The United States Forest Service (USFS) (defendant) developed forest-management plans for the Nicolet and Chequamegon National Forests in Wisconsin. The Sierra Club (Sierra) (plaintiff) suggested that the plans should incorporate conservation-biology science, which involved the preservation of large habitats to maintain biological diversity. The USFS divided the forest into a patchwork of habitats without incorporating Sierra’s suggestions. Instead of using conservation biology to measure diversity, the USFS used management indicator species (MIS) and population-viability analyses, which emphasized the number of species over the relationships between species. The USFS justified its rejection of conservation biology on the basis that the science was untested in Wisconsin forests. After the USFS issued final environmental impact statements and records of decision, Sierra sued the USFS in district court. The district court granted summary judgment for the USFS. Sierra appealed, claiming that the USFS’s failure to use conservation biology violated the National Forest Management Act (NFMA), 16 U.S.C. §§ 1601-04. Specifically, Sierra claimed that (1) the NFMA required an ecological approach to forest management involving conservation biology; (2) the MIS and population-viability analyses did not adequately measure ecological diversity; (3) the NFMA’s diversity regulations, including 36 C.F.R. § 219.27(g), required the USFS to maintain at least some old-growth forest communities; and (4) the USFS’s justification for rejecting conservation biology was improper, because conservation biology was well accepted and respected.