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For most large US park and wilderness areas, legislationand management policies call for preservation, unim-paired, in perpetuity. Central to the notions of protection, preservation, and lack of impairment has been added the concept of “naturalness”, local ecological and environmen-tal conditions imagined to persist over time, in the absence of human intervention. For much of the 20th century, this idea of naturalness as the guiding concept for stewardship of park and wilderness areas remained largely unchal-lenged. Many scientists, managers, and conservationists assumed that natural conditions could be preserved through non-intervention and that this would ensure long-term conservation of biodiversity and ecosystems within protected-area boundaries. Recently, emphasis has shifted, and the conservation of biological diversity has become an increasingly importan