广西森林资源连续清查角规样地体系评价

Assessment of Continuous Forest Inventory System in Guangxi

广西森林资源连续清查(以下简称"广西连清)"角规样地体系,是我国唯一的以点抽样理论为基础,以固定角规样地为监测载体的省(区)级森林资源连续清查体系。广西连清第7次复查,除了增设的方形样地调查以外,还对原有的角规样地进行了复查,因此本文得以用同时进行调查的方形样地调查结果作为参照对象,对角规样地体系的优点和存在的问题进行定性和定量相结合的综合分析评价。分析评价结果表明,与方形样地比较,角规样地除了具有显著的隐蔽性外,外业工作量只相当于方形样地的53%,两套体系的活立木蓄积量差异仅为3.16%,角规样地和方形样地体系总蓄积量抽样精度分别为94.47%与94.57%,均达到国家森林资源连续清查技术规定要求(≥90%)。角规样地复位率大于规定的98%,样木复位率远大于规定的95%,达97%以上,能满足林木蓄积生长量和消耗量监测的要求。角规样地体系的不足主要是由于漏测木和进测木的存在,导致森林资源的现状估计值偏低,且动态估计精度明显低于方形样地体系。

The Continuous Forest Inventory System in Guangxi（CFISGX） is an exclusive provincial forest inventory system in China which based on point sampling. In the 7-th remeasurement of CFISGX, a new sys- tem was set up based on square plots, and all previous point sample plots were remeasured meanwhile. In this paper, an assessment was made synthetically by comparing the point sampling forest inventory system with the square plot system. According to the results of analysis, the point sample plots are more invisible than the square plots, and the load of field work of the former is about 53% of the latter, The difference of total forest stand volume between two forest inventory systems is only 3.16%. The precisions of the volume estimates from the point plot and square plot systems, respectively 94.47 % and 94.57 %, exceeding 90 % which is the precision standard of the technical specification for forest continuous inventory in China. The remeasurement ratios of the point sample plots and trees are more than 98 % and 95 % respectively, which can satisfy the requirements of the monitoring of the forest growth and consumption. The disadvantage of point sampling is that the current estimate of the forest volume is less,caused by inevitable omission of sample trees, and the precision of change estimates are lower than the ones of square sample plots.