A multi-scale assessment of local and contextual threats to existing and potential U.S. protected areas

► A threat assessment framework that accounts for both local and surrounding threats provides a robust yet flexible means to evaluate which areas have the capacity, or offer opportunities, for ecological conservation. ► Areas least at risk from local and adjacent threats tend to overlay existing protected areas, but many protected areas remain at risk from external threats. ► Much of the area identified for potential conservation opportunities lies on private lands. ► While large, buffered conservation areas may remain viable in the West, conservation planning in other areas should focus on networks of stepping-stone conservation islands. ► Ecoregions and national parks vary significantly in their need for management of local and adjacent threats. Assessing threats to protected areas is a critical step to ensure effective resource conservation and to leverage future conservation actions. It is equally important to assess external and internal threats because human activities both in and around a protected area can impair the area's ecological goals or impart important ecological benefits to adjacent lands. We applied a threat framework that accounts for both local and surrounding threats to identify areas in the conterminous United States that provide or offer opportunities for ecological conservation. We find that, of the lands that are least threatened locally, 49% have some existing formal protection, but that more than 35% of the existing protected portfolio is at risk from external threats. However, over 20% of currently unprotected lands provide potential opportunities for conservation. Of the area identified with highest potential conservation opportunities, over 50% is on private lands, highlighting the need to engage owners of private land in conservation. There is greater potential for large, buffered, core conservation areas in the West, but other areas require networks of stepping-stone conservation islands. We summarize our results by ecoregions and within 40 national parks, identifying areas that are notably unthreatened (Colorado Plateau and Northwestern Glaciated Plains ecoregions and Great Basin and Canyonlands parks) versus those that may require more intense management actions (Eastern Great Lakes and Hudson Lowlands and Southeastern Wisconsin Till Plains ecoregions and Cuyahoga Valley and Great Smoky Mountains parks). Finally, we discuss how the approach could be applied and improved for finer-grained, local assessments.