、每公顷株数(M)和冠长(CL)林分变量之后，Bias、RMSE减小，adj-R2明显增大，所以，CW=(a+a1×Ht)/1+exp[(b+b1×M)+(c+c1×CL)ln(D+1)]能更好地模拟当地马尾松的冠幅与胸径的关系。
Crown is an important part for photosynthesis and respiration. As one of the key variables, crawn diameter directly affects the life force of a tree and its productivity. It is also an important index reflecting the long-term competitive level of a tree. In this study, 980 individual trees of Pinus massoniana growing in Jiangle State-owned Forest farm of Fujian Province were selected to extract related data. Based on 11 types commonly used tree diameter models, nls module of R software was used to fit the relationship between crown diameter and diameter at breast height (DBH). Models with the highest accuracy were used as the basic ones, which would be then improved by adding basic variables. The accuracy of the models was tested by adjusted decision coefficient (adj-R2), bias error (Bias), root mean square error (RMSE). The results demonstrated that after stand variables of advantage wood average height (Ht), the number of per hectare (M) and crown length (CL) were added to model 11, its Bias and RMSE decreased, adj-R2 obviously increased, so the model CW=(a+a1×Ht)/1+exp[(b+b1×M)+(c+c1×CL)ln(D+1)] could be used to predict the relationship between the crown and DBH of P. massoniana growing in Jiangle