I'm not sure that this info applies specifically to PA, but this is the agency the PGC uses to obtain the data for determining forest health.
Annual Inventory Design: Phase III
Forest Health Monitoring
(each sample represents 95,000 acres)
Basic Forest Health Monitoring system that began in 1990 will continue until the annual Forest Inventory and Analysis system begins in each state.
The Forest Health Monitoring and Forest Inventory and Analysis sample locations will be co-located and measured using standard Forest Inventory and Analysis and Forest Health Monitoring protocols.
The Forest Health Monitoring grid will be converted to a 5-year measurement cycle with no overlap and the intensity will be boosted.
Working towards a single visit by field crews.
Data compilation and database systems will be merged.
Note that each sample represents 95,000 acres. That means each plot represents 148 SM of forested habitat. Applying that to a WMU like 2G that would equate to 28 sample plots in the entire WMU. If that is true ,that would be a much smaller sample size than they use to determine herd health and the PGC says that sample size is too small so they have to use 3 year averages.