Forest health analysts seek to define the location, extent, and magnitude of changes in forest ecosystems, to explain the observed changes when possible, and to draw attention to the unexplained changes for further investigation. The data come from a variety of sources including satellite images, field plot measurements, and low-altitude aerial surveys. Indicators estimated from the data are assessed in a variety of ways. For example, national assessments typically aggregate information across sites within states, biophysically defined regions (ecoregions), or other large strata. The strata that are characterized by extreme average indicator values become candidates for further investigation.
Coulston, John W.; Riitters, Kurt H. 2003. Geographic analysis of forest health indicators using spatial scan statistics. Environmental Management 31(6): 764-773