各种森林资源清查的目的、范围和强度,包括其实施方法,都有了重大的变化。国家森林资源清查,一般为制定、修改和调整林业发展计划提供资料。这类资源清查,芬兰、挪威和瑞典的历史最长。早在1830年,str(o|¨)m首先提出带状抽样调查,十九世纪普遍用于国有林的调查。早期的资源清查,全力注意在一定时期内和重复间隔期采平行带状样地或线上样地。现在,这些国家都采用系统组群抽样。组群样地是由设置在一个方块的边上或右角上的若干个定积圆形样地组成。这些国家的调查重复期为5—12年。美国的国家森林资源清查从1930年开始,到1949年,60%的森林都做过调查。层化设计 Significant changes have taken place in the purpose, scope and intensity of inventory of various forest resources, including their methods of implementation. National inventory of forest resources generally provides information for formulating, modifying and adjusting forestry development plans. Inventory of such resources, Finland, Norway and Sweden have the longest history. As early as 1830, str (o | ¨) m first proposed a strip sampling survey, which was commonly used for surveys of state-owned forests in the nineteenth century. Early inventory of resources, full attention to a period of time and repeated intervals taken parallel strip sample or online sample. These countries now use systematic cohort sampling. The group plots consist of a number of fixed-circle plots set on the edge or right corner of a square. The surveys in these countries have a repeat period of 5-12 years. National forest inventory in the United States began in 1930 and by 1949, 60% of all forests were investigated. Layered design