THE PACIFIC-NORTHWEST REGION - VEGETATION AND INVENTORY MONITORING-SYSTEM

A grid sampling strategy was adopted for broad-scale inventory and mon itoring of forest and range vegetation on National Forest System lands in the Pacific Northwest Region, USDA Forest Service. This paper docu ments the technical details of the adopted design and discusses altern ative sampling designs that were considered. A less technical descript ion of the selected design will be given elsewhere. The grid consists of a regular, square spacing with 5.47 kilometers (3.4 mi) between gri d points. The primary sampling unit (PSU), established at each grid sa mpling point, consists of a circular, 1-hectare (2.47-acre) plot. The PSU is subsampled with a set of different-sized fixed-area subplots, a s well as line transects, to assess all components of vegetation. The design is flexible and can be used with many types of maps. The theory of point and change estimation is described, as well as estimates of variation that assess the statistical precision of estimates.