WWETAC Projects

Project Title: Pathways and risk assessment of emerald ash borer movement into and within the Western United States

Principal Investigator: William R. Jacobi


Key Issues/Problems Addressed:
The emerald ash borer (Agrilus planipennis), an exotic wood boring insect, was introduced to the Detroit, Michigan area in the early 1990s causing significant tree mortality in the area and has subsequently spread (by nursery stock, logs, firewood and naturally) to Indiana, Ohio, Illinois, and Ontario Canada. The risk of emerald ash borer spreading to/within the Western United States through the transport of minimally processed wood products (including firewood) has not been fully evaluated.

Setting and Approach:
This study analyzed five potential wood related pathways that may help emerald ash borer move into/within the Western United States. (States included in the study are Arizona, Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North Dakota, South Dakota, Utah, Wyoming, California, Oregon, and Washington.) The five pathways researched were nursery stock, natural tree connections between regions, firewood, logs/minimally processed wood, and pallets/packing materials.

Key Findings:

  • The nursery business poses a high risk of transferring exotic insects and pathogens due to a large volume of inventory movement in the western U.S.
  • Natural movement of emerald ash borer to the west (without human help) is a low risk since it may be slowed or stopped when it reaches less dense ash stands in the middle of the prairie states.
  • Fifty-nine percent of collected bundles of firewood in Colorado in 2007 had evidence of insects.  An estimated 9,342 cords of retail firewood moved into western states from out of state.

Multiple potential wood product related pathways exist for exotic insects and pathogens to move into and within the western United States.   This is significant risk contributing to the spread of damaging invasive insects such as the emerald ash borer.


Jacobi, W.R., Goodrich, B.A., and C.M.  Cleaver, C.M. 2011. Firewood transport by national and state park campers: A risk for native or exotic tree pest movement. Arboriculture and Urban Forestry 37(3): 126-138. (PDF, 1.6 MB)

WWETAC Project ID:  FY07TS17