Study on verification and updating of one-way tree volume equations in Hainan province
CHEN Zhenxiong1,2, ZHOU Xianghong1, XIAO Qianhui1, HE Peng1
(1. Central South Forest Inventory and Planning Institute of State Forestry Administration, Changsha 410014, Hunan, China;2. The Afforestation Department of Forestry Department of Tibet Autonomous Region, Lasa 850000, Tibet, China)
The timber is an important content of forest resource monitoring in China. Forest volume estimation of continuous forest inventory in Hainan province has been adopted one-way stand volume which was established in 70s in Guangdong province. Therefore,it is the urgent task to test and update stand volume equations for main tree species in Hainan province, such as rubber, eucalyptus,acacia, Caribbean pine and Casuarina equisetifolia, using measured data. In this paper, the adaptability of old one-way stand volumes used in continuous forest inventory in Hainan province are tested. The new stand volume equations of 5 tree species are established. At the same time, tree volume estimation deviation of 5 tree species by using old stand volume equations are analyzed. The results showed that: The deviations of the old one-way tree volume equations are extraordinary large. The total relative deviations and the mean system deviation are above 15%. The estimated values are significantly lower than the actual value. The old stand volume equations are no longer applicable in volume estimation in continuous forest inventory in Hainan province. The prediction precision of new established one-way tree volume equations are higher than 95%. The total relative deviations are basically between 3% and -3% and the mean system deviations are close to 0. The stand volume estimation using the new equations rise 23.80%, compared with estimation using the old equations, the increment reached to 13.8985 million cubic meter.
引言
一元立木材积表是指根据胸径一个因子与材积回归关系编制的材积数表[1]。在我国一、二类森林资源清查中,采用一元材积表法估计立木材积相当普遍[2],海南省也不例外。海南省森林资源清查是国家森林资源监测体系的重要组成部分,其监测成果是海南省乃至我国生态文明建设与现代林业发展决策的重要依据。海南省森林资源清查体系始建于1979 年, 至2013 年共开展了7 次森林资源清查工作。从建立森林资源清查体系至今,一直沿用广东省70年代未所编制的二元材积表导算的一元立木材积表进行林木蓄积估计[3]。由于与广东省气候、立地条件等差异显著,加之近30 a 森林经营方式的转变,海南省森林资源结构与林木生长特征发生了明显变化,总体上表现为人工林资源逐渐增加、天然林资源逐渐减少,幼中林资源逐渐增加、近成过熟林资源逐渐减少。曾伟生等[4] 认为一旦待估总体的结构特征与原来编制一元表时的总体特征相比发生了明显变化,仍然沿用原来的一元表就会导致材积估计产生偏差。本研究针对此问题,以海南省橡胶、桉树、相思、加勒比松、木麻黄5 个树种实测立木材积数据,对森林资源清查中使用的一元立木材积方程适应性进行检验,更新建立新一元立木材积方程,研究分析森林资源清查林木蓄积估计偏差,以期为完善海南省森林资源清查监测体系等提供科学依据,也为积极推进我国立木材积表的完善、更新修订等提供决策参考。
(4)应注意一元材积表的性质及适用范围,一元材积表主要应用于较大总体(如全省)范围内的估计。由于一元(胸径)控制下的材积变动很大(主要由树高变动引起),它对样地水平乃至小区域范围的估计,不可避免地会产生很大的偏差[14],在生产中可结合相对树高曲线模型使用,以提高一元材积的适用性。由于受现实林分的影响,建模样本胸径主要集中在45 cm 以下,如果林木胸径超过45 cm 时,应用之前应进行适用性检验。