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Forest Disturbance Processes

Firewood as a Pathway for Transport of EAB and Other Pests

Research Issue

[photo:] Log splitter used to dissect logs to find wood boring insects.Firewood is an important pathway in which native and exotic pests can be spread to new areas.  Tree pests are often present in dead and dying trees, which are frequently harvested for firewood. People often transport firewood long distances to camping, hunting, or fishing sites, or to their vacation homes. Firewood may also be moved long distances by firewood producers who sell firewood to large retailers which is then sold to the public. In recognition of the risk posed by firewood to forest health, several states have placed restrictions on all out-of-state firewood and require it to be treated by an approved method to eliminate invasive insect species, fungi and pathogens. Even within a state, people are being encouraged to leave their firewood at home and to buy local firewood when they reach their final destination. For example, Wisconsin is encouraging citizens to transport untreated firewood within the state no more than 50 miles. Websites such as have been developed to inform the public about the risks of moving untreated firewood.

Our Research

In 2008, we conducted a study on the movement of firewood in Michigan. Firewood was inspected that had been confiscated at the Mackinac Bridge, which connects Michigan’s Upper and Lower Peninsulas. Current quarantine regulations for the emerald ash borer (EAB) prohibit the transport of untreated hardwood firewood from Michigan’s Lower Peninsula (where EAB is common) to the Upper Peninsula (where EAB populations are much lower). Firewood is either confiscated or dropped-off voluntarily by drivers when they cross the Mackinac Bridge.  Our objective was to determine what species of wood were being moved by the public and to document if any of the firewood contained live bark- or woodboring insects, especially EAB. 

We conducted surveys in April, July, and September 2008.  We categorized each piece of firewood by tree species (or at least by genus), size (whole log section, half section, or quarter section), and approximate time since cutting or tree death based on the condition of the bark and wood and the types of insects found (0-6 mo, 6-12 mo, 1-2 yr, and >2 yr). We also recorded if bark was present and if there were any insect exit holes. All bark was then removed from each piece of firewood to facilitate examination of the bark and wood for borers and their galleries and exit holes. Next we split the wood with a log splitter and examined all pieces for borers or their signs. We identified the borers to family and recorded their life stage and whether they were alive or dead.

In addition to inspecting firewood, we also summarized survey data provided by Michigan Department of Agriculture (MDA).  These surveys were conducted by MDA employees on individuals who surrendered firewood at the Mackinaw Bridge during the period of March 2006 to October 2009.

Expected Outcomes

Our results provide information on the types and species of transported firewood, as well as the incidence and variety of bark- and wood-boring insects in this firewood.  We also provide some insight on how far firewood is being transported. These results are useful to regulatory personnel and resource managers when setting guidelines for intra- and interstate movement of firewood.

Research Results

We examined and split a total 1045 pieces of firewood from at least 21 tree genera during the three survey periods. The four most common tree genera were Acer (maple; 30% of the total pieces), Quercus (oak; 18%), Fraxinus (ash; 15%), and Ulmus (elm; 12%). Live borers were found in 23% of the pieces, and an additional 41% had evidence of previous borer infestation. Live borers were found in all age classes of firewood, with most (37%) found in firewood that was estimated to have been cut from trees that had died or been felled within the previous two years. The following borer families were represented in our survey: Brentidae, Buprestidae, Cerambycidae, Cossidae, Curculionidae, Scolytidae (Curculionidae: Scolytinae), and Siricidae.  Evidence of emerald ash borer (EAB) was found in 13% of the ash firewood pieces; however no living life stages of EAB were found in any of these firewood pieces. Surveys conducted by Michigan Department of Agriculture for 322 individuals who surrendered firewood at the Mackinac Bridge showed that most firewood originated from Michigan (82%); however, the remaining 18% originated from 17 U.S. states and 3 Canadian provinces.

Haack, R. A., T. R. Petrice, and A. C. Wiedenhoeft.  2008.  What is inside the firewood confiscated at the Mackinac Bridge?  Newsletter of the Michigan Entomological Society 53: 43.

Haack RA, Petrice TR, and Wiedenhoeft AC. 2010. Incidence of bark- and wood-boring insects in firewood: a survey at Michigan's Mackinac Bridge. Journal of Economic Entomology. 103(5): 1682-1692. 

Research Participants

Principal Investigators

  • Robert Haack, US Forest Service- Northern Research Station Research Entomologist, Emeritus
  • Toby Petrice, US Forest Service- Northern Research Station Entomologist

Research Partners

Last Modified: March 1, 2016