Comparing evaluations of forest health based on aerial surveys and field inventories: Oak forests in the Northern United States

Aerial sketch-map surveys and systematic forest field inventories may be used separately or in combination to indicate the status of regional forest health. During recent decades, aerially conducted sketch-maps of forest damage and forest inventories have been used to assess oak (Quercus spp) forest health across a 24-state region spanning the northern U.S. In order to more fully inform the monitoring of oak forest health and integrate these independent datasets, the effect of the quality, timing, and repeated sampling of aerial data on correlations with field-based oak forest assessments was assessed. Study results indicated that aerial damage surveys were weakly correlated with indicators of oak forest sustainability (e.g., oak seedlings and saplings), but more highly correlated with overstory attributes such as tree mortality and standing dead. The highest correlations between aerial damage surveys and oak mortality/standing dead were found when the time between the aerial survey and subsequent forest inventory was 4-6 years. Aerial surveys may have their greatest efficacy in supplementing field inventories of oak forest health when they are conducted in a high quality manner with bi-annual or longer remeasurement periods (due to rare pest damage events).