Oak Forest Response to Lymantria dispar Defoliation in Central Massachusetts since 2019

Invasive forest insects are a major global change driver, and the Northeastern U.S. is an invasion hotspot. Lymantria dispar is one of the region’s most destructive defoliators. After thirty years of quiescence, a surprisingly severe outbreak began in 2015 in southern New England, and by 2018 had caused dramatic oak mortality across thousands of forested acres. Lymantria dispar is considered a generalist, but in New England, oaks (Quercus sp.) are its preferred host trees. Oaks are key overstory trees in eastern North America. In New England, they have been a dominant component of the forest for thousands of years, and play a leading role in providing habitat, timber, and carbon sequestration. However, oak prominence is declining throughout New England. The reasons for oak’s decreasing abundance are the subject of lively debate but the role of L. dispar is likely underappreciated. Therefore, we need to understand the causes and consequences of oak dieback and mortality to this disturbance event, so that we can better predict responses to future outbreaks. To address this need, we established a set of permanent plots in central Massachusetts, chosen to capture a range of defoliation severity.