Abstract
Although many roadless areas on federal lands have been mapped in the United States since the 1970s, there has been little specific research on how and to what degree roadless areas contribute to biodiversity conservation. We examined the ecological attributes of mapped roadless areas for the Klamath‐Siskiyou ecoregion of northwestern California and southwestern Oregon (U.S.A.). Attributes examined include special elements (such as natural heritage, serpentine geology, late‐seral forests, Port Orford cedar [ Chamaecyparis lawsoniana ] ), and key watersheds; elevation and habitat representation; and overall landscape connectivity. We compared designated wilderness to roadless areas, giving special attention to the relative importance of small roadless areas (405–2024 ha). We mapped nearly 500 roadless areas of ≥405 ha. Roadless areas occupied more than twice the land area of wilderness (approximately 27% of the entire ecoregion) and contained approximately 36% of the known occurrences of heritage elements, 37% of the mapped serpentine habitats, 36% of the remaining late‐seral forests, 60% of Port Orford cedar strongholds, and 42% of key watersheds for aquatic biodiversity. In addition, roadless areas were composed of significant amounts of low‐ and mid‐elevation sites and a substantial number of the 214 mapped physical‐biological habitat types with strong complementarity with designated wilderness. Fragmentation analyses showed that roadless areas contributed to regional connectivity in important ways. Also, small roadless areas were an important component of the roadless‐areas conservation assessment. For the Klamath‐Siskiyou ecoregion, roadless areas and designated wilderness provide an important foundation upon which to develop a comprehensive regional conservation strategy.