Section 4(d)(1) of the Wilderness Act (Act), 16 U.S.C. § 1133(d)(1), authorized the U.S. secretary of agriculture (secretary) (defendant) to take actions within wilderness areas if necessary to prevent fire, insects, or disease from harming neighboring private or commercial interests. Under the secretary’s direction, the United States Forest Service (USFS) enacted the Southern Pine Beetle (pine beetle) program (program). The program’s purpose was to control pine-beetle infestations in wilderness areas located within various southern states, in order to protect commercial-timber interests and private property located outside of the wilderness areas. The program involved the extensive cutting and chemical spraying of pine trees within wilderness areas. The Sierra Club (plaintiff) and the Wilderness Society (plaintiff) challenged the program under the National Environmental Policy Act (NEPA), 42 U.S.C. §§ 4321-47; the Endangered Species Act, 16 U.S.C. §§ 1531-43; and the Act. The plaintiffs claimed that (1) “necessary” under § 4(d)(1) of the Act meant “effective,” and (2) the program was ineffective because it had not eliminated pine beetles and had unnecessarily harmed wilderness areas protected by the Act. The secretary claimed that the Act gave him broad discretion to manage wilderness areas. However, the secretary presented little evidence regarding the pine beetle’s ability to move outside of wilderness areas. The secretary also failed to present evidence indicating whether pine trees infected on adjacent lands could be controlled by actions taken outside of wilderness areas. The district court enjoined most of the program, pending the preparation of an environmental impact statement under NEPA. The plaintiffs moved for summary judgment.