SAMPLING DESIGNS IN FOREST INVENTORIES

This chapter discusses the application of sampling theory and techniques to forest resource evaluation applicable to both timber and nontimber parameters. A sampling design is determined by the kind of sampling units used, the number of sampling units employed, and the manner of selecting and distributing these sample units over the forest area, as well as the procedures for making measurements and analyzing the results. The chapter concentrates on sampling designs using fixed-area plots, although the basic sampling designs are applicable to sampling units of any type. Simple random sampling (SRS) is the fundamental selection method. In systematic sampling (SYS), sampling units are spaced at fixed intervals throughout the population. Selective or opportunistic sampling is an example of nonrandom sampling used in forest inventory work. Clusters are frequently used in forest inventories of large areas, such as regional or national inventories, especially in remote areas with difficult access or long distances between plots.