The spread of damaging invasive forest pests is only partially powered by the insects' own wings. People moving firewood for camping can hasten and widen the insects' spread and resulting forest destruction. A new U.S. Forest Service study gives state planners a tool for anticipating the most likely route of human-assisted spread they can use to enhance survey and public education efforts.

The study, "Using a Network Model to Assess Risk of Forest Pest Spread via Recreational Travel," was published in the journal PLOS ONE and is designed to help agencies enforcing or considering firewood bans determine how to deploy resources for surveillance, firewood inspections, or other activities. The study is available here.

The role of humans in the spread of invasive insects such as the emerald ash borer and Asian longhorned beetle is well established, according to the study's lead author, Frank Koch, a research ecologist with the Forest Service's Eastern Forest Environmental Threat Assessment Center, a part of the Southern Research Station (SRS).

"Although more than 65 percent of campers carry firewood from home, and that wood often comes from dead or dying trees that may be infested, the dispersal of invasive insects via recreational travel has not been well studied."

Research has demonstrated that firewood harbors many bark- and wood-boring insects. In 2008, co-author Robert Haack of the Forest Service's Northern Research Station found that nearly 25 percent of firewood intercepted at the Mackinac Bridge between Michigan's Upper and Lower peninsulas carried live bark- and wood-boring insects, and an additional 41 percent displayed evidence of prior borer infestation.

Scientists constructed the model covered in the new study from U.S. National Recreation Reservation Service data documenting more than seven million visitor reservations (including visitors from Canada) at federal campgrounds nationwide. The model can be used to identify likely origin and destination locations for a camper-transported pest.

Summary maps for the 48 contiguous U.S. states and seven Canadian provinces showed the most likely origins of campers traveling from outside the target state or province. In the eastern United States, the most common and thus potentially riskiest out-of-state origin locations were usually found in nearby or adjacent states.

In the western United States, the riskiest out-of-state origin locations were typically associated with major urban areas located far away from the state of interest. "Damaging non-native forest insects are a serious issue for public and private land managers," said SRS Director Rob Doudrick.

"Forest Service research is providing tools and information that strengthen policies aimed at controlling and slowing the spread of invasive insects."