The primary mission of the National Park Service (NPS) is to protect and preserve natural and cultural resources for future generations. Responding to criticism that it lacked basic information on the condition of natural resources within national parks, the NPS initiated a servicewide Inventory and Monitoring (I&M) Program to determine status and trends in ecological resources (NPS 1992).
Established in 2001, the Sonoran Desert Network (SODN) Inventory and Monitoring Program includes 11 parks in south- ern Arizona and New Mexico that range in size from 356 (Tumacácori National Historical Park) to 133,882 hectares (Organ Pipe Cactus National Monument). Collectively, these parks are representative of most of the ecological communities present within the Sonoran Desert and Apache Highlands Ecoregions (NPS 2005).
Natural Resource Technical Report NPS/XXXN/NRTR–2009/0XX. National Park Service, Fort Collins, Colorado.