基于干曲线方程的桉树立木单株材积测算研究

Volume Assessment of Standing Eucalypt Trees Based on Stem Curve Equations

以3个不同林龄的桉树品系16株样木为材料,以2种区分段所得干曲线方程,构建立木三维立体结构并对其单株材积测算方法,就所获得5种单株材积以及其形数进行了计算比较。结果表明:来自不同2种区分段所建立的干曲线方程模型拟合效果好,最大多数的模型决定系数R2大于0.99,SEE(Standard Error of the Estimate)较小,能很好对样木的树干干形进行解析;但不同的区分段差别较大,其中1 m区分段所获得树干曲线方程拟合效果(R2>0.98)优于1.3 m区分段;5种单株计算方法所得材积(2种区分段求积法、2种三维立体结构求积法与常规桉树二元材积法)之间没有显著差异,但存在着极显著的线性相关性;对4个林分的形数分析表明,不同林分立木在胸高形数差异显著,表现出胸高形数随着林分林龄增大而逐步减小的趋势。在胸高形数上5种单株材积测算存在着差异显著。1 m区分段下所得三维立体所得材积V4以及胸高形数均与其相应的区分求积法所得材积V2和胸高形数接近,因此可利用1m区分段建立干曲线方程获得树干三维立体结构,测算接近真实的单株材积。

Sixteen sample trees of various ages representing three Eucalyptus species were used to develop standing tree stem taper equations,and then to calculate individual tree volumes and form factors by two sectional methods.The stem curve equations established from the two sectional methods proved to fit well with,the coefficients of determination being over 0.99,and their SEEs(Standard Error of the Estimate)were small indicating the stem form of the sampled trees to be well defined by the stem curve equations developed.However,the fit of the stem curve equations differed between the two different sectional methods,with the equation from the 1 m sectional method having higher coefficients of determination than did the 1.3 m sectional method.There were no significant differences among the 5 kinds of individual volume estimates,which included two methods of sectional measurements,three-dimensional structure volume estimation using two sectional methods,and a conventional method based on a binary standing volume equation.However,significant differences were found among the form factors of four stands,and the form factor values gradually decreased as stand age increased.There were also significant differences in the form factors among 5 kinds of individual volume estimates;V4 estimates obtained from the 1 m sectional method were close to V2 estimates.It was concluded that the three-dimensional stem structure could be ascertained best using a stem taper equation obtained using the 1 m sectional method,and individual tree volumes estimated using this equation were close to actual individual tree volumes.