Natural resource monitoring is a major component of park stewardship, and a cornerstone of the NPS Natural Resource Challenge a program to revitalize and expand the natural resource program within the Park Service and improve park management through greater reliance on scientific knowledge. The overall purpose for natural resource monitoring is to determine the status and trend in the condition of selected park resources. Monitoring results will be used to assess the efficacy of management and restoration efforts, provide early warning of impending threats, and provide a basis for understanding and identifying meaningful change in natural systems characterized by complexity, variability, and surprises. Monitoring data may help to determine what constitutes impairment and to identify the need to initiate or change management practices.