基于广义代数差分法和因子选择的杉木人工林立地质量评价

Site quality evaluation of Cunninghamia lanceolata plantation based on generalized algebraic difference approach and factor selection

【目的】研究浙西南杉木Cunninghamia lanceolata人工林立地质量,探究影响人工林立地质量的主要因素,为杉木人工林经营提供理论依据。【方法】以浙江省庆元县杉木人工林为研究对象,采用解析木数据,利用广义代数差分法,构建了杉木人工林地位指数模型,以此为因变量,使用随机森林算法从二类杉木小班数据中筛选出影响杉木林地位指数的主导因子,在此基础上,通过地位指数得分值确定立地质量等级,对庆元县杉木小班进行立地分类与立地质量评价。【结果】以Richards为基础构建的广义代数差分方程最符合庆元县杉木人工林的生长过程,其决定系数(R 2)为0.969,均方根误差(ERMS)为1.778,平均绝对误差(EMA)为0.400,且模型的多形曲线符合杉木林生长的生理学意义。通过随机森林的因子选择得出:影响杉木人工林地位指数的主要立地因子有地貌、腐殖质厚度、土层厚度,与传统的偏相关系数法相比,基于随机森林的因子选择具有更大的贡献度和更合理的因子非线性关系解释性。结合小班数据,以地貌、腐殖质厚度、土层厚度等3个立地因子将小班划分为17个立地类型,通过计算得分可知研究区立地质量处于中等及以上。【结论】基于广义代数差分法的地位指数模型适用于浙西南杉木人工林,与基于置换的因子选择方法筛选出的主导因子相结合能够对立地质量进行有效评价。

[Objective]With an investigation of the site stand of Cunninghamia lanceolata plantation in southwest Zhejiang Province,this study is aimed to explore the main factors affecting the site quality of the plantation so as to provide a theoretical basis for C.lanceolata plantation management.[Method]First,with C.lanceolata plantation in Qingyuan District of Zhejiang Province taken as the research object,the parse tree data and generalized algebraic difference approach was employed to establish the site index(SI)model of C.lanceolata plantation.Then,with SI chosen as the dependent variable,random forest algorithm was used to screen out the dominant factors affecting the forest position index from the data of ClassⅡC.lanceolata sub class data,on the basis of which,the site quality level was determined by the score value of SI,and the site classification and site quality evaluation were carried out for C.lanceolata sub classes in Qingyuan District.[Result]The generalized algebraic difference approach based on Richards equation was the most consistent with the growth process of C.lanceolata in Qingyuan District with the coefficient of determination(R 2),root mean squared error(ERMS)and mean absolute deviation(EMA)being 0.969,1.778 and 0.400 respectively and the multishape curve of the model was in accordance with the physiological significance.The main site factors affecting the SI of C.lanceolata plantation are landform,humus thickness and soil layer thickness,as was shown in the factor selection of random forest,which had a greater contribution and more reasonable interpretation of the nonlinear relationship between factors when compared with the traditional partial correlation coefficient method.With landform,humus thickness and soil layer thickness selected as the site factors,the sub class was divided into 17 site types,among which the sub classes under investigation were of medium site quality or above.[Conclusion]The site index based on generalized algebraic difference method is suitable for C.lanceolata plantation in southwest Zhejiang Province,and when combined with the dominant factors selected by permutation importance method,it can effectively evaluate the site quality.