An Assessment of the Potential Impacts of Emerald Ash Borer (Agrilus planipennis Fairmaire) on Virginia's Municipal Street Trees

Emerald ash borer (Agrilus planipennis Fairmaire) (EAB) is an invasive, wood-boring beetle (Coleoptera: Buprestidae) introduced unintentionally to the United States from East Asia that infests and eventually kills native ash trees (Fraxinus spp.). First detected near Detroit, Michigan in 2002, EAB had spread to fifteen U.S. states by 2011, killing an estimated 50 million ash trees along the way. EAB was first discovered in Virginia in 2003 and re-infested the state in 2008, raising concerns over impacts that the invasive pest might have on municipal urban forests and street trees. Despite these concerns, little is known about native ash abundance in Virginia's urban forests; as a result, potential EAB impacts have been difficult to project. In this study, street tree assessments were conducted in fourteen Virginia municipalities using i-Tree Streets®, which is a software program developed by the U.S. Forest Service that uses field inventory data to estimate street tree abundance and composition along with the quantity and monetary worth of functional benefits provided by these street trees. In addition to estimating potential losses of functional benefits provided by native ash street trees, information obtained from Virginia Dept. of Transportation was used to estimate the potential cost of removing these trees from the street side. The assessment indicated that there are about 4,600 native ash street trees in the fourteen studied localities and that native ash species comprise about 2% of municipal street tree populations on average. The highest relative abundance of native ash was found in Winchester City (5.8% of all street trees) whereas Richmond City had the greatest number of native ash street trees (estimated at 1,417). In terms of species importance (which accounts for both the relative abundance and relative size of trees in the population), only two localities (City of Roanoke and Town of Abingdon) had a native Fraxinus species among the top-five most important street tree species in the locality. In contrast, every municipality had at least one Acer species among the top-five, and eight of fourteen localities had at least one top-five Quercus species. Native ash street trees in the studied localities were estimated to provide functional benefits (energy conservation, stormwater mitigation, air pollution abatement, carbon sequestration, and aesthetic contributions) valued at over $535,000 annually, or roughly $38,000 per locality. In addition, carbon stored in these trees (about 17 million kilograms) was valued at nearly $277 thousand. The total estimated cost of removing lost ash trees was estimated at nearly $1.75 million, averaging about $124,000 for each municipality, and replacing the canopy cover and basal area provided by existing native ash street trees would exceed $17 million. In total, the studied localities would incur a gross financial impact of about $20.26 million due to losses of functional benefits and structural assets provided by native ash street trees.