NPS PHOTO ARCHIVE

A view of Saguaro National Park and residential development beyond park boundaries.

Parks and other protected areas are importatn sources of highly valued ecosystem services that include preservation of biodiversity, provision of freshwater, detoxification of pollutants, recreation, and scenic enjoyment. When the National Park Service (NPS) was established in 1916, the prevailing thought was that these resources would be retained by simply “building a bigger fence”—that is, by isolating parks from threats and insults that originated outside park boundaries.

We now know that land use changes outside parks have profoundly affected virtually all U.S. national park units, and they will continue to do so in the future (U.S. General Accounting Office 1994; Radeloff et al. 2010; Davis and Hansen 2011; Monahan and Gross 2012). Furthermore, recent land use intensification has occurred at a disproportionately rapid rate near the boundaries of protected areas (Wittemyer et al. 2008; Wade and Theobald 2010). If this trend continues, projections are for an additional 17 million housing units to be constructed within 50 km (31 mi) of protected areas in the United States, with more than 1 million units within 1 km (0.6 mi) (Radeloff et al. 2010). Impacts of external threats on parks are already so prevalent that well-considered essays have questioned the ability of the National Park Service to retain even large wilderness parks in an “unimpaired” condition (Cole et al. 2008; chapters in Cole and Yung 2010).

Our appreciation for the importance of broad-scale influences on park resources has grown more rapidly than our ability to identify and assess the specific locations and magnitudes of risk posed by these factors. Most protected areas are threatened by invasive species, climate-driven changes, habitat conversion, and loss of connectivity. Recognition that the effective scale of these critical threats is much broader than individual management units has motivated actions at local to national scales to form new partnerships, and has stimulated the establishment of the emerging Department of the Interior (DOI) Landscape Conservation Cooperatives and regional Climate Science Centers (DOI Secretarial Order 3289). In concert with these higher-level activities, DOI bureaus are conducting assessments at watershed to ecoregional scales. The broad geographical scope of these assessments is consistent with our current ecological thinking, but it is well beyond the area traditionally addressed in park-based natural resource studies and it far exceeds the data holdings and analytical capabilities of most U.S. land management units administered by the National Park Service or any other U.S. bureau.