ABSTRACT
Worldwide concern over environmental threats and sustainable development has led to increased efforts to monitor status and trends in environmental condition. In the past, environmental monitoring focused on obvious, discrete sources of stress such as chemical emissions. It became evident that remote and combined stressors, while difficult to measure, can also significantly alter environmental conditions. Consequently, monitoring efforts began to examine valued ecological components that reflected effects of multiple and sometimes unknown stressors. To characterize the condition of these components, national, state, and community-based environmental programs increasingly explored the use of ecological indicators. These are biological, chemical, or physical measurements, indices or models used to characterize or summarize a critical, and usually complex, component of an ecosystem. Indicators are signs or signals that relay a complex message, potentially from numerous sources, in a simplified and useful manner. Indicators are essential when it is implausible to measure and interpret all the factors that comprise an ecological issue.
