The core mission of the National Park Service (NPS), as outlined in the agency's 1916 Organic Act, is to protect and conserve natural and cultural resources for future generations. Responding to criticism that it lacked basic knowledge of natural resources within parks, the NPS initiated the Inventory and Monitoring (I&M) Program to detect longterm changes in physical and biological resources (NPS 1992). Parks with signifi cant natural res ources were assigned to one of 32 monitoring networks, each based on ecological similarity and geographic proximity. Each network was charged with developing a monitoring program capable of detecting long-term changes in physical and biological resources within each network.