Lymantria dispar Defoliation and Mortality Survey at the Quabbin Watershed in Central Massachusetts 2017-2022

For most of the 20th century, the invasive Lymantria dispar was the most serious insect threat to forests and shade trees in the northeastern United States, but outbreaks have been sporadic and light since 1989, after the successful establishment of a fungal pathogen, Entomophaga maimaiga. However, in 2016 a surprising new outbreak of Lymantria dispar began in southern New England, resulting in dramatic oak (Quercus spp.) mortality across thousands of forested hectares by 2018. In 2017, during the height of the outbreak, a rapid assessment of defoliation across 486 plots in six clusters (aka ‘hotspots’) across the Quabbin Watershed Forest in central Massachusetts was conducted. These sample points can be related to satellite-based defoliation estimates, and the tree and site data analyzed for predictors of defoliation severity. In 2022, we returned to 204 of these plots to assess oak mortality, understory vegetation, and oak regeneration.