Development of a Compatible Taper Function and Stand-Level Merchantable Volume Model for Chinese Fir Plantations

Chinese fir (Cunninghamia lanceolata [Lamb.] Hook) is one of the most important plantation tree species in China with good timber quality and fast growth. It covers an area of 8.54 million hectare, which corresponds to 21% of the total plantation area and 32% of total plantation volume in China. With the increasing market demand, an accurate estimation and prediction of merchantable volume at tree- and stand-level is becoming important for plantation owners. Although there are many studies on the total tree volume estimation from allometric models, these allometric models cannot predict tree- and stand-level merchantable volume at any merchantable height, and the stand-level merchantable volume model was not seen yet in Chinese fir plantations. This study aimed to develop (1) a compatible taper function for tree-level merchantable volume estimation, and (2) a stand-level merchantable volume model for Chinese fir plantations. This “taper function system” consisted in a taper function, a merchantable volume equation and a total tree volume equation. 46 Chinese fir trees were felled to develop the taper function in Shitai County, Anhui province, China. A second-order continuous autoregressive error structure corrected the inherent serial autocorrelation of different observations in one tree. The taper function and volume equations were fitted simultaneously after autocorrelation correction. The compatible taper function fitted well to our data and had very good performances in diameter and total tree volume prediction. The stand-level merchantable volume equation based on the ratio approach was developed using basal area, dominant height, quadratic mean diameter and top diameter (ranging from 0 to 30 cm) as independent variables. At last, a total stand-level volume table using stand basal area and dominant height as variables was proposed for local forest managers to simplify the stand volume estimation.杉木（Chinese fir，Cunninghamia lanceolata [Lamb.] Hook）是中国核心人工林用材树种之一，兼具材质优良与生长迅速的特性。其人工林种植面积达854万公顷，占全国人工林总面积的21%，蓄积量占全国人工林总蓄积量的32%。随着市场需求持续增长，精准估算并预测单木与林分水平的可采伐材积，已成为人工林经营主体的关键需求。尽管已有诸多基于异速生长模型的单木总材积估算研究，但现有异速模型无法针对任意可采伐高度实现单木及林分水平可采伐材积的预测，且目前国内杉木人工林尚未建立林分水平可采伐材积模型体系。本研究旨在构建两大模型体系：（1）适配单木可采伐材积估算的相容性削度函数；（2）杉木人工林林分水平可采伐材积模型。本“削度函数系统”由削度函数、可采伐材积方程及单木总材积方程三部分构成。研究团队在中国安徽省石台县采伐46株杉木以构建削度函数。采用二阶连续自回归误差结构，校正单木内多组观测值固有的序列自相关性。完成自相关校正后，同步拟合削度函数与材积方程。所构建的相容性削度函数对本研究数据集拟合效果优异，在直径与单木总材积预测方面表现极佳。基于比率法构建的林分水平可采伐材积方程，以林分断面积、优势木平均高、二次平均胸径及顶径（取值范围0~30cm）作为自变量。最后，本研究提出了以林分断面积与优势木平均高为变量的林分总材积表，以助力当地森林经营管理者简化林分材积估算工作。