FIA conducts inventories in three phases. Remotely sensed data are used in Phase 1 to obtain initial plot land-cover observations to determine whether a fi eld visit is required. Phase 1 data also are used to classify total area in the population of interest, for latter use in the post-stratifi cation process, to increase the precision of estimates. In Phase 2, fi eld crews visit the physical locations of permanent fi eld plots to measure traditional inventory variables such as tree species, diameter, and height. In Phase 3, fi eld crews visit a subset of Phase 2 plots to obtain measurements for an additional suite of variables associated with forest and ecosystem health. Th e three phases of the enhanced FIA program as implemented in this inventory are discussed in detail in the sections that follow.