Increasing global trade and travel are resulting in the unintentional arrival of non-indigenous species. Although only a minority of new invaders successfully establish, the costs associated with these invasions has been estimated at $122 billion annually in the USA alone. The gypsy moth, Lymantria dispar (L.), is responsible for a portion of these costs. Prior research on gypsy moth has largely focused on its negative ecological and economical effects in managed forests and natural ecosystems. In contrast, attempts to quantify gypsy moth impacts in urban environments are limited, which is surprising since most of the economic impact is thought to occur in urban areas. Moreover, biological invasions, in general, that occur in urban and suburban forests are particularly problematic because of the costs associated with outbreaks in populated areas, such as nuisance to residents and tree removal, which occur to a far lesser degree in less populated areas. We thus quantified the cost of a biological invasion in urban and suburban forests, using the gypsy moth as a model system.

Results/Conclusions

We developed a conceptual framework to assess the consequences of gypsy moth low- and high-intensity outbreaks over three years in urban and suburban forests. Percent defoliation and mortality was varied by host tree species susceptibility. Gypsy moth attacks over 300 species of host trees, including the highly preferred species of oak, aspen, willow, and apple, and will attack secondary hosts, such as pine, ash, and maple, during intense outbreaks. We combined these scenarios with the costs (i.e., out-of-pocket expenditures on suppression, tree removal and replacement) and losses (decreases in monetary and non-monetary values associated with aesthetics, energy consumption, air quality, loss of recreational opportunities) associated with these outbreaks, and applied this framework to urban forest inventory data available from two cities (in and around Baltimore, Maryland and Jersey City, New Jersey) currently dealing with gypsy moth outbreaks. Our study not only quantifies gypsy moth impacts in urban areas, but also provides a framework that could be applied in future studies that seek to quantify impacts of other non-indigenous invasive pests in urban and suburban forests.