Using a Network Model to Assess Risk of Forest Pest Spread via Recreational Travel

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.

Iterative Models for Early Detection of Invasive Species across Spread Pathways

“…These two lines of evidence indicate the model is overpredicting in this region, leading us to hypothesize that biological limitations, such as supraoptimal temperatures [114], high winter temperatures precluding a required diapause development stage [115], or dessication [116], may be limiting life stage development in this area. We also detected several false negatives in the intermediate range regional model, which may be a result of missing pathway predictors, such as firewood movement [117][118][119] and recreational activity [16,120] in non-urban landscapes. The lack of origin-destination data sources to estimate these pathways likely results in underestimation of risk in this region.…”

“…For invasive species distribution models (iSDMs), dispersal may be assisted by human movement, which can transport organisms across long distances [12][13][14][15]. The inclusion of dispersal mechanisms or "pathways" within iSDMs may be an effective approach for optimizing early detection programs to areas with high potential for invasion [16][17][18].…”

Variability in commercial demand for tree saplings affects the probability of introducing exotic forest diseases

“…Phytosanitary inspections in trade networks and local eradication of infected stock then can prevent the pathogen from escaping into forests (Eschen et al, 2015;Koch, Yemshanov, Haack, & Magarey, 2014;Shaw & Pautasso, 2014). When a pathogen does escape from a trade-network, the final defence is to organize an eradication campaign within infected forests.…”

Coupled Human-Environment Dynamics of Forest Pest Spread and Control in a Multi-Patch, Stochastic Setting

“…Infestation of North American forests by non–native insect species like Emerald ash borers (EAB), Asian long–horn beetles (ALB) and Citrus long–horn beetles (CLB) has had severe impacts on many ecologically and economically important tree species, such as Ash trees [ 1 ]. These non–native forest pests were often first introduced through international trade in the 1990s and 2000s or before [ 1 , 2 ]. Since their introduction, these forest pest species have subsequently spread widely in North American regions, causing the death of billions of trees, and thereby extensive economic and environmental damage [ 1 , 3 ].…”

“…Several mathematical models have been developed to investigate forest pest invasions and explore possible control strategies to mitigate the resulting ecological and economic losses. These models have focused on the spread rate of non–native insects in North America [ 2 , 8 , 11 ], their possible future impacts [ 3 , 12 ], and their social and financial impacts [ 13 ]. Some of these models explore control strategies such as early detection of infestation and control of insects by means of insecticide treatment, and pre-emptive removal of all Ash trees in a region with replacement by non–Ash trees [ 13 – 15 ].…”