The spread of ecological pests around the world is an unfortunate side effect of the modern era of global travel. Dubbed invasive species, these pests can wreak havoc when introduced to new habitats. While international trade is the primary culprit in introducing non-native species, domestic recreational travel is often responsible for spreading invasions into a country’s interior. A major example in recent U.S. history is the spread of insects as stowaways in untreated firewood.

Firewood first drew the concern of conservationists in 1996, when it was implicated in the spread of Asian longhorned beetle (Anoplophora glabripennis). The invasion of this tree pest was first documented in Brooklyn, probably introduced as an accidental passenger inside  the wood of crates used in international trade. Within a month, the beetle was found 50 km east in Amityville, N.Y. This distance is far outside the normal dispersal rate of the beetle, so ecologists pointed to infested wood transported from Brooklyn and being sold as firewood as the vector of spread.

A species of concern today and known to travel in firewood is the emerald ash borer (Agrilus planipennis) another Asian beetle. As the name implies, the emerald ash borer is a pest to all North American ash species (Fraxinus spp.) and the economic costs alone (to say nothing of ecological impacts) has been projected to cost more than $10 billion over a ten year period. Let’s look at three articles published this year that detail the prevalence of firewood transport, the risk of infestation, and the effectiveness of laws aimed at untreated firewood.

Dispersal of Invasive Forest Insects via Recreational Firewood: A

Quantitative Analysis

Published in the Jounral of Economic Entomology, this paper attempts to put some hard numbers on the prevalence of untreated firewood transport. Previous surveys at U.S. campgrounds  indicate the percentage of campers transporting their own firewood is between eight and 57 percent. However, the authors of this study wanted to develop a clearer picture of the potential for long distance transport of firewood.

Since data on actual firewood was lacking, the authors decided to model the distances traveled by American campers as a surrogate. Compiling data from the National Recreation Reservation Service over a five year period, the authors mapped the home ZIP codes of campers and connected them to the ZIP code of their destination park. While this model involves many simplifications of actual behavior, they found that the majority of campers traveled less than 250 km, with most of those trips being less than 100 km. Some connections with moderate volume of travel did measure greater than 1,000 km, and the longest connections were associated with very few reservations.

So while most campers make trips within two hours of home a portion do travel long distances, and some of those are likely to bring their own firewood. But how dangerous is untreated firewood?

Retail Firewood Can Transport Live Tree Pests

Published in Forest Entomology, this paper aimed at determining the likelihood of infestation for untreated firewood. A survey of retail firewood in 18 states found that 52 percent of the wood came from out of state and 50 percent of the wood showed signs of infestation. To produce a more quantitative picture, the authors of this paper purchased 419 firewood bundles from retailers in Colorado, New Mexico, Utah, and Wyoming. They put the bundles in a controlled setting and waited to see what crawled out.

The authors observed the firewood for a period of 18 months. Live insects emerged from 47 percent of the bundles. An average of 11 insects emerged from each bundle, with a range of one insect to a staggering 520. The long term risk is also great, with insects emerging up to 558 days after purchase date.

The authors of this paper recommend a simple heat treating, but the most commonly legislated precaution is simply to forbid the transport of all untreated firewood across state borders or into parks. But what makes for the most effective regulations?

Motivation for compliance with environmental regulations related to forest health

The authors of this study, published in the Journal of Environmental Management, conducted a mail survey with 495 usable returns. The survey was aimed at identifying the strongest influences governing compliance with environmental regulations. In the context of the survey, firewood users had irregular,  short-term interests in compliance, the cost of complying is reasonable, and the costs of non-complying are low (such as having to surrender firewood at the park gate).

The authors consider a number of factors influencing compliance and found that normative motivations (such as sense of civic duty) have a mild influence while calculated motivations have the strongest influence. Calculated motivations include the price of locally-sold firewood and the convenience of purchasing it. The authors see this survey as a guide for designing effective environmental regulations.