Monitoring Gypsy Moth defoliation in near real time

By late 2012, forest health monitors in western New York and Pennsylvania knew that they were about to experience a severe outbreak of the non-native Gypsy Moth. Surveys showed an unusually high density of egg masses on the branches and trunks of trees, but neither egg densities, nor the distribution of primary host trees are ever perfectly known across the forest, so translating general predictions to a map remains a challenge. Using the best information available, forest managers prioritized their lands for spraying, then they watched this event unfold.

While this troublesome defoliator first arrived in the US a century and a half ago, it reached these forests only in the late 1970s. On the Allegheny National Forest, many thousands of acres were defoliated between 1985-7. During this current outbreak, the hardest hit area lies just east of the Allegheny Reservoir in Warren and McKean Counties, PA and Cattaraugus County, NY, an area that includes the Allegany Indian Reservation.

Repeated outbreaks of the Gypsy Moth have led to the decline and death of host trees, such as oaks. At the stand scale, mortality and other undesired environmental effects also increase with the severity of the defoliation. Making an accurate prediction of where these outbreaks will occur and where they will be most severe can allow managers to spray more efficiently. While ForWarn's maps reveal severity after the fact, this knowledge provides additional information that can eventually improve predictions of future outbreaks and where Gypsy Moth effects might be mitigated.