2009 Research Highlights
Crown power
The goal of Detection Monitoring as implemented by the Forest Inventory and Analysis (FIA) Program is to identify forest ecosystems where conditions might be deteriorating in subtle ways over large areas. At the relatively sparse sampling intensity of the forest health plot network, a rough measure of success for the forest health indicators developed for this purpose is the ability to detect meaningful change when indicator data are pooled across two or three States.
Scientists working with the Eastern Forest Environmental Threat Assessment Center applied a technique known as statistical power analysis to FIA Crown-Indicator variables (crown density, foliage transparency, and crown dieback) to determine how many plots are necessary to detect various degrees of change at various levels of statistical power. The scientists concluded from the power analysis that for most plausible scenarios involving the crown indicator, about 100 plots (or 50 paired plots) would be adequate. Paired plots resulting from repeated observations over time reduces the number of grid points to less than half the observations that would be required from independent observations. These results are consistent with previously unverified assumptions that the crown indicators as implemented on FIA’s Phase 3 Detection Monitoring grid could reliably support analyses at the regional level, but probably not for many individual States.
Contact: Kurt Riitters, acting Forest Health Monitoring team leader, (919) 549-4015, kurt.h.riitters@usda.gov
Partners: North Carolina State University; USDA Forest Service Southern Research Station
