Using a network model to assess risk of forest pest spread via recreational travel.

Frank H Koch,Robert A Haack,Roger D Magarey,Denys Yemshanov,Darren J Kriticos

doi:10.1371/journal.pone.0102105

Abstract

Long-distance dispersal pathways, which frequently relate to human activities, facilitate the spread of alien species. One pathway of concern in North America is the possible spread of forest pests in firewood carried by visitors to campgrounds or recreational facilities. We present a network model depicting the movement of campers and, by extension, potentially infested firewood. We constructed the model from US National Recreation Reservation Service data documenting more than seven million visitor reservations (including visitors from Canada) at campgrounds nationwide. This bi-directional model can be used to identify likely origin and destination locations for a camper-transported pest. To support broad-scale decision making, we used the model to generate summary maps for 48 US states and seven Canadian provinces that depict the most likely origins of campers traveling from outside the target state or province. The maps generally showed one of two basic spatial patterns of out-of-state (or out-of-province) origin risk. In the eastern United States, the riskiest out-of-state origin locations were usually found in a localized region restricted to portions of adjacent states. In the western United States, the riskiest out-of-state origin locations were typically associated with major urban areas located far from the state of interest. A few states and the Canadian provinces showed characteristics of both patterns. These model outputs can guide deployment of resources for surveillance, firewood inspections, or other activities. Significantly, the contrasting map patterns indicate that no single response strategy is appropriate for all states and provinces. If most out-of-state campers are traveling from distant areas, it may be effective to deploy resources at key points along major roads (e.g., interstate highways), since these locations could effectively represent bottlenecks of camper movement. If most campers are from nearby areas, they may have many feasible travel routes, so a more widely distributed deployment may be necessary.

Highlights

Long-distance dispersal is a critical factor in the spread of invasive alien species
The growing invasive alien species problem is more broadly associated with increased human mobility in a variety of contexts, including recreational travel [1,2,6,7,8]
With respect to Arizona (Figure 2), high-risk cells can be seen in western US cities like Denver (CO), Salt Lake City (UT), and Las Vegas (NV), and in cities like Chicago (IL), Washington (DC), Boston (MA), and Montreal (QC)

Summary

Introduction

Long-distance dispersal is a critical factor in the spread of invasive alien species. Many long-distance dispersal pathways are associated with human activities [1,2]. The growing invasive alien species problem is more broadly associated with increased human mobility in a variety of contexts, including recreational travel [1,2,6,7,8]. Pathways of human-mediated dispersal not directly related to trade, such as recreational travel, have often been overlooked. For campers in the US and Canada, national parks, state/ provincial parks, and other public lands are among the most preferred destinations [12,13]. Many of these destinations are within or near large areas of forest or woodland. It is logical that camper travel – and in particular, the movement of untreated firewood by campers – has received much attention as a potential invasion pathway for forest pests [14,15,16,17,18,19]

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Conclusion